MIL-PRF-81757/2C
REQUIREMENTS:
1. Part or identifying number. Table I contained herein is a list of the part or identifying numbers
(PINs) for the vented filler caps to be purchased under this specification sheet. The table also
identifies the body size, style of electrolyte deflector, color, and other construction characteristics
for each PIN. Each vented filler cap supplied shall display the PIN specified in the contract, and
the item shall comply with the unique requirements specified.
2. Dimensions. The dimensions of the vented filler caps shall be as specified on figure 1. The
dimensions for any attached electrolyte deflector shall be as shown on figure 2 and in table I. The
dimensions of the specified O-ring shall be as indicated on figure 3.
3. MIL-PRF-81757 variance. The vented filler cap shall comply with MIL-PRF-81757 except
as follows.
3.1 Add the following paragraphs:
"3.7.12.1 Vents. The body of each vented filler cap shall have a vertical axis channel with
two side holes to allow venting of gasses. Gasses generated within the cell shall flow upward
through the channel and vent through the two side holes. Venting shall be controlled by a
pressure-actuated check valve. The valve shall actuate (open) at a pressure differential not
greater than 10.0 pounds per square inch (psi) and permit a continuous flow of air. The valve
shall close within the 10.0 to 2.0 psi range."
"3.7.12.2 Drains. The outer perimeter of the upper body shall contain not less than two
holes to drain liquids. The holes shall be centered between two splines, and their sidewalls shall
not penetrate the curvature of the splines. The drain holes shall conform to that shown on
figure 1 of the specification sheet."
"3.7.12.3 Check valve. The check valve shall prevent gas flow when tested in accordance
with 4.5.5.4."
"3.7.12.4 Seal. Each vented filler cap assembly shall contain an O-ring that conforms to
table I of the specification sheet. The O-ring seal shall not leak when tested in accordance with
4.5.5.5."
"3.7.12.5 Electrolyte deflector. When an electrolyte deflector is required, the design shall be
as specified in table I and shown on figure 2, both of the specification sheet."
3.2 Modify the following paragraphs:
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