A positive displacement compressor is a machine that compresses air by mechanically linkage, reducing its volume and increasing its pressure. The piston type is the oldest type of industrial compressor and is available in single-acting, double-acting and oil-free variations. A positive displacement compressor is a versatile tool for transferring a wide range of gases and liquids.
The simplest form of a positive displacement compressor is a bicycle pump. The air is drawn into a cylinder, where it is compressed by a moving piston. The piston is usually driven by a crankshaft or connecting rod, with a single or double action. When the air is compressed, a port opens, allowing fresh air to enter the system.
Rotary screw compressors use two meshed positive-displacement helical screws to compress air. They are commonly used for continuous operation in industrial and commercial settings. They are available in various sizes and can range from a few hundred to over one thousand horsepower. They are available in both stationary and portable versions, and are suitable for low to moderate pressure applications.
A positive displacement compressor has more than one stage and is able to compress a greater volume of air than a reciprocating one. It also produces a high pressure due to the physical pressure created by the air trapped between the moving components. In addition to this, it generates a magnetic field around the air. The Maxwell principle postulates that the displacement current is proportional to the change in the electric field.