Proper Maintenance of Several Screw Air Compressor Spare Parts – Highly Practical!
Correct maintenance of air compressor spare parts plays a vital role in extending the service life and improving operational reliability of screw air compressors.
1. Maintenance of Air Intake Filter Element
The air filter removes dust and contaminants from intake air. Clean filtered air enters the screw rotor compression chamber. The internal clearance of the screw machine only permits particles smaller than 15μm to pass through. If the air filter is blocked or damaged, massive particles larger than 15μm will circulate inside the unit. This will not only drastically shorten the service life of the oil filter and air-oil separator element, but also allow particles to enter the bearing cavity directly, accelerating bearing wear, widening rotor clearances, reducing compression efficiency, and even causing rotor seizure.
The air filter should preferably be maintained weekly. Unscrew the cover nut and take out the filter element. Blow dust particles outward from the inner cavity of the filter element using compressed air at 0.2–0.4 MPa. Wipe contaminants off the inner wall of the air filter housing with a clean rag. Reinstall the air filter, ensuring the sealing ring at the front end of the filter closely fits the inner end face of the filter housing. For diesel-driven screw compressors, maintenance of the diesel engine air filter shall be carried out simultaneously with the compressor air filter by adopting the same maintenance method.
Under normal operating conditions, replace the air filter every 1,000–1,500 operating hours. For severely dusty working sites such as mines, ceramic plants and cotton mills, replacement every 500 hours is recommended.
When cleaning or replacing the air filter, match all components properly and strictly prevent foreign objects from falling into the intake valve.
Regularly inspect the intake expansion hose for cracks or collapse, and check whether connections between the expansion hose, air filter and intake valve are loose or leaking. Repair or replace components immediately if defects are found.
2. Replacement of Oil Filter Element
The oil filter element shall be replaced after the new unit runs for the first 500 hours. Remove the oil filter by turning it counterclockwise with a special wrench. It is recommended to add screw compressor oil to the new filter before installation. Screw the filter back onto the filter base manually and tighten firmly.
It is advised to replace the oil filter every 1,500–2,000 hours. Replace the oil filter together with lubricating oil during oil change. Shorten the replacement cycle for operation in harsh environments.
Never use the oil filter beyond its service life. Severe filter blockage will cause the pressure differential to exceed the limit of the bypass valve. The bypass valve will automatically open, allowing large quantities of dirt and particles to enter the screw main unit together with lubricating oil and resulting in serious damage.
For diesel-driven screw compressors, replacement of the diesel engine oil filter and fuel filter shall comply with diesel engine maintenance requirements, and the replacement procedure is similar to that of the screw compressor oil filter.
3. Maintenance and Replacement of Air-Oil Separator Element
The air-oil separator separates screw lubricating oil from compressed air. Under normal operation, its service life is approximately 3,000 hours. However, oil quality and air filtration precision exert a great influence on its service life. Therefore, the maintenance and replacement cycle of the air filter must be shortened under harsh operating conditions, and installation of a pre-filter may be considered.
The air-oil separator element must be replaced upon expiry or when the pressure differential across it exceeds 0.12 MPa. Otherwise, motor overload or element rupture and oil carry-over will occur.
Replacement Procedure:
Disconnect all control pipe connectors mounted on the top cover of the air-oil tank. Pull out the oil return pipe extending into the tank from the top cover, and remove the fastening bolts of the air-oil tank top cover.
Remove the top cover and take out the air-oil separator element. Clear asbestos gaskets and contaminants adhering to the top cover.
Install the new air-oil separator element. Ensure the upper and lower asbestos gaskets are properly positioned and evenly compressed to prevent gasket blowout.
Refit the top cover, oil return pipe and all control pipes in original order, then check for leakage.
4. Maintenance and Replacement of Screw Compressor Lubricating Oil
The quality of screw compressor oil has a decisive influence on the performance of oil-injected screw compressors. High-quality lubricating oil features excellent oxidation stability, rapid separation performance, good anti-foaming property, high viscosity and outstanding anti-corrosion performance. Users must adopt genuine special screw compressor oil specified by the manufacturer.
Complete the first oil change after 500 operating hours of the new unit running-in period. Thereafter, replace lubricating oil every 2,000 hours. Replace the oil filter together with oil change. Shorten the replacement cycle for operation in harsh environments.
Oil Change Procedure:
Start the air compressor and run for 5 minutes to raise the oil temperature above 50°C and reduce oil viscosity.
Shut down the unit. When the internal pressure of the air-oil tank remains at 0.1 MPa, open the drain valve at the bottom of the air-oil tank and connect an oil storage tank. Open the drain valve slowly to avoid splashing of pressurized hot lubricating oil which may cause personal injury. Close the drain valve once oil drips slowly. Unscrew the oil filter and drain all residual lubricating oil inside pipelines, then install a new oil filter.
Remove the filler plug, inject new oil until the oil level falls within the scale range of the oil gauge. Tighten the filler plug and check for leakage.
Lubricating oil level must be inspected frequently during operation; replenish new oil promptly if the oil level is too low. Condensate must be drained regularly. Normally drain condensate once a week, and once every 2–3 days under high-temperature climate. After shutdown for more than 4 hours and with zero pressure inside the air-oil tank, open the drain valve to discharge condensate, and close the valve immediately once lubricating oil flows out.
Mixing different brands of lubricating oil is strictly prohibited. Never use lubricating oil beyond its service life. Degraded oil will lead to poor lubricity and lower flash point, easily triggering high-temperature shutdown and even spontaneous combustion of oil.
5. Maintenance of Cooler
The heat dissipation performance of the cooler directly affects the operating temperature of the air compressor. The plate-fin structure is prone to dust accumulation. Therefore, the cooler shall be blown with dry compressed air above 0.4 MPa from top to bottom every shift. For coolers of diesel-driven screw compressors arranged vertically, blow dry compressed air above 0.4 MPa from outside inward during maintenance. After blowing, clean all dust and particles inside the air guide hood to prevent the fan from blowing contaminants back into the cooler and causing blockage and high unit temperature. If the unit operates in harsh environments and the cooler surface is covered with oil dirt, clean the cooler thoroughly with carbon remover.
6. Cleaning of Minimum Pressure Valve (Pressure Maintaining Valve)
Although the minimum pressure valve of a screw air compressor appears compact, it controls the whole unit. The maintenance method for the minimum pressure valve is provided below to ensure stable normal operation.
The minimum pressure valve consists of valve body, valve plug, adjusting nut, spring and sealing components. Its main functions are to build internal unit pressure to facilitate lubricating oil circulation and satisfy the operating pressure requirement of the unloading valve. In addition, it acts as a check valve to prevent compressed air inside the air receiver from flowing back into the air compressor during unloading operation.
The structure of the minimum pressure valve is relatively simple. Unscrew the nut between the valve plug and valve body to take out internal components. For small units where the valve plug is installed inside the valve body, remove the valve body cover to extract all internal parts.
Clean the minimum pressure valve following the cleaning procedure for unloading valves.
Assembly steps are omitted due to its simple structure. Note the installation direction of the U-ring if equipped. After full cleaning, set aside the minimum pressure valve ready for installation on the air compressor.
7. Cleaning of Oil Return Check Valve
The check valve is composed of valve body, steel ball, steel ball seat and spring. The oil-gas mixture compressed by the air compressor main unit undergoes primary separation inside the air-oil tank by centrifugal force. Since oil is heavier than air, most oil in the mixture falls into the oil tank under centrifugal force and flows back to the main unit under internal pressure for the next lubrication cycle. Compressed air containing trace oil passes through the air-oil separator for secondary separation. The lubricating oil separated by the air-oil separator accumulates at the bottom of the separator. To avoid carrying this oil away together with compressed air, an oil pipe is inserted into the separator bottom to guide recovered oil back to the main unit under internal pressure. An oil return check valve is fitted on this oil pipeline.
Its function is to smoothly return oil from the air-oil separator back to the main unit and prevent oil inside the main unit from flowing backward into the separator. Unscrew the joint on the valve body of the oil return check valve, then take out the spring, steel ball and steel ball seat.
Cleaning procedure for oil return check valve: Use cleaning agent to wash the valve body, spring, steel ball and steel ball seat. If an internal filter screen is fitted inside the check valve, clean it together with other components.
8. Cleaning of Thermostatic Valve for Screw Air Compressor
The thermostatic valve comprises valve body, valve plug, temperature sensing element and spring. It realizes constant temperature control. When the oil temperature measured by the temperature sensing element is lower than the actuation value (normally 71°C), lubricating oil flows directly from the air-oil tank back to the main unit. When the measured oil temperature exceeds the actuation value, the thimble of the temperature sensing element extends, pushing the valve plug to open the built-in bypass passage and divert lubricating oil into the cooler for cooling. The bypass opens wider as the detected temperature rises. Cooled lubricating oil then flows back to the main unit.
A side cover is fitted on the side of the thermostatic valve with threaded holes. Screw a suitable nut into the side cover, use a circlip plier to remove the retaining circlip of the side cover, then pull the installed nut with pliers to remove the side cover and all internal components. Clean all parts of the thermostatic valve following the cleaning method for unloading valves.
After all above components are cleaned and dried, commence assembly onto the air compressor. Upon completion of installation, recheck for omissions and collect all tools used during assembly.
1. Maintenance of Air Intake Filter Element
The air filter removes dust and contaminants from intake air. Clean filtered air enters the screw rotor compression chamber. The internal clearance of the screw machine only permits particles smaller than 15μm to pass through. If the air filter is blocked or damaged, massive particles larger than 15μm will circulate inside the unit. This will not only drastically shorten the service life of the oil filter and air-oil separator element, but also allow particles to enter the bearing cavity directly, accelerating bearing wear, widening rotor clearances, reducing compression efficiency, and even causing rotor seizure.
The air filter should preferably be maintained weekly. Unscrew the cover nut and take out the filter element. Blow dust particles outward from the inner cavity of the filter element using compressed air at 0.2–0.4 MPa. Wipe contaminants off the inner wall of the air filter housing with a clean rag. Reinstall the air filter, ensuring the sealing ring at the front end of the filter closely fits the inner end face of the filter housing. For diesel-driven screw compressors, maintenance of the diesel engine air filter shall be carried out simultaneously with the compressor air filter by adopting the same maintenance method.
Under normal operating conditions, replace the air filter every 1,000–1,500 operating hours. For severely dusty working sites such as mines, ceramic plants and cotton mills, replacement every 500 hours is recommended.
When cleaning or replacing the air filter, match all components properly and strictly prevent foreign objects from falling into the intake valve.
Regularly inspect the intake expansion hose for cracks or collapse, and check whether connections between the expansion hose, air filter and intake valve are loose or leaking. Repair or replace components immediately if defects are found.
2. Replacement of Oil Filter Element
The oil filter element shall be replaced after the new unit runs for the first 500 hours. Remove the oil filter by turning it counterclockwise with a special wrench. It is recommended to add screw compressor oil to the new filter before installation. Screw the filter back onto the filter base manually and tighten firmly.
It is advised to replace the oil filter every 1,500–2,000 hours. Replace the oil filter together with lubricating oil during oil change. Shorten the replacement cycle for operation in harsh environments.
Never use the oil filter beyond its service life. Severe filter blockage will cause the pressure differential to exceed the limit of the bypass valve. The bypass valve will automatically open, allowing large quantities of dirt and particles to enter the screw main unit together with lubricating oil and resulting in serious damage.
For diesel-driven screw compressors, replacement of the diesel engine oil filter and fuel filter shall comply with diesel engine maintenance requirements, and the replacement procedure is similar to that of the screw compressor oil filter.
3. Maintenance and Replacement of Air-Oil Separator Element
The air-oil separator separates screw lubricating oil from compressed air. Under normal operation, its service life is approximately 3,000 hours. However, oil quality and air filtration precision exert a great influence on its service life. Therefore, the maintenance and replacement cycle of the air filter must be shortened under harsh operating conditions, and installation of a pre-filter may be considered.
The air-oil separator element must be replaced upon expiry or when the pressure differential across it exceeds 0.12 MPa. Otherwise, motor overload or element rupture and oil carry-over will occur.
Replacement Procedure:
Disconnect all control pipe connectors mounted on the top cover of the air-oil tank. Pull out the oil return pipe extending into the tank from the top cover, and remove the fastening bolts of the air-oil tank top cover.
Remove the top cover and take out the air-oil separator element. Clear asbestos gaskets and contaminants adhering to the top cover.
Install the new air-oil separator element. Ensure the upper and lower asbestos gaskets are properly positioned and evenly compressed to prevent gasket blowout.
Refit the top cover, oil return pipe and all control pipes in original order, then check for leakage.
4. Maintenance and Replacement of Screw Compressor Lubricating Oil
The quality of screw compressor oil has a decisive influence on the performance of oil-injected screw compressors. High-quality lubricating oil features excellent oxidation stability, rapid separation performance, good anti-foaming property, high viscosity and outstanding anti-corrosion performance. Users must adopt genuine special screw compressor oil specified by the manufacturer.
Complete the first oil change after 500 operating hours of the new unit running-in period. Thereafter, replace lubricating oil every 2,000 hours. Replace the oil filter together with oil change. Shorten the replacement cycle for operation in harsh environments.
Oil Change Procedure:
Start the air compressor and run for 5 minutes to raise the oil temperature above 50°C and reduce oil viscosity.
Shut down the unit. When the internal pressure of the air-oil tank remains at 0.1 MPa, open the drain valve at the bottom of the air-oil tank and connect an oil storage tank. Open the drain valve slowly to avoid splashing of pressurized hot lubricating oil which may cause personal injury. Close the drain valve once oil drips slowly. Unscrew the oil filter and drain all residual lubricating oil inside pipelines, then install a new oil filter.
Remove the filler plug, inject new oil until the oil level falls within the scale range of the oil gauge. Tighten the filler plug and check for leakage.
Lubricating oil level must be inspected frequently during operation; replenish new oil promptly if the oil level is too low. Condensate must be drained regularly. Normally drain condensate once a week, and once every 2–3 days under high-temperature climate. After shutdown for more than 4 hours and with zero pressure inside the air-oil tank, open the drain valve to discharge condensate, and close the valve immediately once lubricating oil flows out.
Mixing different brands of lubricating oil is strictly prohibited. Never use lubricating oil beyond its service life. Degraded oil will lead to poor lubricity and lower flash point, easily triggering high-temperature shutdown and even spontaneous combustion of oil.
5. Maintenance of Cooler
The heat dissipation performance of the cooler directly affects the operating temperature of the air compressor. The plate-fin structure is prone to dust accumulation. Therefore, the cooler shall be blown with dry compressed air above 0.4 MPa from top to bottom every shift. For coolers of diesel-driven screw compressors arranged vertically, blow dry compressed air above 0.4 MPa from outside inward during maintenance. After blowing, clean all dust and particles inside the air guide hood to prevent the fan from blowing contaminants back into the cooler and causing blockage and high unit temperature. If the unit operates in harsh environments and the cooler surface is covered with oil dirt, clean the cooler thoroughly with carbon remover.
6. Cleaning of Minimum Pressure Valve (Pressure Maintaining Valve)
Although the minimum pressure valve of a screw air compressor appears compact, it controls the whole unit. The maintenance method for the minimum pressure valve is provided below to ensure stable normal operation.
The minimum pressure valve consists of valve body, valve plug, adjusting nut, spring and sealing components. Its main functions are to build internal unit pressure to facilitate lubricating oil circulation and satisfy the operating pressure requirement of the unloading valve. In addition, it acts as a check valve to prevent compressed air inside the air receiver from flowing back into the air compressor during unloading operation.
The structure of the minimum pressure valve is relatively simple. Unscrew the nut between the valve plug and valve body to take out internal components. For small units where the valve plug is installed inside the valve body, remove the valve body cover to extract all internal parts.
Clean the minimum pressure valve following the cleaning procedure for unloading valves.
Assembly steps are omitted due to its simple structure. Note the installation direction of the U-ring if equipped. After full cleaning, set aside the minimum pressure valve ready for installation on the air compressor.
7. Cleaning of Oil Return Check Valve
The check valve is composed of valve body, steel ball, steel ball seat and spring. The oil-gas mixture compressed by the air compressor main unit undergoes primary separation inside the air-oil tank by centrifugal force. Since oil is heavier than air, most oil in the mixture falls into the oil tank under centrifugal force and flows back to the main unit under internal pressure for the next lubrication cycle. Compressed air containing trace oil passes through the air-oil separator for secondary separation. The lubricating oil separated by the air-oil separator accumulates at the bottom of the separator. To avoid carrying this oil away together with compressed air, an oil pipe is inserted into the separator bottom to guide recovered oil back to the main unit under internal pressure. An oil return check valve is fitted on this oil pipeline.
Its function is to smoothly return oil from the air-oil separator back to the main unit and prevent oil inside the main unit from flowing backward into the separator. Unscrew the joint on the valve body of the oil return check valve, then take out the spring, steel ball and steel ball seat.
Cleaning procedure for oil return check valve: Use cleaning agent to wash the valve body, spring, steel ball and steel ball seat. If an internal filter screen is fitted inside the check valve, clean it together with other components.
8. Cleaning of Thermostatic Valve for Screw Air Compressor
The thermostatic valve comprises valve body, valve plug, temperature sensing element and spring. It realizes constant temperature control. When the oil temperature measured by the temperature sensing element is lower than the actuation value (normally 71°C), lubricating oil flows directly from the air-oil tank back to the main unit. When the measured oil temperature exceeds the actuation value, the thimble of the temperature sensing element extends, pushing the valve plug to open the built-in bypass passage and divert lubricating oil into the cooler for cooling. The bypass opens wider as the detected temperature rises. Cooled lubricating oil then flows back to the main unit.
A side cover is fitted on the side of the thermostatic valve with threaded holes. Screw a suitable nut into the side cover, use a circlip plier to remove the retaining circlip of the side cover, then pull the installed nut with pliers to remove the side cover and all internal components. Clean all parts of the thermostatic valve following the cleaning method for unloading valves.
After all above components are cleaned and dried, commence assembly onto the air compressor. Upon completion of installation, recheck for omissions and collect all tools used during assembly.
