Hydraulic System 149
Figure 5-28
Relief adjustment screws
Adjusting Low Pressure on 300-Gallon Grippers
To adjust low pressure on 300-gallon gripper built-in valves:
1. Lock out and tag out the vehicle (see Locking Out and Tagging Out the Vehicle on page 12).
2. Secure the area around the path of the arm with barrier tape or barricades.
3. Turn the switch on the control panel to the LOW PRESSURE position and move the manual levers
back and forth to release any residual pressure.
4. Make sure that all hoses are tight and not leaking.
5. Connect a pressure gauge (0–4000 psi) to the quick-connect coupler on the proportional valve
(see Figure 5-27).
6. Put the transmission in Neutral, start the engine, and engage the hydraulic pump.
7. Adjust the gripper pressure:
7 a. Close the gripper using the corresponding lever on the valve and maintain the lever in
place.
7 b. Adjust the external relief valve to 1200 psi (see Figure 5-29).
“Gripper open” relief
adjustment screw
Main relief valve
“Gripper close”
relief adjustment
screw
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