According to the failure statistics of F8 air distribution valve (hereinafter referred to as F8 valve) in operation, there are three specific failures: natural venting, continuous exhaust and poor venting. We made a statistical analysis of the F8 valve failures introduced by "18 1" from June 20 12 to June 2065438. * * * There were 37 failures, and natural mitigation accounted for 28 cases, which was the main failure. Therefore, how to reduce natural mitigation is the focus of our maintenance work.

The second is to find out the cause of self-slow failure, find out the countermeasures, improve the maintenance quality and reduce the failure rate of F8.

1. We conducted a follow-up investigation on these 28 groups of valves that caused natural pressure relief, and found that the causes of self-pressure relief were leakage of auxiliary valve, one-way valve of auxiliary air cylinder and balance valve, among which the number of natural pressure relief failures of F8 valve caused by leakage of auxiliary valve was 20. Therefore, as long as the leakage of the auxiliary valve is reduced, the natural pressure relief failure of the F8 valve can be effectively controlled, thus reducing the failure rate of the F8 valve.

2. The working principle and function of 2.F8 valve auxiliary valve. The auxiliary valve adopts two kinds of pressure balance mechanisms. The compressed air in the auxiliary cavity is above the piston of the auxiliary valve and the compressed air in the brake pipe is below. Compressed air from the main valve is charged into the auxiliary chamber through the upper channel and located above the diaphragm plate 7, and the compressed air in the auxiliary chamber and the brake pipe is balanced. When braking, due to the decompression of the brake pipe, the auxiliary valve reaches the braking position, and the compressed air in the auxiliary room is discharged into the atmosphere through the common brake exhaust plug 13 and the emergency brake exhaust plug 14.

The role of the auxiliary valve:

(1) When the vehicle is released after braking, the air pressure of the brake pipe rises, and the compressed air of the pressure air cylinder is filled into the auxiliary chamber again through the communication groove on the auxiliary valve sleeve 10 and the auxiliary valve stem 5, and the pressure of the pressure air cylinder drops rapidly, thus accelerating the release of the main valve.

(2) When the brake pipe is depressurized due to emergency braking, the air pressure below the auxiliary valve piston rapidly decreases, and the auxiliary valve piston 8 and the auxiliary valve stem 5 are pushed downward by the air pressure in the auxiliary chamber, so that the emergency ventilation valve below is opened, thus leading to the emergency ventilation function of the brake pipe.

3. After repeated field tests on F8 valve, we found that there are two main reasons for the leakage of auxiliary valve:

(1) The thickness of the O-ring at the top of the plunger of the auxiliary valve is inconsistent, resulting in the leakage of the auxiliary valve.

(2) The diaphragm is elastically reset, and the plunger of the auxiliary valve in the common brake pressure maintaining position moves up, resulting in the leakage of the auxiliary valve.

4. The reason for the leakage of the auxiliary valve has been found out. How to solve these problems, we have done a lot of work and tried again and again.

The thickness of (1)O-ring is inconsistent, resulting in leakage. The standard size of O-ring is 2.25 0.10mm ... In daily maintenance, we have experienced many experiments of increasing or decreasing the thickness of O-ring, and found that the closer the thickness of O-ring is to its upper limit, that is, 2.35mm, the less likely it is to cause leakage. Therefore, when choosing O-ring, try to be close to its upper limit (2.35mm). It is verified that the leakage problem of auxiliary valve is effectively controlled and the maintenance quality is improved.

(2) The diaphragm is elastically reset, resulting in the leakage of the auxiliary valve. By analyzing the faulty valve, it is found that the plunger of the auxiliary valve has an upward displacement, indicating that there is an upward force on the plunger, which, although weak, can lead to air leakage of the auxiliary valve. Therefore, through a large number of experiments, we reduced the upward force of the plunger and suppressed the displacement of the plunger. (After maintaining the pressure for 65438 0 minutes, the leakage of the working air cylinder should not be greater than 65438±00 kPa)

Test 1: 6 sets of unqualified auxiliary valves were taken out. The raw material belt is wound on three O-ring grooves on the piston of the auxiliary valve column, and then the O-ring is added to increase the friction of the upward movement of the plunger. The test results on the test bench show that 1 set is qualified.

Test 2: 5 sets of unqualified products are decomposed again, the raw material belt is taken out, a flat washer is added to the piston of the auxiliary valve column, and the plunger length is changed. The test on the test bench shows that two sets are qualified.

Test 3: Disassemble the remaining three sets of unqualified auxiliary valves, remove the flat washer and install the brake spring on the upper side of the auxiliary valve stem. The bench test results are all qualified.

Although these three tests have different means and good or bad effects, they all aim at reducing the upward force of the plunger and restraining the displacement of the plunger. Because the resistance of the diaphragm is small, the piston of the auxiliary valve column moves upward. We contacted the manufacturer and discussed this issue many times. Finally, confirm that the curvature of the diaphragm is incorrect and the drawing is modified. The height difference δ between the outer ring and the inner ring of the diaphragm plate is reduced by 0.5 mm.

By taking the above measures, the failure rate of F8 valve is greatly reduced, and the maintenance workload and the impact on production scheduling organization are also reduced. The reduction of hidden dangers not only reduces the sudden stop or other faults that may be caused by brake failure in train operation, but also safeguards the vital interests of passengers and the good social image of the railway department.