Reverse flow at multi stage pumps 1

[Ayden]

What can happen to a multi stage pump when turning it out and check valve doesn't work? Will this destroy the pump, seize damaged?

thanks for any help....

 

[smckennz]

In general it depends on the pump.
It will normally run a little faster backwards than forwards, so it needs to be checked that safe speeds are not exceeded. Also some shaft seals are unidirectional so this also needs to be checked.
I have recently put in a 300kW, 3000rpm multistage booster pump deliberately with no discharge check valve.
I calculated the no load reverse speed to be 3400rpm. The manufacturer said the pump assembly (pump, motor, coupling, seal) can stand in excess of 4000rpm, so we will see.

The practice of permitting reverse rotation, is reported by Stepanoff as being common with deepwell (multistage) pumps with no mechanical damage arising.

Cheers

Steve

 

[vanstoja]

See my 2/5/04 and 2/7/04 posts in thread407-86310. Generally centrifugal pumps with specific speeds below about 4000 (RPM-GPM-Ft.) will run away under reverse flows at higher rotational speeds than the maximum driven forward running speed. Shaft and impeller stresses at motor driving speeds up to 3600 RPM usually have sufficient structural design margins to withstand such reverse flow runaway speeds without problems. Whenever centrifugal pumps are being driven by reverse flows, attempts to start the motor can lead to stall or crawling conditions that may overheat and damage the motor windings. Hence, there should be some warning device to detect pump reverse flow runaway conditions and to prevent energization of the pumpmotor.