Water Hammer Arrestor Sizing

PDI WH-201 designation from total fixture units.

Run the calculator

Example

You enter

Total fixture units (WSFU) 30
Branch length (ft) 25
Pipe internal diameter (in) 1

You get

Designation AA-B
WSFU total 30
Pipe diameter (in) 1
Pre-charge (set air side, system depressurized) 60

Checked against published worked examples from: PDI.

Details, formula, and sources

Formula or tablePDI WH-201 method: size A–F selected by the branch's total fixture units (WSFU); a branch over 20 ft is flagged for an additional unit at each fixture group.

Source and editionPDI WH-201 by name.

Free accessPDI specifications licensed; manufacturer data sheets (Sioux Chief, Watts) free at each manufacturer site.

What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

API field nameswsfu, length_ft, internal_diameter_in, designation, wsfu_total, pipe_diameter_in, precharge_psi

Closure speed assumption fast-closing solenoid valvePDI WH-201 by name