Page 282 - Valve Selection Handbook
P. 282
Sizing Pressure Relief Devices 269
K v = Capacity Correction Factor Due to Viscosity
When a pressure relief valve is to be employed for viscous service, the
orifice area has to be determined through an iterative process.
1. Solve initially for non-viscous flow and determine the next avail-
able standard orifice size.
2. Determine the Reynolds number, RE, for the initially calculated ori-
fice area from either one of the Equations (7-16) through (7-18).
3. Find value of K v from Figure 7-7 and apply to the initially calculat-
ed discharge area. If the thus corrected initial area exceeds the cho-
sen area, the above calculations should be repeated using the next
larger standard orifice size.
Reynolds Number US Units
Volume flow Q = USgpm
Reynolds Number SI Units
Weight flow W = kg/h
where
|i = dynamic viscosity at the flowing temperature, in centipoise
U = viscosity at the flowing temperature, in Say bolt universal seconds
Note: Equation 7-17 is not recommended for viscosities less than 100
Saybolt universal seconds.
