1. Cleaning the Unloading/Intake Valve
If the intake valve is heavily soiled, use a fresh cleaning agent. During the cleaning process, clean the cleaner parts first and the dirtier parts last to avoid cross-contamination or corrosion that could shorten the components' service life. Parts washed with water should be placed in a clean area to dry to prevent rusting, particularly on iron-based components.
When cleaning the valve plate and the corresponding valve body surface, pay close attention to surface flatness; clean or replace parts as necessary. Failure to do so may result in a "start-under-load" issue (where a large screw air compressor fails to start because it is under load).
2. Cleaning the Minimum Pressure Valve (Pressure Maintenance Valve)
Although the minimum pressure valve in a screw air compressor is small, it plays a critical role in controlling the entire machine. To ensure proper operation under normal conditions, the maintenance method for the minimum pressure valve is outlined below.
The minimum pressure valve consists of a valve body, valve core, adjusting nut, spring, and sealing elements. Its primary functions include establishing internal unit pressure, facilitating lubricating oil circulation, and meeting the operating pressure requirements for other components.
Additionally, the minimum pressure valve acts as a check valve, preventing compressed air from the air tank from flowing back into the compressor when the unit is in an unloaded state.
The structure of the minimum pressure valve is very simple. Unscrew the nut connecting the valve core and body to remove the internal components; for smaller units, the valve core fits inside the body, and all internal parts can be removed by taking off the valve body cover.
The minimum pressure valve can be cleaned using the same method as the unloading/intake valve.
Given the simple structure, the assembly process is not described step-by-step here; however, if a U-ring is present, pay close attention to its orientation. Once the cleaning process is complete, reinstall the valve into the air compressor.
3. Cleaning the Oil Return Check Valve
The check valve consists of a valve body, a steel ball, a ball seat, and a spring. The oil-air mixture compressed by the air compressor's main unit is first separated within the oil tank using centrifugal force. Since oil is heavier than air, the majority of the oil within the oil-air mixture drops into the oil reservoir due to centrifugal force. Driven by internal pressure, this oil returns to the main unit to complete the lubrication cycle, while the compressed air—still containing a small amount of residual oil—undergoes further separation via the oil-air separator. The oil separated at this stage collects at the bottom of the separator. To prevent this oil from being carried away by the compressed air, the unit is designed with a return line extending to the bottom of the separator. Internal pressure forces this oil directly back to the main unit for lubrication; this line is equipped with a one-way valve known as the oil return check valve.
Its function is to ensure the smooth return of oil from the separator to the main unit while preventing backflow from the main unit into the separator. The valve is connected to the valve body; by loosening the body, one can remove the spring, steel ball, and ball seat.
Cleaning the oil return check valve: Use a cleaning agent to wash the valve body, spring, steel ball, and ball seat. If the valve contains a filter, clean that as well.
4. Cleaning the Temperature Control Valve
The temperature control valve consists of a valve body, valve core, temperature-sensing element, and spring. It regulates the temperature: when the oil temperature sensed by the element is below the operating threshold (typically 71°C), the lubricating oil returns directly from the oil-air reservoir to the main unit. When the sensed temperature exceeds the threshold, the sensing element activates a bypass valve; this directs the lubricating oil into the cooler (the higher the temperature, the wider the bypass valve opens), and the cooled oil then returns to the main unit.
To service the temperature control valve, locate the screw hole on the valve cover and screw in a suitable nut. Use a snap-ring plier to remove the retaining spring holding the cover in place, then pull on the nut to extract the cover and all internal components. Clean all parts of the temperature control valve using the same method applied to the pressure-reducing valve. After cleaning and drying, all the aforementioned components should be installed on the air compressor. Once installation is complete, perform a final check to ensure nothing has been overlooked, and clear away any tools or other items used during the process.