Rupture Disk Assembly Pressure Drop

The ruptured or burst disk on a vessel or pipe system presents a pressure drop to flow at that point, and it can be estimated by assuming the disk is a flat plate orifice [37] with a discharge coefficient, Kj, of 0.62. As an alternate, the disk assembly can be assumed to be the equivalent of a section of pipe equal to 75 nominal disk diameters in length. 

The sizing is based on use of the ASME Code [17] flow coefficient  

Kd = actual flow/theoretical flow = coefficient of discharge 

To select the proper sizing equation, determine whether the flowing conditions are sonic or subsonic from the equations. When the absolute pressure downstream or exit of the throat is less than or equal to the critical flow pressure, Pc, then the flow is critical and the designated equations apply [33a], When the downstream pressure exceeds the critical flow pressure, Pc, then sub- 

When Pj is increased, the flowr through an open disk increases and the pressure ratio, P2/P1, decreases when P2 does not change, until a value of Pt is reached, and there is no further increase in mass flow through the disk. The value of P] becomes equal to Pc, and the ratio is the critical pressure ratio, and the flow velocity is sonic (equals the speed of sound). 

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