MIL-PRF-27720G
3.5.15.1 Shutoff and control valves. Valves shall provide positive shutoff when closed, and
minimum resistance to flow when open. Each manually-operated control or shutoff valve shall
be provided with an easily-turned handle with a diameter of 3.0 inches per inch of nominal size,
but not less than 1.0 inch. If globe valves are used, those valves 0.5 inch and larger nominal size,
handling low-temperature liquid or gas, shall incorporate seats than can be replaced without
removal of the valve from the tank piping. Sealing discs or plugs for these valves shall also be
replaceable without replacing the valve stems. All valves handling low-temperature liquid and
gas shall have their packing glands located not less than the distance specified in table I from the
valve center connection centerline (see 4.5.1).
TABLE I. Separation of Valve Packing Gland from Valve Connection Centerline.
Valve Nominal Size (inches)
Separation of Packing Gland from
Connection Centerline (inches)
1/4
4
3/8
4
1/2
7
3/4
7
1
9
1-1/4
9
1-1/2
11
2
11
2-1/2
12
3
12
3.5.15.2 Drain valves. Manually-operated valves shall be provided for draining liquid from the
fill line disconnect coupling after removing the fill hose, and from the servicing line and its hose.
The drain valves shall be readily accessible outside the control housing assembly. The drain
valves shall discharge outside the control housing assembly (see 4.5.1).
3.5.16 Instrumentation.
3.5.16.1 Liquid level gage. A gage, flush mounted on the control panel, shall be provided to
indicate the quantity of liquid oxygen or liquid nitrogen contained in the tank inner shell with an
accuracy of ± 3% of tank design capacity. The gage shall be easily readable and shall have a
diameter of not less than 2.5 inches. The gage shall be graduated in gallons of liquid oxygen or
liquid nitrogen. If a differential pressure gage is used, the design shall ensure that breakage of
the glass face will not subject the sensing element to damaging pressures when the inner shell is
pressurized to 65 psig. If this type of gage is used, the assembly shall incorporate pulsation
snubbers in the sensing lines to prevent undue fluctuation of the indicating needle.
3.5.16.2 Vapor phase pressure gage. A gage, flush mounted on the control panel, shall be
provided to indicate the inner shell pressure. The gage shall be easily readable and shall have a
diameter of not less than 2.5 inches. The gage shall be graduated over at least 270° of the dial
face, and shall be accurate to within ± 2% of full-scale range. The indicating range shall be
10
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