Calculate surge pressure with the Joukowsky formula, size arrestors per PDI WH-201, and check FPC 604.10 compliance for Florida's high-pressure supply systems
PDI WH-201 SIZING
Surge Calc
Arrestor Size
FL Code
Quote
β‘ Water Hammer Surge Pressure Calculator
Joukowsky Formula: ΞP = Ο Γ a Γ ΞV / 144 (in PSI), where Ο is water density (62.4 lb/ftΒ³), a is pressure wave speed (ft/s), and ΞV is the velocity change (ft/s). In FL, high municipal supply pressures (60β100+ PSI) amplify water hammer significantly.
Check your gauge at a hose bib with no flow. FL average: 60β80 PSI. Above 80 PSI requires PRV (FPC 604.8).
β‘ FL Note: FL's high municipal water pressures (often 70β100 PSI before PRV) significantly amplify water hammer. A washing machine in an 80 PSI FL home can generate 300β600 PSI surge spikes that damage fixtures, joints, and water heater connections over time.
π‘οΈ PDI WH-201 Arrestor Sizing Calculator
PDI WH-201 (Plumbing and Drainage Institute) is the standard method for sizing water hammer arrestors. Arrestors are classified by letter (A through F) based on the number of fixture units they protect. FPC 604.10 requires arrestors on quick-closing valves.
Add Fixtures with Quick-Closing Valves
PDI WH-201 Sizing Result
Add fixtures above to calculate arrestor sizing.
π PDI WH-201 Arrestor Size Reference
PDI Class
Fixture Units
Pipe Size
Common Use
A
1β11 FU
β " to Β½"
1β3 fixtures; single washer
B
12β32 FU
Β½"
Small residential branch
C
33β60 FU
Β½" to ΒΎ"
Most residential main lines
D
61β96 FU
ΒΎ"
Large residence / small commercial
E
97β154 FU
ΒΎ" to 1"
Commercial / multi-family
F
155β330 FU
1"
Large commercial buildings
Popular FL Arrestor Brands
Sioux Chief Mini-Rester 660 Series β
ClassesA, C, D β most common FL
InstallSweat or threaded; stands or inline
Most popular FL plumber choice; pre-charged permanent piston
Watts Series 15M Series
ClassesA through F available
InstallThreaded; brass body
Zurn Wilkins WHA / WHAB
ClassesA, B, C, D
InstallSweat or push-fit connections
π‘ Placement tip: Install on the hot AND cold supply to each appliance with a quick-closing valve. Locate within 6 ft of the valve, on the supply side. Vertical orientation preferred for self-recharging piston models.
π FL Plumbing Code β Water Hammer
FPC 604.10 β Water Hammer
FPC 604.10: The flow of water shall not produce a water hammer condition. Where quick-acting valves are used, they shall be provided with water hammer arrestors designed and installed in accordance with the PDI Standard WH 201, ASSE Standard 1010, or AWWA Standards C651 through C654.
Quick-acting valves include: solenoid valves (dishwashers, washing machines, ice makers, irrigation), diaphragm valves, ball valves operated mechanically by appliances, and flush valves for toilets.
FPC 604.8 β Maximum Supply Pressure
FPC 604.8: Where the water pressure in the public water main or the individual water supply system exceeds 80 psi (552 kPa), an approved pressure-reducing valve conforming to ASSE 1003 or CSA Standard B356, with strainer, shall be installed.
Critical for water hammer: High supply pressure amplifies hammer. A PRV set to 60β70 PSI significantly reduces surge pressure β often eliminating hammer symptoms without adding arrestors. FPC 604.8 makes PRV installation mandatory above 80 PSI.
ASSE 1010 β Water Hammer Arrestors Standard
ASSE 1010 (American Society of Sanitary Engineering) is the product standard for water hammer arrestors. FPC references both PDI WH-201 (sizing) and ASSE 1010 (product compliance). Always specify ASSE 1010-listed arrestors for FL building permit compliance.
Key ASSE 1010 requirements: Pre-pressurized sealed piston design; rated for 250 PSI working pressure; 200Β°F max temperature; shall not require periodic maintenance; cycle-rated to 500,000+ cycles.
Water Hammer Compliance Checklist
Static supply pressure measured and documented Measure at hose bib with no flow; FL systems commonly 60β100+ PSI; above 80 PSI requires PRV per FPC 604.8
PRV installed and set to 60β70 PSI if static pressure exceeds 80 PSI FPC 604.8 β ASSE 1003-listed PRV with integral strainer; typically at main entry; verify downstream pressure after installation
Water hammer arrestors on all quick-closing valve appliances FPC 604.10 β washing machine, dishwasher, ice maker, solenoid irrigation valves; ASSE 1010-listed; PDI WH-201 sizing
Arrestors installed within 6 ft of appliance, supply side PDI WH-201 installation guidance β closer is more effective; one on hot supply, one on cold supply for washers
Irrigation system solenoid valves have arrestors or slow-close valves Multiple zone solenoids closing simultaneously can create severe hammer; arrestor at manifold or each zone valve recommended
Water supply pipes properly secured and supported Unsupported pipes amplify hammer noise and vibration β copper: every 6 ft horizontal, 10 ft vertical; straps at each joint recommended
Air chambers (if used) checked and recharged Traditional air chambers lose air over time and become waterlogged β replace with ASSE 1010 piston arrestors which do not require recharging
Check valve on booster pump has slow-close feature Fast-closing check valves on booster pumps create severe water hammer β specify slow-close (10β30 sec) check valves for booster applications
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Joukowsky water hammer formula: surge pressure delta P equals rho times a times delta V divided by 144 to convert to PSI; rho is water density 62.4 lb per cubic foot; a is pressure wave speed in feet per second depending on pipe material; delta V is velocity change in feet per second; velocity V equals flow rate Q in GPM times 0.4085 divided by inside diameter squared in inches; for copper pipe a equals approximately 4000 feet per second; for PEX a equals approximately 500 feet per second; wave speed ratio explains why PEX is much quieter than copper for water hammer
Pipe inside diameter reference for water hammer velocity calculation: 1/2 inch copper type L inside diameter 0.545 inch; 3/4 inch copper type L 0.785 inch; 1 inch copper type L 1.025 inch; 1/2 inch PEX 0.475 inch; 3/4 inch PEX 0.671 inch; velocity at 4 GPM through 3/4 copper equals 4 times 0.4085 divided by 0.785 squared equals 2.65 feet per second; surge at copper equals 62.4 times 4000 times 2.65 divided by 144 equals 4581 PSI theoretical instantaneous for complete instant closure
PDI WH-201 fixture unit table for water hammer arrestor sizing: clothes washer 4 fixture units; dishwasher 2 fixture units; toilet flush tank 2 fixture units; toilet flush valve 4 fixture units; shower 2 fixture units; lavatory 1 fixture unit; kitchen sink 2 fixture units; refrigerator ice maker 1 fixture unit; irrigation zone solenoid 5 fixture units; standard residential home typically 15 to 40 total fixture units; PDI class C covers 33 to 60 FU and is most common for full house residential applications
Florida water pressure issues: FL municipalities often deliver 70 to 100 PSI at the meter especially in hilly areas; Collier County known for very high pressures; PRV is required by FPC 604.8 above 80 PSI; properly set PRV at 60 to 65 PSI dramatically reduces water hammer severity; PRV setting combined with water hammer arrestors on all solenoid valves eliminates virtually all water hammer complaints in FL homes