The NPT5 Air Compressor is a reciprocating piston compressor. It can be continuously operated when the ambient temperature is not higher than 40. It is widely used in Dongfeng (4), DF8B, GK and Laoshan electric locomotives. The air compressor supplies the compressed air required by the auxiliary air device such as the locomotive air brake system, the wind horn and the driver's cab front windshield wiper.

The NPT5 air compressor adopts pressure lubrication. The crankshaft and connecting rod bushings, piston pin and connecting rod bushing are lubricated with 0 43M Pa; the cylinder and piston, cylinder and piston ring, and the main bearings at both ends are splash-lubricated. Appropriate viscosity of the cleaning lubricant can reduce the wear of the air compressor moving parts, reduce power consumption and improve work efficiency. After the oil is emulsified, the conditions of the crankshaft of the air compressor and the friction pairs of the bearing bush, the piston and the cylinder liner are deteriorated, which causes the air compressor to burn the tile and bite the cylinder, which seriously affects the driving safety.

2 Fault Overview When the DF4B locomotive produced by the NPT5 air compressor before 1999 was used in the Jinwen Local Railway and the Nanchang Changjiang Locomotive Depot, the air compressor of multiple locomotives was emulsified with engine oil. After repeated changes of engine oil, air filter and piston ring, the effect is not obvious. The oil emulsification failure is mainly manifested by the fact that after a period of use, the color of the oil in the air compressor body becomes milky yellow, and most of the failures occur in the summer.

3 Analysis of the cause of the failure Through the comprehensive analysis of the fault air compressor, it is found that the oil emulsification is due to the water in the air compressor body, the water and the oil in the body are dissolved, the moisture content in the oil is increased, the viscosity is lowered, and the lubricating performance is lowered. . There are two reasons for water in the body.

3 1 Condensed water enters the NPT5 air compressor The compressed air discharged from the low pressure cylinder enters the air cooler. The normal pressure is 0 3M Pa. The pressure of the compressed air discharged from the high pressure cylinder after entering the total air cylinder can reach 0 9M Pa, according to The principle of thermodynamics, the relationship between the air compressor exhaust temperature T 2 and the exhaust pressure is: T 2 = T 1 (P 2 /P 1) (m - 1 ) / m where: T 1 is the air compressor inlet temperature T 2 is the air compressor exhaust temperature; P 1 is the air compressor inlet pressure; P 2 is the air compressor exhaust pressure; m is a constant greater than 1.

Therefore, when the air compressor is working, the temperature of the compressed air rises as the pressure rises. After the air is compressed by the low pressure cylinder, it must be cooled before entering the high pressure cylinder. Otherwise, the work of the high pressure cylinder will be affected, and the air discharged from the high pressure cylinder will be affected. The temperature is up to 150.

Since the water in the natural environment will vaporize, the air always contains some water vapor, which is called wet air. At a certain air temperature, when the water vapor contained in the humid air increases to a certain amount, it reaches a saturated state, which is called saturated steam. The humid air at this time is called saturated humid air. If the amount of water vapor is increased, condensed water will be separated from the humid air. If the water vapor content in the humid air does not change and the temperature of the wet air drops to a certain level, the water vapor in the wet air will also reach a saturated state, which is called the dew point of the water vapor. If the temperature of the humid air drops again, condensed water will precipitate in the humid air.

The above-mentioned water vapor state change principle can be applied to the analysis of oil emulsification failure. In summer, the air contains more water vapor, and the relative humidity of air in some areas can reach about 80%, that is, the water vapor content in the humid air reaches saturated steam. 80%. The air inhaled in the air compressor contains water vapor. The water vapor is pressurized with the humid air in the cylinder, and is heated. After being compressed by the low pressure cylinder, it enters the intercooler to cool, and the amount of water vapor does not change during cooling. . According to the condensation principle of water vapor, when the compressed air is cooled below the saturation temperature of the water vapor, condensed water will be deposited on the wall of the intercooler cooling pipe and in the pipe, and accumulated in the lower cover of the air compressor. There is also a small amount of condensed water that enters the high pressure cylinder with compressed air.

If the friction parts of the piston and other friction parts exceed the reasonable requirements, the water will enter the body oil tank from the high pressure cylinder and cause the oil to emulsifie. The specific leakage causes are as follows: (1) the opening clearance of the piston ring exceeds the standard; (2) the high pressure cylinder piston ring and cylinder The matching of the wall is excessive; (3) the lateral clearance between the piston ring and the ring groove exceeds the standard.

3 2 check valve function bad air compressor exhaust port to the total air cylinder is provided with a check valve, its role is to prevent backflow of compressed air in the total air cylinder. The high-temperature compressed air discharged from the air compressor will also have condensed water deposited after cooling in the pipeline, and some of it will accumulate in the pipeline. When the check valve is ineffective, when the air compressor stops working, the water will flow back to the high pressure cylinder of the air compressor with the pressure air, and enter the body, thereby causing the oil to emulsifie.

4 Fault handling (1) The opening clearance of the piston ring of the high-pressure cylinder is controlled within the range of 0 15 0 3mm to prevent the condensed water entering the high-pressure cylinder from leaking into the body. High pressure cylinder piston ring.

(2) Ensure the tightness of the piston ring and the cylinder. During assembly, the radial non-closed range of the high pressure cylinder piston ring and the cylinder wall must be controlled within 30 arc angle arc length, and the gap is not more than 0 02mm.

(3) Ensure the lateral clearance between the piston ring and the ring groove. The piston ring and ring groove lateral clearance must be controlled within the range of 0 015 0 10mm during assembly.

(4) Check if the check valve starts and stops. If the total air cylinder pressure gauge shows that the air compressor does not hold pressure or keep pressure for a short time after the air is blown, the backstop valve should be treated or replaced when there is no other air leakage point.

(5) Open the drain hole of the intercooler and plug the water to seal the water, and check whether the drain hole is normally unblocked. Make sure that the drain hole can drain normally. By checking here, it can be determined whether the fault is caused by the drain hole being blocked or the water accumulating too much.

5 Conclusion Since June 1999, the new air compressors have been assembled according to the above gaps, and they have not been used for the emulsification quality of the engine oil. The above method can be used for the treatment, and the fault can be eliminated in time, and the treated air compressor has no oil emulsification failure.

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