As a complex mechanical equipment, the compressor is composed of hundreds of different parts in an orderly combination. The smooth and efficient operation of the compressor depends on the sound operation and organic cooperation of various components, especially key components, and valves are one of them.
Due to different compression types, different design ideas, and different brands, the types of valves required in compressors are also different. Although it is not possible to summarize all compressor valves, we can select the important types to make a summary.
Eight Typical Valves in Air Compressors
Whether you are an air compressor sales person, or mechanical maintenance staff member, or a purchaser for your factory, you should have heard or very familiar with the following 7 famous valves in air compressors:
- Intake Valve
- Minimum Pressure Valve/MPV
- Safety Valve
- Temperature Control Valve
- Oil Cut Valve
- Check Valve
- Solenoid Valve
- Regulating Valve
01 Intake Valve (Unloader or Loading Valve)
The intake valve is the breathing port of the air compressor. The ordinary air enters the intake valve and then goes to the compressor head, where it is compressed to produce compressed gas. It can control the loading and unloading of the air compressor and the size and flow of the air pressure. It is a main component (intake control system) on the air compressor.
The working principle of the intake valve, the intake control valve is mainly composed of a valve body, a valve, a piston, a cylinder, a spring, a sealing ring, etc. It is equipped with a control block and a control solenoid valve on its side, which integrates on-off adjustment, load reduction, and dissipation. Sound, depressurization, and shutdown and vent functions. When unloading, a small part of the gas is released through the small hole in the valve to balance the intake air volume of the small hole of the intake control valve, so that the pressure in the separation oil tank is maintained at 0.2-0.3MPa, and the normal air compressor oil is maintained. cycle. The opening and closing action of the intake control valve is automatically controlled by the pressure sensor and solenoid valve of the regulating system. Whether the opening and closing action of the intake control valve is flexible is very important to the reliability of the screw machine.
What are the failures of the intake valve usually? The failure of the air valve is generally that the screw machine does not unload and the intake valve is not closed. If it is not loaded, the solenoid valve of the intake valve is damaged. The screw machine is injecting oil, and the valve body control block is faulty. The screw compressor is overloaded, and the intake valve is opened early when starting. Therefore, the intake control valve should be replaced with maintenance kits regularly to maintain good working conditions. During each maintenance, the parts must be removed to check the wear of each friction surface. Special attention should be paid to the surface of the rubber sealing ring. If there is damage or cracks, new parts must be replaced. After the repair kit is replaced, the parts should be replaced. Clean, the friction surface of the metal parts should be coated with lubricating oil.
Generally, the manual of the air compressor manufacturer stipulates that the intake valve repair kit should be replaced at 8000 hours, but in order to reduce the cost, some users basically do not maintain according to the service cycle. They are all repaired after the intake valve fails. It is recommended to delay the replacement time according to the specified time before the failure occurs. After all, the use environment of each screw compressor is different, but it is best to control it. Replace within a reasonable range.
02 Minimum Pressure Valve – MPV
The minimum pressure valve, also known as the pressure maintenance valve, is located at the outlet above the oil-gas separator. It is composed of valve body, valve core, spring, sealing ring, adjusting screw, etc.
The function of the minimum pressure valve in the compressor is as follows: the cycle pressure necessary for lubrication is quickly established when the equipment is started to avoid the equipment from being worn due to poor lubrication; it acts as a buffer to control the gas flow rate through the oil-gas separation filter element to prevent high-speed airflow damage The oil and gas separation effect brings the lubricating oil out of the system to avoid the excessive pressure difference between the two sides of the oil and gas separation filter element from damaging the filter material; the non-return function has the function of a one-way valve. When the compressor stops working or enters the no-load state, the pressure in the oil and gas barrel drops, and the minimum pressure valve can prevent the gas from the gas storage tank from returning to the oil and gas barrel.
There are many compressor failures caused by the minimum pressure valve, mainly as follows: the cylinder safety valve jets during operation, this failure is because the minimum pressure valve is not opened, resulting in excessive pressure, safety valve pressure relief protection; motor during operation Overload protection, because the minimum pressure valve is not opened, the pressure is too high, the motor is overloaded, and the thermal relay protects the shutdown; the compressor fails to start, and the minimum pressure valve is not closed tightly, resulting in the return of compressed air in the pipe network, and the startup failure under pressure; when unloading The oil pressure is high and the energy consumption increases. Because the minimum pressure valve is not tightly closed, the compressed air of the pipe network returns when the unit is unloaded, which causes the pressure in the compression chamber to rise and the oil pressure rises.
The reasons for the improper closing, damage and failure of the minimum pressure valve are: poor air quality or external impurities entering the unit, impurity particles driven by the high-pressure airflow, impact the minimum pressure valve, causing damage to the minimum pressure valve components, or Dirt is trapped between the sealing surfaces, causing the minimum pressure valve to fail; the compressor is filled with too much oil, and too much lubricating oil will form oil viscosity in the minimum pressure valve, causing the valve plate to close or open; the minimum pressure valve is based on a specific Depending on the design of the working conditions, if the working conditions fluctuate greatly or deviate from the design value for a long time, the minimum pressure valve will quickly fail; when the compressor is stopped for a long time and then turned on, the moisture contained in the lubricating oil and air will be inside the equipment unit. Accumulate, corrode various parts of the minimum pressure valve, and form oil viscosity.
03 Safety Valve
The safety valve is also called the overflow valve, which plays a role of safety protection in the compressor system. When the system pressure exceeds the specified value, the safety valve opens to discharge part of the gas in the system into the atmosphere, so that the system pressure does not exceed the allowable value, so as to ensure that the system does not cause accidents due to excessive pressure.
The common faults of safety valves are as follows:
(1) Gas leakage or failure to start. Insufficient airtightness is mostly caused by the lack of maintenance for the compressor for a long time, and the surface of the accessories is too dirty or worn, and should be cleaned and replaced in time. Another possibility that cannot be started is that the settings are inaccurate.
(2) Constant vibration. The matching spring is not suitable, the stiffness is improper, and it needs to be adjusted.
Compressor safety valves belong to the category of automatic valves. According to the “Safety Valve Safety Technical Supervision Regulations”, the regular verification of safety valves is generally at least once a year. The formal safety valve calibration methods include: off-line calibration of the calibration platform, online instrument calibration, and step-up jump method validation. It can also be checked by a simple method, that is, when the compressor is working with full load, gently open the valve cover, if the safety valve can exhaust outward, it is regarded as normal. High-temperature oil mist will be brought out when the safety valve is vented outwards, so pay attention to safety.
04 Temperature Control Valve
The function of the temperature control valve is to control the exhaust temperature of the machine head. Its working principle is that the temperature control valve core adjusts the oil passage formed between the valve body and the housing through expansion and contraction according to the principle of thermal expansion and contraction. Control the proportion of lubricating oil entering the oil cooler to ensure that the rotor temperature is within the set interval.
When the exhaust temperature of the machine head is too low, moisture will precipitate in the oil and gas barrels, causing the lubricating oil to emulsify. When the cold machine starts, the temperature control valve forces the lubricating oil directly into the machine head without passing through the oil cooler. When the oil temperature rises to a certain value, the temperature control valve completely opens the passage through the oil cooler. At this time, all the lubricating oil is cooled by the oil cooler and then sprayed into the machine head.
Since the lubricating oil entering the temperature control valve is not filtered, the internal passage of the temperature control valve is more complicated, which is easy to cause dirt accumulation. After long-term use, the failure rate of the temperature control valve is relatively high, which often leads to high temperature protection of the machine. In addition, after the temperature control valve completely opens the passage through the oil cooler, it cannot completely cut off the passage of hot oil directly into the machine head. The temperature of the lubricating oil entering the machine head is always higher than the outlet temperature of the oil cooler, resulting in low cooling efficiency. Therefore, some manufacturers’ models do not have a temperature control valve, and control the oil temperature by controlling the start and stop of the fan motor. When the exhaust temperature of the machine head rises to 90°C, the fan starts to run. If the temperature is lower than 70°C, the fan stops. , Keep the temperature within a certain range.
By checking the four oil pipes connected with the temperature control valve, it can be judged whether the temperature control valve is working normally. The four oil pipes are: oil barrel to temperature control valve, temperature control valve to oil cooler, oil cooler to temperature control valve, and temperature control valve to oil filter; normal temperatures are: high, high, low, slightly higher .
05 Oil Cut Valve / Oil Stop Valve
The oil cut-off valve is a switch used to control the main oil path into the screw head. Its function is to cut off the oil supply to the main engine when the compressor is stopped, so as to prevent the lubricating oil from spraying out of the main engine port, and the oil backflow occurs at the moment of shutdown.
During the use of the compressor, a small part of the impurities in the air will inevitably be mixed into the cooling oil, which may cause sedimentation and blockage when flowing through the oil cutoff valve, so that the oil cutoff valve cannot be opened with the opening of the equipment. In the closed or semi-closed state, the cooling oil flow is reduced, which seriously affects the cooling effect of the machine head, causing rapid high temperature trip after starting up, high temperature alarm or back spray of lubricating oil when shutting down.
Therefore, users need to clean and maintain the oil shut-off valve regularly, optimize the compressor operating environment, use it in an environment with good ventilation and heat dissipation, away from volatile gases, debris and floating debris, and replace the air filter in strict accordance with the pressure difference parameter requirements.
06 Check Valve or One-Way Valve
One-way valve is also called check valve, commonly known as one-way valve. In the compressed air system, it is mainly used to prevent the compressed oil and gas mixture from being suddenly back-injected into the main engine when the machine is shut down due to a sudden failure, causing the rotor to reverse rotation.
One-way valve sometimes fails to close tightly. The main reasons are: the rubber sealing ring of the one-way valve falls off, the spring is broken, the spring and the rubber sealing ring need to be replaced; there is a foreign body supporting the sealing ring, and the impurities on the sealing ring need to be cleaned.
07 Solenoid valve
The solenoid valve belongs to the control system, including a loading solenoid valve and a vent solenoid valve. In the compressor, the solenoid valve is mainly used to adjust the bias, flow, speed, on-off and other parameters of the medium.
(1) Load solenoid valve
The loading solenoid valve is a two-position three normally closed solenoid valve, which controls the oil and gas barrel to the intake valve to perform the on and off of the cylinder pipeline under the instruction of the PLC. When the loading solenoid valve is energized, the compressed air in the oil and gas tank is allowed to enter the intake valve actuator cylinder, and the intake port is opened. When the loading solenoid valve loses power, it cuts off the passage from the oil and gas barrel to the intake valve execution cylinder, vents the gas in the execution cylinder, and closes the intake port.
(2) Vent the solenoid valve
The vent solenoid valve is a two-position, two-position solenoid valve, whose diameter must match that of the intake bypass valve. The diameter of the vent solenoid valve and the intake bypass valve should be able to ensure that the pressure in the oil and gas barrel is about 0.2MPa when the compressor is empty. When the compressor is unloaded and stopped, the vent solenoid valve loses power and releases the gas in the oil and gas tank to the intake filter.
- a. The solenoid valve terminal is loose or the thread terminal is dropped. The solenoid valve must not be energized, and the thread terminal can be tightened to solve the problem.
- b. The solenoid valve is leaking. Air leakage will result in a lack of air pressure, making it difficult to open and close the valve. The reason is that the sealing gasket is damaged or the slide valve is worn to form blow-by.
- c. The solenoid valve coil is burnt out. If the solenoid valve coil is burned out, the wiring of the solenoid valve can be removed and measured with a multimeter. If it is open, the solenoid valve coil is burned out.
- d. The solenoid valve is stuck. The cooperation gap between the slide valve sleeve of the solenoid valve and the valve core is very small, and it is usually installed as a single piece. When mechanical impurities are brought in or there is too little lubricating oil, it is easy to get stuck.
Disposal method: Use a steel wire to poke into the small hole in the head to make it rebound. The complete solution is to remove the solenoid valve, take out the valve core and valve core sleeve, and clean, so that the valve core moves sensitively in the valve sleeve. When disassembling, pay attention to the installation sequence of the components and the orientation of the external wiring, so that the reinstallation and wiring are correct. Also check whether the oil spray hole of the lubricator is blocked and whether the lubricating oil is satisfactory.
08 The last but not the least: Compressed Air Pressure Regulating Valve – Regulator
When you operate an air compressor, the success of your project depends largely on the pressure of the air itself. To get the proper pressure for each application, you need to make sure that the settings are correct. In order to make these adjustments and make sure that you have indeed made the correct settings, there is a function called the air compressor pressure regulating valve.
One of the most important components of an air compressor is the pressure regulator, which controls the air flow through the system. Without this type of control function, the pressure and intensity of the air flowing from the compressor tank into the pneumatic tool cannot be adjusted. The regulator protects each tool from too high or too low power, thereby helping to ensure the quality of pneumatic applications.
Why adjust the air compressor?
Air pressure regulators are important because different types of pneumatic tools require different pressure levels. If you try to power a slow-moving tool with the same pressure required for fast-moving operations, you may overwhelm the tool. If you do the opposite, the latter operation may produce plain results.
When you adjust the air compressor, you can reduce the energy required to run pneumatic operations. Without the function of a pressure regulator, you may consume a lot of energy in each working day to meet peak demand, even if only a small part of the application requires so much energy. Essentially, there are three reasons to adjust your air compressor: to properly service your pneumatic tools, simplify applications, and save energy.
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