Bulletin 71.1:S200
10
Figure 7. Type S203 Regulator with True-Monitor
the diaphragm will travel upwards (or downwards)
operating a lever which in turn releases the ball.
Once the ball is released, the spring force on the stem
will push the stem and 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.
In order for the Underpressure Shutoff (UPSO) of
any slam shut to be triggered, the downstream pipe
pressure must drop below the UPSO setpoint. In
the case of a downstream line break, numerous
factors can prevent the downstream pipe pressure
from decreasing below the slam-shut UPSO setpoint.
These factors include the distance of pipe to the
break, the diameter of the pipe, size of the break, and the
number of restrictions, such as valves, elbows and bends,
downstream of the regulator and/or slam-shut device.
Due to these factors additional protections should be
installed to stop ow in the event of a line break.
The S200 Series regulators have outlet pressure
ratings that are lower than their inlet pressure
ratings. A pressure relieving or pressure limiting
device is needed for Types S201, S201H, S201K,
S201P, S201PK, S204, and S204H if inlet pressure
can exceed the outlet pressure rating, since these
regulators do not have internal relief, high outlet
pressure shutoff, or integral slam-shut device.
Type S202, S202H, S202P, S203, S203H, or S203P,
Types S206 and S206H have internal relief or relief
monitoring to provide partial capacity relief, limiting
total outlet pressure as shown in Figures 6 and 8.
This partial internal relief may be adequate; if not,
an additional pressure relieving or pressure limiting
device should be installed downstream.
Types S208 and S209 regulators rely on the
Type VSX-2 slam-shut device for overpressure
protection. The Type VSX-2 will shut the system down
until the problem can be rectied and the Type VSX-2 is
reset. Type S209 regulators have internal relief which
provides token capacity relief for thermal expansion.
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