End of Curve Operation

[DustinP770]

Hey all,

I have a question regarding operating a pump at the end of its curve. I have a system where a regenerative turbine centrifugal pump is pumping a fluid up ~400ft at 50gpm. At this point, it's at its peak efficiency on the pump curve. I would like to be able to use these pumps to recirculate fluid to the tank it's pulling from, or a nearby tank. In doing so, I would reduce the system head to almost nothing, which puts the pump way out at the end of its curve, which is still only around 100gpm according to the pump curve.

My question is, if I operate at this point for limited periods of time occasionally to test a pump operation or transfer fluid from one tank to another, am I damaging my pumps? I can't imagine the scenario would come up often, but it is something I want to have implemented.

Thanks in advance.

 

[LittleInch]

Never a good idea to do this.

You tend to get vibration issues and often the NPSH climbs to very high levels resulting in cavitation at the inlet.

Having said that it's not a large unit so might be Ok, but why take the chance? Just flow trough a back pressure valve / pressure relief valve or orifice plate to generate a head similar to your normal head loss.

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[TenPenny]

What do you mean by limited periods of time?

 

[DustinP770]

LittleInch - I like the idea of using an orifice plate to simulate the head loss, but am having difficulty figuring out how to determine the dimensions. I have a 6" SCH40 pipe that I would have the plate flange mounted on, and would need to have around 150psi head loss at a flow rate of 50 gpm. This means my flow velocity is around .55 ft/s and with a fluid density of 1.65 slug/ft^3 I would need a head loss coefficient (k) around 86500. Sounds like a difficult task...

TenPenny - I mean that this would not be it's normal operation, and the only time it would run at the end of it's curve is when we want to run a pump without pumping fluid all of the way up to the day tank 400 ft up a cliff.

 

[LittleInch]

Search "restriction orifice" on this site and you'll get some useful information.

A simple relief valve set at 155psi and flow rate of 50 gpm (sizing by relief valve) will suffice for an occasional use.

Might make a bit of noise though.....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.