Faults of Reciprocating Piston Compressors with Completely Oil-free Lubrication

Faults of reciprocating piston compressors with completely oil-free lubrication

After decades of development, the technology of fully oil-free lubricated reciprocating piston compressors has become mature and widely used. The fault analysis of fully oil-free lubricated reciprocating piston compressors is as follows:

The fully oil-free reciprocating piston compressor belongs to the reciprocating motion of the crank connecting rod mechanism, similar to the faults of reciprocating compressors, mainly divided into two categories: mechanical performance faults and thermal performance faults. Mechanical performance faults mainly include excessive noise during compressor operation, abnormal vibration, and overheating of the machine body; Thermal performance faults mainly include abnormal thermodynamic parameters such as pressure, displacement, and temperature of the compressor, or exceeding the set value of the compressor.

1.1 Mechanical performance faults

(1) Abnormal compressor vibration

Loose and worn components of the compressor are the main causes of abnormal compressor vibration. The compressor will experience certain vibrations during normal operation, and as long as the vibration amplitude is within a certain range, this vibration is normal; If the vibration amplitude exceeds a certain value, it is considered abnormal vibration. When the running time of the compressor is too long, it is inevitable that various components will become loose and worn, which will result in poor connections between the components, inertial forces that cause the unit to no longer maintain balance, and significant airflow pulsation, ultimately exacerbating vibration.

The rotary motion pair of a completely oil-free reciprocating piston compressor uses sealed rolling bearings, and the sealed lubricating grease is often disposable. Compared to sliding bearings, its load-bearing capacity is weak. Once these bearings are damaged, the vibration of the compressor is often significantly intensified.

(2) Abnormal compressor noise

Compressors are a type of high noise equipment and a comprehensive source of mechanical noise. In terms of nature, it includes two types: mechanical noise and aerodynamic noise. The mechanical noise during the operation of a completely oil-free reciprocating piston compressor is mainly the knocking sound inside the cylinder and the friction sound caused by the wear of the bearings in the crankshaft connecting rod mechanism. The knocking sound can be divided into normal knocking sound and abnormal knocking sound. The normal knocking sound includes the knocking sound generated by the action of the regulator, the knocking sound generated by the opening of the valve, etc; Abnormal knocking sounds include knocking inside the cylinder and inside the body. The main reasons for the knocking sound inside the cylinder are water ingress, foreign objects inside the cylinder, piston tilting, loose fit between the piston and piston rod, and severe wear of the cylinder and piston support ring; The main reasons for the knocking sound inside the fuselage include excessive clearance between the crosshead and the slide, loose balance iron of the crankshaft, loose fasteners of the crankshaft, and excessive clearance between the crosshead pin and the crosshead body.

A reciprocating piston compressor with completely oil-free lubrication is used for the cylinder, which adopts self-lubricating sealing and piston support materials. Compared to metal sealing rings, the gap between the cylinder and piston is much larger, and its wear can also affect the operation noise of the compressor, which is significantly abnormal.

Improper installation of the compressor flywheel, poor assembly of the coupling, and loose fit between the shaft and flywheel can also cause abnormal knocking of other components.

When designing the compressor, if the piston force is too large and the flywheel torque is too small, it will cause uneven rotation and excessive knocking sound. This situation usually occurs with new machines.

(3) Compressor overheating

During the operation of the compressor, due to continuous compression of the compressed medium, more heat is generated. Although cooling water or cold air can take away some of the heat, the heat generated by high power consumption is more. In addition, the heat exchanger is limited, and the heat generated during the compression process cannot be completely taken away by cooling water or cold air. This leads to high temperatures in components such as pistons, cylinders, and valves, which often maintain the temperature of the body at high temperatures. High temperatures can pose a threat to the normal operation of the compressor. If the exhaust temperature of the compressor cylinder is above 260 ℃, the non-metallic self-lubricating sealing ring may directly vaporize, leading to complete failure of the compressor. In such a situation, if the compressor does not stop in time and continues to operate, the compressor piston will directly contact the cylinder, causing dry friction and rapid wear of components. In severe cases, it may even cause explosions and cylinder collision accidents. There are many reasons for the overheating of the compressor body, mainly including insufficient cooling water, poor inter stage cooling effect, poor performance, bent piston rod, and excessive friction between components. Therefore, in general, the stage compression ratio of fully oil-free reciprocating piston compressors cannot be achieved too high.

The reciprocating piston compressor without oil lubrication is currently limited by the bearing capacity, and the basic installed power will not be too large. So in terms of cooling methods, there are many air-cooled machines. For air-cooled compressors, attention should be paid to the ambient temperature and the operation of fans and heat exchangers. Once the ventilation is poor, a sharp increase in compressor temperature can easily lead to malfunctions.

1.2 Thermal performance failure

(1) Abnormal gas volume

Abnormal gas volume refers to the significant difference between the intake or exhaust volume of the working medium processed by the compressor and the value during normal operation. There are many reasons that can cause abnormal gas flow in compressors. This is because, according to the Clapeyron equation, various thermodynamic parameters such as gas flow, pressure, and temperature are interrelated, and any change in thermodynamic parameters will cause a change in gas flow. Overall, the main causes of abnormal compressor air flow are poor sealing of the compressor valve, excessive wear and failure of sealing components such as the compressor piston sealing ring and packing sealing ring, as well as poor sealing of the cylinder and connecting pipes leading to leakage.

(2) Abnormal inter stage pressure

Completely oil-free reciprocating piston compressor, with single-stage and multi-stage compression according to different operating conditions, can save energy consumption and improve compressor performance. The working form of multi-stage compression and interstage cooling is that during normal operation, the inlet stress of the later stage should be approximately equal to the exhaust pressure of the previous stage. If any pressure parameter in the compressor is abnormal, it will cause abnormal interstage pressure in the entire compressor. Generally speaking, the main reasons for abnormal interstage pressure are piston wear and tear, and damage to components such as air valves. If the exhaust pressure of a certain stage increases, it is a malfunction of the subsequent stage air valve.

(3) Abnormal exhaust pressure

The abnormal situation of exhaust pressure is mainly due to a decrease in the exhaust pressure of the compressor. The compressed gas volume of the compressor cannot meet the normal flow demand, and the compressor cannot meet the designed gas volume requirements. If it is not due to process changes and an increase in gas consumption, when the exhaust pressure decreases, it is very likely that the compressor has malfunctioned. The causes of these faults are somewhat similar to those of abnormal gas volume and inter stage pressure, mainly including sealing ring and gas valve failures.

(4) Abnormal exhaust temperature

During the operation of the compressor, there may sometimes be an increase in exhaust temperature. The most likely reason for this is the deterioration of the inter stage cooling effect of the compressor, which will cause an increase in the exhaust temperature of the next stage. This not only affects the efficiency of the compressor, but also endangers its normal operation. In the case of abnormal exhaust temperature, the relationship between various parameters such as pressure, temperature, and gas volume should be comprehensively considered to identify the root cause of the problem.

BaiLian is a professional factory for oil-free gas compressors,

Our products include more than 30 types of gas chemical compressors, including oil free lubrication air compressors, oxygen compressors, nitrogen compressors, hydrogen compressors, carbon dioxide compressors, helium compressors, argon compressors, sulfur hexafluoride compressors, etc., with a maximum pressure of up to 70Mpa.