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|  MIL-S-64052
gun. The pressure gages shall then be observed for a period of not less than one
minute. Any visible damage to or permanent deformation of any part of the spray
gun, or a drop in air pressure of more than 10 psig during the one minute
observation period shall be cause for rejection (see 3.12.2).
4.4.2.4 Pop-off pressure safety relief valve test. With the spray gun in fully
operating condition, the spray gun shall be supplied with compressed air at a
pressure of more than 60 psig. An air pressure gage shall be installed capable of
measuring the air pressure in the spray gun cup. The pressure gage shall be
accurate within one percent of reading over the range of 45 to 65 psig and readable
to the nearest psig. The gage shall be calibrated, traceable to a National Bureau
of Standards. Adjust the spray gun cup air regulator to an air pressure of 40 psig.
Adjust the regulator slowly upward, carefully observing the air pressure on the
gage, until the pop-off pressure safety relief activates. Record this air pressure.
Failure of the pop-off pressure safety relief valve to activate at not less than 50
psig or no more than 60 psig shall be cause for rejection (see 3.13.2).
4.4.3
Performance tests.
4.4.3.1 Spray pattern. Prior to this test the contractor shall prepare the
necessary quantity of pigmented alkyd enamel, black to charcoal in color and thinned
to a viscosity of 25 to 30 seconds using a Number 4 Ford Cup at 77 plus/minus 5
degrees F. The weight of 14.5 fluid ounces plus/minus 1 fluid dram of the thinned
alkyd enamel shall then be determined to the nearest dram avoirdupois. The spray gun
shall then be filled with the thinned alkyd enamel and attached in series with an
air flow meter and an air pressure gage to a source of compressed air. The
flowmeter shall be calibrated for air at 29.92 inches of mercury, standard
barometric pressure, and +70 degrees F.; and all readings shall be corrected for
variances from those condition. The flow meter shall be calibrated, traceable to
the National Bureau of Standards. It shall be accurate to within .25 cfm and
readable to the nearest cfm over a range of 5 to 10 cfm. The air pressure gage
shall be accurate within plus/minus 2 percent over the range of 25 to 75 psig and
readable to the nearest psig. The source of compressed air shall be capable of
providing regulated pressures of O to 100 psig over an air flow range of 0 to 10
cfm. The spray gun shall be adjusted for operation within the air pressure and air
flow constraints of Table 11. Liquid flow rate shall be determined by weighing the
spray gun to within the nearest dram avoirdupois both before and after performing a
timed spray of more than one minute in duration. The spray gun shall then be
operated to produce acceptable spray patterns in accordance with 3.7.3 and Figure 1
on a vertical, flat, non-porous surface, with a single burst of spray less than one
second in duration for each pattern. The patterns shall include one circular
pattern, two vertical fans, and two horizontal fans. The fan patterns shall be
produced beginning with a vertical fan and continuing by rotating the air cap to
90, 180, and 270 degrees from the original position. The spray gun shall then be
operated in the same manner to produce acceptable patterns on horizontal, flat,
non-porous surfaces positioned both below the spiny gun and above the spray gun,
i.e., overhead. Following the test, the spray gun shall be cleaned in accordance
with the manufacturer's instructions. Failure of the spray gun to produce aceptable
patterns in accordance with 3.7.3 and Figure 1 within the operating constraints of
3.8 shall be cause for rejection.
4.4.3.2 Finish. Prior to this test, the contractor shall prepare the necessary
quantity of pigmented alkyd enamel, black to charcoal in color and thinned to a
viscosity of 25 to 30 seconds using a Number 4 Ford Cup at 77 plus/minus 5 degrees
F. The spray gun shall be filled with the thinned alkyd and adjusted for operation
as needed. The spray gun shall then be operated to completely paint three flat,
non-porous surfaces, each 3 feet by 3 feet; one placed horizontally below the gun,
one placed vertically, and one placed horizontally above the gun, i.e., overhead.
11
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