# Approximating volume flow based on valve opening

I want to approximate the volume flow going through heating/cooling units, but all I have are valve openings (unit=%). Since the valve does not have a linear relationship between its opening and its volume flow, I will have to approximate it based on standard values.

The datasheet specifies "Equal percentage flow control is ensured by the special design of the ball."

I do have the maximum volume flow powered by the pump (at 100% valve opening). Since, to my understanding, valves are designed that way to create linear relationships between valve opening and heat transfer of the downstream heat transfer unit, I assume that there are "standardised" valve characteristics and approximating the volume flow based on the valve opening is possible. But how?

• Look up the Cv curve for the valve. Most valves are not designed to have a linear relationship to flow, ones that do are called "proportional valves". (and they have a significant offset which has to be accounted for depending on what they are used for). – Pete W Feb 23 at 14:15
• Thanks. I've looked into it, so far only able to identify equations in which pressure has to be an input, but sadly there are no pressure sensor measurements available. I'm looking for a formula in which I can enter the current valve opening (in %) and it returns an approximate flow rate (or an interval of realistic values), based on the maximum flow rate at 100% valve opening. Is that possible? – cheesus Feb 23 at 14:32
• That might be approximately true for cases where the flow/pressure just upstream of the moving part of the valve are restricted by an orifice, but for the most part, it depends on pressure – Pete W Feb 23 at 14:42