Does the water-cooled oil-free screw air compressor need drainage?

Water-cooled oil-free screw air compressor needs drainage however, its drainage requirements are different from those of oil models, and it needs to be comprehensively judged in combination with the overall design of the compressed air treatment system. The following is a specific analysis:

drainage principle of 1. water-cooled oil-free screw air compressor

1. moisture source for compression process
   • moisture content of air itself: The water vapor contained in the atmosphere reaches a saturated state due to the increase in temperature and pressure during the compression process, and part of the water vapor condenses into liquid water.
   • Effect of cooling system: The water-cooled model takes away the heat of compression through the cooling water. If the cooling water temperature is low or the flow rate is too large, it may aggravate the temperature drop of the compressed air, resulting in more water vapor condensation.
2. Particularity of oil-free models
   • no lubricating oil involved: In the traditional oil air compressor, the lubricating oil can absorb part of the water and discharge with the oil circuit, while the oil-free type does not have this mechanism, and the water needs to be discharged through other channels.
   • Compressed air temperature: The compressed air temperature of oil-free models is usually higher (due to oil-free cooling), but condensate may still be generated after cooling by the aftercooler.

Reasons and Scenarios of 2. Drainage

1. condensate after aftercooler
   • after the compressed air is cooled by the aftercooler (usually water-cooled or air-cooled), the temperature drops below the dew point, and the water vapor condenses into liquid water, which needs to be discharged through the drain valve.
   • If not drained: Condensate will enter the pipeline with the compressed air, resulting in:
     • pipeline corrosion (especially carbon steel pipes);
     • damage of pneumatic equipment (such as pneumatic tools and spray guns);
     • product quality problems (e. g. water stains on sprayed surfaces).
2. Accumulation of water in gas tank
   • the air storage tank is a buffer and sedimentation device for compressed air. Condensate will accumulate here and need to be discharged regularly through the bottom drain valve.
   • If not drained: The volume of the gas storage tank is reduced, which affects the stability of the gas supply; long-term water accumulation may cause corrosion of the tank.

3. Drainage Methods and Precautions

1. automatic drain valve
   • it is installed in key positions such as after-cooler and air storage tank, and the drainage is controlled by float ball or solenoid valve without manual operation.
   • Maintenance Points: Regularly check whether the drain valve is blocked or malfunctioning to avoid water accumulation due to poor drainage.
2. Manual drainage
   • suitable for small systems or as a supplement to automatic drain valves, which need to be manually opened regularly.
   • Operational recommendations: Set the drainage frequency according to the air consumption and ambient humidity (e. g. once per shift).
3. The role of the dryer
   • if the system is equipped with refrigeration or adsorption dryer, it can further reduce the dew point of compressed air and reduce the displacement.
   • But note that: Drainage is still needed before the dryer to prevent condensed water from entering the dryer to affect performance.

Special considerations for 4. water-cooled oil-free models

1. influence of cooling water quality
   • if the cooling water contains impurities or the hardness is too high, it may scale in the after-cooler, reduce the heat exchange efficiency, indirectly lead to the increase of compressed air temperature, reduce the generation of condensed water.
   • Recommendations: Use softened water or clean the cooler regularly to ensure the cooling effect.
2. Ambient temperature and humidity
   • high humidity environment (such as coastal areas), compressed air moisture content is higher, the drainage demand increases.
   • Countermeasures: Increase the number of drain valves or choose automatic drain valves with stronger drainage capacity.

5. summary and suggestions

• must be drained: The water-cooled oil-free screw air compressor needs to discharge the condensed water regularly through the drain valve at the position of the after cooler and the air storage tank to protect the system and the gas equipment.
• Optimization recommendations:
  • installation of automatic drain valve and regular maintenance;
  • equipped with dryer to reduce dew point;
  • adjust the drainage frequency according to the ambient humidity;
  • regularly check the compressed air pipeline and gas tank for corrosion.