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Common Faults And Maintenance Of Pneumatic Circuit Of CNC Machine Tools

The main points of CNC machine tool pneumatic system maintenance ensure the supply of clean compressed air. Compressed air usually contains impurities such as moisture, oil and dust. Moisture will corrode pipes, valves and cylinders; oil will deteriorate rubber, plastics and sealing materials, and dust will cause valve body failure. Selecting a suitable filter can remove impurities in the compressed air. When using the filter, the accumulated liquid should be removed in time. Otherwise, when the accumulated liquid is close to the water baffle, the airflow can still roll up the accumulated material.

Make sure the air contains the right amount of lubricating oil. Most pneumatic actuators and controls require moderate lubrication. If the lubrication is poor, the following faults will occur:

  • Due to the increased frictional resistance, the cylinder thrust is insufficient, and the valve core action fails.
  • Air leakage due to wear of the sealing material.
  • The operation and action of the components are out of order due to the raw material.

Pneumatic Circuits And Maintenance Practices

The pneumatic circuit of CNC (Computer Numerical Control) machine tools plays a crucial role in their operation. Here are some common faults that can occur in pneumatic circuits and maintenance practices to keep them in optimal condition:

1.Air Leakage

Air leakage is a common issue in pneumatic circuits. It can occur due to loose connections, damaged seals, or worn-out components. Regularly check for air leaks by listening for hissing sounds or using a leak detection solution. Tighten loose connections, replace damaged seals, and repair or replace faulty components to prevent air leakage.

2.Pressure Drops

Pressure drops in the pneumatic circuit can lead to reduced performance and inefficiency. Ensure that the air compressor is properly sized and capable of supplying sufficient air pressure. Check for restrictions or obstructions in the air lines, filters, and regulators. Clean or replace clogged filters and adjust regulators to maintain optimal pressure levels.


Contaminants such as dirt, dust, oil, and water can enter the pneumatic circuit, leading to component failures and reduced performance. Install appropriate filters and separators in the air supply system to remove contaminants. Regularly inspect and clean filters, and drain water from air lines and pneumatic components. Lubricate pneumatic components with recommended oils to prevent excessive wear and friction.

4.Malfunctioning Valves

Valves control the flow and direction of compressed air in the pneumatic circuit. Malfunctioning valves can cause erratic machine behavior or complete system failure. Inspect valves for any signs of damage, sticking, or blockage. Clean or replace faulty valves to restore proper operation. Ensure that valve actuation mechanisms, such as solenoids or actuators, are functioning correctly.

5.Inadequate Lubrication

Proper lubrication is essential for the smooth operation and longevity of pneumatic components. Insufficient or improper lubrication can result in increased friction, wear, and premature failures. Follow manufacturer recommendations for lubrication intervals and use compatible lubricants. Apply lubricants to moving parts, such as cylinders and air motors, as per the manufacturer’s guidelines.

6.Misaligned Or Damaged Actuators

Actuators, such as cylinders or pneumatic motors, convert compressed air energy into mechanical motion. Misalignment or damage to actuators can cause uneven or inefficient movement. Regularly inspect actuators for any signs of misalignment, bent rods, or leaks. Properly align and secure actuators, and repair or replace damaged components to ensure smooth operation.

7.Electrical and Control System Issues

CNC machine tools rely on electrical signals and control systems to operate pneumatic circuits effectively. Faulty sensors, wiring, or control boards can lead to pneumatic circuit malfunctions. Regularly inspect electrical connections and components for any signs of damage or loose connections. Test sensors and control signals to ensure proper operation. Repair or replace faulty electrical components as needed.

It’s important to note that maintenance practices may vary depending on the specific CNC machine tool and its pneumatic circuit design. Refer to the manufacturer’s guidelines and maintenance manuals for detailed instructions and recommendations specific to your machine. Additionally, regular preventive maintenance, including cleaning, lubrication, and inspection, can help identify and address potential issues before they cause significant problems.


The method of lubrication is generally to use a lubricator for spray lubrication, and the lubricator is generally installed after the filter and the pressure reducing valve. The oil supply of the oil power device should not be too much, usually 1ml of oil per 10m3 of free air (ie 40`50 drops of oil). One way to check whether the lubrication is good is to find a clean white paper and put it near the exhaust port of the reversing valve. If the valve has only light and milky spots on the white paper after three to four cycles of operation, then Frog lubrication is good.

Keep the airtightness of the pneumatic system. Air leakage not only increases energy consumption, but also leads to a drop in air supply pressure, and even causes pneumatic components to work. Severe air leakage is easy to detect when the pneumatic system stops running, and the sound caused by air leakage is easy to detect; for minor air leakage, use the instrument or use soapy water to check.

Guarantees the sensitivity of pneumatic moving parts without imitations. The compressed air discharged from the air compressor contains compressor oil particles with a particle size of 0.001`0.008um. Under the high temperature of the exhaust temperature of 120~220 degrees, these oil particles will be rapidly oxidized, and the color of the oil particles will change after oxidation. Deep, viscosity increases, and gradually solidifies from liquid to sludge.

This kind of particles below the um level cannot be filtered out by general filters. When they enter the reversing valve, they are attached to the valve core, so that the sensitivity of the valve is gradually reduced, and even the action fails. In order to remove the sludge and ensure the sensitivity, an oil mist sharer can be installed after the filter of the pneumatic system to share the sludge. In addition, regular valve cleaning can also ensure valve sensitivity.

Ensure that the pneumatic device has suitable working pressure and movement speed. When adjusting the working pressure, the pressure gauge should work reliably and count accurately. After the pressure reducing valve and throttle valve are adjusted, the pressure regulating valve cover or lock nut must be firm to prevent loosening.

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