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Three general operating practices used to minimize water hammer during CCW pump start up and normal shutdowns

WATER HAMMER

The very large CCW flow rate results in huge kinetic energy of the flowing water, and hence it promotes severe water hammer during CCW pump start up, shutdowns and trips.

How to Minimize Water Hammer

To minimize water hammer the following general operating practices are used during CCW pump start up and shutdown.

1. A sufficient time delay before the next pump Is started up or shut down.

This allows the energy of pressure waves in the system to destroy before the system is subjected to another flow surge.

Time delay : About 5 minute

2.Proper position and slow opening / closing of the CCW pump discharge valve during pump start up and shutdown

a)      Each CCW pump is started against its discharge valve fully closed or slightly pre-opened (depending on the plant) and then the valve opens gradually.

b)      During normal pump shutdown first the discharge valve closes gradually and when it is fully closed (or nearly fully closed depending on the plant) the pump motor is switched off.

Note : Both these techniques minimize flow and pressure surges in the CCW system

3. Opening the condenser outlet isolating valves before the first CCW pump is started up.

  • This prevents a water collision with these valves when the first water is delivered by the pump.
  • In most plants, the above practices are incorporated into the automatic controls of the CCW pumps and valves.

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