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How Do Rotary Screw Air Compressors Work?

A rotary screw air compressor is a piece of machinery found in many industrial plants all around the world.

Many industrial processes require an on-demand supply of compressed air to operate various tools and equipment e.g. in manufacturing, packaging, and construction.

This article will review the operation and applications of rotary screw air compressors.

What Is a Rotary Screw Air Compressor?

A rotary screw or screw type compressor is like a reciprocating piston compressor but utilizes a rotary-type positive-displacement mechanism for air compression.

Unlike piston compressors, rotary screw gas compressors have a 100% duty cycle and supply a non-pulsating flow of compressed air – making these machines ideal for use in large industrial plants that require a continuous supply.

Components of an industrial screw compressor

A rotary type air compressor can be single screw or twin-screw. The less-common single screw compressor is mostly used in refrigeration applications and is not suitable for use in large plants with high demands for compressed air.

For the rest of this discourse, we’ll be focusing on twin-screw rotary air compressors.

A twin screw rotary air compressor consists of two meshing helical rotors (screws) enclosed in a metal housing. This is the part of the machine responsible for compression and is referred to as the ‘air end.’

Below are some key components of twin-screw air compressors:

  • Inlet port – The suction valve that introduces uncompressed air into the air end.
  • Outlet port – The supply valve for compressed air.
  • Rotors – The compression mechanism consisting of male and female screws. (Male screws usually have fewer lobes than the female and rotate faster).
  • Compression chamber – The section of the machine where compression occurs, also known as the air end.
  • Bearings – Bearings reduce friction between various parts of the machine ensuring quieter operation and maximum efficiency.
  • Air filters – In oil-flooded compressors, air filters are used to clean out excess moisture and oil residue left behind in the air end after compression.
  • Oil filters – Oil filters works alongside the oil separator to remove contaminants from the compressed air and also lubricate the machine parts.
  • Oil separator – The oil separator removes residual oil from the compressed air.

How Does a Rotary Screw Air Compressor Work?

rotary screw compressor

Uncompressed air is sucked into the air end via the inlet valve and flows through the meshing male and female screws. The positive-displacement action of the rotating screws compresses air by reducing its volume. Compressed air flows through an outlet port on the opposite side.

Rotary Screw Compressor Types

A rotary screw type air compressor can be oil-free or oil-flooded. The difference between the two is the presence of oil in the air end.

Oil-free vs. Oil-flooded Screw Compressor

An oil-flooded screw compressor has a thin film of oil between the male rotor (rotated by the engine or motor) and female rotor (driven by the male).

The oil serves as a hydraulic seal for the air end, transmits the mechanical energy that rotates the screws, and acts a coolant for the compressed air which would otherwise have a very high temperature. Thus, the machine compresses air more rapidly and runs cooler.

In the oil-free screw compressor, there is no oil seal between the male and female screws. Instead, it utilizes timing gears to synchronize screw rotation. The rotors do not make direct contact with each other.

However, since there is no oil seal in the air end, there will be some clearance between the rotors. Thus, it’s common to find a multi-stage gear system (multiple screw pairs) in oil-free machines which increases the pressure for faster compression.

Rotary Screw Compressor Uses

Rotary screw air compressors are extensively used in large scale industrial plants that require a constant supply of compressed gas. The compressed air is used to operate critical pieces of machinery such as rotary, control, and conveyor equipment.

Some important applications include:

Food Packaging

Compressed air from screw-type compressors supply compressed air required to operate machinery used for blow-molding to create product packaging, cleaning, and filling of product containers, vacuum sealing, conveying products along package lines, and product sorting. Nitrogen gas in food packaging is a common form of modified atmosphere packaging that may require compressed air.

Manufacturing

Screw-type air compressors are used to operate pneumatic, hydraulic, and mechanical equipment used in assembly lines of automated manufacturing plants.

Construction

Rotary screw air compressors are widely used in the construction industry to supply compressed air for operating heavy-duty tools like jackhammers, pneumatic pumps, riveting equipment, and sandblasters.

Different Sizes of Screw-Type Air Compressors

The ideal-sized screw air compressor required will depend on the compressed air requirements of a particular application. ‘Size’ here refers to the capacity of the machine.

Rotary screw air compressors are rated in Horsepower (HP), Pounds per square inch (PSI), and Standard Cubic Feet per Minute (SCFM). 5 – 500 HP compressors are popular in the industry, and capable of compressing air of up to 2500 SCFM.

Superior Air Compression with NiGen compressors

From air compression to gas generation, filtration, and storage, machines designed and fabricated by NiGen International are the subtle powerhouses behind a plethora of industrial processes across the country.

NiGen boasts a robust selection of high-performance air compressors available on a rental basis and suitable for the most demanding applications. Contact us today to learn more about our industrial air compressor rentals.