In practical applications, the working environment of air compressors is often complex, with dust, oil and various particulate matter.

After the air compressor has been used for a long time, there will be oil dirt, carbon deposits, sediments, rust, etc. inside. If an air compressor with different brands of lubricating oil has been used, there will also be black glue similar to asphalt. Therefore, it is necessary to clean the machine head, paint bucket, radiator, oil pipe interior, and various valves regularly to eliminate safety hazards.

1. Whole machine cleaning

Air pressure cleaning method:

First, run the air compressor for a few minutes to allow the oil to reach normal temperature;

Turn off the air compressor, wait until the internal pressure is released, open the filling cap, pour in the air compressor cleaning agent, and tighten the filling cap;

Turn on the air compressor and run it for 30 minutes;

Drain the old oil and add new oil.

Generally, the temperature of the air compressor after cleaning will drop by about 10 degrees.

2. Cooler cleaning

In China, air compressor coolers are generally divided into two types: air-cooled and water-cooled. Therefore, there are different cleaning methods for different coolers.

2.1 air-cooled cooler

Open the air duct and clean the cover, or remove the cooling fan;

Use compressed air to blow back the dirt, and then take the dirt out of the air guide; if it is dirty, spray some degreaser and blow it again. When the screw air compressor cannot be cleaned by the above methods, the cooler needs to be removed, soaked or sprayed with cleaning fluid and cleaned with the help of a brush (wire brushes are strictly prohibited).

Install the cover or cooling fan.

2.2 water-cooled cooler

Disassemble the cooling water inlet and outlet pipes.

Inject cleaning solution to soak or use pump circulation to flush (recoil effect is better).

Rinse with clean water.

Install the cooling water inlet and outlet pipes.

When the oil cooler is severely scaled and cleaning with the above method is not ideal, you can remove the oil cooler separately, open the end caps at both ends, and use a special cleaning steel brush or other tools to remove scale. When cleaning the medium side of the cooler cannot effectively reduce the temperature, the screw air compressor needs to clean the oil side. The method is as follows:

Disassemble the inlet and outlet oil pipes;

Inject cleaning solution for soaking or use pump circulation for flushing (recoiling effect is better);

Rinse with clean water;

Blow dry with dry air or remove water with dehydrated oil;

Install the inlet and outlet oil pipes.

3. Clean the water and gas separator

The structure of the water and gas separator of a screw air compressor is similar to an oil and gas tank. The air inlet is designed against the wall to form centrifugal force. Due to the weight of water and gas, it can effectively separate the moisture in the compressed air.

Cleaning of the water and gas separator: Remove the water and gas separator cover and soak it with cleaning agent.

4. Cleaning of unloading valve (inlet valve)

The unloading valve is composed of a valve body, a valve core (piston), a gas circuit manifold, a solenoid valve and a proportional valve (capacity regulating valve). The unloading valve mainly controls the loading (screw air compressor heavy truck), unloading (empty truck), and proportional (capacity adjustment) control functions of the air compressor. In addition, it can prevent lubricating oil from spraying out from the main engine when the air compressor is shut down.

Disassembly of the unloading valve: (1) Remove the hose connecting the unloading valve to the air filter; (2) Remove the air pipes connecting all other components to the unloading valve; (3) Remove the solenoid valve coil; (4) Remove the nuts that assemble the unloading valve and the main engine and take them off; (5) Move the unloading valve to a floor paved with clean paper or related clean paving.

Cleaning the unloading valve: (Screw air compressor cleaning agents should use soapy water, diesel, clean gasoline, Tianna water, etc. The above cleaning agents should be selected according to the degree of dirt. It is generally recommended to use soapy water or diesel for cleaning).

Disassemble the solenoid valve: Remove the solenoid valve and check whether the O-ring and sealing disc in the solenoid valve need to be replaced (reminder: if you are not familiar with the intake valve, please note the location of the removed component to avoid errors when reinstalling it). If there is no need to replace, put the disassembled screws, O-rings, sealing sheets, solenoid rods, cores and other components into a prepared container, and soak them in appropriate cleaning agents (Note: When using gasoline and Tianna water as cleaning agents, please do not soak O-rings and other rubber products for too long to avoid corrosion).

Disassemble the proportional valve: Remove the proportional valve from the valve body, and then unscrew the adjusting nut (it is best to mark the nut before tightening to avoid too large a deviation in the proportion value when reinstalling), take out the valve core, O-ring, U-ring, and spring and check whether the O- and U-rings need to be replaced (all sealing rings and springs removed from the screw air compressor must undergo this inspection, which will not be repeated in the following description). Soak the removed components in cleaning agent.

Disassemble the manifold block of the gas line: Remove the manifold block from the valve body. There are air holes on the four sides of the manifold block (the holes in screw air compressors are used to clear the air line when the integrated air line is clogged). Unscrew the sealing nuts on the air holes and put the manifold block together into the cleaning agent to soak.

Disassemble the valve core of the unloading valve: use circlip pliers to remove the circlip located at the connection between the valve core and the valve body, then use a pipe wrench to unscrew the valve core, take out the cylinder, valve plate, O-ring, U-ring, and spring inside and soak them in cleaning agent, then remove the air inlet on the valve body, and put the entire valve body into soaking. At this time, the disassembly process of the unloading valve has been completed.

Cleaning: If the dirt on the intake valve is serious, use a new cleaning agent during cleaning. During the cleaning process, clean parts should be washed first and then parts with more dirt. The cleaned parts should be rinsed again with clean water to avoid corrosion and shorten the service life of the parts. Parts washed with clean water should be placed in a clean place to dry to prevent iron-containing parts from rusting.

When cleaning the valve plate and the place where the valve body contacts the valve plate, attention should be paid to the flatness of the surface, and it should be cleaned and replaced if necessary. Otherwise, the air compressor will start with load (large screw air compressor units will fail to start when they start with load).

Install components: Install components according to the reverse steps of disassembly. It should be noted that when installing components, the location where the sealing ring is installed and the movable components should be coated with an appropriate amount of engine oil, which can make the sealing ring better installed and the movable parts more flexible.

Since the unloading valve has many parts, if you are not sure about the location of each part, you can disassemble each part and clean it before installing it. However, do not install the parts on the valve body first. After all parts are cleaned, they can be assembled together into the valve body. After the entire cleaning process of the unloading valve is completed, put it aside to be installed into the air compressor.

5. Minimum pressure valve (pressure maintenance valve) cleaning

Although the minimum pressure valve in a screw air compressor looks relatively small, it controls the entire machine despite its small size. In order to allow it to operate normally under normal operation, the following provides maintenance methods for the minimum pressure valve of the screw air compressor.

The minimum pressure valve is composed of a valve body, a valve core, an adjusting nut, a spring, and a sealing element. The minimum pressure valve mainly plays the role of establishing the internal pressure of the unit, promoting the circulation of lubricating oil, and meeting the working pressure of the unloading valve. In addition, the minimum pressure valve also functions as a one-way valve to prevent the compressed air in the gas storage tank from flowing back to the air compressor when the unit is unloading.

The structure of the minimum pressure valve is very simple. Unscrew the nut of the screw air compressor between the valve core and the valve body to take out the components inside. The minimum pressure valve core of the small unit is built into the valve body, and all the internal components can be taken out by removing the valve body cover.

The minimum pressure valve can be cleaned according to the method of cleaning the unloading valve.

Since the structure of the minimum pressure valve is very simple, the assembly process will not be described one by one, but it should be noted that if there is a U-ring inside, the direction of the U-ring must be paid attention to. After the entire cleaning process of the minimum pressure valve of the screw air compressor is completed, put it aside to be installed into the air compressor.

6. Cleaning of oil return check valve

A check valve consists of a valve body, steel ball, ball seat, spring, and other components. The oil-air mixture compressed by the air compressor's main unit first undergoes preliminary centrifugal separation in the oil-air tank. Because oil is heavier than air, most of the oil in the mixture falls into the oil tank under centrifugal force. Internal pressure then returns it to the main unit of the screw air compressor for the next lubrication cycle. The compressed air, containing a small amount of oil, undergoes another separation in the oil-air separator. The separated lubricating oil collects at the bottom of the separator. To prevent this oil from being carried away with the compressed air, the unit is designed with an oil pipe extending to the bottom of the oil-air separator. Internal pressure directs this oil back to the main unit for lubrication. A check valve is installed in this pipe and is called the oil return check valve in a screw air compressor.

Its function is to smoothly recover the oil from the oil and gas separator to the main engine without allowing the oil from the main engine to flow back to the oil and gas separator. The oil return single-way valve has a connection point on the valve body. Unscrew it from there and take out the spring, steel ball, and steel ball seat.

Clean the oil return check valve: Use cleaning agent to clean the valve body, spring, steel balls, and steel ball seats. Some check valves also have filters inside. If so, clean them together.

7. Clean the temperature control valve of screw air compressor

The temperature control valve consists of a valve body, spool, temperature-sensing element, spring, and other parts. It provides thermostatic control. When the oil temperature measured by its sensing element is below the actuation setting, generally 71 degrees, lubricating oil returns directly from the oil-air separator tank to the main unit. When the measured oil temperature exceeds the actuation setting, the sensing element's push pin moves, driving the spool to open the built-in bypass valve and direct the lubricating oil into the cooler. The higher the sensed temperature, the wider the bypass valve opens. The cooled lubricating oil then returns to the main unit.

There is a side cover on the side of the screw air compressor temperature control valve. There are screw holes on the cover. Find a suitable nut and screw it into the cover. Then use circlip pliers to remove the circlip that fixes the cover. Then use pliers to pull the nut just screwed in to remove the cover and all internal parts. Clean all parts of the temperature control valve according to the method of cleaning the unloading valve.

After all the above components have been cleaned and dried, installation into the air compressor begins. After all components are installed into the air compressor, check again for any omissions and clean up the tools and other items used during installation.

8. Calibrate all parameters

After the machine is cleaned and installed, the operating parameters of the air compressor should be adjusted to ensure normal and safe operation of the air compressor:

(1) Preparations before starting the screw air compressor:

Belt (coupling) correction: If the air compressor is driven by a belt, the tightness of the belt should be between 10 and 20 millimeters. If the air compressor is driven by a coupling, after installation, you should turn the motor and main unit by hand and check the balance of the coupling during rotation. Screw air compressor couplings basically use elastic couplings, which can be ignored when the solid balance deviation is not large.

Screw air compressor host steering correction: If the main power supply has been removed during maintenance, pay attention to the forward and reverse rotation of the motor after reconnecting the power. The motor's steering should be based on the steering of the host. For the correct rotation of the host, please check the steering icon marked on the host.

Correction method: Just swap any two power lines in the three-phase power supply.

(2) Calibration of the loading, unloading, and proportional-control settings: When setting these three parameters, first determine the unloading value based on both the air compressor's rated pressure and the pressure required at the point of use. Then set the loading value, keeping the pressure difference between the two within 0.1–0.2 MPa. After setting the unloading and loading values, set the proportional-control value between them. For example, if a factory requires a screw air compressor to supply relatively stable air at 0.8 MPa, set the three parameters as follows: unloading pressure, 0.8 MPa; loading pressure, 0.65 MPa; proportional-control pressure, 0.73–0.75 MPa.

Screw air compressor calibration method: Set this parameter in the microcomputer controller (if the air compressor is controlled by push buttons, the loading and unloading parameters should be adjusted from the pressure switch, and the proportional value should be adjusted at the adjusting nut of the proportional valve on the unloading valve).

(3) The internal pressure effect of the unit is positive: the internal pressure of the unit should be between 0.2～0.45MPa.

Correction method: The pressure value should be carried out when the unit is unloaded and the value is adjusted on the adjusting nut of the minimum pressure valve. In order to facilitate reading of the set value, a pressure detection point should be taken before the minimum pressure valve and a pressure gauge should be installed (some microcomputer controllers have an internal pressure parameter display function. If there is no such function, a pressure gauge should be installed before the minimum pressure valve).

(4) High temperature protection value is valid: When the screw air compressor is working normally, its temperature should be between 65~98℃. The automatic shutdown temperature of over-temperature protection shall not exceed 105℃.

Correction method: Adjust the high temperature automatic shutdown temperature value in the controller to 1.2 (i.e. enlarge the 20% margin).

Summary

Correct care and maintenance play a vital role in the service life and operational reliability of screw air compressors, and air compressor cleaning is a skill that after-sales maintenance service personnel and even equipment operators must master.

(Source: Internet)