TM 5-848-1/AFM 88-12, Chap. 1
type of users or services affected by each potential
service conditions under which they will operate or
shutdown.
to which they may be subjected. In addition to the
(2) Low-pressure systems. Valves are required
pressure regulating devices, suitable protective
on low-pressure systems only to meet the condi-
devices to prevent accidental overpressurizing must
tions given in subparagraph f below.
be provided. Suitable protective devices are as
f. Location of distribution system valves. A
follows:
valve will be installed on the inlet piping of each
(a) Spring-loaded relief valves conforming to
regulator station controlling the flow of pressure of
ASME Boiler and Pressure Vessel Code, Section
VIII, Division 1.
gas in a distribution system. The distance between
(b) Pilot-loaded back pressure regulators
the valve and the regulator or regulators must be
used as relief valves and designed so that pilot
sufficient to permit the operation of the valve
system or control line failure will open the regula-
during an emergency, such as a large gas leak or a
tor.
fire in the regulator station. Valves on distribution
(c) Weight-loaded relief valves.
mains, whether for operating or emergency pur-
(d) A monitoring regulator installed in series
poses, will be readily accessible and easily operable
with the primary pressure regulator.
during an emergency. Where a valve is installed in
(e) A series regulator installed upstream from
a buried box or enclosure, ready access only to the
the primary regulator and set to continuously limit
operating stem or mechanism is implied. The box
the pressure on the inlet of the primary regulator to
or enclosure will be installed in a manner to avoid
the maximum allowable operating pressure of the
transmitting external loads to the main.
distribution system, or less.
g. Pressure regulators. Pressure regulators are
(f) An automatic shutoff device installed in
necessary at all points where equipment or design
series with the primary pressure regulator and set
requires reduction in or regulation of pressure.
to shut off when the pressure on the distribution
Bypasses around pressure regulators will not be
system reaches the maximum allowable operating
installed unless continuity of service is imperative
pressure, or less. This device must remain closed
until reset manually. It should not be used where it
and the bypass is suitably regulated to prevent
might cause an interruption in service to a large
possible overpressure of downstream lines.
number of mains or service lines.
h. Central regulating and metering station. A
(g) Spring-loaded diaphragm type relief
central regulating and metering station is generally
valves.
provided by the gas supplier and is usually located
(2) Controlling and limiting pressure in low-
near the entrance to the reservation. When
pressure gas distribution systems. Each low-
provided by the Government, all necessary equip-
pressure distribution system or low-pressure main
ment will comply with the requirements of the gas
supplied from a gas source which is at a higher
supplier. An enclosure, if required, will be of fire-
pressure than the maximum allowable operating
resistant construction, such as masonry. Adequate
pressure for the low-pressure system will be
provision will be made for ventilation. The design
equipped with pressure regulating devices of ade-
of the enclosure will be coordinated with the using
quate capacity. Other devices will be designed to
agency and gas supplier. A valve will be installed in
meet the pressure, load, and other service condi-
the main supply line approximately 100 feet ahead
tions under which they will have to operate. In
of the station.
addition to the pressure regulating devices, a
i. Protection against accidental overpressurizing.
suitable protective device to prevent accidental
Every distribution system and meter and connected
overpressurizing must be provided and may in-
clude:
facilities will be provided with suitable pressure
(a) A liquid seal relief device that can be set
relieving or pressure limiting devices.
to open accurately and consistently at the desired
(1) Controlling and limiting pressure in high-
pressure.
pressure gas distribution systems. Each high-
(b) Weight-loaded relief valves.
pressure distribution system or main which is
(c) An automatic shutoff device as described
supplied from a source of gas at a higher pressure
in (1)(f) above.
than the maximum allowable operating pressure for
(d) A pilot-loaded back pressure regulator as
the distribution system will be equipped with
described in (1)(b) above.
pressure regulating devices of adequate capacity
(e) A monitoring regulator as described in
designed to meet the pressure, load, and other
(1)(d) above.
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