Control Valve Design 1

[mou]

Hi All,

If we have a water reservoir (say with a water level of 100m), then 2km of 300mm watermain to a pressure reducing valve, how is the 'maximum allowable pressure drop' across the valve calculated. Just to note that downstream of the Pressure Reducing Valve is a normal water reticulation system with customers.

Im reading

http://www.cheresources.com/valvezz.shtml

which states that usual rule of thumb is that a valve should be designed to use 10-15% of the total pressure drop or 10 psi, whichever is greater. How would you calculate the total pressure drop in the above example. Is it just 100m minus the head loss in the 300mm watermain upstream of the valve ??

Any assistance would be appreciated.

Mark

 

[TD2K]

The rules of thumb apply to most systems but not all. Let's say you are letting down steam from HP to LP through a control valve. Since the piping is typically short, pressure drop is minor and the dP for the control valve sizing is the difference between the two steam pressures.

In your case, use the 100 m head minus line losses to calculate the inlet pressure to the control valve (which is also the dP it sounds like).

The 10% to 15% rule (which usually I've seen higher as 1/3) simply doesn't apply in this case.

 

[mou]

Thanks for the reply....

Cheers

Mark