V-Port Ball Valve Question

[EMorel]

Good afternoon everyone,

I've got a general fluid mechanics type question here. I'm drawing up a V-Port ball valve for a flow throttling application, and am having trouble figuring out how to calculate something.

If I am given an upstream pressure, and a required flow rate, how can I calculate what percent open my 60° ported ball must be to achieve that flow rate? I am new to the throttling game so I do not have any flow testing or proofing done on this design, just trying to run some preliminary numbers. I'm hoping there's a way to do this without CFD.

The required flow rate is very low (1 gpm) and I have estimated Cv for this v-port design.

Thanks for any insight!

 

[gerhardl]

From textbooks or net you can find the formula for cv expressed by flow, differential pressure, mass flow rate and in addition correction for temperature and vicosity.

From your already known data you can then calculate an approximate area of an ideal opening. If data is missing you can stipulate and calculate a number of values 'near' the necessary opening area.

Now to real life: a V-port ballvalve can, and will often have, turbulent and unpredictable flow at the first degrees of the valve opening, or if the valve opening is 'small' related to the differential pressure and the total pipeline opening. In addition the V-form is vastly different from the round, ideal opening, also adding to turbulence.

In my personal opinion you can calculate and find an approximate form and opening degree. As cv, by definition, is a measured figure for any valve, you will not be able to accurately calculate cv or opening degree for a new constructed valve or regulating opening member.

Also:if you start your regulation at empty downstream pipeline, with high inflow and high differential pressure, you must check if you get cavitation conditions, and if the valva (in any case) can withstand opening, normal and emergency flow conditions.

The real, practical opening of any valve, for any flow, have thus to be measured and controlled in situ (valve mounted at place in pipeline), to give exact data.