Pump Flow calculation from level

Has any one used a good volumetric flow algorithm utilizing level and pump run indication? I know some ultrasonic level transducers will calculate volumetric flow pumped but I need to use the existing pressure level transmitter. I could use a standard volume formula to calculate the amount pumped but that does not take into acount the changes that occur with the influent while the system is pumping. This is for a lift station with no influent or effluent flow meters and of course the influent is always changing. Any assistance would be greatly appreciated!
By the way this is a great site! I wish I had this resource available when I started in this crazy field!

You've identified the problem exactly. I am going to assume this is a wet well level with intermittent pumping.

The first step is to calculate the volume pumped from the level change during the pump run cycle - area times depth change. You can get the level in feet from your "level" pressure transmitter since 1 psi = 27.7" H2O.

The tricky part is to get the additional flow rate from inflw during the pump run cycle. The typical way to do this is to measure the time and level change to go from the pump off to the next pump on. This identifies the flow rate into the wet well. You have to assume that this is the same during the pump cycle, and add it to the first flow rate.