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|  MIL-H-8891A
Lock valves - Use of lock valves to hydraulically
3.10,16
lock actuating cylinders shall require approval of the procuring activity.
where lock valves are used, provisions shall be made for fluid expansion
and contraction throughout the temperature range. . Where several actuating
cylinders are mechanically tied together, only one lock valve shall be used
to hydraulically lock all actuators so tied together.
Motors - All motors shall be accessible for mainten-
3.10.17
ance and inspection, Proper case flow connections to the reservoir shall
be provided. Installation of hydraulic motors shall be such that the motor
housing shall not be subjected to overpressurization. Shaft seal drain
shall be vented to prevent return of this fluid to the hydraulic systems.
Relief valves, system and thermal expansion -With
3.10.18
specific approval of the procuring activity, relief valves may be incor-
porated as-part of another unit, Provided they comply with applicable
relief device to prevent bursting of, or damage to, the system in the
event the normal pressure regulation device in the system malfunctions;
or, in a blocked line condition to relieve excessive pressure due to
either thermal expansion of the fluid or overload forces on actuating
units, Therefore, relief valves shall not be used as the sole means of
limiting pressure in a power circuit but shall function only as a safety
valve.
System relief valves - Provisions shall be made to
3.10.18.1
insure that pressures in any part of the power system will not exceed a
safe limit above the cutout pressure of the hydraulic system. Pressure
relief valves, as specified herein? shall be located in the hydraulic
system wherever necessary to accomplish this pressure relief (see Table I).
The system relief valve shall have a capacity equal to or greater than the
combined rate of flow of pumps where fixed-displacement pumps with common
cutout regulators are used, or equal to or greater than the rated flow of
the largest pump when variable-volume pumps with a common pressure line
are used.
Thermal expansion relief valves - Relief valves shall
3.10.18.2
be installed as necessary to prevent excessive pressure rise and system
damage resulting from thermal expansion of hydraulic fluid. Internal
valve leakage shall not be considered an acceptable method of providing
thermal relief. (For relief valve setting, see Table I.)
*
Restrictor valves - Adjustable orifice restrictor
3.10.19
valves may be used in experimental vehicles but only fixed orifice restrictor
valves shall be used in service test and production vehicles. For one-way -
restrictors, the direction of restricted and unrestricted flOW shall be in
dicated on the restrictor valves. (For orifice filtration requirements,
see 3.9.2)
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