Parallel Pumping

[jamaican]

I am faced with a situation where I want to sap up 280GPM of over flowing water. Problem is there is an existing pump that operates at 1122GPM @ 40 PSI. I wish to use a smaller pump to parallel with the present pump. My system is not equiped with variable speed drives, I use autotransformer start for the 125hp motor. Is it possible to parallel pump beside the 125hp pumping unit, without causing damage to the smaller unit.

 

[Artisi]

It will depend entirely on the operating performance of the smaller unit.
You will need to show us the performance curves for both units and establish exactly what head the larger unit is pumping against.

As parallel pumping can be a very complex installation you may be better off to install a second independent discharge line for the smaller unit and run them as separate units.

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.)

 

[LittleInch]

Looking at your data, the pump seems quite small compared to the motor size. with an efficiency of 70% I get your shaft power to be about 35 hp, but you say you have a 125hp motor??

Why not put a bigger impellor into the existing pump or put a bigger pump onto your motor.

~parallel pumping is not easy to get right, especially with small discharge heads. If you get it wrong your smaller pump could easily stall.

What you need to ensure is that the pump curves are not the same shape and only intersect at the required duty point which will probably change when you put more flow through the same pipe.

It usually better to put in a bigger pump or put in two separate systems.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[SNORGY]

Can you tee off the suction on the larger pump and put in an on/off level control valve and loop to take care of the overflow stream? You might need to tune some smoothness into the controls involved, but if the discharge from the proposed new pump ties into the discharge for the exsisting one, it might be feasible to do this with controls rather than a new pump, motor, etc.

 

[DubMac]

I think we are all assuming these are both centrifugal pumps. Is this in fact the case?

Performance curves for the pumps and a hand drawn sketch of your setup would allow for any of the experts above to quickly solve your problem.