Series Operation Question 1

[KernOily]

Hi guys. I should know the answer to this, but.

For two pumps in series, namely a booster pump with a main pump, how do you know what the discharge pressure will be of the booster pump?

I know that the operating point of the two pumps in series will be at the point of intersection of the combined series operation pump curve (booster + main) with the system curve. That tells me the discharge pressure of the two combined pumps. How do I determine the actual discharge pressure of just the booster?

I have forgotten something fundamental here. Thanks guys! Pete

 

[FredRosse]

You have two pump curves, the common parameter is the system flow rate.
The suction pressure of the booster is the source pressure (tank or lake or whatever) minus the friction from the source to the booster pump suction, plus the static elevation pressure change. The discharge pressure of the booster is the suction pressure plus the differential pressure of the booster at the flow rate for the problem. Suction pressure of the main pump is booster discharge pressure minus the friction from the booster to the main pump suction, plus the static elevation pressure change. The discharge pressure of the main pump is the its suction pressure plus the differential pressure of the main pump at the flow rate for the problem.

 

[KernOily]

OK I got it. I will make a system curve for the booster only, the system consisting of the booster discharge flange going on to the main pump suction flange. The intersection of the booster pump curve with the booster system curve will be the operating point and from that I can back out the discharge pressure using the TDH calculation. Thanks Fred!! Pete

 

[LittleInch]

I think you're over complicating this. The discharge pressure of the booster pump will vary with flow on the pump curve plus the varying inlet pressure. Whatever the booster pump discharges will be taken away by the second pump so there is no booster pump system curve. If these are fixed speed units then if the inlet pressure to the booster pump changes ,e.g as a tank level decreases, then the total pressure from both pumps will change and hence flow will change.

My motto: Learn something new every day

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

 

[BigInch]

This should explain. You can change values in yellow cells only.

I hate Windowz 8!!!!

 

[FredRosse]

While connecting the discharge of the booster pump directly to the suction of the main pump is theoretically possible, this is not common practice for two reasons:

1. High turbulence in the booster discharge may cause performance issues with the main pump.

2. Allowable pump nozzle loads would potentially be difficult with this direct connection