Special gas compressors are a machine that compresses a gas to raise its pressure. These are a pump that transports gas from one location to another. Positive displacement compressors and dynamic compressors are the two different categories of gas compressors. The way that positive displacement compressors operate is by first trapping a volume of gas and then reducing it. The gas is now under more pressure as a result. An impeller is used by dynamic compressors to accelerate the gas. As a result, the gas flows into a smaller space, increasing the gas pressure. Special gas compressors come in various specifications.