Water Hammer Pressure Calculator

Inputs

View results

Flow rate (Q)

Volumetric flow before the valve, pump trip or transient event.

L/min

Pipe inside diameter (D)

Actual inside diameter of the pipe or tube.

Pipe length to wave reflection (L)

Distance from the event to the reservoir, pump, closed end or main reflection point used for the 2L/a timing screen.

Wall thickness (t)

Pipe wall thickness used in the elastic-pipe wave-speed approximation.

Closure / trip time (tc)

Time for the valve, pump trip or event to change the flow.

Velocity change (dV/v)

Percent of initial pipe velocity removed or changed by the event. Use 100% for a full stop.

Static line pressure (P0)

Operating pressure before the surge event.

bar

Pressure rating (Pr)

Pipe, valve or equipment pressure rating used for the margin check.

bar

Fluid density (rho)

Water is about 998 kg/m^3 near room temperature.

kg/m³

Fluid bulk modulus (K)

Effective liquid bulk modulus. Entrained air can reduce the effective value significantly.

GPa

Pipe material modulus (E)

Young modulus used for pipe-wall elasticity. Use manufacturer data for plastic pipe, hose or reinforced tube.

Results

Default result

Edit inputs

Total surge pressure(P_total)

14.17bar

Pass

56.7% of rating

Also computed

Effective surge pressure(dP)10.17bar

slow-closure factor 0.426

Pressure rating margin(Pr - P_total)10.83bar

Critical closure time(2L/a)0.04258s

entered event is slower than critical

Estimated wave speed(a)1,409m/s

Initial pipe velocity(v)1.698m/s

Instantaneous surge(rho*a*dV)23.88bar

Surge pressure stays at the instantaneous Joukowsky value until closure is slower than 2L/a, then is reduced by critical time divided by closure time.

Method notes 4 notes

Joukowsky surge pressure: dP = rho*a*dV. This is the classic sudden-flow-change water hammer relation.
Wave speed uses a thin-wall elastic-pipe approximation: a = sqrt((K/rho)/(1 + K*D/(E*t))). Plastic pipe, hose, lining, restraints and entrained air can change the real wave speed.
If closure/trip time is slower than 2L/a, this calculator applies a simple (2L/a)/closure-time reduction. Complex networks need transient analysis, valve curves and pump/system data.
This is a screening model only. Final surge control can require manufacturer ratings, supports, branch topology, air pockets, accumulators, surge tanks, relief valves and a qualified designer.