M318C Excavator Hydraulic System Caterpillar

This procedure is utilized to adjust the pressure setting for the medium pressure relief valve and the medium pressure line relief valves. The medium pressure relief valve limits the maximum pressure of the medium pressure function. The line relief valves limit the maximum line pressure and the line relief valves protect the control valve from pressure spikes that are induced by external forces. The pressure settings for the hydraulic cab riser circuit are also adjusted with this procedure.

Table 1

Required Tools
Part Number	Part Description	Qty
8T-0859	Pressure Gauge	1
6V-3989	Unvalved Nipple	1
6V-4143	Coupler Assembly	2
6V-3014	Hose	1

1. Prior to any adjustment, refer to the "Preparations" section in Testing and Adjusting, "Operational Checks".

2. Start the engine.

3. Place the engine speed dial in position 10.

Test and Adjust for the Line Relief Valves

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Illustration 1	g00981166
(1) Medium pressure attachment line relief valves (2) Medium pressure attachment relief valve (M3) Pressure tap, which is located on the end of manifold

1. Connect a 25000 kPa (3600 psi) pressure gauge to pressure tap (M3) .

2. To check the setting of the two line relief valves for the medium pressure at pressure tap (M3), increase the pressure setting of relief valve (1). Remove the plug from relief valve (1) and turn the adjusting screw clockwise in order to increase the pressure setting.

3. Stall the medium pressure attachment. Check the pressure at pressure tap (M3). When the pressure stops increasing, read the pressure on the gauge. Refer to Testing and Adjusting, "Specifications" in this manual for the correct line relief pressure.

4. Check the line relief valves in both directions (left and right).

5. To adjust the pressure on the line relief valves, remove the cover and loosen the locknut on line relief valve (2). Turn the adjustment screw clockwise in order to increase the pressure setting. Turn the adjustment screw counterclockwise in order to decrease the pressure setting.

   Note: Always make the final pressure adjustment on the pressure rise.

6. When the adjustments are complete, tighten the locknut for the adjustment screw to the proper torque and place the cover on the adjusting screw.

7. Once the line relief valves are adjusted to the recommended setting, use the following procedure to adjust relief valve (1) .

Test and Adjust for the Relief Valve

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Illustration 2	g00981166
(1) Medium pressure attachment relief valve (2) Medium pressure attachment line relief valves (M3) Pressure tap, which is located on the end of the manifold

1. Operate the medium pressure attachment against the end position of the cylinders. Check the pressure at pressure tap (M3). Refer to Testing and Adjusting, "Specifications" in this manual for the correct pressure setting.

2. To adjust the pressure setting of the relief valve, remove the plug from relief valve (1) and loosen the locknut.

3. While the attachment is stalled, turn the adjustment screw until the pressure at pressure tap (M3) is set to the correct pressure. Turn the adjustment screw clockwise in order to increase the pressure. Turn the adjustment screw counterclockwise in order to decrease the pressure.

   Note: Set the pressure to a pressure that is less than the pressure that is recommended by the manufacturer of the tool by 1000 kPa (145 psi).

   Note: Always make the final pressure adjustment on the pressure rise.

4. When the adjustments are complete, tighten the locknut for the adjusting screw to the proper torque.