Principle and maintenance of forklift hydraulic system

1、 The principle of the forklift hydraulic system is to use the principle that the liquid in the sealed volume can transfer force and transfer movement. The movement is transmitted to the working hydraulic cylinder (lifting hydraulic cylinder, tilt hydraulic cylinder and steering hydraulic cylinder) through oil to realize the purpose of loading and unloading goods. When the forklift hydraulic pump is driven to rotate by the forklift engine, it continuously sucks the working oil from the oil tank. It sends it to the distribution valve after pressurization. Then the forklift driver operates each valve rod of the distribution valve to send the working oil to the required working cylinder to realize the operations of lifting, lowering, tilting forward and tilting backwards.

2、 Maintenance method of hydraulic system

The hydraulic oil of the forklift hydraulic system should be changed every 2000 hours or once a year. Since the hydraulic oil may be at a high temperature during the oil change, wear protective equipment and operate carefully to avoid personal injury. Replace the hydraulic oil as follows:

1. Park the forklift on a flat and open site, place the shift lever in the neutral position, pull up the parking brake valve button, and install the frame fixed bumper. The forklift starter shall be operated at idle speed for 10min, during which it shall repeatedly lift the boom, lower the boom, tilt forward and tilt back.

2. Finally, lift the boom to the highest position, tilt the forklift back to the top position, and stop the forklift engine.

3. Push the control handle of the pilot control valve forward to turn the forklift on under the action of self-weight and discharge the oil in the rotary bucket cylinder; After the bucket is turned to the position, 3. Push the boom control lever of the pilot valve forward, and the boom will descend under the action of self-weight to drain the oil in the hydraulic boom cylinder.

4. Pull the pilot oil cut-off solenoid valve switch to the “off” position.

5. Clean the oil drain under the hydraulic oil tank, screw the open oil plug, drain the hydraulic oil, and hold it in a container. At the same time, unscrew the filler cap to speed up the oil drainage process.

6. Disassemble the oil inlet pipe of the forklift hydraulic oil radiator and drain the residual hydraulic oil in the radiator.

7. Remove the top cover of the hydraulic oil return filter from the hydraulic oil tank, take out the oil return filter element and replace it with a new one. Open the filler cap, take out the filler screen and clean it.

8. Remove the flange cover of the cleaning port of the hydraulic tank under the oil filler, flush the bottom and four walls of the hydraulic tank with diesel oil, and finally wipe it dry with a clean cloth.

9. Install the oil drain plug, oil return filter and top cover, refuelling filter screen, blue cover at the hydraulic tank’s cleaning port, and the oil inlet pipe of the hydraulic oil radiator of the forklift.

10. Remove the oil return pipe at the upper part of the hydraulic oil radiator and add clean hydraulic oil from the oil return port of the hydraulic oil radiator. After filling, install the hydraulic oil radiator return pipe.

11. Add clean hydraulic oil from the oil filler of the forklift hydraulic tank to make the oil level reach the upper scale of the hydraulic oil level gauge, and screw the oil filler cap.

12. Remove the fixed bumper of the frame and start the engine. Operate the joystick of the pilot valve to lift the boom and the maximum angles of forwarding tilt, backward tilt and left-right steering 2-3 times to fill the oil cylinder and oil pipe of the forklift with hydraulic oil. Then run the forklift engine at idle speed for 5min to exhaust the air in the system.

13. Stop the forklift engine, open the oil filler cap of the hydraulic oil tank, and add clean hydraulic oil to the 2 / 3 scale of the liquid level gauge of the hydraulic tank.

In case of deterioration due to poor working conditions or serious pollution of forklift hydraulic oil, please replace the hydraulic oil in time if the colour is black and the oil foams.