The pneumatic auxiliary system is an indispensable power transmission unit of extrusion blow molding machines, which is mainly responsible for driving key actions such as mold clamping and opening, parison cutting, blow pin lifting and lowering, feeding door switching, and automatic stacking of finished products. Its operating stability directly affects the synchronization accuracy of each process of the extrusion blow molding machine, the forming quality of products, and the continuity of production. Due to factors such as long-term operation of air compressors, frequent switching of solenoid valves, blockage of air circuits, and aging of sealing components, the pneumatic auxiliary system of extrusion blow molding machines is prone to various faults. This document focuses on common faults of the pneumatic auxiliary system in extrusion blow molding machines, analyzes the causes in depth based on fault phenomena, and proposes corresponding solutions and preventive maintenance measures.

1. Insufficient Pneumatic Pressure

(1) Fault Phenomena

The pressure display value of the air pressure gauge of the extrusion blow molding machine is lower than the set working pressure (usually 0.6-0.8MPa); the mold clamping speed is significantly slowed down, and the clamping force is insufficient, resulting in mold leakage during blowing; the blow pin acts sluggishly, failing to pierce the parison in time; the feeding door cannot be opened or closed completely, affecting the continuity of feeding.

(2) Fault Causes

• Air compressor failure: The air compressor of the extrusion blow molding machine is aging, resulting in insufficient exhaust volume; the pressure switch of the air compressor is faulty, and the pressure cannot be adjusted to the set value; the air filter of the air compressor is clogged, leading to poor air intake and reduced exhaust efficiency.
• Air circuit leakage: The air pipes, pipe joints, and quick connectors of the pneumatic system are worn, cracked, or loose, causing air leakage; the sealing rings of cylinders and solenoid valves are aging or damaged, resulting in internal leakage of the components.
• Clogging of air treatment components: The three-in-one air filter (filter, pressure reducing valve, oil mist separator) of the extrusion blow molding machine is clogged with impurities or moisture, affecting air flow; the pressure reducing valve is faulty, failing to stabilize the output pressure.
• Excessive air consumption: Multiple pneumatic components of the extrusion blow molding machine act simultaneously for a long time, exceeding the exhaust capacity of the air compressor; the air consumption of individual components (such as large-diameter cylinders) is abnormally increased due to faults.

(3) Solutions

• Overhaul the air compressor: Check the operating status of the air compressor of the extrusion blow molding machine, and repair or replace the aging air compressor; calibrate or replace the faulty pressure switch; clean or replace the air filter of the air compressor to ensure smooth air intake.
• Detect and repair air circuit leakage: Apply soapy water to the air pipes, joints, and component connections of the pneumatic system to check for air leakage (bubbles indicate leakage); replace worn or cracked air pipes, and re-tighten loose joints; replace aging or damaged sealing rings of cylinders and solenoid valves.
• Clean and maintain air treatment components: Disassemble the three-in-one air filter of the extrusion blow molding machine, clean the filter element and moisture separator; check the pressure reducing valve, and repair or replace it if it is faulty to ensure stable pressure output.
• Optimize air consumption: Adjust the action sequence of the pneumatic components of the extrusion blow molding machine to avoid simultaneous action of multiple high-consumption components; check the components with abnormal air consumption, and repair or replace faulty parts to reduce unnecessary air loss.

2. Unstable Pneumatic Pressure

(1) Fault Phenomena

The pressure display value of the air pressure gauge of the extrusion blow molding machine fluctuates up and down around the set value (fluctuation amplitude exceeding ±0.05MPa); the mold clamping and opening speed is unstable, and the parison cutting position deviates; the blow pin acts intermittently, affecting the blowing effect of the product.

(2) Fault Causes

• Unstable operation of the air compressor: The motor speed of the air compressor of the extrusion blow molding machine is unstable; the belt of the air compressor is loose or slipping, leading to unstable exhaust volume; the pressure switch is sensitive, causing frequent start and stop of the air compressor.
• Faulty pressure reducing valve: The pressure regulating spring of the pressure reducing valve is fatigued or deformed; the internal valve core is worn or stuck, leading to unstable pressure regulation.
• Intermittent air leakage: The sealing performance of the air circuit joints of the extrusion blow molding machine is poor, and intermittent air leakage occurs under the action of pressure changes; the solenoid valve is stuck intermittently, resulting in abnormal on-off of the air circuit.
• Moisture accumulation in the air circuit: A large amount of moisture accumulates in the air pipes and components of the pneumatic system, which affects the stability of air flow and pressure; the automatic drain valve of the air storage tank is faulty, and moisture cannot be discharged in time.

(3) Solutions

• Stabilize the operation of the air compressor: Check the motor of the air compressor of the extrusion blow molding machine and repair faults affecting speed stability; adjust the tightness of the air compressor belt to avoid slipping; replace the sensitive pressure switch and adjust the start-stop pressure difference reasonably.
• Repair or replace the pressure reducing valve: Disassemble the pressure reducing valve, clean the valve core and valve seat; replace the fatigued or deformed pressure regulating spring; if the wear is serious, replace the pressure reducing valve with the same model.
• Eliminate intermittent air leakage: Re-process the air circuit joints of the extrusion blow molding machine, replace aging gaskets, and ensure reliable sealing; disassemble and clean the solenoid valve, and replace the faulty solenoid valve core or coil.
• Drain moisture in the air circuit: Manually drain the moisture in the air storage tank, air filter, and other components; repair or replace the faulty automatic drain valve; install additional drying equipment in the pneumatic system if necessary to reduce the moisture content of the compressed air.

3. Pneumatic Component Action Failure

(1) Fault Phenomena

The cylinder of the extrusion blow molding machine does not act or acts sluggishly after receiving the signal; the mold cannot be clamped or opened in place, resulting in production interruption; the parison cutting knife does not act, or the cutting is incomplete; the blow pin does not lift or lower normally, affecting the blowing process.

(2) Fault Causes

• Solenoid valve failure: The solenoid valve coil of the extrusion blow molding machine is burned out or short-circuited, failing to receive the control signal; the solenoid valve core is stuck due to impurities or oil pollution; the solenoid valve is not supplied with electricity or the control signal is abnormal.
• Cylinder failure: The piston rod of the cylinder is bent or worn; the sealing ring of the cylinder is aging or damaged, resulting in internal leakage; the cylinder is clogged with impurities, affecting the movement of the piston; the buffer device of the cylinder is faulty, leading to unsmooth action.
• Air circuit blockage: The air pipes, throttle valves, and other components of the pneumatic system are clogged with impurities, oil dirt, or solidified moisture, resulting in unsmooth air flow; the throttle valve is adjusted improperly, leading to too slow component action.
• Abnormal control signal: The proximity switch, photoelectric sensor, and other detection components of the extrusion blow molding machine are faulty, failing to send correct action signals to the solenoid valve; the PLC control program is abnormal, resulting in signal transmission errors.

(3) Solutions

• Repair or replace the solenoid valve: Detect the solenoid valve coil of the extrusion blow molding machine with a multimeter, and replace the burned-out or short-circuited coil; disassemble the solenoid valve, clean the valve core and valve body with cleaning agent; check the power supply and control signal of the solenoid valve, and eliminate signal transmission faults.
• Overhaul the cylinder: Check the piston rod of the cylinder, and straighten or replace the bent and worn piston rod; replace the aging or damaged sealing ring; disassemble the cylinder, clean the internal impurities; repair or replace the faulty buffer device of the cylinder.
• Clear air circuit blockage: Disassemble the clogged air pipes, throttle valves, and other components of the extrusion blow molding machine, and clean them with cleaning agent; adjust the throttle valve reasonably to ensure the normal action speed of the components.
• Troubleshoot control signal faults: Check the proximity switch, photoelectric sensor, and other detection components, and replace faulty parts; debug the PLC control program, and eliminate signal transmission errors.

4. Excessive Air Leakage and Abnormal Noise

(1) Fault Phenomena

Obvious air leakage sound is heard at the joints of the pneumatic system of the extrusion blow molding machine, solenoid valves, and cylinders; the air compressor runs continuously but the pressure is difficult to maintain; abnormal noises (such as hissing, knocking) are emitted from the air compressor, solenoid valves, or cylinders during operation.

(2) Fault Causes

• Poor sealing of components: The sealing rings, gaskets, and other sealing components of the air circuit joints, solenoid valves, and cylinders of the extrusion blow molding machine are aging, deformed, or damaged; the connecting bolts are loose, leading to poor sealing.
• Air compressor faults: The valve plate of the air compressor is worn or damaged, leading to air leakage; the bearing of the air compressor is worn, resulting in knocking noise; the air intake valve is faulty, causing abnormal air intake noise.
• Solenoid valve faults: The valve core of the solenoid valve is worn or stuck, leading to air leakage; the coil of the solenoid valve is loose, resulting in electromagnetic noise during operation.
• Cylinder faults: The piston rod of the cylinder is worn or bent, causing air leakage between the piston rod and the cylinder cover; the inner wall of the cylinder is worn, leading to internal leakage and abnormal friction noise.

(3) Solutions

• Replace sealing components and tighten connections: Replace the aging, deformed, or damaged sealing rings and gaskets of the extrusion blow molding machine’s pneumatic system; use a torque wrench to re-tighten the loose connecting bolts to ensure reliable sealing.
• Overhaul the air compressor: Disassemble the air compressor, replace the worn valve plate and bearing; repair or replace the faulty air intake valve; add lubricating oil to the air compressor according to the requirements to reduce friction noise.
• Repair or replace the solenoid valve: Disassemble the solenoid valve, clean or replace the worn or stuck valve core; re-fix the loose solenoid valve coil to eliminate electromagnetic noise.
• Overhaul the cylinder: Replace the worn piston rod of the cylinder; repair or replace the cylinder with excessive inner wall wear; apply lubricating oil to the cylinder piston rod and inner wall to reduce friction.

5. Preventive Maintenance Suggestions for Pneumatic Auxiliary System

1. Regular inspection of air circuit and components: Regularly check the air pipes, joints, solenoid valves, cylinders, and other components of the extrusion blow molding machine’s pneumatic system for wear, leakage, and blockage; clean the air filter, pressure reducing valve, and other components regularly.

2. Air quality management: Ensure the compressed air quality of the extrusion blow molding machine, regularly drain the moisture in the air storage tank and air treatment components; replace the filter element of the air filter regularly to avoid impurities entering the pneumatic system.

3. Lubrication maintenance: Add lubricating oil to the pneumatic components (such as cylinders, solenoid valves) that require lubrication according to the process requirements; avoid excessive or insufficient lubrication to prevent component damage.

4. Electrical control system inspection: Regularly check the solenoid valve coil, proximity switch, photoelectric sensor, and other electrical components of the extrusion blow molding machine’s pneumatic system; ensure stable power supply and reliable signal transmission.

5. Standardized operation: Operators of the extrusion blow molding machine should follow the correct startup and shutdown procedures of the pneumatic system; avoid frequent switching of pneumatic components during operation to reduce wear; adjust the working pressure reasonably to avoid overpressure operation of the system.