The structure and working principle of the minimum pressure valve assembly of the Atlas Copco screw compressor
Component composition: It usually includes the valve body, valve core (piston type or diaphragm type), spring, sealing elements, pressure gauge interface, and bypass valve and other auxiliary components.
Working mechanism: After the compressor starts, when the system pressure reaches the set value (generally 4-5 bar), the valve core overcomes the spring force and opens, allowing compressed air to enter the downstream system; when the compressor stops or the pressure is lower than the set value, the valve core is closed under the action of the spring force, preventing the gas flow from flowing back, while maintaining the pressure in the oil separator to ensure that the lubricating oil can be smoothly circulated (pushed into the main unit by the pressure difference). Core function
Establish minimum pressure: Ensure that there is always sufficient pressure in the oil separator to allow the lubricating oil to enter the lubrication system through the pressure difference, avoiding the host from grinding dry due to lack of oil.
Oil-gas separation guarantee: Adequate system pressure is a prerequisite for the efficient operation of the oil separator, ensuring that the oil mist can be fully condensed and separated.
Prevent backflow: When the machine is shut down, block the compressed air from the downstream pipeline from flowing back to the host to avoid rotor reversal or internal components being impacted.
Unloading protection: Some models integrate unloading functions, maintaining a low system pressure during unloading to reduce energy consumption.
Adaptation characteristics and parameters
Pressure setting: The set pressure varies slightly for different models. Common screw machines typically have 4-5 bar, while high-pressure models (such as the ZT series) may be higher (6-8 bar). The specific values should be referred to the equipment manual.
Flow matching: Design the diameter based on the exhaust volume of the compressor to ensure small pressure loss at full load (usually ≤ 0.2 bar). Common interface sizes are DN25-DN100 (flange or threaded connection).
Material selection: The valve body is mostly made of cast iron or cast steel, the valve core uses wear-resistant metal, and the sealing element is an oil-resistant rubber (NBR) or PTFE, suitable for the compressed air containing oil environment and a working temperature of 80-120℃.
Common faults and maintenance
Typical problems:
Valve core stuck: Due to oil contamination or impurities, the valve cannot be opened or closed normally, resulting in abnormal pressure (too high or unable to rise) and reduced exhaust volume.
Sealing failure: Aging and wear of the sealing element lead to leakage, with the system pressure dropping too quickly after shutdown.
Spring fatigue: Decreased elasticity causes the set pressure to decrease, affecting lubrication and separation effects.
Maintenance points:
Regularly (suggested every 8000-16000 hours) disassemble and clean, remove oil contamination and carbon deposits, and check the condition of the valve core and sealing element.
Replace aged sealing elements and worn springs to ensure the valve operates flexibly.
When installing, pay attention to the direction (the medium flow direction should be consistent with the valve body marking), and the sealing surface should be clean and flat.
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