SS304 Water Injected Oil Free Screw Air Compressor for Food & Pharmaceutical Industries

Water injected screw compressor is an oil free screw air compressor. It uses water as a lubricant. We are oil free screw compressor manufacturer. Because of water, there is 100% no oil vapors in compressed air. So it has wid applications for sanitary industries. For example, we usually use it for food and pharmaceutical industries.

Compared to normal oilless air compressor, it has many advantages. For instance, it has low noise. Besides, the discharge temperature is not high.

1. Technical paramters of oil free screw air compressor

2. Features of water injected screw compressor

(1) High efficiency

Lubricating water can absorb a lot of the heat of compression. So it improves compression efficiency. Besides, water can achieve air tightness. Thus, the efficiency of oil free screw compressor is high. It’s better than general dry screw compressors.

In addition, the specific heat of water is large. The working process is similar to isothermal compression. Theoretically there is no clearance volume. The compression chamber temperature can be lowered to close to the intake temperature. So it can reduce the work load of refrigerated air dryer.

(2) Low noise

The motor is directly connected with the screw. So there is no intermediate transmission gear. In addition, lubricant water can also reduce the noise caused by high-frequency compression.

Moreover, the oilless screw compressor has a superior power balance system. It can effectively restrain the vibration source.

(3) Oil free compressed air

Water injected compressor is common oil free screw air compressor. It doesn’t use the lubricant oil. So compressed air is 100% free of any oil.

Furthermore, the drained water is also oil-free. So no need special treatment. It meets environmental requirements.

3. Why choose our oilless screw compressor? (1) Long lifetime full 304 stainless steel single-screw airend

Oil-free airend adopts PEEK rotor. The rotor and other components are all 304 stainless steel. So ensure that the air oil content is grade 0. Our airend production process comes from Japan. Besides, we use original SKF bearings.

Compression volume ratio of our oil free screw air compressor ≥ 95%. The design service life is 15 years. It can run continuously 24 hours a day. Moreover, the structure is good. Thus the vibration is small.

There are two star wheels on both sides of the screw. So water injected screw compressor has no unbalanced inertial force. And the axial force and radial force on the screw also cancel each other out.

(2) Completely oil-free air quality

Oil free screw compressor replaces oil with water. So there are 4 major benefits. That is, lubrication, cooling, sealing and noise reduction. Provide high quality 100% oil-free air. No pollution. The discharged water also does not need special treatment.

It is an ideal isothermal compression due to the action of water. Compared with dry oil free compressor, the air volume increases by 15%.

(3) Superior electrical control system

Each air compressor has a microcomputer control system. Moreover, it’s with self-diagnosis and protection functions. The panel can display the actual operation of water injected screw compressor.

If compressor fails, the system will respond accordingly. So the user can replace parts in time. With 485 interface, it has remote control. Therefore, it guarantees safe operation 24 hours a day.

(4) Energy saving permanent magnet variable frequency motor

40,000 hours working without failure. Free maintenance. High starting torque. Direct drive.

(5) 304 stainless steel air and water separation tank

The separation tank and piping also use the SS304. So there will be no corrosion.

(6) Pure copper radiator

Air-cooled oil free screw air compressor uses the copper radiator. So the heat dissipation is stable and efficient. And it is with a silent fan.

(7) Power-saving air capacity adjustment

When the air consumption decreases, the system pressure starts to increase. The controller receives the signal. It begins to gradually reduce the opening of the intake valve. At this time, the air flow volume of oil free screw air compressor will also decrease. Of course, the motor current will also drop.

Conversely, when the gas consumption increases, the system pressure begins to drop. The opening of the intake valve will increase. At this time, the air flow of water injected screw compressor will also increase.

4. How does water injected oil free rotary screw air compressor works?

Its working principle is different from that of dry oil-free air compressors. Water injected compressor has only one screw.

The screw and the two star wheels form a meshing pair. Usually there are six grooves on the screw. Each of the star gear teeth will mesh with it. The screw groove has upper and lower spaces. Each realizes the working process of the compressor. Oil free screw compressor generate pressure. During compression, there will inject lubricating water into compressor chamber.

When working, there is pure water spray cooling between the rotors. Thereby cleaning the air. At the same time, the rotor and pure water will form a good water film seal. Make the system efficiency more than 95%. Therefore, it can realize full energy saving.

The airend compresses the water-air mixture. Then enter the stainless steel water air separator. Mechanically separate them into compressed air and pure water. The system temperature is below 45℃. So the water content of compressed air is less than 80g/m³.

Compressed air will be on top of the separator. They pass through the minimum pressure valve and into the vent. Then will be discharged. Purified water is at the bottom of the separator. The filter will removal impurities in the water. After cooling, the water enters water injected screw compressor again. So it starts a second compression cycle. The oil-free screw air compressor can realize automatic water exchange. Therefore, it reduces labor intensity.

5. Water injected oil-free screw compressor maintenance

① When it needs to stop for a long time, check whether the machine circuit is normal. At the same time, drain the lubricating water in the system. Also close all openings of the oilless screw air compressor. In order to prevent moisture, dust intrusion and rust.

② The water injected screw compressor is not used for some time. When restarting the machine, add lubricant water to the separator first. Add until the middle water level. Then open the compressor airend. Manually add purified water to the middle level of airend. In addition, manually rotate air compressor several times. Prevent the airend from burning due to lack of water when startup.

③ When the temperature is lower than 0℃, should stop oil free rotary screw air compressor. And drain the water in the system. Otherwise, if it freezes, it will damage the airend.

④ Compressor filters maintenance

First time maintenance: exchange the air filter and water filter when 200~800 hours.

Regular maintenance: replace the filters each 2000~3000 hours.

Airend maintenance: each two year.

6. How to choose the water injected screw air compressor?

(1) Determine the basic parameters of the air compressor

The power of our oilless screw air compressors is generally 7.5KW to 250KW. The air flow is 1.0m³/min to 40.0m³/min @8 bar. Also, it is important to confirm the pressure.

Regular normal pressures are 8 bar and 10 bar. But we can also customize low pressure oil free screw air compressor. That is, 3 bar air compressor. High pressure oil-free screw compressors are also avaiable. I.E. 16~25 bar, 30~40 bar.

(2) VSD or fixed speed drive

This depends on whether the air consumption of the customer varies greatly. If the change is large, the VSD water-lubricated air compressor can save more electricity. On the contrary, choose the fixed speed air compressor.

(3) Select the dryer at the back end

Oil-free screw compressor is mainly used for food and pharmaceutical, and medical industries. There is no oil in the compressed air. But there will be water. And these industries have very high dew point requirements. That is, the water content in the compressed air should be very low. Therefore, there must be air-treatment equipment. Besides, generally need a refrigerant dryer + desiccant dryer. Only in this way it can reach -40°C or even -70°C dew point.

In addition, there is one important thing. These industries often require stainless steel. So the dryers should also be SS304 material.

7. Oil free rotary screw air compressor vs oil injected screw compressor (1) Higher compressed air quality

Firstly, oilless screw air compressors produce 100% oil-free air. This advantage is obvious. Another point cannot be ignored. The temperature of the water-lubricated air compressor system can reach 45°C. This is lower than that of oil-injected screw compressor. So the air moisture content will also be lower.

So cleaner air is better for the dryer behind. It can reduce the working load of the dryers. Increase the water removal performance. Also reduce the corrosion to the refrigeration dryer pipeline. In addition, it can also increase the service life of desiccant dryer adsorbent.

(2) More energy saving

This is because of lower air loss. For the latter, it needs to remove the oil in the air. So need to add the corresponding filter. Eventually it will increase pressure loss.

But we must meet the final air pressure. Therefore, the discharge pressure of the latter must be higher than that of an oil-free screw air compressor. The exhaust pressure of the oilless screw compressor is 1.5 bar lower than the latter. The energy consumption is 10% lower. Therefore, the electricity bill of the oil-free compressor is lower.

(3) Lower maintenance cost

8. Water lubricated oil-free screw compressor VS dry oil-free air compressor

(1) Compressor airend structures are different

The water injected screw compressor airend has a simple structure. It is single screw and single stage compression. However, dry oil-free compressor airend is more complex. It is two-stage compression.

In addition, the latter airend has gaps. Thus the efficiency is low. However, the former has a water seal. So it’s efficient.

Also, dry oil-free compressor require a gearbox to increase speed. Therefore, the mechanical loss is large. But, water-lubricated air compressors are directly connected to the motor. Therefore, the mechanical loss is small.

Therefore, dry oil-free air compressors consume more energy. The airend structure is complex. Besides, maintenance is expensive.

(2) Noise and temperature are different

Water lubricated oil-free screw compressor has lower noise. It is 10 decibels lower than the dry type. Besides, the former exhaust temperature does not exceed 50℃. The discharge temp. of dry oil-free compressor is usually 200℃. So the dryer behind the former can be an ordinary dryer. But the dryer behind the latter can only be a compression of heat desiccant dryer.

9. Water injected vs scroll type oil-free air compressor

(1) Working principles are different

The oil-free water-lubricated air compressor is a single screw. The work flow is mainly completed by the screw and the star wheel.

The scroll air compressor has two scrolls. That is, dynamic and static. They mesh with each other. Besides, form several compression cavities. And the air is gradually compressed. Finally, the air is discharged from the axial hole.

(2) Air capacity is different

The air flow of former is fixed. But oil free scroll compressor is different. It can set different airend quantity according to the air capacity requirements. Of course, under the same power, the air capacity of the former is larger.

10. FAQ (1) Oil-free water injected air compressor uses water for lubricating. So is the water content in the air larger than other air compressors?

Water injected screw compressor is isothermal compression. The discharge temperature is around 45℃. The production of gaseous water is conditional. That is, need heat up to above 65 ℃. Therefore, there is also no vaporous water.

Generally the compressed air has no liquid water. The determining factor of its water content comes from the water-air separation system. In summary, there is no gaseous water in the compressor. Liquid water can also be completely separated.

The water content of our oil free screw compressor is 15% lower than that of ambient air. It’s lower water content than oil injected screw type. Besides, every oil-free machine will be tested by a professional dew point meter. The water content is qualified before leaving the factory.

(2) Is the oil-free water-lubricated airend like a natural “bacteria ship”? Is the exhaust air high in bacteria?

There are preconditions for the growth of bacteria in water. That is, stay in a sealed space for more than 72 hours. But the water in oil free screw air compressor is always circulating.

Part of water is automatically drained every 200 hours. At the same time, it will add some water. Water can wash away germs and dust. Moreover, the filter can also remove some bacteria. Therefore, compressed air contains very few bacteria.

In addition, the intake valve and pressure valve are all sealed. The water inside cannot be contact with the air at all. So there are no conditions that could breed bacteria. Of course, sometimes we have extreme air quality requirements. In this case, it can add a anti-bacteria filter.

(3) Will oil-free water injected screw compressor consume a lot of water?

You don’t need to keep adding water to the air compressor. It’s like a washing machine. There is a water level sensor inside. It can drain and supply water automatically.

For example, there is a 110KW water injected screw compressor. The amount of lubricant water is 130 liters. A year is calculated as 8000 hours. It needs to exchange 6000 liters of water. That is, 6 tons of water. Even if doubled, that is 12 tons. 5 CNY per ton of water. The annual water bill is only 60 CNY. So it saves water and money.

(4) Does water lubricate well? Does the air compressor have a long service life?

Firstly, water has several roles in oil free screw air compressor. That is, cooling, sealing and lubricating. Secondly, we usually use SUS304 material in the airend and system of water injected screw compressor. Its stability has been tested by the market.

In terms of air quality, it’s pure oil-free. Energy saving is high. So prove its advanced technical quality.

In addition, its structure is perfect. This results in its fully symmetrical balanced compression. It vibrates less and noise is lower. Bearing service life can reach 70,000 to 100,000 hours. So it will not affect the normal use of the whole compressor. The design life of our water lubricated screw compressor is 25 years. And it can run continuously 24 hours a day.