How to Calculate the Flow Rate of a Pump

You need to get on to the makers of the equipment, Guvnor. Phone 'em up and ask 'em for a pump curve. <Splutter>

Sp"s right. Either test the output yourself or get a pump curve from the manufacturer. There is no way to calculate the flow without it.

It might be on the internet somewhere. Try Googling the Mfg's name.

There is a formula to calculate, given the water power, calculate it by multiplying the engine input power by its efficiency then calculate:

Ph = q * density* g *h/ (3.6 10^6) metric units

Ph is the water power.

Only q is unknown.

You can get a hand held tach for RPM check. Most automotive stores sell them relatively inexpensive. With model of the pump the manufacturer can tell you the displacement.

Do not know where you live, but in most countries the fire regulations or your insurance company will demand a pressure at the hydrant at a given flow.

Start the pump. open up the hydrant(s) until the desired pressure is reached and then measure the drop in level in the supply tank over a period of time and calculate the flow.

Hi Jananjaya,

If the system was design properly you could safely assume the velocity of water is with 1-2 m/s (3.0 m/s Max) - you could estimate the flowrate based on this. A properly designed system will be like this to minimise the pressure loss in the piping (due to friction), and to prevent Water Hammer problems.

It is possible to calculate the flowrate, by measuring the pressure loss along a length of pipe. But this is a complex calculation, and there are many factors involved (including friction of the pipe wall, viscocity, temp and SG of the water), and of course relies on accurate measurement of the pressure and distance between measurment points.

And many other factors will influence this - such as valves, elbows, reduced line diameter, etc.

If you did want to go down this path, and use this method to determine an accurate flowrate, I suggest you get hold of the CRANE Handbook for Flow of Fluid through pipe valves, and fittings. It was written many years ago, but it is very good (data and process' is accurate). If you systematically follow this book, you'll work it out.

http://www.flowoffluids.com/tp410.htm

But certainly the easiest and best method of finding the info you're after is to get hold of the correct Pump Curve from the pump manufacturer (or sales). Be careful to select the correct pump (including diameter of the impeller, and kW of the motor).

Accurately determine the inlet and outlet pressure, read from the graph the flowrate. Note: the age of the pump can also affect the efficiency. The pump curve was accurate when the pump was new, however with older pumps they can be up to 10% lower than indicated from the pump curve.

Hope this helps,

Kind Regards,

Anthony

Way, Way, way tooo little information.

Change in pressure is just that, change in pressure! and by itself gives no indication of flow.

Whatever the power rating of the motor, it also only indicates that it could work up to that power/effort, but it could simply be churning water inside the pump case. Again, power usage does not mean that flow is even happening.

To calculate volume delivered (flow rate), you need a flow/velocity of the water and cross section measurement. Your 4" pipe cross section is easy to calculate, but you must measure the actual velocity of material in the pipe.

(There are other ways that could be used if you knew the "resistance" of the delivery pipework and suction, actual efficiency of the motor and pump and a few other parameters.)

As suggested by previous member, the easiest way is measure time to fill/empty a known volume and do the sums.

Pump HP is calcualted by knowing the flow and head. By reverse way, you know the head, the KW power consumption in elec meter, you can calculate the reasonable flow by considering the motor efficiency

You can't tell the depth of a well by the length of the handle on the pump.

Similarly it is difficult to tell the capacity of the pump with little known.

Let us start at the basics to get you started.

What is the color of the pump - don't say red because that may indicate paint.

jacojan - please say something even if it is goodbye.

Get a tachometer and measure the rpm of the engine. Is there a possibility for you to fill a water container of known volume (plastic tank, cement tank or something of the kind), and time it to see how fast it fills? Maybe this method won´t work, but at least is gives you an idea.

Let's get the terms correct first. Flow rate and flow capacity need some explanation. To measure the flow rate, you must have flow which is difficult to do in a fire water system, as all the anticipated 'consumers of the water' (sprinklers, monitors [permanently mounted spraying nozzles directed by an operator], fire hoses, etc) must be switched on and flowing. Then you can rent or buy an external clamp on flow meter to go on the discharge pipe of the pump and measure flow rate.

In the fire water system business, we don't care about anything except flow to cool down the hot spots. To arrive at that flow, you must have sufficient 'flow capacity [capability] and head capacity [pressure capability] to force the water through restrictions to increase its velocity and therefore provide distance from the distribution device (nozzles, sprinklers, etc. Let's call these things "End Devices") over to the area you wish to cool [the flame itself or surrounding structures].

In the above discussion, anytime we see the words capacity or capability, this is a calculation. Calculations only give us a guess that everything will be OK during a fire. The begin, as others have suggested, you need to get the curve of the pump. This is termed the "H Q curve" (H = head = 'pressure' [OK...I don't need a lecture on SG from pedantics please ... keeping this practical for Jacojan] and Q = pump industry code talk for flow). If you can ask for the curve to be corrected to 'pressure' instead of 'head' it will help you better. Then you need a process, piping or fire system engineer to calculate all the restrictions (resistance) you have in the piping, fittings, sprinklers, etc.... and determine how much flow you will need through the end devices to successfully fight the fire or cool structures [letting the fire itself burn until fuel is gone]. The HQ Curve will have a pump speed shown, or multiple speeds. Then as others have suggested you need to measure the speed OF THE PUMP SHAFT, not the engine (OK... not another lesson on direct drive please... it is just that engine speed if often taken from pulsing devices and can be inaccurate if the electronic modulator is incorrectly set up). Use a strobe tachometer and check the pump shaft RPM and compare it to a newly installed engine RPM monitoring device. If the pump shaft RPM does not match the HQ curve, there are some affinity laws we can apply which are beyond the scope of this answer.... for now, just hope that the pump speed and HQ curve match. Google "Centrifugal Pump Affinity Laws" to go outside this post answer.

Hope this helps.

hello

i think u in big problem

u will have a small solution may be really use. i think u have not the manufacturer performance , so u must know the performance of the pump

test the pump under constant RPM(ford motor) with the variable flowrate and head

u may ask me how ? i will say take 1 cupic meter of water and withdrawn by pump (in a known time calucalted) and gauge the head.

try that .and draw the curve and find it

(if 1 m3 of water wathdrawn in 30 sec that mean that the flowrate at this head is 0.033333 m3/sec)

i wish i can help u

best wishes

good bye