Pump Performance 1

[jsearl]

I have a pump that has a capacity of 1019 l/s at a total head of 24 metres. Will the pump be damaged if I increase the suction head so that the total head is reduced. Is there a "minimum" total head requirement for a centrifugal pump?

Also what is the pump "run out" condition.

Many thanks in advance for replies.

 

[MortenA]

The total head for a centrifugal pump is not dependent on the suction pressure (as long as you are above NPSH). If you increase the suction head (pressure) then the discharge pressure (not head) will go up. Unless you are talking about suction head LOSS. In this case try to look through some of the numerous posting re. NPSH.

Best Regards

Morten

 

[tstead]

Allow me to elaborate just a bit. The head added by the pump (call it TDH) plus the suction head (e.g. suction pressure, converted to units of length) equals the total head.

Now, the TDH of the pump is a result of the frictional losses in the system. To move a certain amount of fluid through your pipes requires a certain amount of excess energy in the form of head - or pressure. That amount of energy will not change regardless of what you do to the suction of the pump (of course, NPSH issues aside for the moment). To put it in an equation:

Total Head = Suction Head + TDH

At the same flowrate and system curve, the TDH does not change. So, the only way to change the Total Head is to reduce the Suction Head, not increase it. Of course, if you reduce your Suction Head too low, you may cavitate.

So, the only way to reduce your total system pressure is to either reduce your suction pressure (since TDH remains unchanged) or to reduce the resistance in your system (e.g. larger pipe, open valves up some more, etc.) If you reduce the flow, then the TDH will just go up and increase your Total Head.

"Run-out" can mean a couple of differnet things. When you are at zero flow, that is defined as shutoff. When you run all the way out to the end of the curve, that is called run-out.

Also, run-out can refer to how bent the shaft is. A perfectly axial shaft has no run-out. But when you place the shaft in v-blocks, set a dial gauge at one end and rotate a bent shaft, you will see the dial indicator move to indicate how bent the shaft is. In that event, you are measuring the shaft run-out.

Of course, run-out can also refer to what people do in an illegal casino when the cops come busting in....

Tim

 

[pump2000]

what does TDH MEAN

REGARD,

 

[jproj]

Pump2000:

TDH in tstead's post stands for Total Dynamic Head. The equation as stated above is:

Total discharge head = Suction head + Total Dynammic Head

Hope this helps!

jproj