You want to reduce the npsh(a)? Why? Anyway a valve would do just that. Either up or downstream. Downstream would be best because then you wont get a reduction in npsh but still a lower outlet pressure (after the valve).

I would assume that you are talking about lowering the suction pressure because you are worried about high suction pressures being too much for the pump?

You'd have to have a pretty large static height difference for this to be the case, though!!!!

Why don't you try lowering the reservoir (not easy in most cases) or raising the pump (very doable in most cases)?

Tim

Does the fluid level change much during operation? If not use a spring loaded check valve that only opens when the pump is running and flow reduces pressure between the check valve and pump inlet.

Bud Trinkel
Certified Fluid Power Engineer
HYDRA-PNEU CONSULTING, INC.
812-853-3234
fluidpower1@hotmail.com

This case is easy to handle , just  put a open tank at the  intake and handle the level by a floating acting valve , so you can mantain the pressure just enougt to feed the pump.
You had posted other post to do the reverse action.

Would you explain what do you want to.?

Whats your problem.?

You can reach me at k281969@hotmail.com
but keep your post here for mutual benefits.
Pardal

Based on the responses, you need to clarify your question.  I assume that you mean that you are concerned with the changes in the level of the liquid in the reservoir on the pump.   Why does it matter?  Have you determined that those changes will impact the discharge pressure/flow of the pump to an extent that is not acceptable?  If so, pardal's idea would work.  If you can't do that, flow or pressure regulation on the pump discharge - a Griswold flow regulator or a self contained pressure regulator would be one approach thats not too expensive in small systems.

krue0101

The above suggestions are ways of reducing pressure, but all are energy losers.
Depending on the specifics of your application, one way to reduce head is to install a turbine (basically a centrifugal pump running in reverse rotation) / generator set.  This will not only reduce head but also will provide cheap power.

Question.  Why do you want to reduce head and then add more power to increase the head?  Are you worried about high suction pressure to the pump?  If high suction pressure is a concern - consider sourcing a pump that will handle such high suction pressures.

Richard