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# Positive displacement pumps in series or parallel

## Positive displacement pumps in series or parallel

(OP)
Hi all,

Good days. I am getting info that for centrifugal pump,

Theoretically,
centrifugal pump in series= H1+H2 and Q1=Q2
centrifugal pump in parallel = Q1+Q2 and H1=H2

I understand that centrifugal pump may different from positive displacement pump.
Are the positive displacement pump apply the same rules when in series or parallel as above?

If not, how is the effect for pressure head and flow rate for PD pumps?

Reference link material is highly appreciated if there is any information for PD　pumps in series or parallel.

Hope to get some info from all of you.

Thanks lot.

Best regards,
Yong Hong

### RE: Positive displacement pumps in series or parallel

The same rules apply.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

### RE: Positive displacement pumps in series or parallel

Before I answer, where else have you looked for answers to what is a very basic questions?

Try sites like this http://www.pumpfundamentals.com/

and pump vendors often have design guidelines.

Cent pumps in parallel - be aware that Q1 + Q2 is not the same Q as the "rated" value, but for PD pumps it is.

In really simple terms always remember

A Centrifugal pump is a variable flow constant (+/- 10%) differential head device
A PD pump is a fixed flow, variable differential head device.

Running PD pumps is series is very difficult in practice as it is very difficult to balance flow exactly.

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

### RE: Positive displacement pumps in series or parallel

All it takes is some thought.

For the series installation, consider a pipe that runs from pump A to pump B. If 20 gpm is flowing out of pump A, into pump B, what will come out of pump B? If it's not 20 gpm, where does the extra come from or go to?

For the parallel operation, assume the two pumps have a common suction and discharge. How can the suction pressures or the discharge pressures be different, if it's the same place?

### RE: Positive displacement pumps in series or parallel

#### Quote:

For the series installation, consider a pipe that runs from pump A to pump B. If 20 gpm is flowing out of pump A, into pump B, what will come out of pump B? If it's not 20 gpm, where does the extra come from or go to?
It goes out of the relief valve between the mismatched pumps?
(I think that would be an example of the potential difficulty of series pd pumps that LittleInch was referring to).

=====================================
(2B)+(2B)' ?

### RE: Positive displacement pumps in series or parallel

(OP)
Thanks all for the valuable information. Appreciated.

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