An excavator repairs a hydraulic tank with 1/2 of the total oil used in the hydraulic system. The remaining 1/2 of the hydraulic oil is stored in the hydraulic pumps, motors, multiple valves, hydraulic cylinders and pipelines of all parts. When changing oil, if only the hydraulic oil in the tank is replaced, instead of replacing all the hydraulic oil in the hydraulic system of the vehicle, this kind of square is used. The method is to mix old oil ditches with new ones. If the two brands of hydraulic oil ditches are mixed together, the oil will deteriorate.

For example, in an excavator, the hydraulic oil used in the whole vehicle hydraulic system is 420L, while the hydraulic oil in the hydraulic tank is 225L. The remaining oil is stored in the system. The proportions of the oil and fuel tanks of all kinds of excavators and hydraulic systems are identical. 

Tools and raw materials: 

1.Buy oil for vehicle hydraulic system. (2.5 times of the volume of the hydraulic tank.) 

2.Filter cartridge, wash oil, 3 kilograms of flour 

3.Rope, oil plug for closed hydraulic tubing, a steam pump and empty oil barrel in size (made up of tubing on an oil-changing excavator) 

4.Prepare a normal excavator.

Changing steps:

1. Lift the arm of the oil-changing excavator to the highest point, and the engine will be extinguished when the bucket rod and bucket receive the interior point. (The cylinder rods of the boom cylinder, bucket cylinder and bucket cylinder all extend to the apex.)
2. replacement of hydraulic filter cartridge:
3.     I) Release the pressure in the hydraulic tank and press the exhaust valve until no gas is discharged.
4.    II) Open the top cover of the hydraulic tank, take out the oil return filter element and replace it. Carefully check whether there are metal powder or other impurities on the filter element, so as to understand the wear and tear of parts in the system.

There are suction strainer, oil return filter element, pilot filter element and individual pipeline hydraulic filter element for some vehicles in hydraulic filter. The suction strainer has built-in filter element and external filter element.
The built-in filter must be pumped below the filter element before removal; if the filter element is made of metal mesh or copper mesh, it can be soaked in kerosene for a period of time, then washed and blown by electric wind, so that the clogging stain inside can be cleaned up. After cleaning, install it again, clean it every 250 hours, change it every 800-1000 hours, and shorten the time if the environment is bad. The external filter directly dismantling the bolts outside the filter, the filter element comes out. At the same time, the oil is locked by valve and will not flow out. 

The oil return filter element is replaced directly. The replacement cycle is 250 hours for the first time, and then every 500 hours for replacement. Must be replaced according to model specifications, specifications include the same size and material, the same filtering accuracy and pressure resistance, and so on. Seals used in hydraulic filters should be replaced according to material specifications, and attention should be paid to assembly quality, otherwise leakage, oil absorption and drainage loss, or air suction will occur.

3. Hydraulic tank cleaning: all the hydraulic oil in the tank is released, the hydraulic filter is removed, the pipeline between the pump and the tank is dismantled from the pump interface, and the oil in the pipeline is released. Wash the hydraulic oil tank and line with the wash oil. Clean the inside of the hydraulic tank with medical sand cloth. The flour is kneaded and stretched into three parts. The inside of the hydraulic tank, especially the corners of the tank and the filter cartridge, is cleaned three times with the dough. The hydraulic oil tank and filter cartridge must be thoroughly cleaned up. Replace the new hydraulic filter element with a good cover plate.

    4. Flushing of hydraulic plunger pump: Each hydraulic plunger pump on excavator has flushing oil outlet (oil outlet). Turn on the top and bottom oil outlets, release the hydraulic oil in the pump shell, screw on the oil plug under the pump, fill the pump shell with washing oil from the top oil outlet of the pump, then screw off the oil plug under the pump, release the oil in the pump shell, wash it several times, and finally blow the remaining oil in the pump shell clean with the steam pump, fill up the clean hydraulic oil, tighten the oil. Plugging can be.

  5. Replace the seal ring of the oil inlet of the pump, (O-ring), connect the hydraulic tank to the oil supply pipeline of the pump, and fill the hydraulic tank with clean hydraulic oil from the oil outlet of the hydraulic filter element (after replacing the filter element).

 6. Replacement of hydraulic oil in the cylinder of the movable arm: The spare excavator pulls the arm of the excavator ready to change oil with rope (the arm of the excavator ready to change oil has been lifted to the highest point at this time). Remove the oil pipe without rod cavity on the cylinder of the left and right two movable arms, and use the spare empty oil barrel to catch the released hydraulic oil. Attention should be paid to environmental protection and prevent the environment from happening. Pollution. Then put the tubing connected with the mover arm of the disassembled multi-way valve in the spare empty oil barrel to start the engine. At this time, the hydraulic oil flowing out from the multi-way valve to the mover arm tubing is the old hydraulic oil in the multi-way valve. The oil changer pays attention to the change of the oil color, and immediately extinguishes the engine when the new hydraulic oil flows out. Connect the broken pipeline, untie the rope, start the engine, and do the arm lifting and falling repeatedly until the cylinder of the arm is filled with oil. Only this single action is allowed. Pay attention to the liquid level changes in the hydraulic tank, and add the missing hydraulic oil in time.

    7. Hydraulic oil replacement in the bucket rod cylinder: after lifting the boom to the highest point, (only permitting this single action), the engine stalls. (At this time, the bucket rod cylinder rod is all extended), the tubing with the rod chamber of the bucket rod cylinder is removed from the multi-way valve, and the oil in the pipeline is released, and the pipeline is reconnected. Then the rodless tubing of the bucket rod cylinder is dismantled at the back of the driven arm, and the dismantled multi-way valve and the rodless tubing of the bucket rod cylinder are plugged with oil plug. The spare oil barrel is ready to connect the hydraulic oil released from the bucket rod cylinder, start the engine, and retrieve the piston rod of the bucket rod cylinder (the bucket rod retracts into the cylinder cylinder) and the engine stalls. After connecting the dismantled tubing, the engine is started again, the piston rod of the bucket cylinder is stretched several times, and the bucket rod is placed at the angle of the vertical ground. After the engine is out of flames, the oil is changed.

    8. Replacement of hydraulic oil in bucket cylinder: Remove the rodless tubing of bucket cylinder from the back of driven arm, and plug the broken multi-way valve and the hose nozzle of bucket cylinder with oil plug. The empty oil bucket is used to connect the broken oil outlet on the forearm cylinder. After starting the engine, the bucket closing action (all cylinder piston rods retracted back into the cylinder barrel) can only do this single action. The new hydraulic oil enters the rod chamber of the bucket cylinder. After the piston rod retracts, all the hydraulic oil in the rodless chamber of the bucket cylinder is discharged into the empty oil bucket. The engine is flameout to connect the disconnected tubing. Pay attention to the position of the oil level on the hydraulic tank.

    9. Oil replacement of rotary motor system: disconnect one of the two tubing from the multi-way valve to the rotary motor. The oil outlet of the multi-channel valve and the rotary motor is blocked by oil plugging. The spare empty barrel is connected to the oil outlet of the rotary motor which has been dismantled to start the engine and control the excavator to rotate slowly. When turning in one direction, the tubing on the motor must turn in the other direction until the oil is flowing out, which is the correct operation. At the same time, pay attention to check the color change of the outflow oil. When the new hydraulic oil is out, the engine should be shut down immediately. Connect the oil pipe of the broken rotary motor and replace the oil.

   10. Hydraulic oil replacement of left and right walking motor hydraulic system: use excavator arm to support the walking track on one side of the excavator, and remove the side cover of the walking motor on the inside. Remove any of the two inlet and outlet tubing of the walking motor, seal the broken tubing with oil plug, connect the spare empty oil barrel to the oil outlet of the walking motor, start the engine, operate the walking control valve that has been supported on this side, and the track starts to rotate until the oil outlet of the walking motor flows out of the new oil. At this time, shut down the engine immediately, connect the broken tubing, and replace the other side of the traveling motor and the hydraulic oil in the system with the same method. When replacing the hydraulic oil in the hydraulic system of the walking motor with this method, we must take care not to make any mistake in operation. If the crawler on the other side is rotated by mistake, the old hydraulic oil in this side of the walking motor system will flow back into the hydraulic tank.

Matters needing attention

• The oil tank, hydraulic plunger pump, boom cylinder, bucket rod cylinder, bucket cylinder, rotary motor and left-right walking motor can not be changed. Different projects can only manipulate the corresponding parts to make them move, so as to avoid operation errors.
• Requirements for the quality of hydraulic oil: The service life of excavator is directly related to the quality of hydraulic oil. Hydraulic oil whose quality meets the quality standard certification of American Association of Engineers should be selected. The viscosity index of this kind of hydraulic oil is stable at 40 ~100 C. The same brand of hydraulic oil must be used for replacement. 
• Hydraulic fluid viscosity requirements: hydraulic oil has N32HL, N46HL and N68HL and other 3 types of anti-wear hydraulic oil. The excavator with its service life of 1000h hours should use N46HL+N68HL antiwear hydraulic oil (50% of each). Apply N68HL antiwear hydraulic oil to excavators for more than 15000h hours. 
• The service life of hydraulic oil: The service life of hydraulic oil is 4000-6000h, about two years. In the spring and autumn of each year, the temperature difference between day and night is large. After the excavator stops working for a day at night, the oil in the hydraulic tank is high temperature, and the air outside the tank is low temperature. When the hot air in the tank meets the cold air outside the tank, it will condense into water droplets at the top of the tank and fall into the hydraulic oil for a long time. For a long time, hydraulic oil will be mixed with water. It then evolved into acidic material that corrodes the metal surface. Under the dual action of mechanical operation and pipeline pressure impact, metal particles falling off the metal surface will be mixed in hydraulic oil, and large metal particles will be filtered out, while particles less than 10 m hydraulic filter can not be filtered out, and the grinding particles that can not be filtered out will aggravate the re-wear of metal surface when mixed in hydraulic oil. 
• Selection of hydraulic oil filter element: Require filtration accuracy of 10 m 50%, pressure range of 1.4-3.5 MPa, rated flow rate of 40-400 L/min, recommended replacement time of 500 H. 
• All oil pipes must be replaced and sealed. (O ring) should be coated with thread sealant on the thread surface to prevent leakage. 

The accuracy of the product qualification certificate or label of hydraulic oil filter element is nominal accuracy, not absolute filtration accuracy. Only the beta value tested by experiments can indicate the filter ability of the filter element. To test the performance of imported alternative cartridges, the following indicators can be drawn: 

    1. filtering accuracy:
According to the need of hydraulic system, the cleanliness grade of stain is determined. According to the cleanliness grade, the filtering accuracy of oil filter is selected according to the schedule.
The nominal filtration cleanliness of hydraulic oil filter core used in construction machinery is 10 m
Nominal filtration accuracy of hydraulic oil cleanliness (ISO4406) filter m application area
13/10 3 hydraulic servo valve
16/13 5 hydraulic proportional valve
18/15 10 general hydraulic components (> 10Mpa)
19/16 20 general hydraulic components (< 10Mpa)
Under the specified experimental conditions, the maximum diameter of hard spherical particles can be used as the absolute filtration accuracy of the filter to directly reflect the initial filtration capacity of the new filter element.
When evaluating the most important standard of hydraulic oil filter element, according to the beta value measured by ISO4527-1981E (repeated experiments), that is, the ratio of the number of particles on both sides of the inlet and outlet of the oil mixed with the standard experimental powder through the filter for multiple cycles.

     2. traffic characteristics:

The flow rate and pressure drop of the filter element through the oil are important parameters of flow characteristics. The flow characteristic experiment is carried out according to ISO3968-91 standard to draw the flow-pressure drop characteristic curve. Under the rated oil supply pressure, the total pressure drop (the sum of the pressure drop of the filter shell and the filter element) should generally be less than 0.2 Mpa.

     3. intensity of filter element:

Fracture-impact test should be carried out according to ISO2941-83 standard, and the pressure difference of sharp drop when the filter core is damaged should be greater than the prescribed value.

     4. flow fatigue characteristics:

The 100 thousand cycle fatigue test should be carried out according to ISO3724 - 90 standard.

     5. experiment on Adaptability of hydraulic oil:

Pressure flow endurance test should be carried out according to ISO2943 - 83 standard.