Steps and precautions for changing oil in the hydraulic system of excavators

Hydraulic excavators generally need to have their hydraulic oil replaced after running Zoooh; otherwise, the system will be contaminated, causing hydraulic system failures. According to statistics, about 90% of the faults in hydraulic systems are caused by system contamination. This article introduces the process steps and precautions for oil change in excavators.

1. Preparatory work

(1) Be familiar with the working principle, operation procedures, maintenance and usage requirements of the hydraulic system, have a clear understanding and do not act blindly or rashly.

(2) Prepare new oil according to the oil type specified in the manual. Before using the new oil, let it settle for 48 hours.

(3) Prepare the tools for disassembling each pipe joint, the oil filter for adding new oil, the filter element of the hydraulic system, etc.

(4) Prepare cleaning solution, brushes and silk cloth for wiping, etc.

(5) Prepare the oil ladles for holding waste oil.

(6) Select a flat and solid site to ensure that the machine can rotate without obstacles when the bucket and boom arms are fully extended. After the boom is fully lifted, it should not touch any obstacles. The distance from the power lines should be more than 2 meters.

(7) Prepare four sleepers so that they can cover the tracks from front to back

At least four workers are required, including one driver, one on-site commander and two oil changers.

2 Oil change methods and steps

(1) Place the boom parallel to the track direction and stop after turning 45° to the left. Fully extend the piston rod of the bucket cylinder and fully retract it. Slowly lower the boom to place the bucket on the ground. Then turn off the engine, open the fuel tank vent valve, and move each operation handle back and forth and step on the pedal several times to release the system residual pressure caused by self-weight and other factors.

(2) Thoroughly clean all pipe joints, pump and motor joints, fuel drain plugs, the top fuel filler cap and bottom fuel drain plug of the fuel tank and their surroundings with gasoline.

(3) Open the oil drain valve and the oil drain plug at the bottom of the oil tank to ensure that all the old oil flows into the oil drum containing the waste oil.

(4) Open the fuel tank cap, remove the fuel filter element, and check whether the residual fuel at the bottom of the fuel tank and its edges and corners contains metal powder or other impurities. Thoroughly clean the fuel tank. First, clean it twice with diesel, and then dry the interior of the fuel tank with compressed air. Check whether there is any residual oil sludge, impurities, etc. in the internal corners until they are completely cleaned. Finally, rinse them once again with new oil.

(5) Disassemble the following oil pipes

① Remove all the oil pipes in the return oil circuit, such as those from the main control valve to the full-flow filter and the return oil filter, as well as those between the filter and the oil tank and oil cooler, etc.

② Disassemble the return oil pipe from the rotary control valve to the filter and the make-up oil pipe of the rotary motor.

③ Remove the oil inlet pipeline of the hydraulic pump.

④ Disconnect the oil pipe of the return oil line of the pilot system.

⑤ Remove the drain pipes of the main pump and motor. Thoroughly clean its oil pipe. The steel pipes are cleaned twice with diesel oil, and the hoses are cleaned twice with cleaning solution. Then they are dried with compressed air and rinsed once with new oil. Each joint should be blocked with nylon plugs or covers, or wrapped with clean plastic sheeting to prevent dust, moisture, etc. from entering and contaminating the system.

(6) Remove the filter elements of all the filters in the system. When replacing the filter element, carefully check whether there is any metal powder or other impurities on the filter element. This can help understand the wear condition of the parts in the system.

(7) Drain the old oil from the main hydraulic pump, rotary motor and walking motor cavities, and fill them with new oil.

(8) Install the oil pipe that has been disassembled. Before installing each oil pipe, the pipe joints must be thoroughly cleaned and wiped clean with a silk cloth. It is strictly forbidden to wipe the pipe joints with cotton yarn, towels or other fibrous fabrics. When installing threaded joints, sealing tape should be used and adhered in the opposite direction to the rotation of the thread. All pipe joints should be installed and connected in sequence and according to the specified torque.

(9) Refuel the fuel tank through the fuel filler port. First, install the oil filter element properly. Then, open the new oil tank and use the oil filter to fill the tank with new oil until it reaches the upper limit of the oil gauge. Finally, close the oil filling cap.

(10) Replace the old oil in the following action circuits. Before changing the oil in each circuit, the machine should be in three states: the piston rod of the bucket cylinder is fully extended, the piston rod of the bucket cylinder is fully retracted, and the bucket is freely placed on the ground.

① Pilot control system loop. Disassemble the control oil pipe joints of the left and right walking motor parking brakes, position the selection valve in the neutral position, use the starter motor to drive the engine to idle for several turns, thereby discharging the old oil in the pilot system's oil supply line. Then clean the pipe joints and reconnect them properly. Start the engine and let it idle for 5 minutes. Then, loosen the pilot oil pipe joints on the control valves respectively and perform each action back and forth until new oil is discharged. Finally, clean each pipe joint and connect them properly.

② Boom circuit. Place the bucket on the ground, and turn each handle back and forth several times to disassemble the oil pipe joint in the rodless cavity of the boom cylinder, drain the old oil in the rodless cavity of the hydraulic cylinder, then operate the boom handle and slowly turn the handle in the lifting direction until new oil is discharged from the joint. After that, clean the pipe joint and connect it properly. Loosen the oil pipe joint with the rod cavity in the boom cylinder, operate the boom handle, and slowly pull the handle in the downward direction until new oil is discharged from the oil pipe. Operate the boom handle, slowly pull the handle in the lifting direction to drain the old oil in the rod cavity, clean the pipe joint and connect it. Operate the boom to rise and fall several times to expel the air in the system.

③ Bucket circuit. Loosen the oil pipe with the rod cavity in the bucket cylinder, operate the handle, and slowly turn the handle in the direction of turning the bucket outside until new oil is discharged from the pipe joint. Clean the pipe joint and connect it. Disassemble the pipe joint of the rodless cavity, slowly lift the boom to lift the bucket about 1.5 meters off the ground, then slowly operate the bucket handle to turn the outer part to the top, lower the boom to make the bucket touch the ground. Operate the bucket handle, slowly turn the handle towards the inside of the bucket to discharge the old oil in the oil pipe, clean the pipe joint and connect it. Raise the boom to lift the bucket 2.5 meters off the ground. Rotate the bucket several times in the inward and outward directions to expel the air remaining in the circuit

④ Boom circuit. Disassemble the oil pipe joint of the roeless cavity of the bucket rod cylinder, operate the handle, and slowly turn the handle in the direction of the bucket rod to discharge the old oil in the oil pipe until new oil flows out. Clean the pipe joint and connect it. Loosen the pipe joint of the rod cavity in the bucket rod cylinder, drain the old oil in the rod cavity, slowly turn the handle in the direction of the bucket rod rotation to push out the old oil in the pipe until new oil is discharged, clean the pipe joint and connect it. Lift the boom and rotate the bucket rod inward and with external force several times.

⑤ Rotary system. Disassemble the right (rear) end oil pipe joint on the rotary control valve, operate the rotary handle to slowly rotate it to the right by one full circle, then insert the rotary lock pin. When no old oil is discharged, clean the pipe joint and reconnect it. Drain the old oil in the left-turn buffer brake valve in the same way.

⑥ Walking system. Support the left track on one side, ensuring that the circular surface of the bucket is in contact with the ground, and the Angle between the boom and the bull arm is 90° to 110°. Disassemble the front oil pipe joint on the left walking control valve, step on the left walking pedal, and let the left track move forward slowly until new oil is discharged from the pipe joint. Clean the pipe joint and connect it. Drain the old oil in the right-walking pipeline in the same way.

(11) After all the oil has been changed and all pipe joints have been properly connected, the residual air in the system must be discharged once again, as this residual air can cause poor lubrication, vibration, noise and performance degradation, etc. Therefore, after changing the oil, the engine should be run for at least 5 minutes, and then the boom, boom, bucket and rotation actions should be operated back and forth several times slowly. If the walking system is in a state where the tracks are supported on one side, the hydraulic oil can fill the entire system. The remaining air will be automatically discharged through the oil tank after the movement. Finally, close the air release valve properly.

(12) Recheck the oil level in the fuel tank. Fully extend the piston rod of the bucket cylinder and fully retract it. Lower the boom to make the bucket touch the ground. Check whether the oil level in the fuel tank is between the upper and lower limits indicated by the oil level gauge. If the oil level is below the lower limit, add oil until it approaches the upper limit.

3 Precautions

(1) During the oil change process, it is strictly prohibited to start the engine when the oil tank is not filled with oil and the cavities of the hydraulic pump and motor are not fully filled with oil

(2) During the oil change process, stop blocks must be placed in front of and behind the tracks, and lock pins should be inserted into the slewing mechanism. When the bucket, boom and boom are in operation, it is strictly forbidden for anyone to stand under them or within the range of their operation.

(3) When disassembling each pipe joint, make sure the system is freely placed on the ground. Only when it is confirmed that there is no pressure in the pipeline can it be disassembled. When disassembling, people should try to avoid the direction of oil leakage from the joint. When working, protective glasses should be worn.

(4) When the upper part of the excavator rotates or moves, the driver must sound the horn to give a warning. It is strictly prohibited for people to stand on the upper part or within the range of the tracks and rotation.

(5) When disassembling and assembling, do not damage the mating surfaces and threads of each pipe joint in the hydraulic system.

(6) Smoking and open flames are strictly prohibited at the work site.

(7) When changing the oil, it is best to complete it on the same day and not overnight. Because at night or when the temperature drops, the moisture in the air will form water vapor and condense into water droplets or frost, which will enter the system and cause rust on metal parts, creating potential faults.