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Page Title:
Hydraulic cylinder valving and manifold |
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|  MIL-T-46797B(AT)
floor. The hoist cylinder(s) shall be furnished with an automatic cushioning of stroke
approaching the fully extended and retracted positions of the body. The hydraulic system shall
be designed to preclude hydraulic transients. Automatic pilot check valves shall be provided to
preclude body descent in the event of a hydraulic pressure loss. A manual device or valve shall
be incorporated into the system to lower the body in case of hydraulic pressure loss. The device
will bleed the fluid back into the reservoir. The device shall provide metering characteristics.
3.5.5.6.1 Hydraulic cylinder valving and manifold. A check valve, a return line with
filter having antiflow-back characteristics or a ball type shut-off valve shall be provided between
the reservoir and the return line filter to enable shut off of the oil supply to facilitate changing the
element in the filter. A fixed orifice device or an adjustable throttle valve (flow control) shall be
located as close as practicable to the lift cylinder(s) to limit and control the downspeed. The
throttle valve shall be rated for not less than three times the working pressure and shall be
equipped with a lock screw or jam nut to hold the desired preset. When two lift cylinders are
provided, the manifold shall distribute equal pressure and flow rate and furnish simultaneous
operation of the cylinders.
*
3.6 Body mounting. The body shall be mounted to the hoist unit in accordance with the
hoist manufacturer's recommendations and shall be reinforced, when necessary, for added
strength on hoist operations. Rear body mounting shall include hinges securely welded to the
body longitudinal sills, a connecting cross shaft, and a plate securely bolted to the chassis main
frame rails.
3.7 Welding. Adequate preparation of metal prior to welding of the body subframe,
hoist, elevating body, and components shall be provided. The surface of parts to be welded shall
be free of rust, scale, paint, grease, and other foreign matter. Welding rods shall be compatible
with the metal being welded. All critical arc welds shall be magnaflux or dye penetrant
inspected prior to painting. The following defects shall not be acceptable:
(a) Welds which are ground flush with metal
(b) Slug or plug welding
(c) Undersize of fillet welds, overlaps, inadequate fusion and penetration, undercutting
of weldments and vertical down welding
(d) Unremoved slag and spatter
(e) Cracks
(f) Spot, tack, or intermittent welds for strength.
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