2 replies to this topic

[srinivasan]

Dear all

I am doing relief valve sizing and flare net analysis for oil and gas industries. One of the relief valve vendor ask us to provide the minimum and maximum superimposed back pressure.

Kindly correct me if i am wrong

The min superimposed back pressure is constant back pressure and Max superimposed pressure is based on maximum back pressure on global scenario.


Thanks in advance

Regards
A.Srinivasan

[fallah]

Hi,

Your query isn't so clear. In PSV selection/sizing, about superimposed back pressure you need to know if it is constant or variable. In latter case the maximum value of back pressure should be known.

Fallah

[flarenuf]

the minimum superimposed back pressure will in most cases be 0 barg. if the flare is not flowing any relief flows then the PSV will see only atmospheric ( plus small purge gas pressure) on the exit flange.

the maximum superimposed takes two forms as Fallah says .

Constant - pressure on back of the valve from other relief/vent flows passing into the header system. Th evalve vendor may want to adjust his spring setting to compensate for this .
Variable - this is the backpressure on the valve when it is open and venting into the header system. The bp will normally be calculated using Flarenet or similar hydraulic software.

normally conventional pSV's are designed for a maximum BP of 10% of set pressure, balanced valves 40-50%.

hope this helps
flare e nuff