A rotary compressor compresses air using a screw configuration and positive displacement. It can be cooled with oil, air or water and can be single stage or used in series. Oil-cooled compressors use interlocking screws to gradually force air towards the narrower end and oil is cooled before being returned to the compression chamber. Oil-free compressors are preferred for industries such as food processing and pharmaceutical manufacturing. The motor can be connected directly or belt driven and they come in sizes ranging from a few to several hundred horsepower.
A rotary compressor is a machine that compresses ambient air using a rotary motion. The incoming air is gradually compressed using a screw configuration and positive displacement. The unit can be cooled with oil, air or water. Rotary compressors can be single stage or used in series to compress air in two stages.
The function of an oil-cooled rotary screw compressor begins with the introduction of air into a central oil-filled chamber. Most often, two interlocking rotating screws, wider on one side and narrower on the other, rotate in opposite directions to gradually force the air towards the narrower end. As the rotation continues, it creates a vacuum at the intake point, drawing more air into the system. Some drives can be configured with a single screw.
The compressed air exits into a separator which segregates the oil so it can be cooled and directs the clean air to an outlet pipe. Compressed air can continue in service lines connected to the industrial process or in an air tank that stores it for future needs. The oil is cooled with air or water before being returned to the compression chamber. This type of unit is also called wet rotary screw compressor.
For applications where true oil-free air is required, a rotary compressor that uses no oil in the compression chamber is preferred. Oil-free air is commonly specified in industries such as food processing and pharmaceutical manufacturing. These units can be air or water cooled and can also be called dry screw rotary compressors.
When the required pressure is relatively low, the desired level of compression can be achieved in a single pass. Otherwise, the partially compressed air leaving the first chamber of the rotary compressor can be fed into another unit connected in series. The air is further compressed in the second unit to reach the desired pressure level.
The volumetric aspect of the rotary compressor refers to its production of a fixed volume of air at a specific pressure. Rotary screw compressors are designed to run continuously. The limited number of moving parts allows them to be reliable and easy to maintain.
The motor that powers a rotary compressor can be connected directly to the compression chamber or it can be belt driven. Stationary units are often powered by an electric motor, but portable units used for road construction or repair can also run on gasoline or diesel. Rotary screw compressors come in sizes ranging from a few horsepower to several hundred horsepower.
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