Controlling Water Hammer in Hydraulics

At times hydraulic machineries pose the problem of high vibration in pumps, lines and tanks. This problem of constant vibration is termed as water hammer. The concept of water hammer is discussed in detail below:

Water Hammer: The Term
As the term itself suggests, water hammer refers to the banging sound of fluid through the pipe which is created due to the pressure wave, a by product of varying fluid velocity, within the pipe. When the banging effect heightens, it almost sounds as if the pipe is being hammered, thus, the term water hammer was coined to refer the problem. The common traits of this problem are high noise levels, broken pipes and vibrations.

Technical Cause of Water Hammering
Technically, when a moving column of hydraulic fluid hits a solid boundary, its velocity drops down to zero and the fluid column looses its strength to absorb the (kinetic) energy affiliated with its motion. Though as the fluid is incompressible, the deformation henceforth is smaller making the fluid accumulate energy like a spring. The level of pressure rise can be calculated as:

Pr = P + u p c

where “P” refers to initial pressure, “u” and “p” refer to initial fluid velocity and density while “c” represents the speed of sound within the fluid.

Solution
Certain damping devices like accumulators can be used to curb down the noise problem. However, as per the above equation, fluid velocity is the only variable which can be manipulated to address the main problem. The lower the fluid column velocity would be, the lower the subsequent pressure rise would be, hence resultantly, lower sound effect.