Pump Flow Rate Calculation?

Bucket and stopwatch.

A REALLY big bucket, I would guess.

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Even though the TDH is not known, it would be most helpful to have the simple vertical head.

Hi Eagles

sorry, can't help, you do need at least something to work with. Providing the sizes of the intake and discharge in inches does nothing.

You've put pump size - "8x6-17".... what does that mean? To me it means 31!!!

All you've told me is that the pump requires 60HP which is determined by the number of stages within the pump(thats if you have a multi-stage pump), but unless you know HP per stage.... I could not even guess at the number of stages.

Not a good question....

Standard callout for an ANSI pump

8x6-17

• 8" inlet
• 6" outlet
• 17" impeller (this is can be the Max size, it can be turned down)

as you might be aware I do work with submersible pumps.. but of a different type.. never seen those figures to describe a pump.. thanks for the heads up.. and the info

Eagles004 -- Can you elaborate a bit?

It's reasonable to assume a pump of this size is a centrifugal pump; but if that is not the case then you'd best describe it in some detail.

First off has to do with pump size. "8x6" sounds like the suction pipe flange size and discharge pipe flange size respectively. I'm curious about the number "17". Sounds like an impeller diameter. Is this information marked on the pump nameplate or serial number plate? Or did the numbers come from some other source?

The next question you should be able to answer, inasmuch as you have information on the suction and discharge piping, has to do with the elevations involved. What is the elevation in feet of the water surface (tank, pond or whatever) open to atmospheric conditions and pressure for both the suction and discharge ends of the pipe assuming both are submerged? Note the suction has to be submerged to prevent air mixing into the flow. If the discharge pipe exits into the air with the water falling to a reservoir below then the level of the pipe outlet is what is relevant, not the level of the water surface.

Once these bits of information about the piping are provided it will be possible to estimate the amount of head the pump must develop to move a range of water flow rates (referred to as "capacity") through the pipe. This will enable the comparison of reasonably estimated performance curves for the pump with the piping system characteristic curve.

Finally since the performance of the pump in terms of a head/capacity and NPSH required and power required depends to some extent on the service for which it is designed and its general configuration some additional information would be helpful. So also, if we are indeed talking about a specific pump as opposed to a hardware specification, any indication of the manufacturer and the age of the pump would be helpful as would a brief description of the motor or engine that drives it.

Given just this information it will be possible to give a general range of performance in terms of head/capacity and power/capacity. Some additional refining of performance estimates would come from additional dimensions of the internal pasages of the pump casing and impeller. But I'm figuring that internal examination of the pump in question is at this point impractical.

Ed Weldon

To follow on from various others' comments re 8x6-17, an idea of static lift etc - assuming the system parameters are in normal range, you could get some idea as follows

Assume pump efficiency is 65% and motor actual output is 90% of rated 60hp, and work out fluid power.

Assume a sensible velocity in one of the pipes, to get prelim flow estimate. Work out friction losses hence total pump head. Calculate fluid power and compare with above. If it differs (as it likely will first time) adjust the flow to get closer.

Cheers...........Codey

I would refer you to Doorman's answer of a big bucket and stopwatch. It is not possible to rate an pump output based on the information provided. Even look alike pumps by the same manufacturer will vary and the variance is usually related to the size (diameter and thickness) of each impeller and the number of impellers within the housing. Efficiency curves vary with suction head and discharge heads (both missing). All you can do is guess that the output will be high and you will need the BIG bucket referred to by Doorman. Besides a dynamic test will give real results not hypothetical. There are even monitors that can be attached to pipes to record actual flow. The type of monitor to measure flow will depend if the discharge pipe is full or partial full, clean or dirty water. I usually use ultrasonic from Greyline but other measuring devices are available and should depend on all factors. I believe you may be able to rent monitors.

From the data given, it is not possible to calculate the discharge. The discharge also depends up on the impeller design, and impeller trim. If impeller is totally bad design, it may just rotate in the pump body with no discharge.

With this data, we can only guess what may be the possible discharge, if some additional data of suction and discharge head is given. If the discharge and / or suction head is beyond the capacity of the pump, the impeller will rotate, power will be consumed, but no discharge will be there.

For this too, we will have to assume efficiency of the pump. The efficinecy alsoo depends upon many factors, as above.... suction and discharge head, impeller design and trim.

Convention has it that centrif pump sizes are given as suction size x discharge size x impeller diameter, so 8 x 6 - 17 means 8" suction, 6" discharge and 17" impeller.

You can get a very, very approximate idea of flowrate if you can find (online) the performance curve for a pump of the same size and type (eg. 8x6x17, single stage, end-suction centrif). You can calculate the friction losses in your pipework using any of the many friction loss calculators that are available online, and this will give you an approximate head in ft. Do this at, say, 4 or 5 different flowrates across the range, and plot these points on the performance curve. This will give you the "System Curve", and where this curve intersects with the pump curve is where the duty point should be.

HOWEVER, even the same size pump can give different performance and, as has been mentioned, there is still too much missing data to get anything better than a very rough idea of flowrate, eg:

· Impeller type(open, closed, 5-vane, 6-vane, curved/straight blade, etc.)

· True impeller diameter (is it trimmed?)

· Fluid (viscosity, density, etc)

· Type of pipework (affects friction losses)

· Bends, curves, valves, etc in pipework

· Static head (lift)

i have a very basic, simple and fast idea but answer may not be so accurate (maybe can be use as just approximation).

if you come across API RP14E, the suction velocity required for pump is 0.6m/s to 0.9m/s. using this and suction pipe size together with simple equation Q=VA, u will get the simple estimated flowrate.

Dear eagle004,

What is the following Dimensions.

1. Impeller O.D. 2. Impeller Eye. ( With this you can calculate HEAD, since Speed is known - given as 1800 RPM, since H = (Vod^2 -Vid^2)/2g

2. Impeller Width "b" in the Engg. Books, width is denoted by "b", - the Flow can be calculated.

Refer Standard Hydraulics Book. Vector Diagram will help.

DHAYANANDHAN.S