Centr. Pump Flow from kW readings

[birkATO]

I have a bunch of kW data (hour by hour)used by some pumps that are used for pumping water from one area to another. They are rather high volume pumps...around 3000 gpm each. What I want to do is take all the kW data and use that to estimate a flow rate for each pump during each hour to get a total of how much water has flowed. I have never done one of these types of calculations. I have some pump curves. Would the following steps be a correct way to go about it?
1. Determine total head, which is 236 ft.
a. I have estimated the friction head to be around 2 ft using a friction head calculator on the internet (10,000 ft of 30" ID steel pipe)
b. Water level is raised by 234 ft.

2. Using the bowl head vs. flow curve, find the flow rate.

I don't know where to go from here though and it seems as though I am missing something since from what I have assumed, the flow rate does not depend on power input, but that can't be right. I presume I will have to multiply the kW number I have by some efficiency. What I don't understand is if I can get the flow from the head, then I don't even have to consider efficiency. Or do pumps such as these pretty much depend solely on head and not so much on power input?

 

[BenThayer]

you say that you have the pump curves? don't they have the horsepower requirements on the curves?

any set of curves i have ever received from the OEM had the BHP curves as part of the set.

 

[sshep]

birkATO,

BHP=GPM*H*SG/(3960*effi)
where:
BHP=brake horsepower
GPM=gallons per minute
H=feet of head
SG=specific gravity
effi=pump efficiency

Per this formula, your pump curves are needed to get the efficiency, otherwise (i.e. to assume effi=1) your calcs will only give hydraulic horsepower and your flow will be overestimated. Per Ben, horsepower is sometimes available on the pump curve. When dealing with hydrocarbons care must generally be taken to know the SG for which the horsepower curve is referenced (often referenced to water), but since you are pumping water anyway you should be able to use your pump horsepower-flow data directly if available. If there is no horsepower curve then your efficiency lines will allow you to calculate equivalent information per the formula above.

best wishes,
sshep

 

[vpl]

birkATO,

I'm going to request that this post be deleted and that all further replies be made to the identical post in the mechanical engineering pump forum: thread407-148464.

In the future please refrain from making duplicate posts.

Patricia Lougheed

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