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| Illustration 1 | g00814107 |
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| Illustration 2 | g00544252 |
Typical Example (1) Line relief valve (auxiliary) (2) Main relief valve (3) Line relief valve (stick) (4) Line relief valve (bucket) (5) Line relief valve (boom) | |
The implement line relief and makeup valve are in the line that is between each cylinder and the control valve.
Line Relief Valve
When a force acts on a cylinder and the control valve is in the neutral position, a pressure increase occurs in the cylinder and in the line to the control valve. The line relief valve limits the circuit pressure by allowing excess oil pressure to vent to the hydraulic tank.
High pressure oil from the line between each cylinder and the control valve goes through the work port passage. Then, the oil enters the line relief valve. The oil goes through the passage in the orifice check valve and to the spring chamber. If the oil pressure does not exceed the line relief pressure setting, the pilot valve is kept closed by the force of the spring. This equalizes the pressures in the work port passage and the spring chamber. Since more surface area is on the spring chamber side of the dump valve both valves are shifted downward. The valves are held in this position. The oil flow from the work port is now blocked to the tank.
As the oil pressure in the work port passage increases to the line relief valve setting, the pilot valve shifts upward against the force of the spring. The oil from the pilot valve chamber goes to the return passage. The oil pressure in the pilot valve chamber decreases. Pressure oil from the work port passage moves the orifice check valve upward until the orifice check valve contacts the end of the pilot valve. The pressure oil from the work port passage goes around the orifice check valve and into the spring chamber. Because the oil flow is restricted at the outer circumference of the orifice check valve, the oil pressure in the spring chamber decreases.
The dump valve moves upward. This opens the tank passage. The oil flows from the work port passage to the tank passage.
Reference: Refer to Testing and Adjusting, RENR1180, "Pressure Specifications", Testing and Adjusting, RENR1181, "Pressure Specifications", Testing and Adjusting, RENR1182, "Pressure Specifications" and Testing and Adjusting, RENR1183, "Pressure Specifications" for the line relief valve pressures.
Makeup Valve Operation (Implement)
When oil is lost through the operation of the line relief valve for the rod end of a cylinder, the oil must be replaced in the head end in order to prevent a vacuum condition.
Because the work port passage is connected to the spring chamber through a passage in the orifice check valve, a vacuum can occur in the work port and the spring chamber. Pressure oil from the tank passage acts on the shoulder of the dump valve. The back of the shoulder receives the negative pressure from the spring chamber. The dump valve moves upward. Now, the oil flow from the tank passage goes to the work port as makeup oil. This removes the vacuum condition.
Shock Reducing Valve
The shock reducing valve restricts the pilot oil flow from the spring chamber for the control valve spool through the pilot control valve to the tank when the joystick is returned to the NEUTRAL position. The shock reducing valve gradually returns the control spool to the NEUTRAL position in order to prevent surges of high pressure oil in the pump supply circuit. Each main control spool has a shock reducing valve on each pilot oil passage.
To activate a circuit, pilot oil pressure enters the bottom of the shock reducing valve. The orifice check valve opens and pilot oil flows around the check valve to the control valve. Flow through the shock reducing valve is unrestricted in this direction.
When the pilot control valve is returned to the NEUTRAL position, the spring force closes the check valve. Pilot oil in the centering spring cavity must then flow through the orifice before the pilot oil can return through the pilot control valve to the tank. Flow through the shock reducing valve is restricted in this direction.