When the electric water pump is started with combined voltage, it can accelerate from standstill to rated speed in less than 1s, and the flow rate in the pipe increases from zero to rated flow rate. Because the fluid has momentum and a certain degree of compressibility, so the rapid change of flow will cause the impact of over-pressure or under-pressure in the pipeline, and the phenomenon of "cavitation".

The impact of pressure will make the pipe wall force and produce noise, as if hammering the pipe, called the "water hammer effect".

Water hammer effect has a very strong destructive effect, can lead to the rupture of the tube or sore, damage to valves and fasteners.

When the power is cut off and shut down, the potential energy of the pumping system will overcome the inertia of the motor and name the system to stop sharply, which will also cause the impact of pressure and water hammer effect.

In order to eliminate the serious consequences of water hammer effect, in the pipeline need to be subject to a series of buffering measures and equipment.

The use of frequency converter speed control, can be very convenient to lengthen the starting and braking time, delaying the starting and braking process, to completely and thoroughly eliminate the water hammer effect. Thereby, those used to deal with the water hammer effect of various measures and equipment, is included in the team should be streamlined to reduce.