DRESSTA TD-25M EXTRA, Service Manual

Page: 391 / 595

VALVES
SECTION 10B
Page 1
DRESSTA TD-25M EXTRA
SERVICE /SPECIAL TOOLS
1. SERVICE /SPECIAL TOOLS
DESCRIPTION TOOL NUMBER
Digital Optical Tachometer ……................................................................................... 337 7462.
CONTROL VALVE
2. DESCRIPTION
The control valves used in this system are mounted to a bracket at the right side in front of the
reservoir. Either one or three spool control valve is used in the system depending on the
equipment. The valves are controlled by pilot lines from the pilot valves.
The control valve is a directional hydraulic valve. Each section directs oil to the appropriate
hydraulic cylinder controlling the action of a certain equipment. Each section controls one hydraulic
circuit.
Three spool control valve is controlled with two pilot valves. The blade pilot valve controls the blade
lifting and lowering. The ripper pilot valve controls the ripper.
In the neutral position of the pilot valves the oil flows freely through the spool without any response
of the appropriate equipment. If a pilot valve is shifted the oil flow is directed to the cylinder causing
the desired response of the equipment. All the operating positions except the blade FLOAT
position are not detented and all the spools of the valve are spring centered for return to the HOLD
position.
All sections are assembled between the inlet and outlet cover. All section housings are of the same
design although the spools differ in their functioning.
A machine can be equipped with one or three spool control valve. Regardless of the number of
sections each control valve has both the inlet and outlet cover.
Incorporated in the inlet cover is a relief valve, which is used to by-pass oil from the pump back to
the reservoir when the oil pressure exceeds the relief valve setting. Blade lift section and ripper lift
section are equipped with anticavitation valves. Each valve spool has a corresponding check valve
which provides smooth movement of the load when the spool position is changed from the HOLD
position to an operating one.
3. REMOVAL
WARNING! Before working at the machine, be sure that the blade and ripper have
been lowered to the ground, engine is OFF, the drive train control lever is in
NEUTRAL position, drive train lock lever is in ON position and parking brake is set.
The starting switch and the electrical system master switch are turned OFF, keys
are removed and the controls are tagged to prevent inadvertent engine starting.