The Travel Counterbalance Valve on CIPI Undercarriage Arrangements which are Based on 330 Track Type Excavators
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| Illustration 1 | g01035446 |
Travel brake valve (1) Crossover relief valve (2) Spring (3) Stem (4) Passage (5) Throttling slot (6) Stem (7) Cover (8) Spring (9) Crossover relief valve (10) Passage (11) Passage (12) Passage (13) Passage (14) Passage (15) Plunger chamber (16) Passage (17) Ball (18) Spring (19) Spring chamber (20) Spool guide (21) Passage (22) Check valve (23) Port (24) Passage (25) Passage (26) Passage (27) Port (28) Spool (29) Passage (30) Check valve (31) Spring (32) Passage (33) Counterbalance valve | |
Each travel motor has a travel brake valve, consisting of counterbalance valve (33) and two crossover relief valves (1) and (9) .
The travel brake valve is bolted to the travel motor. The travel brake functions in order to prevent the occurrence of a shock load as machine travel is stopped. The travel brake also prevents cavitation or overrunning during travel downslope. The travel brake valve also sends oil to the parking brake in order to release the brake just before the start of machine movement.
Level Travel
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| Illustration 2 | g01035396 |
Travel Motor and Travel Brake Valve (Left Track) (1) Crossover relief valve (forward travel) (9) Crossover relief valve (reverse travel) (23) Port (27) Port (33) Counterbalance valve | |
During normal operation, pump oil that is going to port (23) flows through passages (24) to spool (28). Pressure oil forces check valve (22) to open. This allows oil to flow from port (22), through passages (11) and (10) and to the piston of the travel motor. Oil then drives the travel motor.
A portion of the pump oil in port (23) flows through passage (21) and into spring chamber (19). The oil then flows through passage (12) and check valve (17), and into plunger chamber (15). The pressure oil in spring chamber (19) goes to the left end face of spool guide (20). Spool (28) moves to the right against the force of spring (31). This opens throttling slot (5) .
The motor return oil goes through port passages (13) and (14), through throttling slot (5), through passage (26), and out through port (27), and to the hydraulic tank.
When oil flow from port (23) is blocked, there is a decrease in pressure in chambers (19) and (15). Spring (31) forces spool (28) to the left. This closes throttling slot (5). Return oil flow from the motor is blocked and the motor rotation stops.
If the travel direction is reversed, pump oil flows to spool (28), through port (27), and out through port (23). 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 (23) results. This negative pressure causes a decrease in pressure in spring chamber (19). Spring (31) now forces spool (28) to the left and throttling slots (5) begin to close. This blocks oil flow between passages (14) 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 (23). Part of the oil goes to passage (21). Then, the oil flows in the same manner that is described above in "Level Travel". Spool (28) moves to the right and throttling slots (5) open. The modulation of spool (28) maintains the proper opening of throttling slots (5) 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 the machine stops, spool (28) suddenly closes throttling slots (5). A hydraulic pressure spike can occur. To prevent pressure spikes, a damper is provided at both ends of spool (28). As spool (28) returns to the left from a full open position, the oil in plunger chamber (15) is pressurized. Ball (17) moves to the right, which closes passage (12) thus allowing the oil in plunger chamber (15) to flow out through orifice (16) and into spring chamber (19). Movement of spool (28) slows down and throttling slots (5) are slowly closed.
The proper damper effect is maintained by the size and the position of orifice (16) .
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 (23) of the brake valve. Spring (31) returns spool (28) to the NEUTRAL position. The travel motor is still rotating because of the mass of the machine in motion. Throttling slots (5) are closed and the return oil is blocked. A sudden increase in pressure in passage (13) occurs. High pressure return oil in passage (13) flows through passage (4) and stem (3) of crossover relief valve (1) opens. The pressure oil from stem (3) flows to suction passage (10) of the travel motor.
Crossover relief valves (1) and (9) protect the travel motor against damage by allowing the high oil pressure to escape.
Crossover relief valves (1) and (9) 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 (9) 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 (9) 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 (23) through passage (10) is blocked. The oil pressure in passage (10) increases and stem (6) opens. Oil now flows from passage (10) to passage (13). Crossover relief valve (9) 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 (9) closes in the same manner that is described above.
Crossover relief valves (1) and (9) should be designated according to movement of the travel control lever during pressure adjustment. Crossover relief valve (9) 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 (23) in order to start the travel motor, spool (28) moves to the right and passage (25) opens.
Part of the oil in passage (24) goes through passages (25) and (32) and to the parking brake of the travel motor in order to release the brake. Throttling slots (5) are opened only after passage (25) is opened. Thus, the travel motor will not operate before the brake is released.
When the supply of pressure oil to port (23) is blocked in order to stop the travel motor, spool (28) moves to the neutral position and passage (25) closes. Passage (25) is closed only after throttling slots (5) 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 330B Track Type Excavators
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| Illustration 3 | g00585768 |
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 chamber (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 has a travel brake valve, consisting of counterbalance valve (33) and two crossover relief valves (1) and (16) .
The travel brake valve is bolted to the travel motor. The travel brake functions in order to prevent the occurrence of a shock load as machine travel is stopped. The travel brake also prevents cavitation or overrunning during travel downslope. The travel brake valve also sends oil to the parking brake in order to release the brake just before the start of machine movement.
Level Travel
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| Illustration 4 | g00585706 |
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), and check valves (31) and (34) .
During normal operation, pump oil that is going to port (22) flows through passages (21) and (4) to counterbalance valve (33). Pressure oil forces check valve (31) to open. This allows oil to flow from port (22), through passages (21), (4), and (7), through port (24), and to the piston of the travel motor. Oil then drives the travel motor.
A portion of the pump oil in port (22) flows through passage (23). Ball (3) is pushed to the left against the force of spring (20). The oil then flows through passage (19) and into spring chamber (18). The pressure oil in spring chamber (18) now acts on the left shoulder of valve (12). Valve (12) moves to the right against the force of spring (30). This opens passage (14) .
The motor return oil goes through port (27), through passage (13), through passage (29), and out through port (28), and to the hydraulic tank.
When oil flow from port (22) is blocked, there is a decrease in pressure in 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 to valve (12), through port (28), and out through port (22). The operation is identical to the description above.
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 (22) results. This negative pressure causes a decrease in pressure in spring chamber (18). Spring (30) now forces counterbalance valve (33) to the left and passage (14) begins to close. This blocks oil flow between passages (13) and (29). 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 (22). Part of the oil goes to passage (23). Then, the oil flows in the same manner that is described above in "Level Travel". Valve (12) moves to the right and passage (14) opens. The modulation of valve (12) maintains the proper opening of passage (14) 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 the machine stops, valve (12) suddenly closes passage (14). A hydraulic pressure spike can occur. To prevent pressure spikes, a damper is provided at both ends of valve (12). As valve (12) returns to the left from a full open position, the oil in spring chamber (18) is pressurized. Ball (3) closes. The oil in spring chamber (18) is allowed to flow outward through passage (19), through orifice (2), and to passage (21). Movement of valve (12) slows down and passage (14) is slowly closed.
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 (22) of the brake valve. Spring (30) returns counterbalance valve (4) to the NEUTRAL position. The travel motor is still rotating because of the mass of the machine in motion. Passage (14) is closed and the return oil is blocked. A sudden increase in pressure in passage (13) occurs. High pressure return oil in passage (13) flows through passage (10) and valve (6) of crossover relief valve (1) opens. The pressure oil from valve (6) flows to suction passage (6) of the travel motor.
Crossover relief valves (1) and (16) protect the travel motor against damage by allowing the high oil pressure to escape.
Crossover relief valves (1) and (16) 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.
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| Illustration 5 | g00585913 |
The pressure oil in passage (10) flows through orifice (41) in valve (6), through orifices (40) and (42) in stem (43), and through passage (37). Shock reducing piston (38) moves to the right against the force of spring (5). For a short period of time, until the right end of shock reducing piston (38) touches body (39), a lower pressure than the setting pressure will be maintained by the crossover relief valve. When shock reducing piston (38) completes this movement, the oil pressure in passage (10) is increased to the pressure relief setting, and all of the hydraulic oil goes through valve (6) to passage (7). The oil pressure gradually increases until shock reducing piston (38) completes movement to the right. At this time, valve (6) starts to open. The gradual increase of the hydraulic oil pressure eliminates peak pressure. This is called the two-stage relief operation. This operation reduces the shock when the travel motor is stopping.
Crossover relief valve (1) opens just before the machine stops after forward travel to the left. Crossover relief valve (16) 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 (16) 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 (22) through passage (7) is blocked. The oil pressure in passage (7) increases and valve (11) opens. 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) should be designated according to movement of the travel control lever during pressure adjustment. Crossover relief valve (16) 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 (22) in order to start the travel motor, valve (12) 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. Passage (14) is opened only after passage (9) is opened. Thus, the travel motor will not operate before the brake is released.
When the supply of pressure oil to port (22) is blocked in order to stop the travel motor, valve (12) moves to the neutral position and passage (9) closes. Passage (9) is closed only after passage (14) is 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 330C 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 drive 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 drive 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 Valves During Machine Stop
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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 drive 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 to Systems Operation, "Travel Parking Brake".