Pneumatic Cylinder Troubleshooting

Pneumatic cylinder is a pneumatic actuator. It can convert air pressure energy into mechanical energy and can do linear reciprocating motion. This article will introduce 3 common failures of pneumatic cylinders and give troubleshooting. The 3 types of failures are: Pneumatic cylinder action has failure or mal-operation. Pneumatic cylinder is unable to drive load when working. Pneumatic cylinder piston slippages or crawls.

1. The valve core of the pneumatic cylinder is stuck or the valve hole is blocked. When the valve core of the flow valve or the directional valve is stuck or the valve hole is blocked, the pneumatic cylinder is prone to malfunction or failure. At this time, it is required to check the pollution of oil and gas, check whether there is dirt or colloidal deposits that jam the valve core or block the valve hole, and check the wear of the valve body.
2. The piston rod and cylinder are stuck or the pneumatic cylinder is blocked. At this time, no matter how the operator manipulates, the air cylinder cannot act or move very little. At this time, it is required to check whether the piston and piston rod seals are too tight, whether there are dirt and colloidal deposits, check whether the axis line of the piston rod and the cylinder barrel is aligned, and whether the wearing parts and seals become ineffective.
3. The control pressure of the pneumatic system is too low. The reason for this phenomenon is probably the throttling resistance in the control pipeline is too large, the flow valve is not adjusted properly, the control pressure is not appropriate, and the pressure source is disturbed. At this time, the control pressure source should be checked to ensure that the pressure is adjusted to the specified value of the system.
4. There is air being mixed in the air pressure system. The main reason for this phenomenon is that there are air leaks in the system. At this time, it is required to check the air level of the air pressure tank, the seals and pipe joints on the suction side of the air pump, and if the oil suction coarse filter is dirty. If this is the case, it is required to supplement air pressure oil, handle seals and pipe joints, clean or replace coarse filter elements.
5. The pneumatic cylinder has slow initial movements. In the case of low temperature, the viscosity of the pneumatic oil is large and the fluidity is poor. This causes the air cylinder to move slowly. The improvement method is to replace the pneumatic oil with better viscosity-temperature performance. At low temperatures, it can be heated by a heater or the machine itself to increase the oil temperature at startup.

Pneumatic cylinder is unable to drive load when working

It is mainly manifested by the inaccurate stop of the piston rod of pneumatic cylinder, insufficient pushing force, reduced speed and unstable operation, etc. The reasons are as follows:

1. Internal leakage of the pneumatic cylinder, including the leakage caused by the sealing of the pneumatic cylinder, the sealing of the piston rod and the sealing cover, and the excessive wear of the piston seal.
   The reason for the seal leakage between the piston rod and the sealing cover is: the seal is wrinkled, squeezed, torn, worn, aging, deteriorated, deformed, etc. At this time, new seals should be replaced.
   The main reason for excessive wear of the piston seal is improper adjustment of the speed control valve, resulting in excessive back pressure, improper installation of the seal or air pressure oil contamination. The second reason is that foreign matter enters during assembly and the quality of the sealing material is not good. The consequence is that the pneumatic cylinder moves slowly and weakly. In severe cases, it will cause damage to the piston and cylinder, causing the phenomenon of “scuffing of cylinder bore”. The treatment method is to adjust the speed control valve, do the necessary operations and improvements according to the installation instructions, clean the filter or replace the filter element and air pressure oil.
2. Leakage in the pneumatic circuit, including valve and pneumatic pipeline leakage. The maintenance method is to check and eliminate the leakage of the pneumatic connecting pipeline by operating the reversing valve.
3. The pneumatic oil flows back to the tank through the overflow valve. If dirt is mixed into the overflow valve, causing the valve core to be stuck, and the overflow valve is normally open, the pneumatic oil will flow directly back to the tank through the overflow valve bypass, causing no oil to enter the pneumatic cylinder. If the load is too large, although the regulating pressure of the relief valve has reached the maximum rated value, the pneumatic cylinder still cannot obtain the thrust required for continuous action, thus being unable to operate. If the adjustment pressure is low, the thrust required by the load cannot be reached due to insufficient pressure, which manifests as insufficient thrust. At this time, the relief valve needs to be checked and adjusted.

Pneumatic cylinder piston slippages or crawls

The slippage or crawling of the piston in the pneumatic cylinder will result in unstable operation. The main reasons are as follows:

1. The pneumatic cylinder has internal sluggishness. If the internal parts of the pneumatic cylinder are improperly assembled, the parts are deformed, worn, or the geometric tolerance exceeds the limit, the action resistance will be too large, and the speed of the pneumatic cylinder piston will vary with the stroke position, causing slippage or crawling. This situation is mostly caused by poor assembly quality of parts, scars on the surface or iron filings produced by sintering, which increase the resistance and decrease the speed. For example: the piston and the piston rod are not concentric or the piston rod is bent; the installation position of the pneumatic cylinder or the piston rod to the guide rail is offset; the sealing ring is installed too tightly or too loosely. The solution is to repair or adjust again, replace damaged parts and remove iron filings.
2. Poor lubrication or overproof processing of the pneumatic cylinder bore diameter. Because the piston and the cylinder, the guide rail and the piston rod all have relative motion, if there is poor lubrication or the cylinder bore is too poor, it will increase the wear and reduce the linearity of the cylinder center line. In this way, when the piston is working in the pneumatic cylinder, the frictional resistance will be large and sometimes small, resulting in slipping or crawling. The solution is to grind the pneumatic cylinder first, then prepare the piston according to the instructions, grind the piston rod, and configure the guide sleeve.