How to find flow rate of pump if flowmeter not available

How to find flow rate in (m3/h) of pump if flowmeter not available at field but I have some data : Different Pressure suc. & disc. is 2.33 Bar , dia pipe@ suc 72 in & @ disc 60 in.

Started by Ferry Ruana Suteja, Indonesia

(1) Johnny Qing Sheng Ke, Canada • Fery, A draw down test will tell you the flow rate if there is not flowmeter available if you know the wetwell volume. Or if you can find the pump curve ( by giving a call to the supplier or manufacturer), you can also read from the pump curve too.

(2) Anis Hamdani Zuberi, Pakistan • I have a chart for estimating flow from horizontal and inclined pipes of 2" to 12" diameter. If you ant I can send you the same (let me have your email address). This method of flow measurement is very easy in the field without the use of flow meter.

(3) Saqib Yaseen, Pakistan • If u have V2 i-e- output velocity then you can find using equation

Q = A x V

Q is Discharge/Flow output
A is the cross-sectional area at discharge
V is output velocity

and in lay terms, u can place a tub of say 5 gallons and use stop watch to calculate the flow.

(4) Fernando Bagüés, Madrid, Spain • Can you install any pressure differntial transmitter? maybe iti can be useful this way. let me know.

(5) Kevin Bushnell, Canada • This will give you close estimate-First to determine the condition of the pump as related to the curve. Confirm the impeller Diameter installed, suction pressure. Have a gauge installed between the pump discharge and a discharge valve ( note height of gauge if this location is elevated from the pump discharge ). With pump running close the discharge valve, take/note the discharge pressure. Then within 10 seconds slowly open the discharge valve ( so you don't hammer the system ) or shut the pump off ( with valve still closed ) then open valve.
Take that pressure, minus the suction pressure, minus the elevation of the gauge to the pump discharge. With what you have left convert to Ft or meters and see where you are on the curve, so 0 flow at what TDH, If you meet the correct point for the trim dia then you can take operating pressure and see wghere your flow is. If you are below where the TDH should be you have pump wear, so no way to be sure what your flowrates are. if the TDH is higher ( but would not be by much ) then you're good

(6) Kevin Bushnell • do keep in mind you will end up with a flow +- 5-10%

(7) S. L. Abhyankar on 12 December 2011 in response to a personal email from Mr. Fery –

Mr. Fery also sent a schematic as shown in the figure, (bottommost of the 3 figures).

Since you have mentioned differential pressure across the pump to be 40 psi, (28.13 m), if you have the curve for the pump, you would be able to read total flow.

Since the flow is bifurcated into two, one to the condenser and the other to the cooling tower, these flows can be estimated to be in proportion of the CS areas of the branches

M/s. Secure Meters, Udaipur have a method of estimating flow of a pump by a method of thermal differential. I guess, their method also cannot find flow in branches.

If you would like non-intrusive method, I think an ultrasonic meter would do the job.

I wonder whether CFD can simulate the schematic and then estimate the component-flows also.

Considering that the line to the condenser is dia 30 only, it seems to be a small set-up.

(8) Another email from Mr. Fery on 12 December 2011 –

Now I am on analyzing pump performance at an power plant. Pump type is centrifugal pump double suction with vertical shaft.

The case is I should to measure pump performance base on existing instrument that installed in pumping system (Circulating Water), so it's not base on design analysis.

The question is :

1. What kinds of Key Performance Index for pump performance ?

2. How I should to identification what kinds of instrumentation who significantly can use to monitoring pump performance ? (e.g valve , Piping, Level Control, etc)

3. What kinds of parameter to determine pump performance ?

(9) My response on 15 December 2011 –

I wonder what is the scope of your "analyzing pump performance". Are you analyzing it to find potential for saving energy-consumption or for extending MTBF (Mean Time Between Failures) i.e. for improving reliability or for optimizing pump-performance for the system requirements.

"valve , Piping, Level Control" are not instruments, because they do not give any measurement or reading. Pressure gauges are instruments. In your schematic you did mention differential pressure across the pump as 40 psi (28.13 m)

In a power plant, they would certainly have pump's performance characteristics of a pump in the cooling water circuit. That should be you base reference. Pump's performance characteristics would also include curve for Power versus flow-rate. You can check up what was the power required from the curve and compare it with actual power being consumed. Readings of actual power being consumed would be available in the power plant. This comparison would give hints for potential for saving in energy-consumption.

If you want to analyze pump-performance in relation to performance of cooling tower and the condenser, then you may require to know how much of total flow delivered by the pump is getting bifurcated - part flow to condenser and major flow to cooling tower. In fact I am to wonder why part flow of the pump's discharge (before cooling) should go to condenser. But it is so seen in your schematic. One of your question mark refers to such flow recirculating to the condenser through a dia 30 branch from pump's outlet.

Basically it seems to be a condensate extraction pump drawing condensate from the condenser. I hence appreciate the installation being vertical so that the pump's suction has adequate NPSHa.

I am also left to wonder why pipe size from cooling tower changes from dia 54 to 72. What is meant by "inc" ?

Also, cooled water should go to boiler feed. Why does it return to condenser ? But condenser will also need some cooled water for condensation. Possibly the dia 30 branch should be from the cooled water, say from the dia 54 pipe below the cooling tower. In your schematic it appears from the pump's outlet.

Please clarify your schematic.

(10) Reply from Mr. Fery on

Here I attach clarified schematic as your request.

This is middle figure of the three figures.

I hope you can help me to solve this problem.

it's very help full if you attach with the calculation method & result .

(11) My reply on 9 January 2012 –

Your latest schematic shows the system to be much simpler. That is good. I also notice that the pump discharges into the cooling tower. Is that open end of pipe accessible ? If yes, you can do Google search on "measuring flow at open end of pipe". You will get info on interesting simple (though not accurate) method of measuring flow.

(12) One link w.r.t. above reply is –

http://smallhydro.com/200910/small-micro-hydro/measuring-the-flow-rate-q-from-an-openpipe/

How to Measure your Water Flow Rate Q from an Open Pipe:

There are times when it’s necessary to estimate the flow rate from a stream constrained to flow in a water jet flowing from an open pipe. This flow measurement method doesn’t require us to have precision fluid flow measurement instrumentation, other than a straight edge and plumb bob. Flow meters or weirs would likely be more accurate, but sometimes all you have is a filled pipe with a jet of water streaming out. If that’s the case, then try this method. See topmost of the three figures.

(13) On 16 January 2011 I have sent a further reply as follows -

On further thinking I realize that in your system a horizontal open end of pipe is not available. Also pipe size 60 in. is quite large. I think your best bet is an ultrasonic flow-meter.

I am wondering whether you can use details from the nameplate of the pump which should give flow-rate and head for which the pump must have been ordered by the original buyer. Your problem then would be to check whether the system has caused any difference to the original order specifications.

I am curious as to why there is the bypass line provided. I do not see any chance of the pump running at flow less than safe minimum flow. Only one valve on this line is usually required. 2.33 bar must be the pressure-setting for this valve on the bypass line to open automatically, if the pressure in the 60-in discharge line exceeds this pressure.

You need to have a pressure-gauge on the 60-in line. This will give you some idea of system's operating Head in m. Then by referring to pump's curve you can estimate the flow.

For estimating flow by using power measurement and pressure-gauge reading, one can do some indirect calculation -

(1) Power drawn by pump's motor (kW) = (rho) * (Q in liters per second) * (H in m) / 102 / (Pump efficiency) / (Motor efficiency)

(2) Assuming rho = 1,

(Q in liters per second) = (kW) * 102 * (Pump efficiency) * (Motor efficiency) / (H in m)

Pump efficiency of a cooling tower would be of the order of 0.75 and Motor efficiency would be of the order of 0.92. Using these values in the above equation will obtain an estimate of the flow-rate.

Hope this helps.

-o-O-o-