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 TM 55-1905-220-14-7
3-207. HYDRAULIC CUB PUMP UNIT - BRAKE VALVE - MAINTENANCE INSTRUCTIONS
A.
DESCRIPTION.
(1) The brake valve is provided with an integral check valve which permits reverse free flow from the
secondary port to the primary port when the valve is closed.
(2) The brake valve is internally drained and remotely operated. It is used primarily as an unloading
valve where the secondary port must be connected directly to the tank. Application of external pressure permits
the valve to open fully independent of the primary pressure. Type 4 valves can also be used as remotely
operated counterbalance or brake valves when provided with the integral check valve.
B.
INSTALLATION.
(1) These gasket mounted valves are teed into the supply line. The tee connection is piped to the
bottom, or pressure port in the subplate, or to the back surface of the mounting area. The top, or secondary port
is piped to the tank or to the secondary circuit with the covers arranged for internal or external draining and
direct or remote control depending on the valve action required.
(2) The point at which the valve begins to function is determined by the position of the adjusting screw
(which varies the force exerted by the spring on the spool), referred to as the pressure setting of the valve.
Clockwise rotation of the screw increases pressure. Counterclockwise rotation decreases pressure.
(3) The effective areas of the spool exposed to hydraulic pressure in primary chamber A being equal,
the spool is hydraulically balanced and held in a normally closed position by the force of the spring. When
pressure in primary chamber A - which is effective on the piston through passages C - exceeds the adjusted
pressure setting, the piston is forced upward, moving the spool accordingly.
(4) The spool moving upward opens secondary chamber B permitting pump delivery to flow into the
secondary circuit, while maintaining a minimum pressure in primary chamber A equal to the pressure setting of
the valve.
(5) When the primary pressure decreases, compression of the spring overcomes the hydraulic force
effective on the piston and the spool closes blocking flow to chamber B.
3-3211
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