PANEL AS 1236438 - Caterpillar

Illustration 1 g02740738
Main Control Valve
(1 ) Line relief valve (bucket)
(2) Makeup valve (travel)
(3) Line relief valve (stick)
(4) Line relief valve (boom)
(5) Main relief valve
(6) Line relief valve (VA boom) The implement line relief and makeup valve are in the line that is between each cylinder and the control valve. The implement line relief and makeup valve are installed in the body of the main control valve.
Illustration 2 g02728416
Travel Make up Valve
(7) Dump valve
(8) Passage to tank
(9) Supply oil for cylinder Travel Makeup Valve
The travel makeup valve supplies additional oil from the tank in order to prevent cavitation of the travel motor.During normal operation, the pressure in the spring chamber of dump valve (7) is equal to the work port pressure (9). When the work port pressure decreases below the tank pressure (8), dump valve (7) opens. This action will allow oil from the tank to flow to the travel motor through passage (9).Line Relief Valve
Illustration 3 g02740741
Line Relief Valve and Makeup Valve
(10) Pilot valve
(11) Dump valve
(12) Passage to tank
(13) Orifice check valve
(14) Supply oil for cylinder
(15) Shoulder of dump valve
(16) Spring chamber
(17) Spring chamber 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.Pump supply oil (14) flows through orifice check valve (13) to spring chamber (16) between dump valve (11) and pilot valve poppet (10). When pump supply oil (14) reaches a pressure higher than the line relief valve pressure setting, pilot valve poppet (10) moves up against the spring force. As pilot valve poppet (10) moves upward, oil in lower spring chamber (16) flows through pilot valve poppet (10). Then the oil flows into upper spring chamber (17) and to the tank for short pressure spikes.For long pressure spikes, the flow of oil out of lower spring chamber (16) reduces pressure in lower spring chamber (16). Pump oil pushes dump valve (11) upward and the lower spring is compressed. Pump supply oil flows through return oil passage (12) to the tank.Makeup Valve Operation (Implement)
Note: Refer to Illustration 3 for the following operation.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. This action will prevent a vacuum condition.Because work port passage (14) is connected to spring chamber (16) through a passage in orifice check valve (13), a vacuum can occur in the work port and the spring chamber. Pressure oil from tank passage (12) acts on the shoulder (15) of dump valve (11). The back of the shoulder receives the negative pressure from spring chamber (16). Dump valve (11) moves upward. Now, the oil flow from tank passage (12) goes to work port (14) as makeup oil. This action removes the vacuum condition.