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|  MIL-T-62491C
3.5.15.5 Hydraulic fluid temperature. The hydraulic fluid temperature shall be maintained
within safe limits to prevent seal damage or approach to the flash point of the hydraulic fluid
during all operating conditions of the vehicle and use of the boom and winches for continuous
periods up to one hour. Excessive heating (more than 13C (55F) above ambient) of the
fluid shall be unacceptable under any operating condition. Provisions shall be made to prevent
malfunction or unactuated operation of the hydraulic system due to changes in fluid temperature.
3.5.15.6 Hydraulic cylinders. All hydraulic cylinders shall incorporate seals with rod wipers
to prevent the entrance of moisture and dirt into the cylinders, and leaks of hydraulic fluid from
the cylinders. Preformed packings shall be used in the cylinders where static seals are required.
The cylinders shall be compatible with the hydraulic system and shall have sufficient
cross-sectional area to raise and hold the boom at the rated capacity without the use of pins or
other supporting devices. Valves shall be included in the hydraulic system to prevent load drift.
All hydraulic cylinders for raising and lowering the boom and outriggers, and for extending and
retracting the boom for sizes 25T through 45T, shall be provided with pilot check valves, holding
valves or counterbalance valves to prevent descent of the boom assembly, retraction of the boom,
and retraction of the outriggers in the event of a loss of hydraulic pressure. Means shall be
provided to install pressure gages for testing hydraulic system pressure and relief settings. All
surfaces of hydraulic ram piston rods shall be chrome plated to a thickness sufficient to withstand
a 30-hour salt spray test in accordance with ASTM B117.
3.5.15.7 Hydraulic lines and fittings. Hydraulic lines shall be located for maximum ease of
removal and installation, visual inspection for failure, and maximum protection from damage
during operation of the boom assembly. Flexible hydraulic hose or collector rings shall be used
where flexing of hydraulic lines is encountered and where installation of components requires
a flexible coupling. Hydraulic lines and fittings shall be air- and liquid-tight and shall be installed
to prevent damage from vibration and chafing. The system shall be designed to prevent hydraulic
transients. Provisions shall be made for bleeding air from the hydraulic system and for completely
draining all hydraulic lines when necessary. Hose assemblies and all seamless steel hydraulic lines
shall be adequate to provide the necessary rate of flow, temperature and pressure required to
operate the system smoothly and efficiently. Galvanized pipe and copper tubing shall not be
acceptable.
3.6 Type II mechanical wrecker. Type II mechanical wreckers shall have the dimensions and
load capacities specified in table XIII for the corresponding vehicle size and GVW.
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