3 replies to this topic

[Root]

Hi,
Sizing the control we need to calculate the CV of a control valve but in Equation, units are not matching.
Eg; Cv= Flow/ opening of valve*Sqrt of Delta Pv
where;
Flow is in GPM and Delta PV is in psi or bar or kpa.
Could any one explain about the contradiction of units in this equation.
Thanks
Toor

[fallah]

Hi,
Sizing the control we need to calculate the CV of a control valve but in Equation, units are not matching.
Eg; Cv= Flow/ opening of valve*Sqrt of Delta Pv
where;
Flow is in GPM and Delta PV is in psi or bar or kpa.
Could any one explain about the contradiction of units in this equation.
Thanks
Toor

Toor,

When you consider Cv definition (Number of US gallon per minute of 60 F water that will flow through a valve with a one pound per square inch pressure drop) you will find no contradiction.Of course,no need to remind that because the pressure drop is proportional to square of the flow value,in the relevant formula SQRT of pressure drop has been demonstrated in proportion to flow value.

Fallah

[katmar]

You need to check the definition of the Cv that comes with your valve because there are three different definitions. In the USA the units are SG, USGPM and psi while in Britain they also use the Cv notation, but it is based on Imperial gallons per minute. In continental Europe they often speak of Kv which is based on SG, m³/hour and bar. Sometimes for the pressure the Europeans use kgf/cm², which is almost the same as a bar but not quite exactly. The best is always to check with the documentation from your supplier.

[breizh]

Hi ,

Let you consider this resource:

http://www.engineeri...ents-d_277.html

Hope this helps
Breizh