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The Rotary Screw Air Compressor

The rotary screw air compressor produces an ongoing movement to generate power.For certain heavy-duty industrial operations, or a facility that needs to keep running their compressor 24/7 365 days a year, a piston compressor is considered insufficient. In order to get the pressure intensity needed for complex pneumatic and other high-powered tools, you will need to consider buying a rotary screw air compressor.

In a rotary screw compressor, air is compressed with a meshing pair of rotors. As the screws move in rotation, fluids gets sucked in, compressed and ejected. 

So, how does an oil injected rotary screw compressor work?

AIR

The outside air is sucked in by the screw element (air-end) through the air inlet filter. The inlet filter makes sure that all the dust and dirt stays outside.

Load and unload control

Before the air enters the screw element, it passed the inlet valve or unloader valve. This valve opens and closes the air supply to the screw element.

When it’s open, the compressor is in ‘loaded’ condition:
When the valve is closed, is shuts off the air supply to the compressor element: the motor and screw element are turning, but the compressor is not sucking any air in and is not pumping any air to the system.

H&K PUMP

WHAT DOES THE screw compressor element DO?

When the inlet/unloader valve is open, the air enters the compressor screw element.
The screw element works like a pump and it compressed the air. During this process, oil is injected in the element. The oil is there to cool the air, as the air gets very hot during compression. 

Compressed air/oil mixture

This mixture leaves the screw element through a one-way valve. This valve makes sure that the oil cannot flow back into the compressor element through the exit pipe.

WHAT IS THE PURPOSE OF THE OIL SEPARATOR?

It's job is to basically separate the oil and the air through the separator tank. Most of the oil is separated from the compressed air by centrifugal force . The remaining oil is separated by the separator element which looks exactly like a big filter.


The air with oil flows through the separator element and separates the oil from the compressed air. The separated oil is collected at the bottom of the separator and is removed by the scavenge line. It sucks the collected oil back to the compressor element.

WHAT IS THE MINIMUM PRESSURE VALVE?

The minimum pressure valve is a spring-loaded valve that opens at a certain pressure, about 2.5 bar. The minimum pressure valve makes sure that there is always a minimum pressure inside the compressor

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The after cooler

The compressed air is still very hot, consequently the compressed air is now cooled by the after cooler before it leaves the compressor. The air temperature after the cooler is around 25 – 40 degrees Celsius.
Because of the cooling down of the air, a lot of water vapor has condensed against the inside of the after cooler. This water is carried with the compressed air towards the air outlet of the compressor.

Moisture trap

The condenstate trap (moisture trap) basically separates the water from the compressed air. The water is drained through a small hose.

Oil flow

The oil is cooled by the oil cooler. The amount of cooling is controlled by a thermostatic valve. If the oil is still cold, the oil cooler is completely by-passed. If the oil is very hot, all the oil is led through the oil cooler. 

The Oil filter

Finally, the oil flows through the oil filter. The oil filters removes all the dirt and dust that has collected in the oil.