The Travel Counterbalance Valve On CIPI Undercarriage Arrangements Which Are Based On 325 Track Type Excavators
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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 (4). 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 (4) and left end face of guide (18). Counterbalance valve (4) 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 (4) 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 (4), 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 (4) 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 (4) moves to the right, and throttling slots (10) open. The motor return oil goes out through port (27). The modulation of counterbalance valve (4) 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 (4). As counterbalance valve (4) 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 (4) 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 (4) 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.
The Travel Counterbalance Valve On CIPI Undercarriage Arrangements Which Are Based On 325B Track Type Excavators
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| Illustration 3 | g00864714 |
Travel Brake Valve (1) Crossover relief valve (2) Orifice (3) Ball (4) Passage (5) Spring (6) Valve (7) Passage (8) Passage (9) Passage (10) Passage (11) Valve (12) Valve (13) Passage (14) Passage (15) Passage (16) Crossover relief valve (17) Spring (18) Spring (19) Passage (20) Spring (21) Passage (22) Port (23) Passage (24) Port (25) Passage (26) Passage (27) Port (28) Port (29) Passage (30) Spring (31) Check valve (32) Passage (33) Counterbalance valve (34) Check valve (35) Brake valve | |
Each travel motor contains a travel brake valve. The travel brake valve consists of counterbalance valve (33) and crossover relief valves (1) and (16) .
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 | g00864726 |
Travel Motor and Travel Brake Valve (left track) (1) Crossover relief valve (reverse travel) (16) Crossover relief valve (forward travel) (22) Port (28) Port (33) Counterbalance valve (35) Brake valve (36) Left travel motor | |
Counterbalance valve (33) consists of valve (12), spring (17), check valve (31), and check valve (34) .
During forward travel, pump oil flows through port (22), passage (21) and passage (4) to counterbalance valve (33). The oil forces check valve (31) to open. The oil now flows through port (22), passage (21), passage (4), passage (7) and port (24) into the piston of the travel motor. The oil then powers the travel motor.
A portion of the pump oil in port (22) flows through passage (23). The oil pushes ball (3) to the left against the force of spring (20). The oil then flows through passage (19) and into spring chamber (18). The oil in spring chamber (18) acts on the left end face of valve (12). Valve (12) shifts to the right side against the force of spring (30). Passage (14) opens.
The motor return oil flows through port (27), passage (13) and passage (29) into port (28). The oil now flows back to the tank.
When oil flow from port (22) is blocked, there is a pressure decrease in spring chamber (18). Spring (30) forces valve (12) to the left. This closes passage (14). Return oil flow from the motor is blocked and the motor rotation stops.
If the travel direction is reversed, pump oil flows into valve (12) and through port (28). The oil then flows out of port (22). The operation is similar to the operation which is described above.
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 (22). The oil pressure in spring chamber (18) decreases. Spring (30) forces counterbalance valve (33) to the left. Passage (14) closes. Oil is trapped between passages (13) and (29). 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 (22) increases. Part of the oil flows through passage (23). Valve (12) moves to the right side. Passage (14) opens. The modulation of valve (12) maintains the proper opening of passage (14) 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 (12) suddenly closes passage (14). A hydraulic pressure spike can occur. To prevent pressure spikes, a damper exists at both ends of valve (12). Valve (12) returns to the left from the full open position. The oil in spring chamber (18) is pressurized. Ball (3) closes. The oil in spring chamber (18) flows through passage (19) and orifice (2) into passage (21). The movement of valve (12) slows down. Valve (12) slowly closes passage (14) .
The proper effect of the damper is maintained by the dimension and the position of orifice (2) .
Operation of Crossover Relief Valve
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 (22) of the brake valve. Spring (30) returns counterbalance valve (4) to the NEUTRAL position. The travel motor is still rotating because the machine is still in motion. Passage (14) is closed. This blocks the return oil. There is a sudden increase in oil pressure in passage (13). High pressure return oil in passage (13) flows through passage (10). Valve (6) of crossover relief valve (1) opens. The oil flows through valve (6) and into suction passage (7) of the travel motor.
Crossover relief valves (1) and (16) protect the travel motor against damage. Crossover relief valves (1) and (16) makeup oil flow from the return side to the inlet side. This makeup oil helps to prevent a vacuum condition in the travel motor.
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| Illustration 5 | g00864737 |
Crossover Relief Valve (5) Spring (6) Valve (7) Passage (10) Passage (37) Passage (38) Shock reducing piston (39) Body (40) Orifice (41) Orifice (42) Orifice (43) Stem | |
The oil in passage (10) flows through orifice (41) in valve (6), orifice (40), orifice (42) in stem (43), and passage (37). The oil then shifts shock reducing piston (38) to the right side against the force of spring (5). Piston (38) 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 (38) contacts body (39). When the movement of piston (38) stops, the oil in passage (10) increases to the relief valve pressure setting. All of the oil flows through valve (6) into passage (7). The oil pressure gradually increases until shock reducing piston (38) 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 reduction which reduces the shock when the travel motor stops.
Crossover relief valve (1) opens barely before forward left travel stops. Crossover relief valve (16) opens barely before reverse left travel stops. After blocking the tracks, the following adjustment of crossover relief valves (1) and (16) will reverse the opened valve.
When the left travel control lever is moved to the FORWARD LEFT TRAVEL position and the tracks are prevented from moving, no oil will flow from port (22) to passage (7). The oil pressure in passage (6) increases. This increase in oil pressure opens valve (11). Oil now flows from passage (6) to passage (13). Crossover relief valve (16) 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 (16) closes in the same manner that is described above.
Crossover relief valves (1) and (16) are designated by the movement of the control lever during a pressure adjustment. Crossover relief valve (16) is designated forward left travel and crossover relief valve (1) is designated reverse left travel.
Parking Brake
Pump oil is supplied to port (22) in order to start the travel motor. Crossover relief valve (12) moves to the right and passage (9) opens.
Part of the oil in passage (25) flows through passage (9) and passage (32) to the parking brake in order to release the brake. Since passage (14) is opened after passage (9), the travel motor does not operate before the brake is released.
When the supply of oil to port (22) is blocked in order to stop the travel motor, valve (12) is moved to the neutral position, which closes passage (9). Passage (9) closes only after passage (14) closes. This allows the machine to stop moving before the parking brake is engaged.
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.
The Travel Counterbalance Valve On CIPI Undercarriage Arrangements Which Are Based On 325C Track Type Excavators
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| Illustration 6 | g00821157 |
Left travel motor and travel counterbalance valve (1) Crossover relief valve (reverse travel) (16) Crossover relief valve (forward travel) (24) Port (supply port for forward travel) (27) Port (supply port for reverse travel) (33) Counterbalance valve (35) Travel counterbalance valve (36) Left travel motor | |
Travel counterbalance valve (35) consists of counterbalance valve (33), crossover relief valve (1) and crossover relief valve (16). The travel counterbalance valve is bolted to the travel motor. The travel counterbalance valve has the following four functions.
- The travel counterbalance valve prevents a shock load when travel is stopped.
- The travel counterbalance valve prevents overspeed while the machine is travelling down a slope.
- The travel counterbalance valve prevents cavitation.
- The travel counterbalance valve routes a portion of the oil to the travel parking brake in order to release the brake.
Counterbalance Valve Operation During Level Travel
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| Illustration 7 | g00826351 |
Travel counterbalance valve (level travel) (1) Crossover relief valve (reverse travel) (2) Passage (3) Valve (4) Passage (5) Passage (6) Passage (7) Passage (8) Valve (9) Spool (10) Spring (11) Passage (12) Spring (13) Spring (14) Damper Spool (15) Ball (16) Crossover relief valve (forward travel) (17) Passage (18) Spring chamber (19) Passage (20) Damper Chamber (21) Orifice (22) Passage (23) Check valve (24) Port (supply port for forward travel) (25) Passage (26) Passage (27) Port (supply port for reverse travel) (28) Check valve (29) Passage (30) Spring (32) Passage (33) Counterbalance valve (35) Travel counterbalance valve | |
Counterbalance valve (33) consists of spool (9), check valve (23), check valve (28), spring (13) and spring (30). During forward travel on level ground, pump oil is supplied to port (24). The oil flows through port (24), passage (25), and check valve (23). The oil flow forces check valve (23) to open. This allows oil to flow through port (24), passage (25), check valve (23), passage (2), and the port to the rotary group of the travel motor.
A portion of the oil delivery from the left pump in port (24) flows through passage (22) and passage (17) against ball (15). Ball (15) moves to the right against the force of spring (12) in damper spool (14). The oil delivery then flows through passage (19) into spring chamber (18). The oil pressure in damper chamber (20) acts on the end of spool (9). Spool (9) shifts to the right against the force of spring (30). Passage (7) opens.
As spool (9) shifts to the right, return oil from the travel motor flows through the port, passage (7), passage (26), and port (27) to the hydraulic tank.
When the oil flow from port (24) is blocked, the pressure in damper chamber (20) decreases. The force of spring (30) shifts spool (9) to the left. Passage (7) closes. Return oil from the travel motor is blocked and the rotation of the travel motor stops.
When the direction of travel is reversed, pump oil flows to spool (9) through port (27). Spool (9) shifts to the left. The return oil flows through port (24). During reverse travel, the travel counterbalance valve operates in the same manner as the forward travel operation.
Counterbalance Valve Operation During Slope Travel
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| Illustration 8 | g00826954 |
Travel counterbalance valve (slope travel) (1) Crossover relief valve (reverse travel) (2) Passage (3) Valve (4) Passage (5) Passage (6) Passage (7) Passage (8) Valve (9) Spool (10) Spring (11) Passage (12) Spring (13) Spring (14) Damper Spool (15) Ball (16) Crossover relief valve (forward travel) (17) Passage (18) Spring chamber (19) Passage (20) Damper Chamber (21) Orifice (22) Passage (23) Check valve (24) Port (supply port for forward travel) (25) Passage (26) Passage (27) Port (supply port for reverse travel) (28) Check valve (29) Passage (30) Spring (32) Passage (33) Counterbalance valve (35) Travel counterbalance valve | |
When the machine travels down a slope, the travel motors rotate at a higher speed. The higher speed is due to the mass (weight and size) of the machine. When this condition occurs, the pumps cannot maintain the oil supply to the travel motors. The lack of oil supply will cause cavitation in the travel motor. A pressure decrease occurs at port (24). A pressure decrease occurs in spring chamber (18) as well.
The force of spring (30) moves spool (9) to the left. Passage (7) begins to close. This blocks oil flow between passage (7) and passage (26). The return oil from the travel motor and the oil flow to the suction port of the travel motor are restricted. The rotation of the travel motor slows down.
The pressure of the oil delivery from the left pump at port (24) increases. Part of the oil flows through passage (17). Spool (9) shifts to the right. Passage (7) opens. Return oil from the travel motor flows through port (27). The modulation of spool (9) maintains the proper opening of passage (7) when the machine travels down a slope. The travel motor begins to rotate in accordance with the amount of pump oil supply. This prevents cavitation in the travel motors.
When the machine is travelling down a slope, or the machine is suddenly stopped, spool (9) suddenly closes passage (7). This causes a hydraulic pressure spike to occur. A damper is provided at both ends of spool (9) in order to prevent hydraulic pressure spikes. As spool (9) shifts to the left, the oil in damper chamber (20) is pressurized. Ball (15) moves to the left. The oil in spring chamber (18) flows through orifice (21) and into passage (22). Spool (9) slowly moves to the left. Passage (7) slowly closes. The size and the position of orifice (21) maintains the proper shock damper.
Operation Of Travel Crossover Relief Valve
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| Illustration 9 | g00826925 |
Travel counterbalance valve (travel stop) (1) Crossover relief valve (reverse travel) (2) Passage (3) Valve (4) Passage (5) Passage (6) Passage (7) Passage (8) Valve (9) Spool (10) Spring (11) Passage (12) Spring (13) Spring (14) Damper Spool (15) Ball (16) Crossover relief valve (forward travel) (17) Passage (18) Spring chamber (19) Passage (20) Damper Chamber (21) Orifice (22) Passage (23) Check valve (24) Port (supply port for forward travel) (25) Passage (26) Passage (27) Port (supply port for reverse travel) (28) Check valve (29) Passage (30) Spring (32) Passage (33) Counterbalance valve (35) Travel counterbalance valve | |
If the travel levers/pedals are returned to the NEUTRAL position during machine movement, the oil delivery from the pumps is blocked from the travel motors. The pressure at port (24) of the travel counterbalance valve decreases. The force of spring (30) moves spool (9) to the left to the neutral position. The mass (weight and size) of the machine causes the travel motor to continue to rotate. Passage (7) is closed and the flow of return oil is blocked. A sudden pressure increase occurs in passage (11). The return oil in passage (11) flows through passage (6) to crossover relief valve (1). Valve (3) shifts to the left. The return oil in passage (6) flows past the open valve (3) into suction passage (2) of the travel motor.
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| Illustration 10 | g00827097 |
Travel crossover relief valve (3) Valve (2) Passage (6) Passage (39) Body (40) Orifice (41) Orifice (42) Orifice (43) Stem (44) Passage (45) Shock reducing piston | |
The return oil pressure in passage (6) flows through orifice (41) in valve (3). The oil then flows through orifices (40) and (42) in stem (43). The return oil now flows through passage (44). Shock reducing piston (45) shifts to the right. The travel crossover relief valve maintains the circuit pressure at a lower pressure until the right end of shock reducing piston (45) contacts stem (43). When the shock reducing piston is fully shifted to the right, the oil pressure in passage (6) increases to the pressure setting of the crossover relief valve. All of the oil flow in passage (6) now flows past valve (3) into return passage (2) .
The oil pressure gradually increases until the shock reducing piston shifts fully to the right. Pressure spikes in the travel circuit are eliminated. This is called a two-stage relief operation. The two-stage relief operation absorbs the shock load at the stop of a travel operation.
During forward travel of the left travel motor, oil flow opens crossover relief valve (1) when the machine is stopping. During reverse travel of the left travel motor, crossover relief valve (16) is activated when the machine is stopping.
Crossover relief valves (1) and (16) protect the travel motor by releasing the high pressure oil.
Crossover relief valves (1) and (16) also provide makeup oil from the outlet side of the travel motor to the inlet side of the travel motor. This makeup oil prevents a vacuum condition in the travel motor.
In order to adjust the pressure setting of the crossover relief valves, refer to the crossover relief valves by the functions of the travel control levers. Refer to crossover relief valve (16) as left travel (forward). Refer to crossover relief valve (1) as left travel (reverse).
Reference: For more information concerning the pressure settings of the travel crossover relief valves, refer to Testing and Adjusting, "Relief Valve (Crossover) - Test and Adjust".
Travel Parking Brake Operation
When the oil delivery from the left pump at port (24) of the travel counterbalance valve is blocked, spool (9) moves to the right. Passage (4) opens. A portion of the oil delivery in passage (25) flows through passage (4) and passage (32) in order to release the travel parking brake. Since passage (4) opens before passage (7), the rotation of the motor rotary group does not start until the travel parking brake is released.
When the oil delivery to port (24) is blocked in order to stop the rotation of the travel motor, spool (9) returns to the NEUTRAL position. Passage (4) closes after passage (7) closes. This allows the movement of the machine to stop before the travel parking brake is engaged.
Reference: For more information concerning the operation of the travel parking brake, refer toSystems Operation, "Travel Parking Brake".