What are the common faults of the gas control valve in excavators?

In the dynamic gas circuit system of the W4-60C excavator, a gas control valve is installed between the air pump and the air storage tank. Its main function is to separate oil and water from the compressed air, filter red dust and impurities in the compressed air, prevent the compressed air in the air storage tank from flowing back to the air pump, and ensure that the gas pressure remains stable within the range of 0.490-0.637MPa. The maximum pressure does not exceed 0.784MPa. The following faults often occur during use:

The pressure regulating valve is leaking air due to the damage of the pressure regulating diaphragm

The pressure regulating diaphragm 6 is a rubber product. Due to its frequent repeated compression by air pressure, repeated arching and resetting actions, and corrosion by gas and moisture, the diaphragm is often damaged. This is the most common fault of this control valve. After the diaphragm is damaged, the compressed gas from the air pump enters the upper part of the pressure regulating valve through the diaphragm instead of entering the air storage cylinder, resulting in the air pressure in the air storage cylinder not being able to rise. At this time, the temperature of the pressure regulating valve is prone to rise, and the brake system pressure gauge indicates insufficient air pressure. A leakage sound can be heard at the pressure regulating valve.

The control valve housing is cracked

The valve housing is composed of three parts: upper, middle and lower, which are respectively connected by screws. As the shell is made of aluminium, when it is disassembled or reassembled, if the method of removing and installing screws is improper, the shell is prone to cracking. When disassembling or installing screws, they should be tightened or loosened diagonally and in multiple steps to ensure that the force on the mating surface of the shell remains consistent, preventing damage due to uneven force.

The filter is damaged

Filters are mainly used to remove dust and impurities from compressed air and prevent such substances from entering the braking system of excavators. It is composed of a filter screen 30, a dust suction pad 32 and a fixed screw plug 33. If it is used for a long time without timely maintenance and care, the copper wire of the filter screen is prone to damage and the dust suction pad is likely to be damaged. Therefore, during maintenance, careful care should be taken. If any damage occurs, it should be repaired or modified in a timely manner.

The adjusted air pressure of the pressure regulating valve is either too high or too low

When in normal operation, if the gas pressure inside the gas storage cylinder reaches 0.637MPa, the pressure will be released at the lower part of the pressure regulating valve, preventing the gas pressure inside the gas storage cylinder from rising further. When the pressure inside the air storage cylinder is lower than 0.49MPa, it should no longer be depressurized. The adjustment of this air pressure can be achieved by changing the clamping force of the large spring 19 through adjusting screw 1 (tightening raises the gas; loosening lowers the air pressure). If the air pressure remains abnormal after adjustment, there are two possible situations: one is that the air pressure has exceeded the standard but has not been released to relieve the pressure. At this point, it is necessary to consider whether the operation of the exhaust piston 12 is blocked. If the O-ring 34 on the outer circle of the piston is too tight and the spring 10 at the lower part of the exhaust piston is too hard, causing the normal pressure gas to be unable to push the piston to move, the outer ring of the sealing ring should be evenly ground or the spring should be adjusted or replaced. If the small spring 18 inside the pressure regulating valve is compressed too tightly, the ejector pin 8 is difficult to push, or the axial hole of the plug 9 is blocked, etc., it can all prevent the pressure from being unloaded. The second is to start venting and depressurizing before the pressure meets the requirements. The reasons for this are as follows: first, the pressure regulating diaphragm is leaking air. Second, the small spring inside the pressure regulating valve is too loose (or even broken), or the ejpin can be pushed at a lower pressure, causing continuous air leakage through the small hole on the pressure regulating valve housing, which prevents the system pressure from rising. In such a situation, the adjusting screw 1 on the valve should be removed first. Adjust or replace the small spring first, and then adjust the large spring.

The adjustment pressure of the safety valve is abnormal

The function of the safety valve is to ensure that the air pressure inside the air storage tank does not exceed 0.78MPa. If the safety valve still fails to release the pressure when the pressure exceeds 0.78MPa, the pressure inside the air storage tank will continue to rise. This might be caused by the leakage of the safety valve diaphragm 25 and the hardness of the safety valve spring 16. If the pressure is released before it meets the requirements, the reason is that the spring is weak, the preload is insufficient, and the valve 26 and the valve seat 27 are not sealed properly. At this point, the damaged parts should be adjusted or replaced respectively.

The gas in the gas storage tank flows back after the machine stops

To prevent the gas in the air storage tank from flowing back after the machine stops, a check valve 29 is installed in the control valve. If the gas in the air storage tank flows back to the air pump after the machine stops, this fault is mostly due to the weak elasticity or breakage of the spring 28 of the check valve, which loses its function. This spring should be adjusted or replaced.

The working air pressure of the excavator should be maintained within the range of 0.490 to 0.637MPa, and the maximum pressure must not exceed 0.784MPa. When abnormal pressure occurs, the pressure regulating valve and safety valve should be adjusted. When making mechanical adjustments, the sequence of adjusting the safety valve should be carried out first. The adjustment method is as follows

Loosen the fixed nut on the pressure regulating valve adjustment screw, then turn the adjustment screw all the way to prevent the lower exhaust valve from opening.

② Observe whether the safety valve can release air from the exhaust hole when the pressure is 0.784MPa. If the air pressure is abnormal, it can be adjusted by adding or removing the adjustment gasket 23. When the air pressure is low, add gaskets; conversely, reduce them. For every 1mm increase in gaskets, the air pressure can be adjusted by 0.036MPa.

③ Slowly withdraw the adjusting screw of the pressure regulating valve until the exhaust valve opens for exhaust. If the air pressure is exactly 0.637MPa at this time, it is the best.

④ If you repeatedly rub the brake pedal of the excavator or release air from the air tank, observe whether the rebound pressure (with the exhaust piston closed) is between 0.490 and 0.539MPa. If the rebound pressure is less than 0.490MPa and the upper exhaust hole is simultaneously releasing air, adjust the pressure of the small spring at this time.

⑤ Repeatedly adjust and test until it meets the regulations.