Rotary Compressor Working, Advantages, and Disadvantages

What is a Rotary Compressor?

A rotary compressor is one of the most famous types of positive displacement compressors. A rotary compressor generates compressed air or gas through the rotary motion of the roller or blades. The roller or blades connect to the shaft of an electric motor.

Rotary Compressor

The rotary compressor has a very small clearance volume. Therefore, it has more volumetric efficiency than the reciprocating compressor.

In normal cases, the compressor and motor are compressed in one cylinder, and there is no vapor space between the casing and the compressor. So, these compressors have low weight. This compressor doesn’t have outlet and inlet valves like reciprocating compressors.

Construction of Rotary Compressor

The rotary compressor has a very simple construction. It has a compression cylinder, a roller, an inlet, and outlet ports. The roller rotates inside the cylinder. This roller plays a big role in air or gas compression.

As the roller rotates, it rubs against the inner wall of the cylinder. There is a space between the cylinder and the rotor. As the roller rotates, the gas is sucked from the environment and trapped between the cylinder and the rotor. This trapped gas is then gradually pressurized by reducing the space between the cylinder and the rotor.

Working of Rotary Compressor

The rotary compressor works on the displacement principle. This compressor has a gap between the cylinder and the roller. The roller is connected to an electric motor through a shaft. This motor uses to drive the roller.

Rotary Compressor working

The rotary compressor works in the following ways:

  1. First of all, the electric motor supplies rotary motion to the shaft, which further delivers this motion to the roller and rotates it.
  2. As the roller rotates, a gap generates between the cylinder and the roller. Due to the generation of this gap, a pressure difference generates, and the suction port opens.
  3. When the suction port opens, the fluid from the storage tank enters the produced gap between the roller and cylinder.
  4. After the suction process, the suction port closes, and fluid is trapped in the compression cylinder.
  5. The roller rotates in the cylinder and reduces the cylinder volume due to that fluid compression occurs.
  6. When the fluid is compressed up to a specific pressure level, the discharge port opens, and the compressed fluid is transferred to the desired area.

Read More: Difference between Reciprocating and Centrifugal Compressors

Types of Rotary Compressors

The rotary compressor has the following major types:

  1. Screw compressors
  2. Scroll compressor
  3. Vane Compressor
  4. Lobe Type Air Compressor

1) Rotary Screw Compressor

It is one of the most common types of rotary compressors. It uses multiple screws to compress the fluid.

The rotor or screw of the screw compressor has a special design. Mostly, the screw compressors have two helical screws (driver and driven screws). These screws rotate opposite to each other. The driver screw directly connects to the electric motor shaft. As it receives motion from the electric motor, it further rotates the driven gear.

When these screws rotate, a cavity generates between them. The cooling jackets are used to cover the rotors. Two shafts are put on the rotor and connected with the help of gears to transmit the movement of the shafts / the starting point of the compressor.

Read More: Screw Compressor Working and Types

2) Scroll Compressor

The scroll compressor works in the same way as the screw compressor. This compressor uses two spirals or scrolls to compress the fluid. One scroll is fixed, which guides the motion to the second scroll while the second scroll rotates on a small eccentric circle inside the cylinder.

Read More: Scroll Compressor working and type

3) Vane Compressor

The vane compressor is the most famous type of rotary compressor. The vane compressor has fixed housing with a rotating rotor disc which has slotted holes for attaching the slide plate.

With each rotation of the rotor, the disk also rotates, which allows the sliding plate to slide due to the eccentric inner surface of the housing. As the disk rotates away from the center, a large amount of gas is trapped. The sliding plates compress the trapped gas.

4) Rotary Lobe Compressor

This is one of the simplest types of compressors. This compressor doesn’t contain any complicated moving parts. This compressor contains two lobes connected to the drive shaft. The lobes displace at 90 degrees to one each other. So, when one lobe is horizontal, the other lobe is positioned at exactly 90 degrees (i.e., vertical).

Applications of Rotary Compressor

Rotary compressors are commonly used when a large amount of high-pressure fluid is needed. The rotary compressors are most commonly used for the following applications:

  1. They use high-power pneumatic instruments such as sandblasting jobs, pneumatic pumps, impact wrenches, and jackhammers.
  2. They are also used where the continuous flow of fluid is required, like in food packaging factories and automated manufacturing industries.

Advantages and disadvantages of rotary compressor

Advantages of Rotary Compressor

  • These types of compressors have light weight.
  • They have a compact design.
  • The rotary compressor has low moving parts than the reciprocating compressor.
  • They generate less noise and vibration.
  • This compressor has a very low clearance volume.
  • It has high volumetric efficiency.
  • This compressor works at high speed. Therefore, it has the capability to handle a high flow of fluid.
  • It has well-balanced mechanical parts.
  • It has a low maintenance cost.
  • It has a low initial cost.

Disadvantages of Rotary Compressor

  • It generates less output pressure per stage than the reciprocating compressor.
  • It doesn’t have flexibility in compression ratio and capacity.

 Difference between Reciprocating Compressor and Rotary Compressor

Rotary CompressorReciprocating Compressor
The rotary compressor uses a rotary roller to compress the fluidThe reciprocating compressor uses a reciprocating component such as a plunger or piston to compress the fluid.
This compressor requires low maintenance costs.It has a high maintenance cost.
The compression ratio and capacity of the rotary compressors are not flexible.It has flexibility in the compression ratio and capacity.
The moving parts of this compressor are more secure than the reciprocating compressor.The parts of the reciprocating compressor aren’t much secure.
It generates low noise and vibration.The reciprocating compressor generates more noise than the rotary compressor.
It has fewer parts. Therefore, it has small size and lightweight.It has many moving parts. It has a large size and high weight.
This compressor has very low clearance.It has a high clearance volume.
The screw compressor, lobe compressor, and vane compressor are examples of rotary compressors.The plunger compressor, piston compressor, and diaphragm compressor are the types of reciprocating compressors.

FAQ Section

What are the types of rotary compressors?

  1. Screw compressors
  2. Lobe type air compressor
  3. Scroll compressor
  4. Vane-type rotary compressor

When should you use a rotary compressor?

Rotary Compressors are most commonly used where large volumes of high-pressure fluid are required. They are most commonly used for large industrial applications, powerful pneumatic tools such as jackhammers, sandblasting jobs, and air pumps.

Which type of compressor is best?

A rotary vane mechanism has a simple design, is highly efficient, and has more durability t than a reciprocating compressor. It is the best compressor with better uptime, energy efficiency, and profitability. It has a long service life.

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