Water Hammer Arrestor Sizing
Size arrestors per ASSE 1010/PDI-WH201
Fixture Count
Arrestor Requirements
Required Arrestor Size
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ASSE 1010 Rating
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Equivalent Fixture Units
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Estimated Shock Pressure
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Quantity Required
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Installation Notes:
• Install within 6 feet of quick-closing valve
• Mount vertically or horizontally per manufacturer
• Size A-F per PDI-WH201 fixture unit ratings
• Install within 6 feet of quick-closing valve
• Mount vertically or horizontally per manufacturer
• Size A-F per PDI-WH201 fixture unit ratings
ASSE 1010 Arrestor Sizes
| Size | Fixture Units | Typical Use |
|---|---|---|
| A (SS) | 1-11 | Single fixture |
| B (S) | 12-32 | Small group |
| C (M) | 33-60 | Branch line |
| D (L) | 61-113 | Large branch |
| E (XL) | 114-154 | Main line |
| F (XXL) | 155-330 | Commercial main |
Understanding Water Hammer
What Causes Water Hammer?
Water hammer occurs when flowing water is suddenly stopped or changes direction. The kinetic energy converts to pressure waves that can:
- Create loud banging noises
- Damage pipes and fittings
- Cause premature valve failure
- Lead to pipe joint separation
Shock Pressure Formula
ΔP = ρ × c × ΔV / 144
ρ = Water density (62.4 lb/ft³)
c = Wave speed (~4700 ft/s in copper)
ΔV = Velocity change (ft/s)