End-suction pump Variable frequency
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For the frequency adjustment of end-suction pumps, is it necessary to reduce the frequency first before shutting down the pump? If the pump is stopped without reducing its speed, will water hammer occur?
If the operating conditions permit, it is of course best to first reduce the frequency before stopping the pump, thereby extending the equipment’s service life. It’s not a problem to stop the pump directly, as a check valve is installed at the outlet; the pipeline may experience vibration or unusual noises
In an emergency, the pump will definitely be stopped immediately. Those who are able can gradually stop!
Shutting down the pump by reducing its frequency is normal operation; it is also acceptable to shut it down in an emergency.
If it is stopped suddenly, water hammer will definitely occur. This is because centrifugal pumps transport liquid by utilizing the centrifugal force generated by the rapidly rotating impeller; if the pump operates at full load and is stopped without reducing its speed, the liquid being pumped out will flow back immediately, resulting in water hammer. {:2_40:}
It is certainly better for the equipment to reduce the frequency before shutting down the pump, but the conditions in actual production do not allow this. For example, we have dozens of pumps on site, some with variable frequency drives and others operating at fixed frequency. Due to the frequent start-ups and shut-downs, it is impossible to have someone present to operate each pump manually; therefore, many of the pumps operating at fixed frequency are simply shut down directly, with their restarts being triggered automatically through interlocks. The decision has to be made based on the actual production conditions on site. Of course, the issue of water hammer you mentioned does exist, and the method of operation you suggested is also fine, provided that the conditions permit it