measuring open end pipe flow

snafuman · Apr 21, 2003

We need to measure the flow and pressures at a pump discharge. The pump is an old turbine style irrigation well pump which pumps through a gate valve and approximately 50 foot in length of old rusty 10 inch steel line, which then empties into an irrigation ditch. The pump is a older Western Lands Roller pump. The company has changed hands several times and we have not been able to obtain a pump curve (still trying). We expect the pump to produce somewhere between 500-1000 gpm. We need to measure several different flows at different pressures, enough to develop a rough pump curve. Our purpose is to determine if there is sufficient flow and pressure from this well to provide fire protection for a rural historic structure, and satisfy our Fire Marshall. There is no other significant usable source of water for fire flows at this site.

We are looking at building a weir or flume in the ditch; possibly tapping the pipe for a pressure gauge, or a pitot tube. An ideas that can save us time, trouble, expense, etc., are appreciated.

Ron · Apr 22, 2003

I would use a v-notch weir. Easy to use.

Ginger · Apr 22, 2003

Ron's advice is good, very cheap and simple. If you want to go cheaper, there are two similar flow estimation methods known as:

a) The California Pipe Method
b) The Trajectory Method

In the California method, allow flow to emerge freely from the end of the pipe. Measure with a ruler the height of the air gap from the crown of the pipe down to the surface of the flowing water as it emerges from the pipe. You need to look at the flow/discharge curve published for this method to give a direct flow reading.

The trajectory method is similar and involves measuring the top surface of the water at a distance out from the end of the pipe. Again you take a direct measurement using a ruler and read off from the published flow chart.

These charts should be easily obtainable. they are published in CIRIA Report 113

http://www.ciria.org.uk

(I think)

PS both of these methods require that the pipe has a straight length of 8 diameters prior to discharging.

Regards

Andy

TD2K · Apr 22, 2003

This isn't going to be the most helpful piece of information as I don't have the vendor who had this.

It was a portable venturi meter for measuring water flow through storm or drainage systems. It had an inflatable collar to seal against the pipe's inner wall and then the dP reading and total flow was read off a hand head unit. Sounds like it would fairly easily fit into the end of your piping.

The other one would be a portable ultrasonic flow meter, I've used these with good accuracy.

KRSServices · Apr 23, 2003

I would hook up a flow meter on the discharge and tap a pressure guage on the discharge side of the pump. With a decent flow at the discharge, a pitot will work fine too, that is until the flow drops off to a near dribble, then the accuracy of the guage may be questionable.

KRS Services

http://www.krs-services.com

snafuman · May 9, 2003

Thanks for all the responses. We found a well driller who can supply a meter and pressure gauge to test the well, for a few hundred dollars. I think this is the only way we would be able to generate a pump curve.

permit1 · May 17, 2003

This pump flow can be tested with an oriface plate at the discharge. Or by a Controlotron type flow meter. The valve should be adequate to produce head. My guess is the pump is targeted to 30psi. It may be able to supply water for a fire pump.

Mark

chicopee · May 20, 2003

apply the same test procedure use to test fire pumps.Put pressure guages at inlet and outlet of pump and use a pitot tube at the open end of the pipe to measure flow. You can then plot results on a log graph calibrated to n=1.85. The results will include churn (static) pressure, residual pressure with flow measure at the open end of the pipe.

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