Pump Flowrate with no flow meter? 1

[Ivan69]

Hi, I'm getting some varying answers to this question but I think its a simple principle question.

CAN I read the flow rate of a centrifugal pump if I only know the suction pressure, the discharge pressure and I have a the manufacturer pump curve? (If yes, how do I use the pump curve to get the flow rate?)

Thx!

 

[25362]

Assuming the manufacturer's pump QH characteristic curve is steep (neither flat nor drooping) and indeed represents the pump's performance, enter the "head difference" obtained from the pressure readings and the specific gravity of the fluid at the ordinate, and the intersection with the curve will tell the flow rate on the abscissa.

 

[Artisi]

The above suggestion from #25362 will only give you a very rough indication of the flow rate, you should also check pump speed against the performance curve and make any corrections but more importantly calculate the input power. Having said this, from my experience you will probably end up with a bunch of numbers that will be confusing and contraditory.

 

[vanstoja]

Expanding on artisi's cited need for on-site vs test curve speed comparisons/adjustments, one should also compare line voltages and pumped fluid temperatures between on-site and manufacturer's test curves. It is not a simple matter to obtain correct voltage adjustments (which influence running speed) to head readings and it may be a rare occurence that this is done by the manufacturer for each of his pump designs. For a very large production order, one of our pump vendors tested more than 6 pumps of a particular design just to get reliable line voltage adjustment data to demonstrate compliance with rated head-flow and input power performance for all the pumps on the order which were individually tested. The prospects of using input power to a drivemotor to verify pump head-flow performance is also somewhat difficult since both the motor and pump hydraulic efficiencies must be known rather exactly. Again, this may entail multiple unit testing to determine the best average of efficiencies which are prone to unit-to-unit variations. As artisi says, all of these complications can make the matching of on-site and manufacturer's performance data a royal crap-shoot, even neglecting system piping variations which frequently exist and alter the slope of the head-flow curves from manufacturer's test results.