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# determining centrifugal pump flow rate5

## determining centrifugal pump flow rate

(OP)
Please i'd like to know how you can determine the flow rate of a centrifugal pump that you don't have any characteristics,by knowing only:the pressure of the delivery of the pump (2,3 bar), the size of the pipe (50mm diameter),the material (NaOH solution with specific gravity of 1,2 kgr/lt).Is there a formula to calculate the flow rate or is something else needed?

### RE: determining centrifugal pump flow rate

In addition to the data provided above you will need the static head on the line, the friction head (from line length and fittings) and any other sources of pressure loss.  The flow is that where Total Dynamic Head on the system equals the pump discharge pressure.  The Darcy-Weisbach equation is appropriate for calculating the friction head loss.

### RE: determining centrifugal pump flow rate

Basically, no.

If you know the pump, you can get a copy of the pump curve and estimate the flow based on the head produced by the pump.  BUT, if you have a flate pump curve, you will have a high degree on uncertainity in your answer.

If the discharge piping is long, you might be able to calculate a flow rate if you can measure the pressure drop.  If you have a control valve in the system and can determine what % open it is and therefore the Cv off the valve data sheet, that's another method but all of these have typically a fairly high degree of uncertainity in them.

### RE: determining centrifugal pump flow rate

pil72: Based on your info i would say no. But if you know the make and model why dont you search the internet? A lot of this info (also for old units) can be found on the web.

Best regards

Morten

### RE: determining centrifugal pump flow rate

Presumably the solution is being pumped somewhere.
Sometimes it is possible to measure the flow rate by breaking a joint and measuring the flow rate using the time honoured "bucket and stopwatch" method.
The pump may be drawing out of a tank. Perhaps you can isolate the inflow and time the tank drawdown. By measuring the tank dimensions, the flow can be calculated.
Another way is to measure the "product" made by the solution. For example if the solution is used to neutralize and acid, and the acid rate is known, then the solution rate can be calculated. Alternatively, perhaps you know how much caustic is purchased per month and how many hours per month the pump runs.
If the pump is feeding a ringmain which returns to the feed tank, this complicates things, as the return flow must be diverted, and measurements made.
If you post the make, model, speed and motor power of your pump someone may have a curve or two.

Cheers

Steve

### RE: determining centrifugal pump flow rate

Similiar to TD2K's method,

if pipe line is long enough ,put a pressure gage ,find the pressure drop (Pa/m) then using friction loss table find the flow rate .
of course it doesn't give a precise results

Ercan

### RE: determining centrifugal pump flow rate

There are a few ways to get an estimate of flow if you can get to the discharge point, by measuring trajectory, by using a pitot tube inserted directly into the flow. If you need accuracy use a temporary orifice plate and measure the head differential across it or if you can get a "clamp-on" pipe doppler flow meter you can measure it anywhere that you have a straight run of pipe.

International College
Naresuan University
Phitsanulok
Thailand

### RE: determining centrifugal pump flow rate

Information from other guys are correct. I suggest you to refer to pipe size or discharge nozzle size assuming respectively a velocity of 2-2.5 m/s or 5-6 m/s. In this way it is very easy to roughly estimate the flow.
For. ex. : 2.5*(3.1416*0.05^2/4)*3600 = 17.7 m3/h (checking the result with nozzle size).
Anyway I shold prefer to refer to nozzle size.

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