RIPPER LIFT SYSTEM

TM 5-2410-237-23

HYDRAULIC SYSTEM THEORY OF OPERATION - CONTINUED

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BULLDOZER BLADE TILT SYSTEM - CONTINUED

To tilt the blade to the right, the tilt control lever is moved to the right. This will move the blade tilt pilot valve (2) spool

into the valve body, allowing flow to be ported through the pilot valve (2) to one end of the tilt control spool (39) in the

blade control valve (17). As the tilt control spool moves, the tilt system oil chamber (40) in the blade control valve will

be sealed off from the lift system chamber (28) and pressure will build up quickly in chamber (40). Oil then flows under

pressure to the head end of the cylinder and the blade tilts to the right (up). Exhaust oil from the rod end of the cylinder

returns through the blade control valve to the tank.

To tilt the blade to the left (left side up), the tilt control lever is moved left, reversing the pilot valve spool movement and

changing the porting through the blade control valve. Oil then flows under pressure to the rod end of the cylinder.

Components of the blade tilt system are protected against overpressure by a pilot-operated relief valve (34) which is

built into the blade control valve (17). Cylinder working pressure in chamber (40) is applied against relief valve (34)

through orifice (41). If cylinder working pressure rises above the setting of valve (34), the poppet will unseat and vent

chamber (42) to the tank via return line (24) and the pressure in chamber (42) will drop. The pressure in chamber (40)

will remain relatively high because of the restriction caused by orifice (41), and dump valve (31) will move upward

against its spring. Upward movement of dump valve will open chamber (40) to line (24) and the overpressure will be

"dumped" to tank. When the pressure returns to normal, dump valve (31) and relief valve (34) will both reseat.

RIPPER LIFT SYSTEM

When the ripper lift control lever is moved to the right, the spool of ripper lift pilot valve (1) moves out of the valve

body, allowing pilot pressure through line (10) to the upper end of the ripper lift control valve (9) spool. Pilot pressure

causes the spool to shift, allowing system oil to flow to the head ends of the ripper lift cylinders (22).

As pressurized oil forces the cylinder pistons outward, exhaust oil from the rod ends returns to the ripper control valve

(9). Within the valve, exhaust oil can either be returned to the tank or, when necessary, sent through the makeup valve

(44) and combined with main system flow going to the head ends of the cylinders.

To lower the ripper, the ripper lift pilot valve (1) directs pilot oil to the lower end of the ripper control valve (9). Main

system flow is then directed to the rod ends of the ripper lift cylinders (22). Again, exhaust oil from the cylinders can be

used as makeup oil when demanded.

During both the raising and lowering operations, pilot oil from the ripper lift pilot valve (1) is directed, via line (27), to

the shuttle valve (33) in the blade control valve (17). The shuttle valve shifts to open a passage (28) for main system oil

to flow into the chamber between dump valve (30) and blade lift relief valve (32). This chamber is then at system pres-

sure. If an excessive pressure builds up, the relief valve will unseat and open passage (28) to oil return line (24). When

system pressure drops back to normal, the relief valve reseats and flow back to the tank is cut off.

LOWERING RIPPER WITH ENGINE OFF

The design of the pressure control valve (5) allows the ripper to be lowered while the engine is not running. Oil pressure

to accomplish this is created in the head ends of the ripper lift cylinders (22) by the weight of the ripper acting on the

cylinder pistons.

With the ripper control lever in HOLD, oil pressure in the head ends of the cylinders is transmitted to a port on the ripper

lift pilot valve (1) via line (23), internal passages in the pressure control valve (5), and through line (7). This pressure

also exists in a chamber in the ripper lift control valve (9). Moving the ripper lift control lever to the LOWER position

allows the cylinder pressure to be applied to the spool in the ripper lift control valve (9) just as in normal lowering oper-

ation. All the exhaust oil not needed for pilot flow is routed through the makeup valve (43) of the ripper control valve to

the head ends of the cylinders as makeup oil.

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