Data Sheet

Bulletin 71.1:SR5
8
For Non-Critical Pressure Drops
For pressure drops lower than critical (absolute outlet
pressure greater than one-half the absolute inlet
pressure), use the following formula:
$%'
0
0
#

3).
0#
'4

1

G
$



where,
Q = Gas ow, SCFH (60°F and 14.7 psia)
G = Specic gravity of the gas
T = Absolute temperature of gas at inlet, °Rankine
C
g
= Wide-open sizing coefcient from Table 6
P
1
= Absolute inlet pressure, psia (add 14.7 psi
to gauge inlet pressure to obtain absolute
inlet pressure)
C
1
= ow coefcient from Table 6
DP = pressure drop across the regulator, psi
To obtain capacities in normal cubic meters per hour at
0°C and 1.01325 bar, multiply the capacity determined
in SCFH by 0.0268.
Steam Capacities
Capacities in Table 9 are in pounds per hour and
kilograms per hour of saturated steam. To determine
wide-open ow capacity for relief valve sizing of
steam, use the equation for critical pressure drops
(absolute outlet pressure equal to one-half or less than
one-half absolute inlet pressure).
Q = P
1(abs)
x C
s
where,
Q = Flow, lb/hr
P
1(abs)
= Absolute inlet pressure psia (add 14.7 psi
to gauge inlet pressure to obtain absolute
inlet pressure)
C
s
= Wide-open sizing coefcient from Table 6
Water Capacities
All water capacities in Table 10 are in gallons per
minute and liters per minute. Use the following
equation to determine ow capacity for liquid relief
valve sizing:
0
C
G
Q
v
$

where,
Q = Flow, gpm
P
1(abs)
= Absolute inlet pressure psia (add 14.7 psi
to gauge inlet pressure to obtain absolute
inlet pressure)
C
v
= Wide-open sizing coefcient from Table 6
G = Specic gravity of the uid
DP = pressure drop across the regulator, psi
The K
m
values listed in Table 6 can be used to predict
choked ow on liquid service. See Fisher Catalog
10 for more information on liquid sizing. To convert
capacities to liters per minute multiply gallons per
minute by 3.785.
Installation
The Type SR5 regulator may be installed in any
position, as long as ow will be in the same direction
as that indicated by the body arrow. However, to
ensure self-draining (from outlet to inlet) the regulator
should be installed with the spring case in the upright
vertical position. The regulator should be installed so
that the spring case vent is protected from anything
that might interfere with it.
Fisher provides an instruction manual with every
regulator shipped. Refer to this for complete
installation, operation and maintenance instructions.
Included is a complete listing of individual parts and
recommended spare parts.