Blocked Flow - Gas Relief - Intergraph Smart Instrumentation - Reference - Hexagon

1. Calculate upstream relieving pressure:

   *Pa [psi-a]

   

2. Calculate total back pressure:

   

3. Calculate critical flow throat pressure:

   

4. Effective coefficient of discharge: Kd = 0.975.

5. The condition Pb < Pcƒ (Pb [psi-a]) determines:

   Case A - Critical flow.

   1. Calculate coefficient for critical flow equation:

      

   2. Calculate capacity correction factor due to back pressure (if Kb is not entered by user).

      For conventional and Pilot operated valves, Kb = 1.

      For Bellows valve:

      Y= Pb / Ps

      1. 

      2. 

      3. 

   3. Estimate required effective discharge area:

      

Case B - Sub-critical flow: Bellow valve

1. Calculate Cr:

   

2. If capacity correction factor due to back pressure is not entered by user Kb =1.

3. Estimate required effective discharge area:

   

Case C - Sub-critical flow - Conventional and Pilot operated valves

1. Calculate coefficient for sub-critical flow equation: *Pb [psi-a].

   1. 

   2. 

2. Estimate required effective discharge area:

   

6. For Rupture disk application, calculate required effective discharge area:

A = A0 /Kcc