Type "A" Travel Counterbalance Valve
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| Illustration 1 | g00861967 |
Travel Brake Valve (1) Crossover relief valve (2) Orifice (3) Spring (4) Valve (5) Valve (6) Passage (7) Passage (8) Passage (9) Passage (10) Throttling slots (11) Valve (12) Passage (13) Spring (14) Crossover relief valve (15) Passage (16) Spring (17) Ball (18) Guide (19) Plunger chamber (20) Spring chamber (21) Check valve (22) Passage (23) Port (24) Port (25) Passage (26) Passage (27) Port (28) Port (29) Passage (30) Check valve (31) Spring (32) Passage (33) Counterbalance valve (34) Brake valve | |
Each travel motor contains a travel brake valve. The travel brake valve consists of counterbalance valve (33) and two crossover relief valves (1) and (14) .
The travel brake valve is bolted to the travel motor. The travel brake valve prevents the occurrence of a shock load during a travel stop. The travel brake valve also prevents cavitation and overrun. The travel brake valve sends oil to the parking brake in order to release the brake. This occurs before the start of the machine movement.
Counterbalance Valve
Level Travel
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| Illustration 2 | g00861975 |
Travel Motor and Travel Brake Valve (left track) (1) Crossover relief valve (reverse travel) (14) Crossover relief valve (forward travel) (24) Port (27) Port (33) Counterbalance valve (34) Brake valve (35) Left travel motor | |
Counterbalance valve (33) consists of valve (4), check valves (21) and (30), and spring (31) .
During normal operation, pump oil from port (24) flows through passage (25) to counterbalance valve (33). Pressure oil forces check valve (21) to open. The pressure oil now flows from port (24), through passages (25) and (6), and through port (23) to the piston of the travel motor. Oil then drives the travel motor.
A portion of the pump oil in port (24) flows through passage (22), and into spring chamber (20). The oil then flows through passage (15) around ball (17), and into plunger chamber (19). The oil in spring chamber (20) pushes on the left shoulder of counterbalance valve (33) and left end face of guide (18). Counterbalance valve (33) moves to the right against the force of spring (31). This opens throttling slots (10) .
The motor return oil goes through port (28), through passage (12), through throttling slots (10), through passage (26), and out through port (27), and to the hydraulic tank.
When oil flow from port (24) is blocked, there is a decrease in pressure in both chambers (20) and (19). Spring (31) forces counterbalance valve (33) to the left. This closes throttling slots (10). Return oil flow from the motor is blocked and the motor rotation stops.
If the travel direction is reversed, pump oil flows to counterbalance valve (33), through port (27), and out through port (24). The operation is identical to the description above.
During normal travel operation, counterbalance valve (33) remains inoperable.
Slope Travel
When the machine moves down a slope, the travel motors rotate at a higher speed due to the machine's mass (size and weight). The pumps cannot maintain the oil supply to the motors. The lack of pump oil supply causes cavitation in the travel motors. A decrease in pressure (negative pressure) at port (24) results. This negative pressure causes a decrease in pressure in spring chamber (20). Spring (31) now forces counterbalance valve (33) to the left. Throttling slots (10) start to block oil flow between passages (12) and (26). Return oil flow to the hydraulic tank and oil flow to the suction port of the travel motor are restricted. Rotation of the travel motor slows down.
The oil pressure in the lower pump now increases at port (24). Part of the oil goes to passage (22). Then, the oil flows in the same manner that is described above in "Level Travel". Counterbalance valve (33) moves to the right, and throttling slots (10) open. The modulation of counterbalance valve (33) maintains the proper opening of throttling slots (10) while the machine travels downslope. The motor now begins to rotate according to the amount of oil that is supplied from the pump. This prevents the motor from cavitating.
When the machine moves down a slope or stops, counterbalance valve (33) suddenly closes throttling slots (10). A hydraulic pressure spike can occur. To prevent pressure spikes, a damper is provided at both ends of counterbalance valve (33). As counterbalance valve (33) returns to the left from the full open position, the oil in plunger chamber (19) is pressurized. Ball (17) moves to the left, which closes passage (15). This causes the oil in plunger chamber (19) to go out through orifice (2) and into spring chamber (20). Movement of counterbalance valve (33) slows down and throttling slots (10) slowly close.
The proper damper effect is maintained by the size and the position of orifice (2) .
Operation of Crossover Relief Valve
While the machine is slowing down and the travel control levers are moved to the NEUTRAL position in order to stop the movement of the machine, no oil is supplied to the travel motors and to the travel brake valves. A decrease in pressure now occurs at port (24) of the brake valve. Spring (31) returns counterbalance valve (33) to the neutral position. The travel motor is still rotating because of the mass of the machine in motion. Throttling slots (10) are closed and the return oil is blocked. A sudden increase in pressure in passage (12) occurs. High pressure return oil in passage (12) flows through passage (8) and valve (5) of crossover relief valve (1) opens. The pressure oil from valve (5) flows to suction passage (6) of the travel motor.
Crossover relief valves (1) and (14) protect the travel motor against damage by allowing the high oil pressure to escape.
Crossover relief valves (1) and (14) allow makeup oil to flow from the return side to the inlet side. This makeup oil helps to prevent a vacuum condition in the travel motor.
Crossover relief valve (1) opens just before the machine stops after forward travel to the left. Crossover relief valve (14) opens just before the machine stops after reverse travel to the left. After blocking the tracks, the following adjustment of crossover relief valves (1) or (14) will reverse the opened valve.
- When the left travel control lever is moved to the FORWARD LEFT TRAVEL position and the tracks are blocked, oil flow from port (24) through passage (6) is blocked. The oil pressure in passage (6) increases and valve (11) opens. Oil flows from passage (6) to passage (12) which opens crossover relief valve (14) to passage (12). Crossover relief valve (14) opens and crossover relief valve (1) closes.
- When the left travel control lever is moved to the REVERSE LEFT TRAVEL position, crossover relief valve (1) is open. Crossover relief valve (14) closes in the same manner that is described above.
Crossover relief valves (1) and (14) should be designated according to movement of the travel control lever during pressure adjustment. Crossover relief valve (14) is for left forward travel and crossover relief valve (1) is for left reverse travel.
Parking Brake
When the pump oil is supplied to port (24) in order to start the travel motor, valve (4) moves to the right and passage (9) opens.
Part of the oil in passage (25) goes through passages (9) and (32) and to the parking brake of the travel motor in order to release the brake. Throttling slots (10) are opened only after passage (9) is opened. Thus, the travel motor will not operate before the brake is released.
To stop the travel motor, the supply of oil to port (24) is blocked. Valve (4) moves to the neutral position and passage (9) is closed. Passage (9) closes only after throttling slots (10) are closed. This allows the machine to stop movement before the parking brake is activated.
The oil from the parking brake piston chamber in the travel motor goes through the orifice in the brake pilot valve. The application of the brake is delayed.
The above operation releases the parking brake just before the travel motor starts to rotate. The brake engages only after the travel motor has stopped. The parking brake is always kept released while the travel motor is rotating.
Type "B" Travel Counterbalance Valve
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| Illustration 3 | g00467658 |
Travel Brake Valve (1) Crossover relief valve (2) Orifice (3) Ball (4) Passage (5) Passage (6) Valve (7) Passage (8) Passage (9) Crossover relief valve (10) Spring (11) Passage (12) Port (13) Port (14) Port (15) Passage (16) Port (17) Passage (18) Spring (19) Passage (20) Spring chamber (21) Spring (22) Check valve (23) Brake valve (24) Check valve (25) Counterbalance valve | |
Each travel motor contains a travel brake valve. The travel brake valve consists of counterbalance valve (25) and crossover relief valves (1) and (9) .
The travel brake valve is bolted to the travel motor. The travel brake valve prevents the occurrence of a shock load during a travel stop. The travel brake valve also prevents cavitation and overrun. The travel brake valve sends oil to the parking brake in order to release the brake. This occurs before the start of the machine movement.
Counterbalance Valve
Level Travel
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| Illustration 4 | g00467949 |
Travel Motor and Travel Brake Valve (left track) (1) Crossover relief valve (9) Crossover relief valve (12) Port (16) Port (23) Brake valve (25) Counterbalance valve (26) Left travel motor | |
Counterbalance valve (25) consists of valve (6), spring (10), spring (21), check valve (22), and check valve (24) .
During forward travel, pump oil flows through port (16), passage (17) and passage (4) to counterbalance valve (25). The oil forces check valve (22) to open. The oil now flows through port (16), passage (17), passage (4), passage (5) and port (14) into the piston of the travel motor. The oil then powers the travel motor.
A portion of the pump oil in port (16) flows through passage (15). The oil pushes ball (3) to the left against the force of spring (18). The oil then flows through passage (19) and into spring chamber (20). The oil in spring chamber (20) acts on the left end face of valve (6). Valve (6) shifts to the right side against the force of spring (10). Passage (8) opens.
The motor return oil flows through port (13), passage (7) and passage (11) into port (12). The oil now flows back to the tank.
When oil flow from port (16) is blocked, there is a pressure decrease in spring chamber (20). Spring (10) forces valve (6) to the left. This closes passage (8). Return oil flow from the motor is blocked and the motor rotation stops.
If the travel direction is reversed, pump oil flows into valve (6) and through port (12). The oil then flows out of port (16). The operation is similar to the operation which is described above.
During normal travel, counterbalance valve (25) remains inoperable.
Slope Travel
When the machine moves down a slope, the travel motors rotate at a higher speed. The higher speed is due to the mass of the machine. The pumps cannot maintain the oil supply to the motors. The lack of oil supply will cause cavitation in the travel motor. The pressure decreases at port (16). The oil pressure in spring chamber (20) decreases. Spring (10) forces counterbalance valve (25) to the left. Passage (8) closes. Oil is trapped between passages (7) and (11). The return oil flow to the hydraulic tank is restricted. The oil flow to the suction port of the travel motor is restricted. The rotation of the travel motor will slow down.
The pump oil pressure at port (16) increases. Part of the oil flows through passage (15). Valve (6) moves to the right side. Passage (8) opens. The modulation of valve (6) maintains the proper opening of passage (8) when the machine moves down a slope. The motor rotates according to the output of the pump. This prevents the motor from cavitating.
When the machine moves down a slope, or stops, valve (6) suddenly closes passage (8). A hydraulic pressure spike can occur. To prevent pressure spikes, a damper exists at both ends of valve (6). Valve (6) returns to the left from the full open position. The oil in spring chamber (20) is pressurized. Ball (3) moves to the right side which closes passage (15). The oil in spring chamber (20) flows through passage (19) and orifice (2) into passage (17). The movement of valve (6) slows down. Valve (6) slowly closes passage (8) .
The proper effect of the damper is maintained by the dimension and the position of orifice (2) .
Operation of Crossover Relief Valve
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| Illustration 5 | g00610580 |
Travel Brake Valve (1) Crossover relief valve (2) Passage (3) Valve (4) Passage (5) Valve (6) Passage (7) Crossover relief valve (8) Spring (9) Passage (10) Valve (11) Port (32) Port (33) Passage | |
When the travel pedals are moved to the NEUTRAL position to stop the motion of the machine, no pump oil is supplied to the travel motors and the travel brake valves. There is a decrease in the oil pressure at port (11) of the brake valve. Spring (8) returns valve (10) to the NEUTRAL position. The travel motor is still rotating because the machine is still in motion. Passage (6) is closed. This blocks the return oil. There is a sudden increase in oil pressure in passage (9). High pressure return oil in passage (9) flows through passage (4). Valve (3) of crossover relief valve (1) opens. The oil flows through valve (3) and into suction passage (2) of the travel motor.
Crossover relief valves (1) and (7) protect the travel motor against damage. Valves (1) and (7) allow the high pressure oil to escape. Valves (1) and (7) maintain the oil flow from the return side to the inlet side. This oil helps to prevent a vacuum condition in the travel motor.
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| Illustration 6 | g00470281 |
Crossover Relief Valve (3) Valve (4) Passage (12) Passage (13) Piston (14) Body (15) Orifice (16) Orifice (17) Passage (18) Spring (19) Stem (20) Orifice | |
The oil in passage (4) flows through orifice (16), orifice (15), orifice (20) and passage (12). The oil then shifts piston (13) to the right side against the force of spring (18). Piston (13) is used to reduce the shock. Crossover relief valve (1) operates at a lower oil pressure than the relief valve pressure setting until the right end of piston (13) contacts body (14). When the movement of piston (13) stops, the oil in passage (4) increases to the relief valve pressure setting. All of the oil flows through valve (3) into passage (17). The oil pressure gradually increases until piston (13) completely shifts to the right side. The gradual increase of the hydraulic oil pressure eliminates the peak pressure. This relief operation is called double stage which reduces the shock when the travel motor stops.
Crossover relief valve (1) opens barely before forward left travel stops. Crossover relief valve (7) opens barely before reverse left travel stops.
During an adjustment, when the left travel control lever is moved to the FORWARD TRAVEL position and the tracks are prevented from moving, no oil will flow from port (11) to passage (2). The oil pressure in passage (2) increases. This increase in oil pressure opens valve (5). Oil now flows from passage (2) to passage (9). Crossover relief valve (7) opens and crossover relief valve (1) closes.
Crossover relief valves (1) and (7) are designated by the movement of the control lever during a pressure adjustment. Crossover relief valve (7) is designated forward left travel and crossover relief valve (1) is designated reverse left travel.
Parking Brake
Pump oil is supplied to port (11) in order to start the travel motor. Crossover relief valve (10) moves to the right and passage (9) opens.
Part of the oil in passage (32) flows through passage (33) to the parking brake in order to release the brake. Since passage (6) is opened after passage (9), the travel motor does not operate before the brake is released.
When the supply of oil to port (11) is blocked in order to stop the travel motor, crossover relief valve (10) is moved to the neutral position, which closes passage (6). Passage (9) closes only after passage (6) closes. This allows the machine to stop moving before the parking brake is engaged.