DRESSTA TD-25M EXTRA, Service Manual

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HYDRAULICS
SECTION 10
Page 3
DRESSTA TD-25M EXTRA
GENERAL
Pilot Pressure Valve
This valve serves two basic functions. First, it controls maximum oil pressure available for the
blade and ripper (if equipped) control valve pilot circuits. Second, it provides the means for
lowering the blade or ripper with a dead engine or no pilot pump flow.
Shuttle Valve Circuit
In a pilot controlled hydraulic system, pilot pressure is required to move the main control valve
spools to actuate the cylinders. If the pilot pump would stop working for any reason while the blade
or ripper was raised or the machine is raised on blade lift cylinders or if there would be no pilot flow
available to lower the blade, ripper or machine, an alternate hydraulic power source is needed. It
will be available from within the both side of blade or one side of ripper cylinder circuits.
Blade Double Tilt / Pitch Solenoid Valve (Blade Double Tilt / Pitch Attachment)
The two-coil solenoid valve is used for switching the oil from blade tilt/pitch valve to blade
cylinders. In neutral position the solenoid valve sends oil to cylinder to get tilt the blade. When the
blade double tilt solenoid is energized by switch, the coil shifts the solenoid spool to right position
to get double tilt. The blade pitch solenoid is energized when the pitch button is pushed and the
coil shifts the spool to the left position.
Blade Pilot Control Valve
This valve is a manually controlled for the blade lift, lower and tilt, mounted under vertical plate
cover at right side of operator’s seat in the operator’s compartment. The valve is used to direct pilot
oil pressure to the blade lift and tilt valve sections for blade control. When the lever is released, it
will return to neutral. A magnetic detent mechanism holds the control lever in the FLOAT position.
Pilot pressure enters the control valve at the P port and is distributed through the passages to the
metering spools. When the lever is in the centered (NEUTRAL) position, oil is active in the
passages, but is blocked at the metering spools.
When the lever is moved to any direction, the pivot plate actions the pivot plunger. The plunger
depresses the plunger actuator which, in turn, engages metering spool. In that way the metering
spool opens the pilot pressure oil to the blade lift section or tilt valve. When the lever is released it
will return to neutral. However, it will remain in the FLOAT position held by the magnet located in
the valve retaining plate. The lever has to be manually released from the FLOAT position.
Ripper Pilot Control Valve
This valve is a manually controlled for ripper lift, lower and pitch, mounted under vertical plate
cover at right side of operator’s seat in the operator’s compartment. The valve is used to direct pilot
oil pressure to the ripper lift and pitch valve sections for ripper control. When the lever is released,
it will return to neutral. Pilot pressure enters the control valve at the P port and is distributed
through the passages to the metering spools, oil is active in the passages, but is blocked at the
metering spools.
When the lever is moved to any direction, the pivot plate actions the plunger actuator which
engages the metering spool. In that way the metering spool opens the pilot pressure oil to the
ripper lift or pitch valve section. When the lever is released it will return to neutral.