How to test and adjust the main safety valve of Caterpillar 320C excavator 

 (1) Park the machine on flat ground and turn off the engine. 

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(2) Release the pressure in the hydraulic system. See the "Pressure Relief of Hydraulic Systems" section. 

 (3) Connect a 60000kPa pressure gauge to the pressure measuring joint 1 (Figure 2-3-167). 

 (4) Start the engine.  

(5) Set the machine control volume as follows: the engine tachometer is set to 10, and the AEC switch is set to OFF. See the "Engine Performance Testing" section for engine RPM settings.

  (6) Increase the hydraulic oil temperature to (55 ±5)°C. 

 (7) Open the bucket until the bucket cylinder piston rod is fully retracted.

  (8) Check the pressure setting of the main safety valve at pressure measuring joint 1. 

 (9) Return the bucket control lever to the NEUTRAL position.  

(10) The pressure setting value of the main safety valve should be (34300 ±490) kPa. If the pressure setting of the main safety valve is not within the specifications, adjust it to the correct value. 

 (11) See Figure 2-3-168. To adjust the main safety valve, loosen the lock nut 5 and rotate the adjusting screw 4 until the pressure gauge connected to the pressure measuring joint 1 reads (34300±490) kPa. Note : Turn the adjusting screw 4 clockwise to increase the pressure; turn the adjusting screw 4 counterclockwise to decrease the pressure. Be sure to make final pressure adjustments as pressure increases.  

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(12) Tighten the lock nut 5 to a tightening torque of (50±10) N·m.