Preventing water hammer

What is water hammer in pipes?

Water hammer is a pressure wave that occurs when liquid flows through a pipe and there is a sudden change in the liquid velocity. This results in pressure changes which can lead to damage to the pump or the piping system. Changes in the liquid velocity can be caused by the pump being stopped suddenly or when valves are quickly closed.

What causes water hammer in pipes?  

When a valve is closed suddenly at the end of a long length of piping, the liquid velocity is converted into pressure. This pressure moves like a shock wave along the pipe and reaches its maximum force at the valve. Water hammer in the pipe contains a lot of energy and the resulting knocking sound can be clearly heard. The pressure increase in the pipe can reach up to 100 times the fluid velocity.

Water hammer in the pump

In a pipe system, the liquid is transported through the pump. We routinely see damaged pumps due to the effect of water hammer. In addition to damaged fittings in the pipe, a broken pump shaft is at the very top of the list of water hammer problems.

How can you prevent water hammer in your pump system?

It is the responsibility of the pump operators to prevent water hammer in the pipe system and there are a number of ways this can be achieved. The following points will help prevent this problem: 

• For diesel driven and frequency controlled pumpsets always accelerate and decelerate the pump speed slowly and smoothly. 
• Install a pressure relief valve in the discharge line which can open when a predefined pressure is reached.
• Place a water hammer arrestor in the pipe creating an air cushion which serves as a buffer.
• Fit slow closing valves in the pipe system.

Other issues such as choice of material, keeping the suction inlet free from sudden blockages and using the emergency stop only in case of emergencies can also help to prevent water hammer damage in your pump system.