Data Sheet

Bulletin 71.1:CP400
11
relief will be activated when the pressure rises and
activates the monitoring regulator in order to provide an
indication that the monitor is controlling ow instead of
the primary regulator.
Integral Type VSX4 Slam-Shut Module
The Type VSX4 slam-shut module on the
CP404 Series regulator is a fast acting safety
shutoff device that provides overpressure (OPSO) or
over and underpressure (OPSO/UPSO) protection
by completely shutting off the ow of gas to the
downstream system. The Type VSX4’s actions are
independent of the CP404 Series regulator and
of variations to the inlet pressure. The Type VSX4
provides the option of internal or external downstream
pressure registration, see Figure 6. External
registration requires a downstream sensing line.
The shutoff disk is normally in the open (reset)
position. If the pressure below the diaphragm
increases (or decreases) reaching the Type VSX4
setpoint, the diaphragm will travel upwards (or
downwards) to release the trip mechanism which
allows the spring force on the stem to push the disk
against the seat, shutting off all gas ow. The manual
reset has an internal bypass to equalize the reset
pressure on either side on the shutoff disk.
Overpressuring any portion of a regulator or
associated equipment may cause personal injury,
leakage or property damage due to bursting
of pressure-containing parts or explosion of
accumulated gas. Provide appropriate pressure
relieving or pressure limiting devices to ensure
that the limits in the Specications section is not
exceeded. Regulator operation within ratings does
not prevent the possibility of damage from external
sources or from debris in the pipeline.
Refer to the relief sizing coefcients and the Capacity
Information section to determine the required relief
valve capacity.
Capacity Information
Tables 12 to 27 and 29 to 34 give the CP400 Series
natural gas regulating capacities at selected inlet
pressures, outlet pressure settings and body outlet
sizes. Tables 29 through 34 provide capacities
specically for Pressure Factor Measurement
(PFM) applications. Flows are in SCFH (60°F and
14.7 psia) and Nm³/h (0°C and 1.01325 bar) of 0.6
specic gravity natural gas. To determine equivalent
capacities for air, propane, butane or nitrogen, multiply
the capacity number in the tables by the following
appropriate conversion factor: 0.775 for air, 0.628 for
propane, 0.548 for butane or 0.789 for nitrogen. For
gases of other specic gravities, multiply the given
capacity by 0.775 and divide by the square root of the
appropriate specic gravity.
Relief Sizing
For critical ow:
To determine wide-open ow capacities for relief
sizing of 0.6 specic gravity natural gas at 60°F at
critical pressure drops (absolute outlet pressure equal
to approximately one-half or less than one-half of the
absolute inlet pressure), use the following formula:
Q = P
1abs
(C
g
)(1.29)
For subcritical ow:
If pressure drops are lower than critical (absolute
outlet pressure greater than approximately one-half
the absolute inlet pressure), use the following formula
and convert according to the factors in the preceding
paragraph if necessary:
Q = C
g
P
1
SIN
520
GT
3417
C
1
∆P
P
1
DEG
where:
C
1
= C
g
/C
v
(see Table 3)
C
g
= Gas sizing coefcient (see Table 3)
G = Gas specic gravity (air = 1.0)
P
1
= Regulator inlet pressure, psia
∆P = Pressure drop across regulator, psi
Q = Gas ow rate, SCFH
T = Absolute temperature of gas at inlet, °Rankine
Note
Due to boost, the above formulas
cannot be used to obtain correct
regulating capacities for regulators with
internal registration.
The published capacities were obtained using inlet and
outlet piping the same size as the regulator body size.