4 replies to this topic

[emma14778]

We have a water pump which has about 90% of its feed from one source (Stream A) and 10%  from another (Stream . There is a tee about 5m before the suction of the pump.

 

Recently we had a failure on stream B which resulted in losing the full 10% flow. There were minimal changes in suction pressure but we lost 40% of our discharge pressure and flow dropped by about 20%. As far as I can tell we didn't reach any cavitation, the NPSHr (0.8m) is significantly lower than the NPSHa (13m).

 

Is it expected that a sudden loss of 10% of your feed would result in such drastic discharge pressure loss and loss in flow? I would have expected to temporarily lose the 10% of the flow but no more. Can this be defined as cavitation or is it something else I am unaware of? The main source of liquid comes from a vessel which has enough inventory to compensate for the loss in flow.

 

Thanks

 

Emily

[villivord]

You mention a flow reduction of 20%. Look at the relationship between pressure drop and flow (Darcy-Weisbach) which will explain the 40% reduction in discharge pressure. This can also be seen from your system curve, if available. The minimal changes in suction pressure sounds logic as I assume the system between the sources and pump is small compared to the system on the discharge side. 

 

How do you know source B is only 10% of the incoming feed? 

Edited by villivord, 23 November 2017 - 03:01 PM.

[Bobby Strain]

If you post a sketch with details maybe someone can help. And pump information.

 

Bobby

Edited by Bobby Strain, 24 November 2017 - 10:23 AM.

[breizh]

HI Emily,

You can download for free on internet PSIM , a nice software to simulate your system .

I's a great tool , you can build your system using the examples available and test different cases.

 

http://www.aft.com/psim

 

Hope this could help you .

Good luck.

 

Breizh

Edited by breizh, 25 November 2017 - 05:01 AM.

[spchauhan12]

Dear Forum members,

 

    

                       Is System Curve required for AODD Pump (Air- operated double diaphragm Pump)  ?

 

 

As per my knowledge, I know this is required for Centrifugal Pump to find out resistance in flow system for corresponding flow values for a

 

given pipe size.

 

I have done many Hydraulic calculations for Centrifugal Pumps & AODD Pump in my past porjects, but never drawn system resistance

 

curve for AODD Pump.

 

Any co-operation towards this end would be highly appreciated.

 

Regards,

 

SP