Q & A > Question Details
How can I find the amount of flow passing through a control valve at a given output?
26/04/2017 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Obtain a curve for the CV from the manufacturer. Measure the pressures upstream and downstream.
26/04/2017 A: Yongming Zhang, HQCEC, 13439348666@139.com
The control valve is adjusted by the signal from a flow rate meter, which can measure the flow rate passing through the control valve, you can read the flow rate data from it. Some control valves also have a small flowrate meter on the control valve set.
25/04/2017 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
You use the basic control valve sizing calculation. From the output you know how the % open the valve is. The characteristics for Cv vs. % open are defined in manufacturer's literature for the valve. In addition to this you need to know the pressure drop across the valve and the specific gravity of the liquid. With this data it is quite easy to back calculate to come up with an estimate of flow. Method is similar for vapor and two phase flow but the actual calculations are a bit more complex.
This approach assumes that the valve trim is in good condition and the output represents the actual valve position. These assumptions may or may not be good, but are required to do the calculation.