With the popularization and application of 120 distribution valve, 120 valve gradually occupies a dominant position in China's railway vehicles, and freight trains are developing in the direction of high speed and heavy load. The reliability of 120 valve is the guarantee for the train to speed up again. Therefore, it is very important to ensure the normal operation of 120 valve. The common faults of 120 valve in daily maintenance are briefly described and analyzed. A, common fault analysis 1, main valve A. Natural pressure relief

Cause analysis: Natural pressure relief means automatic pressure relief when the pressure of 120 valve gate is reduced by 40KPa and the pressure is maintained within 1 min. The main reason is the leakage of various joints, friction pairs and templates. B. Quick inflation of auxiliary cylinder

Cause analysis: (1) The filling hole (l 1, l2) of the sliding seat is too large; (2) Accelerating and relieving the slow inflation of the cylinder will also make the auxiliary cylinder inflate quickly;

(3) the rubber of the main piston is punched, so that the pressure air in the l9 cavity at the upper part of the main piston enters the lower part of the main piston through the template, and then enters the auxiliary cylinder;

(4) The interlayer valve Ф 38 of the accelerating pressure relief valve has poor sealing performance with the valve seat, and C. The accelerating pressure relief air cylinder inflates too slowly.

Inflating channel: air flows from the auxiliary air cylinder in the slide valve cavity of the main valve, through the inflation hole f2 of the accelerated pressure relief air cylinder on the top surface of the slide valve, then through the hole h 1 on the slide valve seat, and then through the hole H on the intermediate body to reach the accelerated pressure relief air cylinder.

Cause: (1) The inflation channel or inflation hole F2 (Ф 0.9) of the accelerated pressure relief air cylinder on the slide valve is blocked; (2) In the main valve body, the blockage of the air charging channel of the cylinder is accelerated. C. When accelerating the release test, accelerate the pressure drop of the release cylinder.

Cause: (1) The two check valves of the semi-automatic relief valve are not pressed in place. There are two kinds of semi-automatic safety valve ejector pins of 120 valve, one is copper ejector pin and the other is industrial plastic ejector pin. Generally speaking, copper core rods are better. The ejector pin made of industrial plastics is easy to deform and lose its normal function during use; (2) o-ring rubber sealing ring is not tight;

(3) The diaphragm plate of the safety valve leaks. D. During inflation, the causes of air leakage at the exhaust port of the main valve are: (1) the pressure air in the train pipe leaks through the slide valve; (2) The pressure air in the auxiliary air cylinder leaks from the slide valve;

(3) The train pipe pressure air leaks through the O-ring of the emergency two-stage valve.

Generally speaking, we can distinguish the sound of air leakage. At the beginning of inflation, the pressure in the train pipe rises rapidly. Therefore, if the pressure air in the train pipe leaks through the slide valve, it will make a higher sound at the beginning of inflation. If the pressure air in the auxiliary air tank leaks, the impression must be gradually increased, and the sound will be longer and longer with the inflation time of the auxiliary air tank. E. Stability test, poor stability

Cause: (1) The inflation hole is too small or blocked by foreign objects. If the inflation time meets the requirements, it is not the problem of the inflation hole.

(2) The stabilizing spring is too weak or the main diaphragm is aging.

F in the emergency braking position, there is pressure air leakage from the small hole on the valve cover of the local safety valve.

Reason: When in the braking position, one side of the piston of the local pressure reducing valve is brake cylinder pressure air, and the other side is atmosphere. There is pressure air leakage in the small hole on the valve cover of the local pressure reducing valve, indicating that the piston of the local pressure reducing valve has leakage. The main reasons are as follows: (1) the fastening nut of local variable diameter diaphragm is loose; (2) The local falling film plate has pores;

(3) The upper piston and the lower piston have sand holes. G. excessive leakage at the air outlet at the inflation and pressure relief position.

Cause: The gas paths communicating with the local decompression chamber are all in the slide valve of the main piston, so the causes of leakage are also concentrated here, mainly including:

(1) The top surfaces of the control valve and slide valve are worn out or pulled out, resulting in the pressure air in the auxiliary air cylinder or the train pipe being discharged to the atmosphere from the local reducing exhaust port through the first-stage local reducing channel;

(2) The slide valve is worn out or pulled by foreign objects, and the pressure air rushes into the first-stage local reducing passage and leads to the atmosphere from the local reducing exhaust port;

(3) The main valve body or slide valve sleeve leaks.

2. Emergency valve A has no emergency function.

Cause analysis: (1) Upper cover of emergency valve leaks or emergency piston leaks;

(2) The stabilizer bar spring is excellent. When emergency braking is implemented, the pressure difference between the two sides of the emergency piston is not enough to overcome the resistance of the stabilizer spring, so that the spring is compressed. Although the emergency piston began to move down, it could not open the pilot valve. There is a little gap (3mm) between the lower end face of the emergency piston rod and the top rod of the pilot valve, so the resistance of the stabilizer spring can't produce enough pressure difference.

(3) The movement of the ejector pin of the pilot valve is not flexible. Check whether the pressure of the O-ring in the ejector pin is too high, or there are rubber burrs around the O-ring, which leads to the high movement resistance of the ejector pin. B. Emergency braking after stability test

Cause analysis: (1) stabilizer spring is too weak. When there is a small pressure difference between the two sides of the emergency piston, the piston can move down to produce emergency braking. This is a common problem.

(2) The axial hole Ⅲ (φ 2.3) of the emergency piston is too small or blocked by foreign objects. When the train pipe is used for ordinary braking and decompression, the pressure air in the emergency room flows back into the train pipe through the axial orifice of the piston rod, so that there will be no large pressure difference between the two sides of the emergency piston. However, if the throttle hole is blocked, the pressure in the emergency room will drop synchronously with the pressure of the train pipe, thus forming a large pressure difference on both sides of the emergency piston, which will make the emergency piston move down and produce unexpected emergency braking effect. C. Poor emergency braking sensitivity

Cause: (1) the upper cover of emergency valve or emergency piston leaks;

(2) The limit hole Ⅲ (φ 2.3) in the emergency piston rod is too large, so it is difficult to form the necessary action pressure difference on both sides of the emergency piston, and it is impossible to push the pilot valve ejector rod downward;

(3) The stabilizer spring is very good. Although the acting pressure on both sides of the emergency piston is formed, the emergency piston is not easy to move down because of the excellent stabilizer spring;

(4) The ejector pin of the pilot valve is not firm, the pressure of the O-shaped ring in the ejector pin is too high, or the axial inner hole of the bleeder valve is pulled or the rubber is not cleaned up, which leads to great movement resistance of the ejector pin of the pilot valve. D. Emergency room inflation time is unqualified.

Cause analysis: (1) The inflation time of emergency room is long: the transverse hole ⅴ (Ф1.1) on the emergency piston rod is blocked by impurities or the contact part leaks air;

(2) Short inflation time of emergency room: the transverse limit hole ⅴ (Ф1.1) on the emergency piston rod is too large. Second, the analysis of other reasons

1. In the process of valve manufacturing, firstly, the dimensional tolerance between the о-shaped ring on the piston rod and the copper sleeve does not meet the technical requirements, and there is no strength between the piston rod and the copper sleeve; Second, sometimes the wax in the valve is not cleaned up, and it is directly loaded, which makes the passage blocked during the operation of the valve and affects the normal use of the valve.

2. In operation, the compressed air is mixed with foreign matters such as dust, small particles and grease, which poses a great threat to the operation of 120 valve, especially to the operation of slide valve, control valve and sandwich valve.

When the fine dust in compressed air enters between the slide valve and the slide valve seat, it is equivalent to an abrasive. Under the long-term action of the slide valve, the local area of the slide valve or slide valve seat will be eccentric, resulting in leakage. Other dust will directly scratch the slide valve or slide valve seat, causing leakage.

When small particles in compressed air enter the slide valve body, sometimes the action hole on the slide valve will be blocked, and sometimes the sandwich valve will leak.

3, in the maintenance, to ensure that all rubber parts do not contact with gasoline and other cleaning agents. Generally speaking, most people think that the more silicone oil and silicone grease are coated, the better, so that excess grease sticks to the diaphragm or is blown into the back passage of the valve body. Some data show that too much grease not only has no benefit to the slide valve, but also reduces the cold resistance of rubber parts.

The above only analyzes the common faults of 120 valve in maintenance, and explains the main reasons. Because the maintenance of valve 120 is relatively systematic and comprehensive, I only have a little personal understanding and want to discuss it with you.