Page 271 - Valve Selection Handbook

258 Valve Selection Handbook

Table 7-1. (continued)
Nomenclature
Mixed SI Mixed US
Units Units
f Pipe friction factor = number
of velocity heads lost in length
of pipe equal to diameter
F Gas flow constant for subsonic
nozzle flow, based on isentropic
coefficient k at standard conditions
and the absolute pressure ratio
across the valve
Discharge reactive force N Ib
F d
g Gravitational acceleration 9.807 m/sec 2 32.174 ft/sec 2
Proportionality constant l.Okgm/Ns 2 32.174
g c
lb mft/lb fs 2
G Specific gravity of the liquid referred
to water = 1.00 at 70°F (20°C)
k Isentropic coefficient
K Derated or certified coefficient
of discharge 1
Capacity correction factor accounting
K b
for the effect of built-up and superimposed
back pressure on valve lift of bellows
balanced pressure relief valves
Actual coefficient of discharge 2
K d
Napier capacity correction factor
K N
for pressure
Napier capacity correction factor for
K SH
superheat
Velocity head loss of rupture devices
K R
Viscosity correction factor
K v
1 Length of pipeline mm in.
M Molecular weight kg/kmol Ib/lbmol
2
P Set pressure (gauge) barg Ib/in g
PI Relieving pressure (gauge) = set
pressure plus overpressure plus
2
atmospheric pressure bara Ib/in a
2
Po Pressure at valve outlet bara Ib/in a
1
ASME (1992) Section VIII Division, UG-131(e)(3)
2
ASME (1992) Section VIII Division, UG-131(e)(2)