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 TM 55-1905-220-14-4
3-8.
MARINE GEAR- MAINTENANCE INSTRUCTION (Cont.)
(1)
General. The selector valve assembly contains passages and ports for the transmission and
direction of pressurized oil within the hydraulic system. It is the function of the pressure rate control piston
within the selector valve assembly to provide a rapid, yet smooth, pressure rise for the hydraulic system when
required.
(2)
Selector Valve-Neutral. Oil enters the selector valve body through passage A and fills chamber
B. The oil causes the pressure regulation piston to partially compress the piston outer and inner springs against
the pressure rate control piston. This results in an oil pressure of 60-65 psi (414-448 kpa) in chamber B. The
movement of the pressure regulation piston against the springs exposes port C in the valve body. Port C directs
the pressurized oil to the oil return pipe cavity in the front face of the selector valve body. The piston and spring
in the oil return pipe regulate the cooling and lubricating oil supply to a pressure of 18-20 psi (124-138 kpa).
Passage D (which is the engaging outlet to the forward clutch) and passage E (which is the engaging outlet to
the reverse clutch) are interconnected by slot F in the selector valve stem when in the neutral position. The slot
is aligned with a drilled hole and cored cavity in the front face of the valve body. The drilled hole and cored
cavity are aligned with drilled holes that pass through the manifold and the main housing to atmosphere.
Therefore, passages D and E are at atmospheric pressure at this time. Also, passage J is at atmospheric
pressure since port H interconnects with slot F. The area between the pistons and around the springs is vented
to the sump through drilled holes in the front face of the valve body, the manifold, and the main housing. This
area is at atmospheric pressure at all positions of the valve which permits the return to sump of any leakage oil
past the pistons.
3-282
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