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| Illustration 1 | g00489344 |
Top View of Main Control Valve (1) Main relief valve | |
The main relief valve is located on the inlet section to the main control valve. The main control valve is mounted on the front end frame. The main relief valve limits the pressure from the implement pump to the main control valve.
When the pressure at the inlet to the main control valve exceeds the pressure setting of the main relief valve, the main relief valve opens. The excess hydraulic oil then flows through the main relief valve to the hydraulic oil tank.
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| Illustration 2 | g00488404 |
(2) Inlet. (3) Outlets. (4) Valve. (5) Spring. (6) Spring. (7) Valve. (8) Seat. (9) Passage. | |
Hydraulic oil flows into inlet (1), through the orifice in the center of valve (3), and into the chamber for spring (4). The oil in the spring chamber contacts valve (6). Seat (7) can not move. Seat (7) is pressed into the valve body.
When the pressure of the oil in the circuit is less than the relief valve setting, the force of spring (5) on valve (6) keeps the main relief valve closed.
If the oil pressure in inlet (1) exceeds the relief valve setting, the oil pressure overcomes the force of spring (5). This causes valve (6) to move down. The oil in the chamber for spring (4) flows through the hole in seat (7). The oil then flows through passage (8) to the hydraulic oil tank.
When valve (6) opens, the pressure of the oil in the chamber for spring (4) decreases. The force against the bottom of valve (3) also decreases. The pressure of the oil at inlet (1) moves valve (3) downward. Oil can then flow through outlets (2), and back to the hydraulic oil tank.
Valve (3) remains seated until valve (6) closes. Valve (6) closes when the pressure at inlet (1) drops below the pressure setting of the relief valve.
Reference: For more information on testing and adjusting the pressure setting of the main relief valve, refer to the Service Manual module for Testing and Adjusting, "Relief Valve (Main) - Test and Adjust" for the machine that is being serviced.