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| Illustration 1 | g00501525 |
Counterbalance Valve (1) Chamber (2) Orifice (3) Check Valve (4) Passage (5) Valve port (left turn) (6) Stem (7) Valve port (right turn) (8) Passage (9) Check valve (10) Orifice (11) Chamber (12) Passages (13) Passage (14) Crossover relief valve (15) Motor port (steering motor for right turn) (16) Motor port (steering motor for left turn) (17) Crossover relief valve (18) Passage | |
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| Illustration 2 | g00860600 |
Location of the counterbalance valve | |
The counterbalance valve is attached to the steering motor. The steering motor is located below the operator's station.
The counterbalance valve is used in order to keep the steering motor under the operator's control during overspeed steering load conditions. An overspeed condition exists when the machine is working in conditions that involve an underfoot side slope and the fast track drawbar pull is lower than the slow track. This decreased pull causes feedback torque through the steering gears that are attempting to turn the steering motor faster than the demand of the steering control valve.
During a normal left turn, oil from the steering control valve flows in valve port (5) and through stem (6) to check valve (3). Oil also flows through passage (4), around stem (6), and through orifice (2) into chamber (1). Oil opens check valve (3) and the oil flows through stem (6), through passage (18), and to motor port (16). Oil then flows through the steering motor and the oil turns the steering motor clockwise. Oil through the motor flows to motor port (15). Motor port (15) sends oil through passage (13) to check valve (9). Oil at check valve (9) is temporarily blocked and the pressure of the oil increases. When the oil pressure reaches a threshold of approximately 7000 kPa (1015 psi), stem (6) moves to the right. Now, oil in passage (13) flows through passages (12) and through stem (6) to valve port (7) and to the tank.
As stem (6) moves to the right, oil in chamber (11) is sent through orifice (10) to passage (8). Then, the oil flows through valve port (7) to the tank. Once stem (6) has moved approximately 2 mm (.08 inch), oil in chamber (11) flows directly through passage (8) and valve port (7) to the tank and the stem is allowed to move faster to the right.
During overspeed conditions, feedback torque that comes through the steering gears attempts to turn the steering motor at a faster speed than the speed that is necessary. This feedback causes reduced pressure on the inlet side of the counterbalance valve (valve port (5), passage (18), and motor port (16) ). When the inlet pressure decreases lower than threshold pressure, stem (6) moves to the left. The flow of oil through the outlet side of the counterbalance valve (motor port (15), passage (13), and valve port (7) ) is restricted. The restricted oil flow counteracts the feedback torque that drives the steering motor. Now, the steering motor speed is sustained close to the speed that is demanded by the steering control valve.
Crossover relief valves (14) and (17) prevent damage to the steering system from pressure increases (spikes). These valves are pilot controlled relief valves that open at approximately 41500 kPa (6000 psi). When the crossover relief valves open, the valves send oil to the opposite motor port.