Corpus sync: neutrality remakes, note hygiene, datasheet relocation, transformer-split cross-refs
---
title: Water Hammer Arresters and Shock Control
…32 unchanged lines
## Coordination across trades is mandatory because the triggering valves are frequently furnished by other trades.
−## The most common field failure is not a defective arrester - it is an arrester that was never installed because the solenoid valve that demanded it appeared only on an equipment schedule the plumbing designer never reconciled. Dishwashers, ice makers, clothes washers, and irrigation controllers are routinely scheduled by mechanical, kitchen-equipment, or landscape sub-disciplines. Every such device with an automatic supply valve triggers the arrester requirement and shall be reflected on the plumbing drawings. {note}
+## The most common field failure is not a defective arrester - it is an arrester that was never installed because the solenoid valve that demanded it appeared only on an equipment schedule the plumbing designer never reconciled. Dishwashers, ice makers, clothes washers, and irrigation controllers are routinely scheduled by mechanical, kitchen-equipment, or landscape sub-disciplines. Every such device with an automatic supply valve triggers the arrester requirement and shall be reflected on the plumbing drawings.
# Referenced Standards {toc}
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## The system design operating pressure shall not exceed the arrester's maximum allowable working pressure.
−## Most commercial systems operate at 60-80 psi because the IPC limits static pressure at fixtures to 80 psi and a pressure-reducing valve is set accordingly (see [[sync/domestic-water-piping-specialties]]). A standard 150 psi arrester is well-matched to that service. Where the supply pressure approaches or exceeds 80 psi - for example a PRV set at its ceiling or an unregulated high-static service - a 250 psi high-pressure arrester provides margin. {note}
−
−## Arresters installed on hot-water, recirculating hot-water, or combined hot/cold branches shall be rated for continuous service at the branch's maximum temperature up to 180°F.
−
−## Cold-only-rated arresters shall not be installed on any branch carrying hot water.
−
−## Standard cold-only units are typically rated only to about 80°F. Placed on a hot or recirculating branch they cook the seals and lose their cushion. The default specification on any branch that might ever carry hot water is the hot-rated unit; the cost difference is trivial relative to the failure. {note}
−
```datasheet
label: Maximum allowable working pressure (MAWP)
…6 unchanged lines
```
+## Most commercial systems operate at 60-80 psi because the IPC limits static pressure at fixtures to 80 psi and a pressure-reducing valve is set accordingly (see [[sync/domestic-water-piping-specialties]]). A standard 150 psi arrester is well-matched to that service. Where the supply pressure approaches or exceeds 80 psi - for example a PRV set at its ceiling or an unregulated high-static service - a 250 psi high-pressure arrester provides margin. {note}
+
+## Arresters installed on hot-water, recirculating hot-water, or combined hot/cold branches shall be rated for continuous service at the branch's maximum temperature up to 180°F.
+
```datasheet
label: Temperature rating
…5 unchanged lines
```
+## Cold-only-rated arresters shall not be installed on any branch carrying hot water.
+
+## Standard cold-only units are typically rated only to about 80°F. Placed on a hot or recirculating branch they cook the seals and lose their cushion. The default specification on any branch that might ever carry hot water is the hot-rated unit; the cost difference is trivial relative to the failure. {note}
+
# Sizing and PDI Size Class {toc}
## The arrester for each branch shall be sized to the cumulative water supply fixture units (WSFUs) of all fixtures served downstream of the arrester, per PDI-WH 201.
+```datasheet
+label: PDI size class
+type: select
+options:
+ - A (1-11 WSFU) - single appliance branch
+ - B (12-32 WSFU)
+ - C (33-60 WSFU)
+ - D (61-96 WSFU)
+ - E (97-159 WSFU)
+ - F (160-250 WSFU)
+default: A (1-11 WSFU) - single appliance branch
+```
+
## Sizing shall sum the WSFUs of every fixture on the branch, not the demand of a single fixture.
…21 unchanged lines
## A dedicated branch serving one dishwasher, one clothes washer, or one ice maker carries only a few fixture units and falls squarely in Class A. These single-appliance branches account for the overwhelming majority of arrester installations on a typical project; the larger classes appear at multi-fixture restroom branches and risers. {note}
−```datasheet
−label: PDI size class
−type: select
−options:
− - A (1-11 WSFU) - single appliance branch
− - B (12-32 WSFU)
− - C (33-60 WSFU)
− - D (61-96 WSFU)
− - E (97-159 WSFU)
− - F (160-250 WSFU)
−default: A (1-11 WSFU) - single appliance branch
−```
+## The governing PDI-WH 201 sizing table shall be specified for each branch based on its supply pressure.
```datasheet
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## The internal energy-absorbing mechanism shall be a sealed piston, diaphragm/bladder, or bellows type as scheduled.
+```datasheet
+label: Internal mechanism type
+type: radio
+options:
+ - Piston (standard potable service)
+ - Diaphragm/bladder (corrosive or aggressive water)
+ - Bellows (low-cycle service only)
+default: Piston (standard potable service)
+```
+
## Piston-type arresters are the default for standard potable water service.
…12 unchanged lines
## Calling for stainless or diaphragm construction "to be safe" on ordinary potable water adds cost without adding code compliance or service life. Piston-type brass is the correct and economical choice for the vast majority of installations; reserve the upgraded mechanisms and materials for the water-quality conditions that actually demand them. {note}
+# Body and Wetted-Parts Material {toc}
+
+## The arrester body and all wetted parts shall be of a material compatible with the conveyed water and certified to NSF/ANSI 61.
+
```datasheet
−label: Internal mechanism type
+label: Body and wetted-parts material
type: radio
options:
− - Piston (standard potable service)
− - Diaphragm/bladder (corrosive or aggressive water)
− - Bellows (low-cycle service only)
−default: Piston (standard potable service)
+ - Chrome-plated brass (standard potable)
+ - Stainless steel (DI, high-purity, corrosive)
+ - Polymer (PEX/CPVC systems)
+default: Chrome-plated brass (standard potable)
```
−# Body and Wetted-Parts Material {toc}
−
−## The arrester body and all wetted parts shall be of a material compatible with the conveyed water and certified to NSF/ANSI 61.
−
## Chrome-plated brass is the standard body material for potable water service.
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## On nonmetallic piping systems a polymer-body arrester avoids a dissimilar-metal transition and integrates cleanly with PEX or CPVC branches. Confirm the polymer body's pressure and temperature ratings cover the branch service before selecting it. {note}
−```datasheet
−label: Body and wetted-parts material
−type: radio
−options:
− - Chrome-plated brass (standard potable)
− - Stainless steel (DI, high-purity, corrosive)
− - Polymer (PEX/CPVC systems)
−default: Chrome-plated brass (standard potable)
−```
−
# Connections {toc}
## The arrester connection type and size shall match the branch piping system material and joining method.
−## Connection type shall be coordinated with the branch piping system to avoid field substitution.
−
−## Specifying NPT-threaded arresters into a press-fit copper system, or a sweat connection into a PEX system, forces a field adapter or a substitution RFI at every device. The arrester connection shall be selected to match the branch piping system - threaded, sweat-solder, press-fit, PEX crimp, or PEX expansion - so it lands on the branch tee as designed. Connection fittings shall comply with ASME A112.18.1 / CSA B125.1 (see [[sync/domestic-water-piping]] for branch piping joining methods). {note}
−
−## Male NPT threaded connection is the default because the branch tee is most commonly threaded for the arrester takeoff.
−
−## The typical arrester sits on a tee in the branch line, and a male NPT spud threaded into that tee is the most common and most widely stocked configuration across all six size classes. Sweat, press, and PEX variants exist for systems that do not thread the branch tee. {note}
−
```datasheet
label: Connection type
…20 unchanged lines
```
−# Installation Orientation {toc}
+## Connection type shall be coordinated with the branch piping system to avoid field substitution.
−## The arrester shall be installed in an orientation permitted by its listing for the as-built mounting condition.
+## Specifying NPT-threaded arresters into a press-fit copper system, or a sweat connection into a PEX system, forces a field adapter or a substitution RFI at every device. The arrester connection shall be selected to match the branch piping system - threaded, sweat-solder, press-fit, PEX crimp, or PEX expansion - so it lands on the branch tee as designed. Connection fittings shall comply with ASME A112.18.1 / CSA B125.1 (see [[sync/domestic-water-piping]] for branch piping joining methods). {note}
−## Any-angle-rated arresters are preferred so field mounting is not constrained by orientation.
+## Male NPT threaded connection is the default because the branch tee is most commonly threaded for the arrester takeoff.
−## An arrester listed for installation at any angle can be mounted vertically, horizontally, or inverted as the branch geometry requires, which eliminates a class of field conflicts where an overhead or horizontal run cannot accommodate a vertical-only unit. Avoid vertical-only units except where the mounting condition is known to be vertical. {note}
+## The typical arrester sits on a tee in the branch line, and a male NPT spud threaded into that tee is the most common and most widely stocked configuration across all six size classes. Sweat, press, and PEX variants exist for systems that do not thread the branch tee. {note}
+# Installation Orientation {toc}
+
+## The arrester shall be installed in an orientation permitted by its listing for the as-built mounting condition.
+
```datasheet
label: Installation orientation rating
…5 unchanged lines
```
+## Any-angle-rated arresters are preferred so field mounting is not constrained by orientation.
+
+## An arrester listed for installation at any angle can be mounted vertically, horizontally, or inverted as the branch geometry requires, which eliminates a class of field conflicts where an overhead or horizontal run cannot accommodate a vertical-only unit. Avoid vertical-only units except where the mounting condition is known to be vertical. {note}
+
# Placement {toc}
## Each arrester shall be located within 6 pipe diameters of the quick-closing valve it protects, measured along the pipe run.
+```datasheet
+label: Maximum distance from quick-closing valve
+type: range
+unit: pipe diameters
+min: 0
+max: 6
+step: 1
+default: 2
+```
+
## Placement close to the valve is what makes the device work.
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## Arresters installed in walls, chases, or other concealed locations shall be made accessible for future inspection through an access panel or removable sleeve.
−## Concealed arresters require permanent access.
−
−## An arrester is a sealed mechanical device with a finite service life; it must be inspectable and replaceable without demolishing finished construction. Concealed installations shall be provided with an access panel or removable sleeve, and the access location shall be coordinated with the architectural finish drawings so the panel lands in an acceptable surface. The access provision for each concealed arrester is shown at [[drawing: access panel locations]]. {note}
−
```datasheet
−label: Maximum distance from quick-closing valve
−type: range
−unit: pipe diameters
−min: 0
−max: 6
−step: 1
−default: 2
−```
−
−```datasheet
label: Concealed-installation access provision
type: radio
…5 unchanged lines
```
+## Concealed arresters require permanent access.
+
+## An arrester is a sealed mechanical device with a finite service life; it must be inspectable and replaceable without demolishing finished construction. Concealed installations shall be provided with an access panel or removable sleeve, and the access location shall be coordinated with the architectural finish drawings so the panel lands in an acceptable surface. The access provision for each concealed arrester is shown at [[drawing: access panel locations]]. {note}
+
# Testing {toc}
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## Field acceptance is by operation, not by gauge.
−## Because the arrester's effectiveness is judged at the moment a valve slams shut, acceptance testing consists of operating each quick-closing valve through several open/close cycles and confirming the absence of banging and visible pipe movement. Any branch that still hammers shall be investigated for an undersized, mislocated, or omitted arrester before acceptance. {note}
+## Because the arrester's effectiveness is judged at the moment a valve slams shut, acceptance testing consists of operating each quick-closing valve through several open/close cycles and confirming the absence of banging and visible pipe movement. Any branch that still hammers shall be investigated for an undersized, mislocated, or omitted arrester before acceptance.
# Installation Quality {toc}
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## The warranty shall cover the full replacement of any arrester that loses its cushion within the warranty period.
−## The defining failure mode of an arrester is silent loss of its gas charge, so the warranty that matters is the one covering that exact condition. The specified warranty shall explicitly address loss of cushion, not merely gross mechanical defect. {note}
+## The defining failure mode of an arrester is silent loss of its gas charge, so the warranty that matters is the one covering that exact condition. The specified warranty shall explicitly address loss of cushion, not merely gross mechanical defect.
```datasheet
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## The Contractor shall furnish spare arresters of each size class installed on the project for owner stock, in the quantity scheduled.
−## Spare units rather than repair kits are the appropriate spare for sealed arresters.
−
−## A listed arrester is a sealed assembly; it is replaced as a unit, not rebuilt in the field. The useful spare is therefore a small stock of complete arresters in each installed size class, allowing maintenance to swap a waterlogged or failed unit without procurement delay. {note}
−
```datasheet
label: Spare arresters furnished (per installed size class)
…5 unchanged lines
default: 1
```
+
+## Spare units rather than repair kits are the appropriate spare for sealed arresters.
+
+## A listed arrester is a sealed assembly; it is replaced as a unit, not rebuilt in the field. The useful spare is therefore a small stock of complete arresters in each installed size class, allowing maintenance to swap a waterlogged or failed unit without procurement delay. {note}