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How Does a Rotary Screw Air Compressor Work?

Air compressors are common pieces of equipment at industrial facilities. The reason for this is simple; pressurized air is required to carry out a wide range of industrial processes. This article explores the working principle of rotary screw air compressors as well as the various types, benefits, and applications.

What is a Rotary Screw Air Compressor?

Rotary screw air compressors use a rotary positive displacement mechanism comprised of helical gears (screws) to compress air by reducing the volume of a chamber. Its mode of operation is somewhat like other compressor types, such as reciprocating piston and centrifugal compressors.

The main difference between a rotary screw air compressor vs. reciprocating and centrifugal air compressors is that they deliver a constant (non-pulsating) stream of compressed air and are 100% duty cycle machines.

Single-screw vs. Twin-screw Compressor

Rotary screw compressors fall into two categories depending on the design: single-screw and twin-screw.

  • Single screw air compressors (AKA ported compressors) consist of a single main screw which meshes with two mating gate rotors within a metal housing.
  • Twin-screw compressors contain two helical screws (one called “male” and the other “female”) that mesh with each other to compress air.

Oil-free vs. Oil-injected Compressors

To further categorize screw air compressors, there are oil-free and oil-injected types. Let’s take a closer look at these variants below:

Oil-injected (aka oil-flooded) screw compressors contain a lubricant (oil) in the compression chamber that lowers friction between the moving parts. However, the oil doesn’t only provide lubrication; it also acts as a coolant to lower the temperature of compressed air in the chamber and prevents leakage by serving as a hydraulic seal. Oil-free compressors do not contain oil in the compression chamber. Rather, they use a set of timing gears for the rotation where the mating screws do not directly contact each other.

Oil-flooded compressors achieve higher psig than oil-free types and run cooler due to the presence of oil in the air end which serves as a coolant. However, oil encountering processed air can cause contamination, making oil-flooded compressors unsuitable for industrial processes where a high degree of purity is required.

Oil-free screw compressors generally have lower psig than oil-injected types but keep compressed air free of contamination — a highly desirable quality in food-grade and pharmaceutical applications.

rotary screw compressor

How Does a Rotary Screw Air Compressor Work?

The operating principle of screw compressors is that the pressure of air in an enclosed space increases as the volume decreases. Uncompressed air is drawn into the compressor via the inlet valve. As it flows through the compression chamber, positive displacement action of the meshing screws pressurizes the air by rapidly reducing the volume. A series of filters separate unwanted moisture and residue from the compressed air exits the machine from the outlet.

The Main Components of Industrial Screw Air Compressors

The main components of screw-type air compressors include the following:

  • Inlet Valve – The suction valve that introduces dry air into the combustion chamber.
  • Outlet Valve – The valve that supplies compressed air to a system or process.
  • Compression Chamber – Where air compression occurs; also called an “air-end.”
  • Air Filter – Present in oil-injected compressors, air filters separate moisture and oil residue from the compressed air to produce dry air at the outlet valve.
  • Oil Filter – Oil filters purify oil in the system to prevent contaminants and unwanted build-up of residue. They also provide lubrication to machine parts for smooth operation.
  • Oil Separator – Oil separators help to remove residual oil/grease from compressed air.
  • Rotors/Rollers – The main compression mechanism which consists of mating screws with multiple lobes.
  • Bearings – Bearings help to minimize the force of friction between the meshing screws, ensuring more durable operation and greater efficiency.

Applications of Rotary Screw Compressors

Many industries require a reliable stream of compressed air for their operations, making rotary screw air compressors the ideal choice. The following are some industries that use them:

Oil & Gas

In the oil and gas industry, screw-type air compressors are used for gas lift (secondary oil recovery), where high-pressure gas is injected into the surrounding formation to ramp up the production of hydrocarbons. Other applications include pipeline maintenance services, equipment purging, and gas pipeline pigging.

Manufacturing

In manufacturing facilities such as automobile assembly, pharmaceutical, and chemical plants, operators use screw air compressors to operate compression-powered tools such as pneumatic drills and hydraulic tools. Other applications include equipment cleaning and general maintenance.

Food Packaging

In food manufacturing plants, screw-type compressors provide compressed air to operate blow molding machines for food packaging. They are also used in gas flushing food packaging, product sorting, and shaping. Oil-free screw air compressors are preferable for food-grade applications.

Construction

In the construction industry, rotary screw compressors provide high-pressure air for operating heavy-duty tools such as jack-hammers, pneumatic tools, and sandblasters. Compressed air is also required in slurry blowing, blowing of mud/wash holes, and building piling operations.

Benefits of Rotary Screw Compressors

Rotary screw air compressors offer the following benefits to industrial operators:

  • Continuous operation (full duty cycle)
  • Easy to maintain
  • Quieter operation compared to other compressor types
  • Help to conserve energy
  • Can be operated under a wide range of temperatures
  • Safe and convenient

Contact NiGen for Reliable Air Compression Solutions!

NiGen provides on-site nitrogen generation and air compression solutions to a host of industries including oil and gas, manufacturing, food packaging, and construction. Our portable, diesel-powered rotary screw compressors rated from 100-500 PSIG (flow rates: 400-1500 CFM) enable our clients to carry out their operations safely, reliably, and efficiently.

Contact the NiGen team online today for more information on NiGen products and services.