Lift Station Volumetric Flow Calc


Thread Starter


Does anyone one have a reasonably accurate algorithm to calculate the volumetric flow out of a lift station when the only parameters you have are level and when the pumps are running? There are no influent or effluent flow meters so I need to have a way to compensate for influent while I am pumping it would be one thing if it was a batch system but the flow in is always changing and a pumping cycle begins when the level has hit a preset limit. I know how to calculate the flow out using level and volume so please don’t respond with that. I have seen ultrasonic level meters like Milltronics that have discrete inputs that will do the calculation but I need to do it in my PLC. Thanks!
Consider programming the pump curve into the PLC. The discharge pressure is probably constant (the elevation of the downstream piping will largely determine this) and the suction pressure is the hydrostatic head, which you get from the level instrument. You would then be independent of the influent flow rates.

I would validate the programming by testing the calculated rate against the change in wetwell volume when the pump station is at a relatively low load. Chances are that this will be in the wee hours but that's why they pay you the big bucks.

I thought I knew the Milltronics line fairly well but am not aware of the capability you describe in any of their instruments. Assuming it is there, they may be willing to share some of the math with you. Chase down either their regional sales manager or the product manager.

Good luck.
I have spent many years in the water industry and I can only recommend fitting the right device for the job. i.e. a flowmeter. This can be intrusive or there are now on the market doppler and timeflyte measurements. Using assumed pumping curves does not allow for restrictions and inefficiencies that may occur.

Use the right tools for the job.


Matthew Hyatt

Since the wetwell is probably out fitted with floats (a high level alarm, high level pump on and low level pump off), I would calculate the volume between the on and off points. Lift stations normally run in the cyclic manner 24/7/365. Most wastewater plants usually have a influent flowmeter for each inlet stream. The wetwell is a cylinder, calc the volume, figure out the volume between the on and off points, then time how long the pump runs, simple math can then be used to tell you the flow rate in cubic ft per min, gallons / min, or whatever units you desire. Of the lift stations I have done, it was rare to have a flowrate on the effluent of the lift station. They just want to move the crap down the line.

Otherwise I would put an effluent flowmeter on the system and make my life easy. This can be scheduled when some normal pump maintenance is being done, should take about 2 - 4 hours, not included programming time, setup, calibration, checkout and validation. Send me a PO and I can do it in 2 weeks, its a little more if you need it done sooner.


Ben Beaudoin

There is no simple way to calculate an accurate volumetric flow in a lift station without the help of a computer and sophisticated algorithms. Only two companies offer such software which can produce flow with an accuracy of 98.5% for most lift stations having constant speed pumps.

Isco has the Pumplink software which works only with their 4501 Pump Station Monitor. MAID Labs makes a datalogger that is compatible with Isco’s Pumplink software and also offers its own volumetric software. The same people created both technologies. Marsh-McBirney tried to create a volumetric flowmeter, but discontinued their product after only a year or so. They could not get it right. It’s understandable, 32% of the lift stations have intermittent abnormal behavior that influence volumetric flow.

MAID Labs integrates electrical troubleshooting with their software so those abnormal behaviors could be discovered before they become emergencies. Still, their hardware is required. If you are searching for a software, I do not know where to get one.

I hope this is useful.