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Settlement: Grooved Mechanical Piping Systems
By Larry Thau
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Deflection of pipelines within a structure is often a concern for engineers designing and
specifying for pipe installation. If not adequately accommodated, repeated stress on a piping
system can cause damage to equipment and threaten the structural integrity of the building
itself. There are business implications of inadequate accommodation for deflection that result in
unsatisfied owners, whose occupants may complain about underperforming systems, noisy
pipes, damaged equipment or aesthetic impacts. These issues affect the engineer and
contractor’s bottom-line, since they may need to perform numerous call-backs in an attempt to
fix the problem.
With structures becoming taller, larger, and more complex in design, addressing deflection and
settlement concerns creates an additional challenge for the engineer. Because the business risk
is significant if a system design causes undue stresses on the piping system, forcing rigidly
constructed piping/components to bend— it is essential for engineers to understand the system requirements at the design stage to alleviate or accommodate deflection and settlement.
Grooved mechanical piping systems can address forced pipeline deflection or misalignment in a
piping system due to settlement and accommodate building sway due to thermal transients and
wind loads in vertical risers. They also accommodate linear piping movement from thermal
changes and building creep. Most often specified as a fast, easy, safe and reliable alternative to
welding, grooved mechanical pipe joining has a long history of effectively minimizing deflection
risks and accommodating for settlement in a variety of structures.
Accommodating Deflect ion and L inear Movement w ith Grooved Coupl ings
Grooved mechanical couplings are available with two distinct performance features. One class
is designed as "rigid" and the other as "flexible". Rigid grooved mechanical couplings are
designed to "fix" the joint in its installed position, permitting neither linear, angular nor rotational
movement at the joints, although it is possible to achieve movement by utilizing grooved
expansion joints. On the other hand, flexible grooved mechanical couplings are designed to
allow controlled linear and angular movement at each joint, which can accommodate pipeline
deflection, building creep and settlement.
Grooved mechanical couplings allow for movement in the pipe due to the design of the
components. The dimensions of the coupling key are narrower than the groove in the pipe,
allowing room for that coupling key to move in the pipe groove while maintaining the pressurized seal of the gasket. Additionally, the width of the coupling housing allows for pipe end separation,
therefore leaving room for controlled linear and angular movement. The mechanical coupling
remains a self-restrained joint and the unique pressure responsive design provides sealing even
under deflection and pipe movement.
8/17/2019 Diseño de Tuberias Ranuradas, Victaulic
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Grooved mechanical couplings are a great alternative to welded U-shaped expansion loops,
welded offsets, expansion joints and rubber bellows. These couplings are easier and faster to
install and accommodate deflection and linear movement within the design capability of the
coupling, all the while doing this within the product’s "free range of motion". This means that
imparted deflections can be accommodated in smaller spaces, with low stress on the
components.
Figure 1: Because the dimensions of the coupling key are narrower than the groove in the pipe, and because the
width of the coupling allows for pipe end separation, there is room for controlled movement while maintaining the
pressurized seal of the gasket.
Accommodating fo r Set tlement
Unanticipated pipeline deflection can damage a building’s equipment or even compromise the
structural integrity of the building itself. The piping system designs must work in concert with
the building design. Deflection imposed on a piping system may occur due to uneven settlement, particularly when considering new additions to existing structures. A newer
structure may settle at a greater rate and flexibility must be designed into piping systems
crossing the structures.
Piping misalignment due to uneven building settlement is addressed by using an even number
of flexible couplings and permitting the intermediate pipe to "toggle" as the movement occurs.
To determine the number of couplings required, define the amount of lateral misalignment on a
particular pipe run and the length of that pipe run. The objective in designing for misalignment is
to achieve the required displacement using the minimum number of couplings. Due to symmetry
around a transition point, the point of inflection is a pipe spool and not a coupling. The numberof couplings and the length of the pipe spools are two variables that can be altered to obtain the
desired misalignment. Other factors, such as the maximum angle of deflection at each coupling
and the maximum pipe end separation, are a function of the size and style coupling being used.
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Figure 2: The drawing above shows how flexible couplings deflect from the straight line to allow for building
settlement.
Accommodating for Deflection and Linear Movement Due To Thermal Transients
Thermal transients may impose deflection on a piping system as the pipe grows when heated
and contracts when cooled. All materials, including pipe, machinery, structures and buildings, experience dimension changes as a result of changes in temperatures. This will often occur at
directional changes, or cause "bowing" at the mid points of long straight pipe runs, resulting in
stress on the piping system and equipment.
Three common methods of accommodating thermal expansion and contraction are:
• Provide an expansion joint
• Allow the system to “freefloat” and the pipe to move in a desired direction through the
use of anchoring and/or guidance, if necessary taking into account the capability of
branch connection or changes in direction which may result in harmful bending
moments
• Utilize the linear movement and deflection capabilities of flexible grooved couplings.
Flexible grooved couplings provide deflection capabilities to accommodate pipe movement in
long straight runs or for use in expansion loops, and allow angular flexibility and rotational
movement to take place at joints. To provide for these thermal changes sufficient flexible joints
must be available to accommodate for the anticipated movement. In order to determine the
appropriate number of couplings to use, compute the change in the linear length of the piping
system by taking into account the length and size of the piping system and maximum and
minimum operating temperatures.
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Figure 3: The grooved coupling allows for controlled angular movement that may result from deflection.
The flexible mechanical joint can also be used in expansion loops without inducing stresses in
the pipes, elbows or joints. The deflection capability of flexible couplings allows for thermal
growth/contraction to be absorbed within the couplings at the elbows as the thermal forces
induce deflection. A total of eight flexible grooved mechanical couplings and four grooved end
90 degree elbows and three pipe spools are required to complete each expansion loop. (Figure
A) As system temperatures lower and the pipe run contracts, the loop expands and the
deflection capability of couplings accommodates this movement. (Figure B) As system
temperatures increase the opposite effect occurs as the pipe run expands and the loop
contracts with the couplings accommodating the deflection in the opposite direction. (Figure C)
A significant benefit to using this configuration is that a loop constructed in this manner will be1/2 to 1/3 the size of a welded loop with the same capacity, and will accommodate the
movement without inducing stress into the pipe.
Figures A, B, C: The figures show how a grooved expansion loop can contract and expand to accommodate the
growth and shrinking of a system from thermal transients.
Accommodating for Building Creep or Subsidence
Similar to thermal transients, deflection or linear movement imposed on a piping system may
occur due to building creep. Building creep is the common term for the amount of actual building
shrinkage that will occur over time. This is an important consideration for high rise construction.
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Accommodating building creep can be addressed three different ways using mechanical piping
systems: flexible system, rigid system or a combination of both.
In a flexible grooved system utilizing only flexible grooved mechanical pipe joints, risers are
installed with anchors at the top and bottom with the piping guided every other pipe length to
prevent “snaking” of the line. A sufficient number of flexible couplings must be utilized to
accommodate the anticipated movement. Pipe gapping of the pipe ends within the coupling is
required in order to allow the riser to compress with the building.
In a rigid system utilizing only rigid grooved mechanical pipe joints, risers can be treated similar
to a welded system, and where movement is required expansion joints or offsets are designed
into the riser to accommodate movement and prevent damage to components.
By designing risers with a combination of both rigid and flexible grooved joints, engineers can utilize rigid couplings to reduce guiding requirements and the flexible grooved joints to
accommodate the movement required.
Accommodating Building Sway in Tall Bu ildings
Vertical riser piping in tall buildings is often subject to deflection due to heavy wind loads which
cause the building to sway. Where the pipe is rigidly fixed to the building structure, freedom of
motion must be designed into the piping to permit it to move in unison with the building. Flexible
couplings have been successfully used on vertical risers to provide the necessary freedom of
motion so that the pipe sways harmlessly with the building.
Examples of Accommodating Deflection, Bu ilding Creep and Settlement
Grooved mechanical couplings are a great alternative to welded expansion loops, welded
offsets, expansion joints and rubber bellows because they provide rigid or flexible joints which
gives the system designer a variety of options for managing piping movement and providing an
optimal system design.
On a recent high-rise project in Chicago, the engineer was able to accommodate the piping
movement caused by building creep and thermal transients through the deflection characteristic
of flexible couplings.
Taking into account the maximum Delta T (change in temperature) that the piping would experience and the building creep, the engineer calculated the amount of movement that would
occur within a given run of piping. Based on these calculations and the building layout, he made
a decision to strategically locate anchors on the piping system using rigid couplings on the
straight runs and applying flexible couplings at the systems changes of direction. In one area,
the engineer anchored the run of pipe at the midway point between the basement and the mid-
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level mechanical room. This anchor directed movement to the offsets at both ends of the pipe
run, and minimized the movement that would have occurred if the system was anchored at the
top or bottom of the run. Flexible couplings were applied at these offsets to allow for deflection
which accommodated these movements, minimized the stresses in the system all while performing under tight space constraints typically found in high rise construction.
On a similar high-rise project in Dubai, the engineer was able to accommodate the piping
movement caused by building creep and thermal transients through the linear movement
characteristic of flexible couplings.
Also taking into account the maximum Delta T that the piping would experience and the building
creep, the engineer calculated the amount of movement that would occur within the main
vertical riser, and based on these calculations, he made a decision to strategically place a
series of pre-gapped flexible couplings on the main vertical riser at each floor to accommodate
total piping movement on a per-floor basis.
Several of the world’s tallest buildings have used the grooved system to meet their deflection
needs. The Petronas Towers in Kuala Lumpur, Malaysia are the second tallest buildings in the
world. To accommodate for structural movements and sway they installed flexible couplings on
the riser pipes in order to provide angular deflection. In a recently completed Chicago high-rise,
the engineer specified flexible couplings on the branch piping coming off the main risers
because of their ability to provide a solution which allowed the pipe to grow, shrink and sway.
Several Victaulic flexible couplings placed in a series were used to accommodate the deflection
of the branch movement as the riser moves up and down.
The Bottom Line
Structural designs that include grooved mechanical pipe joints, such as rigid and flexible
couplings, will alleviate the challenges faced in accommodating for settlement and deflection. In
addition to the benefits in reduced footprint and added design flexibility, grooved mechanical
joints assist in the creation of a trouble-free, durable and easy-to-maintain structure for clients.
Contractors benefit from alleviated scheduling pressures and labor challenges due to the ease
of installation with grooved mechanical joints. Grooved mechanical joints also decrease or
completely eliminate the need for welding, which can significantly impact the safety on a job and
through the life of a structure.
Engineers, owners and contractors can save time and increase a structure’s lifespan by
planning for deflection and accommodating settlement in the design phase. Grooved
mechanical pipe joints, whether rigid or flexible, offer a fast, space-saving alternative to welded
joints.
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Using Grooved Mechanical Joining Systems to Accommodate Thermal Piping Movement
By Larry Thau June 2009
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The key to effectively accommodating thermal expansion and contraction in a building is to allow the predictable, controlled movement of the piping itself. This can be done in a variety of ways, and the selection of a specific method is based upon the engineer, the type of piping system and the project parameters.
Thermal transients may impose stress on a piping system as the pipe grows when heated and contracts when cooled. All materials, including pipe, experience dimension changes as a result of changes in temperatures and their coefficient of expansion. This often occurs at directional changes or causes "bowing" at the mid points of long straight pipe runs, resulting in stress on the piping system and equipment.
When a system is subjected to temperature, it may experience horizontal movement, vertical movement and angular deflection simultaneously. Additional strains on the piping system vary based on whether the piping is vertical or horizontal. For horizontal piping, the major obstacle is typically the space constraints around the length and turns of the pipe. For vertical piping, considerations are different and should involve dynamic, static and elevation head calculations
of the pressures and loads that are exerted on the bottom portion of the pipe.
Carbon steel pipe will experience thermal expansion or contraction at a rate of 0.75 inches for every 100° F change in temperature per every 100 feet of pipe. Piping subject to temperature changes is placed in a condition of stress, with potentially damaging reactive forces on components or equipment. The forces generated during this thermal dimension change are often significant and the movement must be accommodated and controlled, to prevent transmission of these stresses throughout the piping system.
Inadequate accommodation of this movement can result in business risks caused by excess stress on the piping system, including increased incidence of ruptures and leaks, increased stress on boilers, chillers, valves and other equipment and components, and increased
downtime and labor expenses. This can negatively impact the owners of the building byresulting in increased maintenance costs and potential business shutdowns.
When accommodating thermal expansion and contraction, the grooved pipe joining system conforms to industry practices while providing design flexibility, reducing stress on the piping system and providing a more compact, inspectable and productive method of installation over other pipe-joining methods such as welding or flanging. Additionally, the grooved method has all sealing elements combined within a metallic housing.
There are four common methods for accommodating thermal pipe movement with a grooved system: 1) providing an expansion joint utilizing grooved mechanical pipe components 2) allowing the system to “free-float”
3) utilizing the linear movement/deflection capabilities of flexible grooved couplings 4) providing an expansion loop utilizing grooved mechanical components
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The selection of one of these methods is dependent on the system type, the scope of the project and the engineer's preference. Since it is impossible to predict all system designs, this article will call attention to the design benefits and mechanical advantages of the grooved piping method when used to accommodate thermal expansion and contraction.
The grooved mechanical pipe joint Grooved mechanical couplings allow for movement in the pipe due to the design of the components. The dimensions of the coupling key are narrower than the groove in the pipe allowing room for that coupling key to move in the pipe groove. Additionally, the width of the coupling housing allows for pipe end separation leaving room for controlled linear and angular movement. The mechanical coupling remains a self-restrained joint, and the unique pressure responsive design provides sealing even under deflection and pipe movement.
Grooved mechanical couplings are a great alternative to welded U-shaped expansion loops, welded offsets, expansion joints and rubber bellows. These couplings are easier and faster to install, accommodate movement within the design capability of the coupling, all the while doing this within the products "free range of motion.” This means that piping system movement caused by thermal expansion and contraction can be accommodated in smaller spaces, with low stress on the components.
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Accommodating thermal movement ut il izing expansion jo in ts
Grooved mechanical couplings are available with two distinct performance features. One class is designed as "rigid" and the other as "flexible.” Rigid grooved mechanical couplings are designed to "fix" the joint in its installed position, permitting neither linear, angular nor rotational movement at the joints. Flexible grooved mechanical couplings on the other hand are designed to allow controlled linear and angular movement at each joint that can accommodate pipeline deflection.
Expansion joints are devices that can be compressed or expanded axially and are generally the most costly alternative for accommodating thermal movement. A welded expansion joint is typically an expensive specialty joint, flanged into the system and requiring regular maintenance. More cost-effective expansion joints utilize grooved mechanical couplings and specially grooved, short pipe nipples with flexible couplings placed in long straight runs of pipe and pre-set to allow the desired amount of contraction and/or expansion. Axial movement can be adjusted by simply adding or removing couplings. When a series of flexible couplings are installed, the resulting grooved expansion joint will further protect equipment by reducing vibrations and stresses in the system.
Whether using specialty expansion joints or a grooved expansion joint, the adjacent piping mustbe properly guided to ensure the movement is directed into the device and no lateral movement is experienced.
For proper operation of the expansion joint, the piping system should be divided into separate expansion and contraction sections with suitable supports, guides and anchors to direct axial pipe movement.
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Anchors should be classified as main or intermediate for the purpose of force analysis. Main anchors are installed at terminal points, major branch connections, or changes of piping direction. The forces acting on a main anchor are due to pressure thrust, velocity flow and
friction of alignment guides and weight support devices.
Intermediate anchors are installed in long runs to divide them into smaller expanding sections to facilitate using less complex expansion joints. The force acting on the intermediate anchor is due to friction at guides, weight of supports or hangers, and the activation force required to compress or expand an expansion joint.
Pipe alignment guides are essential to ensure axial movement of the expansion joint. If the situation allows, the expansion joint should be adjacent to an anchor within four pipe diameters. The first and second alignment guides on the opposite side of the expansion joint should be located a maximum distance of four and 14 pipe diameters, respectively. Additional intermediate guides may be required throughout the system for pipe alignment. If the expansion joint cannot
be located adjacent to an anchor, install guides on both sides of the unit.
Grooved expansion joints may be used as flexible connectors; however, they will not
simultaneously provide full expansion and full deflection. Expansion joints installed horizontallyrequire independent support to prevent deflection, which will reduce the available expansion.
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Accommodating thermal movement ut il izing a Free-Floating System Free-floating piping systems allow thermal expansion and contraction without the use of expansion joints. As long as this movement does not cause bending moment stresses at branch connections, it is not harmful to joints and changes in direction or to parts of structures and
other equipment. A free-floating system can be achieved by installing additional grooved mechanicals joints or by installing guides to control the direction of movement. Engineers must take the effects of pressure thrusts into account when utilizing flexible grooved couplings, as the pipe will be moved to the full extent of the available pipe end gaps when allowed to float.
Ensure that branch connections and offsets are sufficiently long so that the maximum angular deflection of the coupling is never exceeded and that it can accommodate the anticipated total movement of the pipes. Otherwise, it is advised to anchor the system and to direct movements.
Flexible Grooved Couplings For Linear Movement and Deflection Grooved mechanical couplings are an alternative to welded U-shaped expansion loops, welded offsets, expansion joints and rubber bellows. Associated with a free floating system, flexible couplings are used in piping systems to accommodate piping thermal growth— without any additional components or piping configuration required. Certain characteristics distinguish
flexible groove type couplings from other types and methods of pipe joining. When they areunderstood, the designer can utilize the many advantages that these couplings provide.
By using flexible couplings at changes of direction and directing the movement toward the directional change with properly placed anchors and guides, movement is accommodated by the joining method itself. This method also produces little or no additional stresses in the system, unlike a welded expansion loop.
Flexible couplings also can be used strictly for their axial movement capabilities. In this case, straight runs are anchored on each end and the piping is guided at every other length. Each flexible joint is pre-gapped (either fully gapped or fully closed/butted) at installation to ensure that there are enough couplings to accommodate the expected expansion and/or contraction.
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The flexible grooved coupling allows for controlled angular flexibility and rotational movement to take place at joints.
Flexible grooved type couplings allow angular flexibility and rotational movement to take place at joints. In order to determine the appropriate number of couplings to use, compute the change in the linear length of the piping system by taking into account the length and size of the piping system and maximum and minimum operating temperatures.
Where full linear movement is required, a grooved expansion joint can be used. Note, joints which are fully deflected can no longer provide linear movement. Partially deflected joints will provide some portion of linear movement. It is also important to consider that standard cut- grooved pipe will provide double the expansion and contraction or deflection capabilities of the same size standard roll-grooved pipe.
When considering offsets utilizing grooved mechanical joints, the offsets must be capable of deflecting sufficiently to prevent harmful bending moments at the joints. If the pipes were to expand due to thermal changes, then further growth of the pipes would also take place at the ends.
Flexible couplings do not automatically provide for expansion or contraction of piping. Always consider best setting for pipe end gaps. In anchored systems, gaps must be set to handle combinations of expansion and contraction. In free floating systems, offsets of sufficient length must be used to accommodate movement without over-deflecting joints.
Ensure anchorage and support is adequate. Use anchors to direct movement away from or to protect critical changes in direction, branch connections and structure. Spacing and types of supports should be considered in accommodating anticipated pipe movements.
Expansion Loops Utilizing Flexible Couplings and Fittings In vertical straight runs of pipe, expansion loops utilizing a U-shaped pipe configuration can also be designed into the piping system to accommodate expansion and contraction. Expansion
loops can be designed as welded or grooved. Welded expansion loops require eight welded joints and fittings to assemble. In a welded expansion loop, the piping bends or flexes to accommodate the straight run movement. Although this method works, the forces to bend and flex the pipe are much greater than in a grooved loop, and the forces generate a larger magnitude of stress which requires larger anchors and guides to direct the movement and protect components and structures.
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The flexible mechanical joint can be use in expansion loops without inducing stresses in the pipes, elbows or joints. Also, it is important to note that expansion loops utilizing rigid couplings are not designed to accommodate angular deflection, however an expansion loop utilizing rigid grooved copper couplings is designed to conform to industry standards.
The deflection capability of flexible couplings allows for thermal growth/contraction to be absorbed within the couplings at the elbows as the thermal forces induce deflection. A total of eight flexible grooved mechanical couplings, four grooved end 90-degree elbows and three pipe spools are required to complete each expansion loop. As system temperatures lower and the pipe run contracts, the loop expands and the deflection capability of the couplings accommodates this movement. As system temperatures increase the opposite effect occurs as the pipe run expands and the loop contracts with the couplings accommodating the deflection in the opposite direction (See Figures A through C).
Using flexible couplings in an expansion loop configuration reduces the amount of force needed to flex the loop, and the loop itself is much smaller. A loop constructed in this manner will be 1/2 to 1/3 the size of a welded loop with the same capacity.
The space constraints of today’s buildings also make this a more attractive option in HVAC piping, though welded expansion loops are still required in some system applications.
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Making the Best Choice Grooved mechanical systems offer four different methods to provide flexible, controlled movement of a piping system. The selection of expansion joints, free-floating systems, flexible
couplings or expansion loops will be based on the type of piping system, the amount of anticipated movement and the mechanical engineer’s preference.
In addition to effectively accommodating thermal expansion and contraction, engineers should consider the additional benefits of using the grooved method during construction, including a simplified assembly process that is readily inspectable relative to welded systems. Also, mechanical couplings reduce the need for welding and reduce man hours and material handling on the site, making for safer job sites and reduced risk of injury on-site. During operation, the simple disassembly of a coupling reduces chances of deferred maintenance and lengthy downtime for routine or unscheduled maintenance.
Overall, choosing the grooved mechanical method is an efficient way to accommodate excess stress on any piping system, eliminate incidents of ruptures and leaks due to thermal expansion, decrease maintenance needs of equipment, and simplifies the commissioning process.
Larry Thau is Executive Vice President- Chief Technology Officer for Victaulic Company, Inc. A practicing mechanical engineer for 35 years, he holds more than 35 patents and lectures on piping technology around the world.
www.victaulic.com VICTAULIC IS A REGISTERED TRADEMARK OF VICTAULIC COMPANY. © 2009 VICTAULIC COMPANY. ALL RIGHTS RESERVED. WP-03 Rev. A
Circuit balancing: A key to improving HVAC system operationand control
David L. Hudson Victaulic Company, Inc.
Easton, PA
August 2009
As many building superintendents would agree, the symptoms of indoor climate problems within their buildings usually surface as complaints from tenants. The living or working spaces are too cold in winter, too hot in summer—or some combination of both extremes, year-round.
In response to these temperature variations, building occupants often compensate by using space heaters, opening windows and adjusting thermostat settings. Additional adjustments to the HVAC system may include larger pumps, resizing components, changing night setback and morning startup times, and flow adjustments in mains, branch lines and circuits independent of the impacts on the entire HVAC system.
These types of “fixes” to alleviate cold and hot zones in a building are typically ineffective and costly and usually do not correct the situation.
For example, resetting a workplace HVAC system startup time from 7:30 a.m. to 5:30 a.m. means that the plant operates at capacity two additional hours per day. This works out to a 25 percent increase in energy consumption, which cancels out the energy savings that night setbacks were designed to achieve.
As a result of such actions, building owners realize higher energy and operating costs, additional wear on pumps and HVAC components and reduced control valve authority throughout the system.
System designers may be challenged to defend their design, pipe sizing, operating parameters and adequacy of controls when the HVAC system is simply unbalanced. Indoor temperature and climate problems typically are not caused by control malfunctions or sizing errors. Often they are traceable to incorrect flow rates in the HVAC system due to improper terminal unit balancing. Engineers typically design HVAC systems with excess capacity for the building they support. Thus, the ability to provide the necessary heat or cooling energy is present. Getting the energy to the terminal unit and air handling unit (AHU) is the real issue.
Therefore, the key to HVAC system effectiveness and efficiency is properly controlling flows throughout the entire system from production and delivery units to terminal units for the comfort of all building occupants.
Balancing for comfort and control
HVAC systems are designed with balancing valves to maintain flow conditions so that control valves may function properly. Proper control valve function provides the correct flow to the heat transfer coil resulting in the correct energy output (BTU) to the building space.
Flow in an HVAC system is dynamic and always changing throughout a typical 24-hour period. Due to heat gain from the sun and changes in building occupancy rates, the demand for heating and cooling output will vary not only throughout the day and night, but by building sector. An effective and efficient HVAC system must provide energy output when required and where required. Proper Hydronic balancing is the key to making your HVAC system perform properly and at the lowest cost.
Proper circuit balancing is essential to ensure that heating and chilled water systems deliver correct flows to all terminal units in the HVAC circuit, as specified by the system’s design flow. In an unbalanced system, sectors of a building will have underflow or overflow conditions that impact control valve authority and thus the indoor climate in the building. For example, areas located nearest to the energy production and delivery source could receive excess flows, resulting in excessive heating or cooling. Likewise, areas that are remote (farthest away) may experience inadequate heating or cooling levels because of insufficient flow rates.
In terms of pure economics, each additional degree Fahrenheit increase in
thermostat setting can add six percent to a building’s heating costs, while every degree Fahrenheit reduction works out to an additional eight percent increase in cooling costs.
A typical HVAC circuit incorporates balancing valves for each terminal unit coil and AHU. To balance a coil using a manual balancing valve, a technician needs to connect a differential pressure gauge or handheld circuit balancing instrument to the valve’s two metering/test ports. Based upon the valve size, hand wheel position and the measured differential pressure, the system flow rate through the balancing valve is readily determined with a balancing instrument, balancing flow wheel or the valve’s Cv characteristics. The valve hand wheel is then adjusted to
obtain the required system flow rate.
Applying this technique to each balancing valve in the system will achieve proper balance throughout the system so that all circuits receive specified design flows for optimal performance. When pumps, chillers and other components operate at the lowest possible load, owners benefit from less wear and tear, longer equipment service life, and savings in energy and maintenance costs.
Figure 1: Coil-CW/HW schematic drawing and Tour & Andersson Coil Component
Manual balancing valves Engineers and contractors have a variety of manual balancing valve configurations to choose from for HVAC circuit balancing and control applications. Throttling characteristics (the relationship between a valve’s adjustment range and flow rate) also vary by valve type and are a key determinant in each valve’s ability to be set to the desired flow and must be verified using the balancing technique previously described.
For example, a quarter-turn ball valve provides 90 degrees of throttling adjustment range, as compared with the 1,440 degrees of adjustment range
available with a four handwheel turn globe valve. As a result, many engineers specify Y-pattern globe valves because of their ability to be set precisely to control flows.
Depending on valve size, globe valves can offer full throttling ranges using 2, 4, 8, 12 or 16 handwheel turns, and enable users to obtain accurate readings of up to one-tenth of a handwheel turn. Some valve manufacturers also provide vernier scales, digital readouts, concealed memory and locking, tamper-proof settings and other features designed to enhance flow rate accuracy and controllability.
Figure 2: “Comparison of throttling characteristics”
Comparison of throttling characteristics Generally speaking, a higher number of handwheel rotations equates to more precise flow control. This graph illustrates the throttling characteristics of 90 degrees (1/4 turn), 360 degrees (full turn) and 1,440 degrees (four turn) balancing valves.
• A 90 degrees fully open-to-closed valve requires just a 12 degree change in adjustment to equal a 30 percent change in flow.
• A 360 degrees fully open-to-closed valve would require a 96 degrees change in adjustment to equal the same 30 percent change in flow.
• A 1,440 degrees fully open-to-closed valve would require 408 degrees of change in adjustment to equal the same 30 percent change in flow.
Real-time measurement and control
A variety of optional pressure drop ( ΔP) sensors and balancing software programs are available to provide data links to a building’s monitoring system. In addition, some handheld circuit balancing instruments integrate ΔP sensors and microprocessors into a portable, lightweight package that enables contractors to perform circuit balancing without the need for flow charts and pressure drop calculations.
Balancing helps isolate system trouble spots The symptom is typically improper heating or cooling. The cause is an improperly adjusted balancing valve, clogged strainer/coil or other system issue which changes the specified flow rate through a coil or AHU. Diagnostic analysis can be made readily on the suspect coil or AHU by checking the flow rate through the respective balancing valve. Moreover, issues can be identified at a point when they can still be corrected economically during building commissioning and before tenant move-in.
For this reason, circuit balancing valves are integrated as part of a building’s commissioning process. In addition to providing engineers with a comprehensive record of specified and actual flows, balancing helps simplify setup and monitoring of control equipment. These advantages reduce capital costs along with commissioning times.
Conclusion Far too many buildings are unnecessarily plagued by temperature variations that can lead to tenant complaints and high energy and operating expenses for owners. In most cases, these faults can be resolved easily through proper balancing of the heating or cooling system in conformance with original design performance specifications.
In addition to providing occupant comfort and efficient energy and operating costs, effective circuit balancing can aid in troubleshooting the causes for improper heating or cooling. A comprehensive circuit-balancing program should be integrated into new building commissioning as a means of saving time and
energy and improving the long-term value of the building.
In the end, everybody wins. Tenants enjoy a comfortable living and working environment, while building owners benefit from faster startup times, savings in energy and operating costs, and enhanced return on their capital investment.
David L. Hudson is a Senior Product Engineer for Victaulic Company, Inc. He is a practicing mechanical engineer with more than 26 years of experience. He can be reached at [email protected]. Victaulic is the world’s leading producer of mechanical pipe joining systems and the exclusive U.S. distributor of Tour &
Andersson circuit balancing valves.
Abst rac t
The dual agent fire extinguishing system generates a homogeneous suspension of sub-10 micron water droplets and nitrogen gas that is delivered at relatively high momentum with very low operating pressures relative to existing fire suppression technologies. The combined extinguishing characteristics of water and nitrogen enhance the individual components: coupled with high delivery momentum, the suspension has demonstrated fire extinguishment capabilities and benefits that extend the boundaries of existing single fluid systems. The science of generating the homogeneous extinguishing agent is presented followed by a brief explanation of the theory of fire extinguishment using the system. Fire test results are then presented that demonstrate the Vortex capabilities in total flooding and local applications.
1) Introduction
Fire protection systems are available today in a large variety of configurations and with varying complexities. From traditional water based sprinkler systems, the simplest and most widely used, to the halocarbon agents and high pressure water mist systems. Each system has unique advantages and disadvantages, depending on the hazard application.
After an in-depth analysis of all existing fire suppression systems, the researchers identified specific desired characteristics of the new suppression system. The criteria called for minimal wetting of protected surfaces, full fire suppression capabilities, zero environmental impact, extended safe egress time for occupants in case of discharge, simplified system design for multiple zones and scalability that surpasses current water mist technologies.
In order to achieve this, the design team decided that water droplet size should be as small as possible thus reducing the required water volume and simultaneously maximizing heat absorption efficiency. It was recognized that a new water delivery and atomization method would need to be developed in order to produce very small water droplets while overcoming the drag effect inherent with the projection of small water droplets. The resultant provides enough agent momentum that the system can be effectively applied to local application hazards for both combustible and flammable liquid hazards.
The adiabatic flame temperature equation is used to demonstrate the theoretical
advantage of a dual agent extinguishing system. The assumptions made are discussedand analyzed against actual fire test data with interesting results that may, with further testing and analysis, explain some limitations associated with typical water mist systems and lead to greater fire extinguishment efficiencies.
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2) Atomization
The atomization of water droplets is strongly tied to a parameter called the Weber number,
σ
2 Δ
= [Eq. 1]
where ρ is the liquid density (kg/m3) U is the relative gas-liquid velocity (m/s) L is the characteristic dimension of the stream (m) σ is the surface tension coefficient (kg/s2)
At high Weber numbers the aerodynamic forces on the water droplets dominate, causing the water stream to distort and disintegrate in a process known as atomization. The atomization process continues in a cascading manner until a critical value of the Weber number is reached at which point the atomization process is complete. As the Weber number decreases with smaller droplet size the relative velocity also decreases.
The challenge is to create very small water droplets while maintaining high momentum capable of over coming the aerodynamic forces that would normally decelerate the droplets. This is essential in the case of fire suppression where the system must be able to deliver the water droplets to a fuel source while potentially overcoming the fire plume velocities.
2.1) Agent Emitter
The agent emitter was developed using theory analogous to the aerodynamic forces seen on a supersonic aircraft wing.
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Figure 1: Victaulic Vortex emitter cross-section
Figure 1 is a cross section of the Vortex emitter. Nitrogen at 25 psig enters the emitter while water at <5psig enters the water jacket external to the nitrogen flow. The emitter is configured to accelerate the nitrogen flow to a supersonic velocity thus exiting the emitter as under expanded gas flow.
Shock Disks
Figure 2: Schlieren Photograph of Nitrogen Flow
Figure 2 is a picture, taken at the Penn State Gas Dynamics Laboratory, which demonstrates the nitrogen density patterns in the critical flow field.
As nitrogen exits the emitter at a supersonic velocity a shock disk is formed. This is the result of the instantaneous transition from sonic to sub sonic velocity and is seen as the dark area between the emitter outlet and the emitter foil. As the nitrogen contacts the emitter foil it is re-accelerated to localized supersonic velocities which then creates additional shock disks perpendicular to the flow field. Water exits the emitter through the ring of concentric holes (see Figure 1) external to the nitrogen outlet of t he emitter. www.victaulic.com VICTAULIC IS A REGISTERED TRADEMARK OF VICTAULIC COMPANY. © 2009 VICTAULIC COMPANY. ALL RIGHTS RESERVED.
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This water is injected into the nitrogen flow field in the area of the shock disks shown in
Figure 2. At this point the water is exposed to a region of very high Weber number and thus rapid atomization. The resulting water droplet distribution shown in Figure 3 is for the most part comprised of < 10 μm size water droplets with a very tight distribution.
Figure 3: Droplet distribution density, Underwriters Laboratories
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The Victaulic Vortex system uses equal moles of water and nitrogen in producing a homogeneous suspension of water and nitrogen. Figure 4 shows water being injected into the nitrogen flow and the subsequent atomization. Of particular importance is the understanding that after the water is atomized it is carried in the nitrogen flow at equal partial pressures. At this point relative velocity between the water and nitrogen is negligible, resulting in a very small Weber number. Since the water is suspended in the nitrogen, it maintains its momentum and is capable of being projected for relatively large distances and in the process becoming entrained in fire plumes.
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White Paper
Keeping Your Cool: Grooved Technology as a Means to More Efficient Data Center Construction and Operation
By David Gibbons
July 15, 2009
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For many years, air cooled systems provided sufficient cooling capacity for data centers;
however, increased computing density produces more heat and, therefore, requires a more efficient cooling method. In larger data centers, the most cost effective method of cooling is a chilled water system. According to the Science of Aquatics, water is 4,000 times more efficient than air. This is why, in recent years, companies like IBM have developed methods for bringing cooling water directly into server racks.
In a chilled water system, chilled water is pumped out of the mechanical room and into computer room air handlers by way of under-floor water distribution lines. The air handler then removes heat and humidity by drawing warm air through coils filled with circulating chilled water. The water absorbs the heat from the air and circulates back to the chiller where the heat is transferred to a condenser water loop and eventually released through a cooling tower.
Hard piping utilizing carbon steel pipe or copper tubing is common in a chilled water system. Traditional pipe joining methods for hard piping systems consist of welding, brazing or flanging which generally work well in data centers; but, with increased loads, frequent changes, and system expansions, these joining methods have become problematic. Piping systems utilizing a welded, brazed or flanged joining method are not easily accessible, feature limited design flexibility, introduce fire hazards to the jobsite and require lengthy system shutdowns to perform routine or unplanned maintenance activities.
Grooved mechanical piping technology—a method of pipe joining that requires no flame— provides a reliable piping system that ensures efficiency in construction and operation of a data center by reducing deployment time, providing an easily adaptable system and reducing downtime during routine or unscheduled maintenance.
Grooved pipe joining technology In 1925, Victaulic designed the first grooved end pipe joining system for water and air service piping. Recognized for its design flexibility and speed of assembly, grooved end pipe joining technology transformed the piping industry, leading to dramatic gains in building construction productivity. That is why among HVAC specifying engineers, building owners and installation contractors around the world, grooved mechanical pipe joining is the preferred pipe joining solution for both new construction and retrofit.
The mechanical joint, or coupling, is comprised of four elements: the grooved pipe, the gasket, the coupling housings, and the nuts and bolts. The pipe groove is made by cold forming or
machining a groove into the end of a pipe. The key section of the coupling housing engages the groove. The bolts and nuts are tightened with a socket wrench or impact wrench, which holds the housings together. In the installed state the coupling housings encase the gasket and engage the groove around the circumference of the pipe to create a triple seal unified joint that is enhanced when the system is pressurized.

Installing a grooved mechanical piping system The installation of the piping system using the grooved mechanical pipe joining method leads to significant on-site man hours savings. On average, field fabrication of a grooved system is up to 10 times faster than welding and six times faster than installing a field-fabricated flanged joint. The simplified assembly and installation leads to a reduction in project calendar days by as much as one half, optimizing labor risk management. The reduction in calendar days realized by installing a mechanical piping system gives owners the ability to meet, and even beat, compressed construction schedules and avoid liquidated damages.
By reducing on-site man hours and eliminating the risk of fire and release of noxious fumes, the installation of mechanical piping systems increases jobsite safety and decreases overall risk when compared with welding, brazing or soldering.
Most injuries on job sites occur via material handling, but the most significant risks — in terms of potential impact on people and businesses — are caused by fire and fume hazards. Mechanical pipe joining eliminates fire, open arcs, sparks, flames and toxic-fume hazards that are associated with welding, brazing, and soldering. Welding is associated with a number of potential health risks, as well as the risk of severe burns. By specifying a mechanical pipe
joining system, an engineer reduces the owner's overall risks, especially those related to project schedule, costs and potential liability.
Depending on the type of project (e.g., new construction vs. expansion/retrofit), hazards may become a risk not only to construction workers, but also to the occupants of the structure and surrounding facilities. When someone is welding, to comply with mandatory safety regulations, all other work in the area must be postponed, leading to costly downtime and possible employee evacuation. Evacuations are beneficial to safeguard workers, but business realities lead to yet another potential danger: the pressure and rush to catch up from a shut down or loss in
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seal. When the multiple bolts are removed and the flanges are pulled apart, the gasket will tear
and therefore needs to be replaced.
With a mechanical coupling, the compression loads on the gasket are different than the flange. The gasket has a C-shaped cross section seal that is pressure responsive and designed to handle cyclical loading. Systems can be pressurized and depressurized repeatedly for many years without fatiguing the elastomer material. Once installed, these couplings do not require any routine or periodic maintenance and can be left in place for the life of the system.
Grooved piping systems provide a union at every joint for ease of maintenance and future retrofits.
Operating efficiency is maintained during retrofit work, and systems can remain live without
interrupting cooling because properly placed butterfly valves installed using grooved couplings provide “dead-end” shutoff service for isolation allowing for easy system expansions or re- routing with little to no interference with existing operations. Expansion projects can be completed in occupied buildings without vacating the space because mechanical grooved piping does not release noxious fumes or introduce a fire hazard eliminating the need for hot-works permits or fire watch.
Protecting equipment using grooved mechanical piping systems In addition to making maintenance fast and safe, a grooved mechanical pipe joining system accommodates movement and deflections within the piping system reducing the need for periodic product repair or replacement and maintaining the operational integrity of the piping
system. Traditional welded or flanged piping systems have rubber bellows or a braided flexible hose to accommodate these movements; however, these materials often wear out over time requiring costly and time-consuming replacement.
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Flexible mechanical systems are engineered to allow the pipe to move and vibrate within the coupling, therefore localizing vibrations generated by HVAC equipment and reducing the amount of noise transmitted down the pipe line. The elastomeric gasket, contained inside the internal cavity of the ductile iron housing, creates a discontinuity in the piping system which aids in isolating vibrations therefore, protecting vital cooling equipment within the piping system. Furthermore, the ductile iron housings and gasket material have vibration dampening qualities

of their own, also serving to absorb vibrations. Testing has shown that systems utilizing three
consecutive flexible couplings near a source of vibration will experience a similar level of noise dampening as those systems using specialty products. Additionally, the ability of grooved systems to accommodate system movement reduces loads at equipment connections and keeps vital cooling equipment operating at peak efficiency.
The flexible grooved-pipe couplings reduce the transmission of stresses through a piping system, while the gasket and ductile iron housing combine to dampen vibration.
Nowhere is it more important to plan ahead for disasters than in a data center. According to The Uptime Institute, in 2001 a Tier III data center allocated 1.6 hours per year for IT downtime and only 0.4 hours of downtime in a Tier IV. Because the cooling system is vital to the operational integrity of the IT equipment, when the cooling systems goes down it is only a matter of minutes before the IT equipment begins to overheat.
Piping systems in earth quake prone areas will be exposed to forces and deflections beyond normal static conditions. These seismic forces can cause extensive damage when piping systems cannot accommodate these movements. Mechanically joined grooved systems can be designed so that the differential piping movement associated with a seismic event will be accommodated. The inherent deflection capability of the flexible grooved pipe coupling reduces transmission of stresses through piping systems. The deflection allowed by a flexible grooved-
pipe coupling reduces the transmission of stresses through a piping system thereby minimizingpotential system damage. As mentioned above, flexible and rigid couplings also provide discontinuity at each joint which helps minimize pipeline stresses generated during seismic movement.
Testing performed at the Real-Time Multi-directional Experimental Laboratory at the Center for Advanced Technology for Large Structural Systems at Lehigh University in Bethlehem, Pennsylvania; U.S.A proved the suitability of Victaulic grooved mechanical couplings to maintain operational integrity of piping systems during seismic events.
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Conclusion Owners, engineers and contractors are challenged to design, operate and maintain reliable and easily adaptable facilities that accommodate a revolving door of innovative technology. And while there are many construction and operational concerns to take into consideration, a data center’s cooling strategy is vital to all business operations. For cooling strategies that include chilled water systems, grooved mechanical piping technology provides a reliable piping system that maximizes efficiency by reducing deployment time during new construction, reducing downtime during maintenance and/or system expansions and maintaining operational integrity of the piping system and equipment on a day–to-day basis and in the unfortunate event of a natural disaster.
For more information on the Victaulic Seismic Testing Program, visit www.victaulic.com/seismic.
For more information on Victaulic solutions for data centers, visit www.victaulic.com/datacenters.
Contact a Victaulic Sales Representative.
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WHITE PAPER
Piping system design impacts safety in every phase of a project
By John Rutt September 2008
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Under the ASME Code of Ethics of Engineers, it’s the first of the fundamental canons: “Engineers shall hold paramount the safety, health and welfare of the public in the performance of their duties.”
Due to the nature of the work, this is a major challenge in construction. According to the Bureau of Labor Statistics, the construction industry has the second highest incidence rates for cases with days away from work. (Refer to Table 1 below.) More specifically, statistics compiled by the Construction Industry Institute indicate the majority of construction injuries are suffered by pipefitters, welders, plumbers, and the laborers who assist them. (Refer to Table 2 below.)
Table 1
Of all the major industries, construction has the second highest incidence rates of cases with days away from work.

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Table 2
Of all the leading crafts, those relating to piping systems have the highest rate of occupational injuries and illnesses.
The inherent dangers of installing and maintaining piping systems increase the importance of the mechanical engineer’s role in designing for safety and accident prevention – both during the construction of the project and throughout the lifecycle of the facility. There are three fundamental areas where mechanical engineers can positively affect safety: one, system constructability, two, best practices for training construction and inspection, and three, system
maintainability.
By specifying safer technology and methods in greater detail, an engineer can minimize the impact of, or possibly even eliminate the potential for, certain types of accidents and injuries. Although most injuries on jobsites and in the workplace occur from material handling, perhaps the most significant risks, in terms of potential impact on people and business, are the fire and fume hazards associated with welding, brazing and soldering on the jobsite.
Safety in constructability: The mechanical pipe joining advantage In the piping systems environment, mechanical pipe joining removes a number of

U
No volatile tanks
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By specifying mechanical pipe joining, an engineer can reduce these risks in the design phase, and thereby make a powerful contribution to reducing an owner’s risks, costs and potential liability. Furthermore, in keeping with the fundamental canon of “holding paramount the safety, health and welfare of the public”, that engineer can help create a safer environment for all involved.
For example, in addition to the inherent risks of fire, potential health risks associated with welding have been cited in studies and include: • Irritation of the eyes, nose, chest, and respiratory tract • Nausea, headaches, dizziness • Metal fume fever • Lung cancer • Urinary tract cancer • Heart disease • Kidney damage • Parkinson’s disease
Depending on the project environment (I,e., new construction vs. expansion/retrofit), these hazards can become a risk to not only the construction worker, but also to the occupants of the existing structure and surrounding facilities. The initial use of traditional joining technology can also limit the maintenance options for, or efficiency of, future repairs, replacements and retrofits.
Although there are established procedures and requirements for fire prevention and fume ventilation during welding, unfortunate incidents involving welding are
not uncommon in the news. Consider the potential risks to a hospital or school retrofit project, where occupants may not be easily evacuated or protected from these risks. Consequentially, to protect people from these hazards, construction schedules often must be rearranged and extended to allow off-shift work at the times when the buildings are unoccupied. Eliminating hotwork where possible reduces risk for the client, occupants and contractors.
Grooved installation-ready coupling Mechanical pipe joining requires no flame to join pipe, and involves no exposure to hazardous fumes. The grooved mechanical pipe joint shown above installs in
four simple steps. Lube it. Stab it. Join it. Drive it.
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Safety in practice: Increasing safety by specifying procedures In addition to enhancing safety by specifying safer pipe joining technology, an engineer can further contribute to a safe environment by defining best practices in product selection, training, installation and inspection. Performance-based specifications typically provide a good general scope of acceptable product and system performance requirements. In addition, engineers can also name specific manufacturers that they consider to be acceptable for the service and for high quality. Although it is often perceived that “three manufacturers” for a product or system must be specified to ensure an engineer’s non-biased objectivity, the fact is that legal precedents have been set at the District Court level which support the specifier’s right to issue a proprietary specification that designates a sole supplier in certain situations. The principles of the Massachusetts District Court Case, Whitten vs Paddock (1974), established that 1) proprietary specifications do not violate antitrust laws; 2) Few brands of products are exactly alike and specifiers who want to limit choices have every right to do so; 3) Other brands qualify as “or equal” only when the specifier says so; 4) The specifier may waive specifications in order to obtain a more desirable product for the end user, but the specifier is the only one who can determine if the product is more desirable; 5) The burden is on the not-specified manufacturer or supplier to convince the specifier that the product is equal for the purpose of the particular project. This provides specifying engineers with even greater control over the project, while also enabling them to ensure the highest quality and system performance for their clients.
Another way for the engineer to influence the quality of installations is by ensuring that those individuals installing the systems are educated in the proper
installation requirements in accordance with the manufacturer’s published instructions. Specifications can be written to include a section requiring installing contractors to obtain training directly from a manufacturer’s employees, in order to further ensure proper installation of their piping products and systems.
The final way an engineer can ensure that an acceptable system is delivered to the client is by detailing mandatory inspection and test procedures in the mechanical specifications. Selecting products and systems that are easy to install and inspect further increases the chances of having a successful start-up. For example, some grooved coupling manufacturers provide for quality control through easy visual confirmation of complete coupling installation. Complete joint
installation is easily verified because the coupling is designed so that the completed joint achieves metal-to-metal bolt pad contact. Welding, on the other hand, requires x-rays for quality inspection. System testing is an important practice that is typically detailed in specifications to ensure system performance. Specifying that manufacturers’ product (couplings, valves, specialties, etc.) performance ratings allow for proper hydrostatic system testing (typically 1.5 times the system operating pressure).helps to further ensure system integrity.
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Grooved coupling allows for easy visual inspection, as proper installation can be confirmed simply by checking that pad-to-pad contact is made.
Safety after completion: Improv ing the safety of ongoing maintenance Over the operating life of a facility, its piping system will require three basic categories of maintenance. These are: routine periodic inspection, physical changes or expansion, and unscheduled repairs. Due to its intrinsic design qualities, grooved mechanical pipe joining makes maintenance and system access easier, faster and safer minimizing downtime and the negative impact of any maintenance event
The advantage over welding and other methods in this area is self-evident. When pipes are welded together, they have no union point between them. In effect, they become a single, extended piece of metal. On the other hand, a grooved coupling provides a union at every joint, which allows for easy access to the system and flexibility for future system expansion. To access the system all a maintenance worker need only to unscrew one or two nuts and drop the section out. There are no torches, no saws and no welding machines needed. Even with flanged, lug or wafer type valves and accessories, the compression of flanged connections create significant maintenance challenges that dramatically increase the time and manpower needed for replacements and repairs. Components are difficult to remove, and often even more challenging to reinstall. In contrast, grooved joints provide a true union and eliminate many of the challenges associated with traditional weld/flange systems. When the maintenance is complete, a mechanical coupling makes it easy to quickly get the system up and running again. The gasket is reinstalled, the coupling is placed back on the pipe, fitting or component, and the two bolts are tightened. In a welded system, repairs and maintenance demand that workers actually cut out the damaged pipe section and weld it back together: causing potential
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operational issues and safety hazards that are of particular significance in existing facilities and occupied spaces.
Coupling disassembly provides easy access for maintenance or system expansion.
As with any engineering challenge, all system characteristics and design options must be thoroughly considered to find the optimal solution. There are applications such as steam services, for example, for which grooved piping systems are not suitable and weld/flange systems are required. It is imperative that the performance capabilities of the systems and products meet the system performance requirements. For example, the proper gasket material and design selection is one of the most important elements to ensure the safe, long-term performance of a grooved mechanical system. Advances in elastomer technology partnered with innovative coupling and gasket designs provide performance in water applications with temperatures up to 250 degrees F and pressures from absolute vacuum up to 1000psi. However, all gaskets, couplings
and components are not necessarily equal in performance and the capabilities of each manufacturer and product must be evaluated individually to confirm system and client requirements are met.
The engineer has a vital role in improving safety at every stage of a project’s lifecycle: from initial design, to installation, to ongoing maintenance. By specifying mechanical pipe joining solutions and their associated procedures, an engineer can have a powerful and positive impact in creating a safer environment that minimizes risk, increases efficiency, and brings greater value to owners, contractors and occupants. For over 80 years, mechanical pipe joining has been used in the world’s most demanding applications because of its ability to provide
a wide range of design solutions to the engineer, however, nothing is more paramount than the safety, health and welfare of the public and grooved mechanical piping systems provide safety at every phase of a project.
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By Larry Thau
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Noise carried through piping systems is becoming an increasing challenge to owners,
engineers and contractors. The reasons for this include changing design requirements
that place mechanical rooms on intermediate and top-floor building levels, and greater
use of lightweight construction materials that tend to vibrate more than traditional heavy
materials.
The business risk of not specifying systems at the design stage that serve to attenuate
sound is that, frequently noise issues will continue to be a problem throughout the
lifecycle of the structure. This can result in unsatisfied owners, whose occupants may
complain that the objectionable noise is distracting to the point that it effects
concentration and productivity. In this way, noise issues can also have a bottom-line
impact on the Engineer or Contractor, who may need to perform numerous call-backs to
attempt to fix the problem.
Therefore, it’s not surprising that a sizable industry has grown around the idea of
minimizing piping-borne sound. This article will focus on the proven sound attenuation
benefits of a technique commonly thought of as a productivity-enhancing tool: the
grooved mechanical pipe joint. Most often specified when contractors are seeking a
fast, easy, safe and reliable alternative to welding, grooved mechanical pipe joining has
a long history of effectively minimizing noise and vibration in applications around the
globe.
Mechanical equipment in piping systems creates vibration, which can potentially lead to
significant noise issues. In most commercial and industrial applications, occupants can
tolerate certain levels of background noise from the HVAC system. The issue arises
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when the sounds become cyclic and droning, or on the other hand, arrive in sudden
bursts when equipment switches on.
Of course, the surest way to avoid sound issues is to bring an acoustics professional
into the project at the design stage. Yet budgets do not always permit this, and there
are many construction-grade projects where the owner does not consider sound to be a
critical issue, at least until after the fact. Those “conventional” situations are the areas
being addressed here.
Traditional sound attenuation
When faced with the need to diminish noise and vibration from equipment connected to
the circulation system, designers have traditionally specified elastomeric flexible arch
connectors. These connectors create a discontinuity in the metal piping (as opposed to
welding), so that less vibration is transferred down the line. Additionally, they are
commonly constructed of nylon, Dacron® or polyester material to help absorb vibration,
and are formed in a spheroidal shape to permit deflection in all directions. This
advantage, however, is also the weakness of the elastomeric arch.
Because the elastomeric flex connector’s shape allows pressure to exert in all
directions, control units such as restraining rods, plates and/or anchors are required.
These items are used to prevent excessive stretching of the unsupported elastomer due
to system pressure thrusts. But when such thrusts occur repeatedly, and the connector
is overextended through time, use and pressure, failure can result. Additionally Flex
Connectors employ unrestrained rubber as a pressure boundary in systems which
otherwise have continuous metallic encasement. This becomes a particular concern in
high rise construction where large pressure differential are often present.
The complexity of the reinforcing systems also means that installation can be time-
consuming and post-commissioning adjustments can be required. As a result, such
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connectors are usually placed only at the point where the pump or other equipment
connects directly to the piping system.
Mechanical Joining: An alternate solution
In independent tests performed by NUTECH Testing Corporation/SE Laboratories, Inc.,
a laboratory which specializes in environmental and field mechanical testing, another
device was found to be at least as effective in sound attenuation as flexible arch
connectors.
Interestingly enough, this “new” solution was invented over 90 years ago, and has a
major presence in the construction industry as a means for simplifying pipe joining,
assuring reliable connections and shortening production schedules. That method:
grooved mechanical pipe joining, also known as grooved pipe joining.
Proven sound attenuation qualities
When the structure of a grooved pipe coupling is examined, it is easy to see why it
effectively reduces sound transmission. The resilient elastomeric gasket, contained
inside the internal cavity of the ductile iron housing, creates a discontinuity similar to
that of a flex connector. The material from which the gasket is made also serves to
absorb vibration.
Figure 1: The flexibility of grooved-pipe couplings reduces the transmission of stresses through a piping
system, while the gasket and ductile iron housing combine to dampen vibration.
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The key distinctions of a grooved pipe joint over a flex connector are inherent in the
proprietary design of the coupling. Its unique construction enables the gasket to seal
against the pipe, while the ductile iron housing provides both space for the elastomeric
material to flex and containment to prevent overstretching. Overall, the coupling works
to create a permanent leak-tight seal with no need for additional reinforcement.
Additionally, ductile iron has vibration dampening qualities of its own, so the external
housing also serves to absorb sound.
The sound attenuation characteristics of grooved mechanical couplings are not a newly
discovered phenomenon. Testing conducted by L.S. Goodfriend and Associates in 1970
– 1971 concluded that: “A substantial vibration reduction is achieved in pipe systems
which employ the Victaulic Style 77 coupling.” (Actual measure reduction in decibel
level ranged from 2.3 to 12.1 dB over a wide frequency range.) {Note: Victaulic is the
world’s leading manufacturer of grooved mechanical joining solutions.}
More recently, SSA Acoustics in Seattle, Washington conducted field measurements at
the request of their client that showed “three Victaulic couplings placed in series in a
pipe section have a comparable performance to twin-sphere neoprene connectors, and
a superior performance to braided metal hoses. Victaulic couplings dampened the
overall vibration amplitude by 80 – 90%.”
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