Positive displacement compressors are machines that increase the pressure of gases by trapping a fixed volume and then reducing that volume. They work by mechanically compressing the gas, which results in a rise in pressure. Common types include reciprocating compressors and rotary screw compressors, each suited for different applications. These compressors are widely used in various industries, including manufacturing and HVAC systems, due to their efficiency and reliability. They can handle a range of gases and are often preferred for applications requiring high pressure and consistent flow rates.