Water Hammer Calculator
Water Hammer & Surge Pressures
Data Collection
System Pressure:
(psi)
This calculator will produce the results based on the parameters entered. Velocity change, pipe run, material and sizing all are functions that influence the resultant surge. These calculations are based on water (62.4 lb./ft2) transmission within irrigation systems. A - Wave velocity is the speed of the pressure surge/wave through the pipe. The constant of 4660 used, is the velocity (ft/sec) of sound in water at 72°F. E - Modulus of elasticity, in tension, of the pipe materials. 400,000 = PVC 150,000 = HDPE 17,600,000 = Brass/Copper 30,000,000 = Cast Iron K - Bulk Modulus of elasticity, of the fluid in the pipe. Water = 300,000 psi. Tc - Critical Valve Close Time is the minimum time needed for the valve to reduce the actual flow of water, without producing a surge. •• TYPICALLY, IN ELECTRIC VALVES OVER 80% OF FLOW (VELOCITY) IS REDUCED IN THE LAST 30% OF THE TIME. (FROM THE 'CLOSE' SIGNAL TO ZERO FLOW) •• V - Velocity change, of the fluid within the system. In general, flow velocity *LESS* than 5 feet per second, is considered to be *SAFE*. Higher velocities may be used in cases where the operating characteristics of valves and pumps are known so that sudden changes in flow velocity can be controlled. %%%%%%%%%%%%%%%%%%%%%%% The intent of this calculator is to assist in informing users, engineers and others. Interpretation, use, and application is a function and responsibility of the user.
Velocity Change:
(ft/sec)
Pipe Run Length:
(ft)
Pipe Material:
PVC
HDPE
Brass/Copper
Cast Iron
Pipe Diameter:
(IPS)
1/2
3/4
1
1¼
1½
2
2½
3
4
5
6
8
Pipe Schedule/SDR:
SDR 32.5
SDR 26
SDR 21
SDR 17
SDR 13.5
SDR 11
Schedule 40
Schedule 80
Dimension Ratio:
D
R
= Pipe O.D. ÷ Wall thickness
Wave Velocity:
(ft/sec)
A = 4,660 ÷ [1 + {K x D
R
) ÷ E}]
½
Critical Valve Close Time:
(sec)
Tc = (2 x L) ÷ A
Surge Pressure:
(psi)
P = (62.4 x A x V) ÷ 4,636.6
Total Surge Spike:
(psi)
P
T
= P + System Pressure
© 2002 LASCO
Fittings, Inc.
ver.1.1
Copyright © 2010 Lasco Fittings, Inc. All rights reserved.
