Pump minimum recycle 2

[Pons19]

Hello All,

Why we use minimum recycle in the downstream side of the centrifugal pumps.
Is it necessary to have that on the reciprocating pumps?

Regards
Pons

 

[Jason5000]

A centrifugal pump imparts energy into a fluid in the form of velocity. The shape of the pump then turns that velocity into pressure head. The pump puts energy into the liquid and the liquid carries it away. If there is not enough flow, the temperature of the pump will rise and eventually damage to the pump can occur. However, centrifugal pumps have a characteristic curve that ends at shutoff head. If deadheaded, pressure in the discharge will rise to shutoff head and the pump will sit there and thrash. You can run a centrifugal pump deadheaded; just maybe not for very long depending on the pump and the fluid its pumping.

Unlike a centrifugal pumps, positive displacement pumps have no shutoff head. They deliver constant flow regardless of head. They should never be deadheaded. They will continue to try and produce flow until something breaks. That's why positive displacement pumps usually have integral pressure relief or some type of relief valve setup in the discharge line.

I hope this helps.

 

[Pons19]

Thank you for your valuable Reply.

Also would like to know the minimum flow line should be after the check valve or before the check valve?
Using RO will solve the issue instead of a control valve?

Would appreciate your reply.

Many Thanks
Pons

 

[maddocks]

Typically I put the RO inside the check valve and set it up so that it can not be taken out of service. An RO works fine as does a small globe valve locked partially open but the RO is easier to size and you can estimate the flow across the RO quite accurately.

 

[Pons19]

Many thanks for your reply.
Please let me know guidance to size the RO and Control valve coming on the pump minimum recyle line.

Thanks
Pons

 

[maddocks]

Your pump vendor will advise on minimum flow requirements - then you just size the RO so that it will pass this flow at the required pressure drop. Make sure it's not so high as to impair the normal delivery rate of the fluid.

Jim