## Water Hammer

A brief pressure spike, commonly called 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 that assumes a "hard" system with non-compliant fluid passages, and will, therefore, yield a worst case value for the peak pressure.

ΔP = Pressure rise caused by water hammer effects (psi)
I = Flow rate (GPM)
S = Specific gravity, see graph
B = Bulk modulus (psi)
D = Inside diameter of fluid passageway upstream of the Lee component (in.)

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 in. dia. 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) + (1100 psi spike) = 5100 psi total