open bleed valve and change setting of adjusting cap
all residue is removed from crevices and packing ring
installed in body of back pressure valve. Turn cap
grooves.
counterclockwise (out of body) to lower pressure at which
b. Inspect parts for evidence of damage and wear
valve opens. Turn cap clockwise (into body) to increase
such as stripped screw threads, cracking of valve body,
opening pressure. Continue alternate adjustments and
and finished surfaces that are scratched, scored or
tests until back pressure valve operates as specified.
pitted.
e. Fully open shut-off valve. Starting with zero
c. Make sure seat surface of piston is smooth and
approach section pressure, slowly open pressure regulator
undamaged; mating surface of piston seat must be
until gage No. 1 indicates an approach section pressure
sharp and without nicks or other signs of wear or
of 2000 psi. Flow rate as measured by flowmeter shall not
damage.
exceed five cubic centimeters per minute.
d. Check spring for signs of set or out-of-round.
f. Adjust pressure regulator to increase approach
Spring must be cylindrical in shape with ends closed,
section pressure to 2750 psig. Then close pressure
square and ground. Length of spring with a load of 86
regulator to gradually decrease approach section pressure
pounds plus or minus 10 pounds should be 0.687 inch.
to 2000 psig. Measured flow rate shall not exceed 0.15
e. Discard all damaged, worn and questionable
scfm.
parts.
g. Close shut-off valve. Adjust pressure regulator to
4.11.4 REASSEMBLY (Refer to Figure 5-8.)
increase approach and exit section pressures to 4500
psig. Brush a soap-water solution over entire surface of
a. During reassembly, apply a light film of
back pressure valve. There shall be no visual indications
pneumatic system grease (Specification MIL-L-4343) to
of leakage as evidenced by air bubbles.
all gaskets, packings and male threads.
h. After completing all tests, close pressure
b. Install back-up ring (12) and packing (11) in
regulator, open bleed valve and shut-off valve to relieve
groove of piston (9). Install second packing (11) in
air pressure in test set-up, and disconnect test equipment.
groove of piston seat (10).
Safety wire adjusting cap to valve body with 0. 025 inch
diameter stainless steel wire.
c. Install piston seat (10) and piston (9) in valve
body (13).
4.11.6 INSTALLATION. Install back pressure valve, tube
d. Position tube fitting gaskets (5) in grooves of
fitting gasket (5-8, 14), back-up ring (5-8, 15) and nut (5-8,
inlet and outlet fittings (3 and 4). Screw fittings into
16) on filter and separator assembly in accordance with
appropriate ports of valve body (13) and tighten with a
instructions in paragraph 4.5.7. Install check valve and
torque of 45 pound-inches.
fittings as instructed in paragraph 4.10.6.
e. Place spring (8), flanked by two spring plates
4.12 PNEUMATIC DUMP VALVE AND FILTER AND
(7), into valve body (13). Screw valve cap (6) into valve
SEPARATOR ASSEMBLY
body until top surface of cap is approximately flush with
upper edge of valve body.
4.12.1 REMOVAL The pneumatic dump valve and the
filter and separator assembly (see Figure 1-3) should be
4.11.5 TEST AND ADJUSTMENT. Test and adjust the
removed as a unit as follows: (refer to Figure 5-3):
reassembled back pressure valve as follows:
a. Remove pressure relief valve (paragraph 4.8.1),
check valve (paragraph 4.10.1) and back pressure valve
a. Connect back pressure valve to test set-up as
shown schematically in Figure 4-5. Be sure to observe
assembly.
dimensions shown for approach and exit sections.
b. Disconnect lead wires from filter and separator
b. Close bleed valve. Open shut-off valve. Adjust
heater blanket and thermostat switch
pressure regulator to gradually increase inlet pressure
until flowmeter registers a flow rate slightly greater than
c. Disconnect aftercooler-to-separator connecting
two scfm. This should occur when approach section
tube (22) from elbow (27) installed in inlet port of filter and
pressure is between 2550 and 2700 psig.
separator assembly. Loosen nut (30) and remove elbow,
tube fitting gasket (28) and back-up ring (29) from inlet
c. Partially close shut-off valve. Adjust pressure
port.
regulator and shut-off valve until gage No. 2 indicates
2400 psi and flowmeter registers a flow rate slightly
d. Unscrew nut (10) and remove drain tube (8),
greater than two scfm. Approach section pressure, as
sleeve (9) and nut from elbow (11) installed in blowout
measured by gage No. 1, shall not exceed 2400 psig.
port of pneumatic dump valve. Unscrew and remove
elbow.
d. If back pressure valve does not operate as
specified in step c, preceding, close pressure regulator,
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