SHUTOFF HEAD POINT

[sowhatso]

I NEED TO TEST A PUMP AT THE SHUT OFF HEAD POINT, TO CHECK IF I WILL GET THE SAME VALUE SHOWN AT THE CURVE.

From your experience , Do I have to close the throttling valve totally before running the pump OR to close the valve gradually during running the pump till we reach the shutoff head ?

 

[TenPenny]

Run the pump with the valve open for a few minutes to get to 'steady state', then slowly close the valve.
Don't forget to account for suction pressure when you do your calcs, and don't run it this way for too long.

 

[EdStainless]

I would not check shut-in. You should be able to test a pump at low flow, but not so low that you risk damaging the pump.

If you do want to test I suggest setting the valve partially closed and starting the pump, and then closing the valve the rest of the way. Take data quickly, most pumps will not run this way long without significant damage.

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[BigInch]

Just check the pump at 3 relatively low flowrates and draw the curve back towards zero flow.

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[Valvecrazy]

What kind of pump is it? You should never close a valve on a PD pump. Centrifugal is a different story. Fluid and fluid temperature may also be important.

 

[Artisi]

WHY?????

 

[BigInch]

Why what?

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[Artisi]

Why test at shut off head.

 

[BigInch]

I thought you were asking why not close the valve... and I knew you knew better than that, so I became very confused as to what why you wanted to know why.

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[Artisi]

Well it's still early morning here and the brain isn't at full speed as yet - hence the one word sentence.

As you, others and myself are well aware, the shut-off point on many pump curves is just an arbitary point and doesn't serve any real purpose. Your suggestion of a three point test is more than adequate to establish likely head at zero flow.

 

[Valvecrazy]

Three points on a curve will let you extrapolate to shut off head, unless it is a centrifugal pump with an unstable curve. With most centrifugal pumps it will not hurt to go to shut off for a short period of time. I use the shut off head of a pump all the time to figure differential pressure across a control valve.

 

[BigInch]

Right, "we" were only talking about PDs.

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[BigInch]

... and centrifugals in general.

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[bingopin]

"Your suggestion of a three point test is more than adequate to establish likely head at zero flow."

True, unless the pump head falls off at shutoff like many low flow/high head centrifugals.

 

[BigInch]

Right. There's always endless what ifs ...
I don't know about your pumps, but if I shut one off completely for no other reason then to check its head at zero flow, somebody downstreams gets "really upset". It probably doesn't really matter too much in any case, as they ain't supposed to run along down there for any length of time anyway, especially if they give poor system characteristics at low flow. Most of the time its good enough to know the maximum pressure you might get at shutoff, so its not a bad way to estimate shutoff head for most cases.

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[PumpSmart]

sowhatso,
It is a PD , DOES NOT DO THAT. Even thogh PD has valves relief or not.
It is a Centrifugal Pumps Medium Presure and Low Presure Pump, Do but it is a new pump, it is better to ask to Pump representative or verify in Intruction Manual of the pump.
Mechanicals seal could fail if your test take so long.

It is a old pump Centrifugal Pump, it is very often that pumps does not meet Shut off Values.
It is a Axial Pump or Mixed ( vertical turbine) Pumps, you should verify if you could do. In the first case it is very often that could not do that. For mixed pumps you should check Thrust load and Power rating behavior before do that.