Water Hammer

A brief pressure spike, commonly called a water hammer, occurs when a high velocity fluid is suddenly stopped. It is often brought on by the fast closing of a valve somewhere in the system. The hydraulic system designer can approximate the magnitude of the pressure spike with the following formula. This formula assumes a “hard” system with non-compliant fluid passages, and will, therefore, yield a worst-case value for the peak pressure.

∆P = Pressure rise caused by water hammer effects (psi)

I = Flow rate (GPM)

S = Specific gravity, click here to learn more

B = Bulk modulus (psi), click here to learn more

D = Inside diameter of fluid passageway upstream of the Lee component (inches)

EXAMPLE: A Lee component (such as JEHA1875500L) is flowing 1 GPM of MIL-H-83282 at 80°F with 4000 psi upstream and 3500 psi downstream. The component is being fed through a 0.15 inch diameter passage upstream. If a valve is suddenly shut downstream of the component, the pressure spike will be:

The maximum upstream pressure would then be: (4000 psi steady state) + (1340 psi spike) = 5340 psi total.