Level lowering of pump station

[alienitmeca]

Hello,

When designing a pump with a specific HMT (123 m), and we come across a client update (lowering the pump level ΔL=-1.6m),

Suction tie-in point ( with Residual pressure Pr = 15 m minimum) and discharge point elevation are still intact.

Do we need to update the pump spécification : HMT = 124.6 to make up for the loss in elevation
or it is all the same since as we lose in the discharge, we gain in the suction line

Please find attached a simple image to explain the situation

 

[LittleInch]

If the inlet head increases the same amount then the differential head, which is what a centrifugal pump actually does is not affected. Accuracy of head produced across the pump is not normally that accurate any way (+/- 3%).

By the way, what is HMT? I assume this means something in French?

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

 

[bimr]

Differential head is the difference between inlet head and outlet head. If you only increase the outlet, you should update the pump specification.

 

[Artisi]

Advising the inlet condition would help in clarification.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[JohnGP]

Suction tie-in point ( with Residual pressure Pr = 15 m minimum) and discharge point elevation are still intact.

I'm with LittleInch, it would appear from this that the differential head is not altered by the change in pump elevation.

 

[LittleInch]

Also if inlet tie in point is only a minimum of 15m, if this increase then so will discharge head. 1.6m in 123 is nothing. No normal pump is that accurate especially if inlet head isn't rigidly fixed.

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

 

[bimr]

HMT: total manometric height (m)

 

[alienitmeca]

Thanks for your quick replyes,

HMT in indeed a frech designation for the " total discharge head "

Hears the situation:

We have a pump with a BEP (1100 l/s ----> 123 m) demanded by the client (assuming that he did his topographic mesurments accurately for the discharge head "123 m").

Now the pump level must be lowered down because he decided that the pump suction line have to be burried.

The pumpe BEP is a contractual detail and must be respected, therefore, we need to know weather lowering the pump level affects it's ablitily to provide 1100 l/s @ 123 m head.

In pumping systems, we have the following formula: System head = total discharge head - total suction head

Should this formula be a convincing reason to keep the pump caracteristics ? (Basically the discharge head lost due to lowering the pump level, is gained in the suction line)

Hears a sketch to explain the situation

 

[LittleInch]

Based on the sketch there is no need to change the pump characteristics.

The extra 1.6m required on the discharge head is matched by the extra 1.6m on the inlet head. The pump has to do the same work. I think you can ignore any minor additional friction in the extra pipe length.

When you say "system head" most people call that TDH or total differential head.

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

 

[JohnGP]

The differential head (total discharge head - total suction head) is not altered by lowering the pump as shown, so the operating point on the pump curve should not change. If that is the BEP then it will remain so.
Cheers,
John

 

[bimr]

Agree with the previous comments, the differential head will be same in either case.

 

[alienitmeca]

Thanks every one for your replyes it was very helpful,

Hears below a link to a website that elaborates cleary the calculation procedure for future references:

Link