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|  MIL-P-5238C
3.6.5.1 Pipe threads.
Pipe threads shall not be used except for permanent
closures.
3.6.6 Locking of parts. All threaded parts shall be locked by safety wiring,
or cotter pins in conformance with MS33540 or the use of self-locking nuts in
conformance with MS33588 or other approved methods. Wherever loosening of the
self-locking nut could possibly result in the nut or other parts entering the
fuel system, approval of the installation shall be obtained from the procuring
activity. The use of cotter pins on studs, or the use of lockwashers or stak-
ing is prohibited.
The outlet fitting shall utilize couplings in accordance with
3.6.7 Outlet.
MIL-C-22263.
3.6.7.1 Check valve. A check valve shall be incorporated in the outlet of
each pumping unit in accordance with the detail specification in order to
prevent any reverse flow of fuel through the pump into the tank. The check
valve shall be capable of satisfying all applicable performance requirements
of MIL-V-7899. Reverse flow leakage shall not exceed lcc per minute initially
(or 5CC per minute at the conclusion of the test program) from 4 inches of
fuel head up to 60 psig.
3.6.7.2 Proof pressure. The outlet and check valve(s) shall be capable of
withstanding an applied pressure of 120 psig (or higher in accordance with
the detail specification) without failure or permanent distortion.
3.6.8 Negative G and inverted operation. The pump shall be capable of being
operated under negative G conditions or during inverted flight. The pump
output under these conditions shall be in accordance with the detail specification.
3.6.9 Start-up. The rate of power input, acceleration, and output during
start-up shall be stated in the detail specification. At any point during
or following the climb of 3.2.3, when a non-operating pump is started, it shall
develop the required flow and pressure within 5 seconds after power is applied.
3.6.10 Variations in power input. The pump assembly shall demonstrate com-
patibility with all the variations in the aircraft power supply system(s),
without overspecd, overheating, stopping, or other failure. The minimum
requirements are MIL-STD-704, MIL-H-5440, or MIL-H-8891, as applicable. It
is not required that 3-phase electric motors must operate on 2 phase power.
3.6.11 Leakage. There shall be no external leakage from the pump assembly
except from drains provided for that purpose. For plug-in pump units, the
detail specification shall state the maximum allowable fuel loss during removal
and reinstallation in a full fuel tank.
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