A compressor is an automatic device that increases the strain of a gas by reducing its measure. An air compressor is an express variety of gas compressors. Compressors are similar to pumps. Both increase fluid pressure and can transport fluid through the pipe. Since the oil can be compressed, the compressor also reduces the oil volume. The fluid is also incompressible. Some can be compressed, but the main role of the pump is to supply and transport the fluid.