pump damage?

[puckman31]

We have a system, hot water circulating through 4" lines with 4 pumps with 10hp motors . Only 1 motor / pump working at a time. The hot water is circulating through all the pumps even thoug they are not running . Is this a bad design for the non running pumps because when the water passes through the pumps it makes a lot more noise than going through the running pump.

the pumps are in pairs at differrent locations of the systems.

 

[MikeHalloran]

Does the system do what it was intended to do?
Is there some problem other than acoustic noise?



Mike Halloran
Pembroke Pines, FL, USA

 

[Artisi]

Of course you can expect some noise with water being forced thru' stationary pumps.

 

[relentlessratt]

if the standby pumps are not running, install check valves. assuming the flow is from discharge side to suction...

 

[pumpking]

It is always wise to install check valves to avoid reverse rotation of the pumps, and when it is time to start a different pump, if it is running in reverse, you can cause damage to impellers and seals.

Another consideration is if Impellers are fixed with screwed bosses, then wrong rotation can cause them to unscrew from the shaft and cease on the casing.

Ash Fenn

http://www.cdrpumps.co.uk

 

[Artisi]

Screwed on impelers driven backwards by reverse flow will not unscrew, whereas driven backwards by the drive motor / engine is a completely different story and usually ends in an expensive disaster

 

[pumpking]

In theory Artisi you are correct, however, when working for a large multinantional pump manufacturer whom uses the screwed on Impeller design, we were called, in a few instances where reverse rotation had caused unscrewing from the shaft.

Parallel bore and keyway is by far the best way to secure Impellers, but i guess were diverting away from the actual question being asked here !

Ash Fenn

http://www.cdrpumps.co.uk

 

[Artisi]

Pumpking, I sold something like 3000 paper stock pumps over a number of years ranging in size from 6x3 to 16x14 all with screwed on impellers with many being utilised by a pump hire company for wellpoint and general purpose high head sump with the balance going to the paper industry. The only failures ever recorded of impellers unscrewing were units started in reverse.

But I agree with you on starting pumps that are running in reverse however, I know of one very large installation of a few thousand HP where the starting torque on a stationary pump was too high for the electric drive to get in underway, the cure was to to allow the pump to start rotating in reverse with return flow before pushing the start button - this overcame the high starting torque.

 

[QualityTime]

You won’t get much water “circulated” through your loop because it is taking the short cut through the non working pump. If you put a pressure gauge on the operating pump discharge you will find a difference in discharge pressure when no water is circulating through the non working pump and when there is water circulating through the non working pump. Bottom line is to put a check valve on each pump discharge. Things will work better

 

[Artisi]

I should have said break-away torque not starting torque.