The sudden change of water flow in the water pump outlet pipe due to valve opening, valve closing and pump stopping causes a sudden change of flow velocity in the pipe, which causes the change of momentum in unit time, and inevitably generates the corresponding inertial force, thus causing the alternating change of sudden rise and drop of pressure in the pipe. The phenomenon that the velocity and pressure of water flow change with time and position is called water hammer (or water hammer).

Pump station water hammer includes starting water hammer, valve closing water hammer and pump stopping water hammer (caused by sudden power failure, etc.). The first two types of water hammer will not cause problems endangering unit safety under normal operating procedures. The water hammer pressure value formed by the latter is often very large, leading to accidents.

Therefore, the purpose of studying and calculating water hammer is to:

① Propose protective measures when the maximum water hammer pressure causes damage to pipelines and units;

② Formulate the protective measures when the minimum water hammer pressure causes impermissible negative pressure in the pipeline and causes damage to the pipeline;

③ Prevent damage caused by unit reversal.