20
Maximum Emergency
Pressures
NOTE: The use of an internal
or external relief valve is rec-
ommended for installations
subjected to no flow for
extended periods of time, such
as pilotless ignition systems.
A travel stop stem is located in
the 243-12-1 and 243-12-4 to
provide over-pressurization
protection to internal compo-
nents during overpressuriza-
tion.
The maximum pressure the regu-
lator inlet may be subjected to
under abnormal conditions with-
out causing damage to the regu-
lator is the maximum allowable
inlet pressure (from the capacity
tables, pages 8 through 19) plus
50 psi.
The maximum pressure the
diaphragm may be subjected to
without causing damage to the
internal parts of the regulator is:
243-12-1......... set point + 3 psi
243-12-2, 243-8-1 and
243-8-2........... set point + 5 psi
243-8HP........ set point + 5 psi
Set point is defined as the outlet
pressure a regulator is adjusted
to deliver.
If any of the pressure limits are
exceeded, the regulator must be
taken out of service and inspect-
ed. All damaged or otherwise
unsatisfactory parts must be
repaired or replaced.
The maximum pressure that
can be safely contained by the
diaphragm case is:
243-12-1 and
243-12-2........................ 15 psi
243-8-1 and 243-8-2...... 15 psi
243-8HP....................... 25 psi
Safely contained means no
leakage as well as no bursting
Before using any of the above
data, make sure this entire sec-
tion is clearly understood.
Overpressurization
Protection
Protect the downstream piping
system and the regulator’s low
pressure chambers against over-
pressurization due to possible
regulator malfunction or failure to
achieve positive lockup. The
allowable outlet pressure is
the lowest of the maximum
pressures permitted by fed-
eral codes, state codes, Bul-
letin RDS-1498 or other
applicable standards. The
method of protection can be a
relief valve, monitor regulator,
shut-off device or similar
mechanism.
Monitoring
A monitor set consists of two reg-
ulators in series as shown. The
monitor is the standby. It takes
control if a failure in the operating
regulator causes outlet pressure
to exceed normal.
Either regulator may be used as
the monitor. In both cases the
upstream regulator must have a
blocked throat and external con-
trol line as shown for the 243 on
page 7. Also, the control line for
the upstream regulator connects
into the outlet piping all the way
downstream. . . that is, down-
stream of the downstream regu-
lator.
The illustration shows a typical
243 monitor set. While the
downstream regulator is shown
as operating and the upstream
regulator is shown as the moni-
tor, the two can be reversed.
There are reasons for doing it
one way or the other depending
on user’s practice. Stop and
bypass valves, not shown, like-
wise would depend on user’s
preference and practice.
Either way, the operating regulator
is adjusted for the normal outlet
pressure. The monitor is adjusted
somewhat higher so it is normally
full open. If a failure in the
operating regulator causes
excessive increase in outlet
pressure, the monitor will go
into operation to hold outlet
pressure at its set point.
Monitoring is an effective and
dependable method of provid-
ing overpressure protection.
A significant advantage is that
it provides the protection with-
out wasting gas to atmos-
phere. Refer to Bulletin RDS-
1306-2 (Package monitor sets
243-DOT) for more informa-
tion.
When a 243 is used to monitor
another 243 with an identical
orifice size, the total maximum
capacity through both can be
figured at 70% of the rated
capacity for one regulator.
This applies with the monitor
located upstream or down-
stream.
Periodic Inspection:
Regulators are pressure control devices with numerous moving parts sub-
ject to wear that is dependent upon particular operating conditions. To assure continuous
satisfactory operation, a periodic inspection schedule must be adhered to with the frequency
of inspection determined by the severity of service and applicable laws and regulations.
See Bulletin RM-1306 field service instructions.
