MIL-DTL-27188C
3.3.1.3 Filling medium. The filling medium shall be of at least 98 percent purity, free of
dust particles, and shall contain no more than 0.006 milligram (mg) of water vapor per liter (dew
point -65 °C) at the filling pressure. The filling medium shall be 88 percent to 92 percent
nitrogen and the remainder helium. The absolute pressure of the filling medium in the case shall
be 12 pounds per square inch (psi) to 14.7 psi. Other concentrations of filling medium shall not
be used except with prior approval of the procuring activity.
3.3.2 Lighting. The indicator shall be integrally lighted and shall meet all requirements
specified herein. The indicator shall be lighted in accordance with MIL-L-27160.
3.3.3 Pointer. The pointer shall conform to figure 1 and shall be suitable for integral
lighting. The length shall be such that the tip of the pointer will extend into the scale a distance
equal to 1/3 to 2/3 the length of the shortest graduation.
3.3.3.1 Pointer finish. The lighted portion of the pointer shall be finished in accordance
with FED-STD-595, color number 37875.
3.3.4 Dial. The dial shall conform to figure 1. A minimum diameter of 1-3/4 inches shall
be maintained across the outside ends of the graduations. The 30-psi graduation shall be located
on the horizontal centerline at the left side of the dial.
3.3.4.1 Dial markings. The following markings shall be finished in durable white in
accordance with FED-STD-595, color number 37875. The dimensions of the markings shall be
as specified in table I.
TABLE I. Marking dimensions.
Height or length
Width of line or graduation
Marking
in inches ±1/64 inch
in inches ±0.005 inch
Numerals 0, 20, 40, 60,
5/32
0.025
80, and 100
10-pound graduations
3/16
0.031
Graduation at 50 psi
9/64
0.031
Lettering "OIL PRESS"
1/8
0.020
Lettering "PSI"
1/8
0.020
5-pound graduations
3/32
0.020
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