MIL-H-8891A
General system design requirements - Hydraulic systems
3.5
shall be as simple and foolproof as possible and in accordance with design,
operation, inspection, and maintenance objectives specified in the vehicle
design requirements,
Strength -
3.5.1
Additional loads - All hydraulic systems and components
3.5.1.1
which are subjected, during operation of the vehicle, to structural or other
loads which are not of hydraulic origin shall withstand such loads when applied
simultaneously with appropriate proof pressure as specified in Table I, with-
out exceeding the yield point at the maximum operating temperature.
Accelerated loads - Actuating cylinders and other com-
3.5.1.2
ponents and their attaching lines and fittings, subject to accelerated loads,
shall be designed and tested on the basis of a pressure equal to the maximum
pressure that will be developed, without exceeding the yield point at the
maximum operating temperature.
Pressure limitations -
3.5.2
System pressures - System pressure shall be in accord-
3.5.2.1
ance with Table I, Peak pressure resulting from any phase of the system
operation shall not exceed 135 percent of the main system, subsystem or
return system operating pressure when measured with electronic equipment,
or equivalent. Lines, fittings, and equipment in return circuits shall be
designed for one-half the nominal system operating pressure.
Proof and burst - The systems individual components
3.5.2.2
shall be designed to withstand the proof and burst pressure requirements of
Table I throughout the ambient and fluid temperature range after loss of
strength of materials caused by aging at elevated temperatures for the life
of the systems or component.
Back pressure - The system shall be so designed that
3.5.2.3
proper functioning of any unit will not be affected by the back pressure
or changes in the back pressure in the system. The system or systems shall
also be so designed that malfunctioning of any unit in the system will not
render any other subsystem, emergency system, or alternate system inopera-
tive because of back pressure.
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3.5.2.3.1
Brakes - Back pressure resulting from the operation of
any unit while the vehicle is on the ground shall create no greater back
pressure at the brake valve return port than 90 percent of that pressure
which will cause contact of braking surfaces. In addition, supply pressure
to the brake system shall not drop-below the maximum brake-operating pressure
during the operation of any other subsystem in the vehicle during taxiing,
landing, or takeoff.
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