A piston compressor is the oldest and most common type of industrial compressor. It uses the principle of displacement to increase the pressure of the enclosed volume of air. It is available in single-acting or double-acting, oil-lubricated or oil-free variants, with various numbers of cylinders in different configurations. With the exception of very small compressors having vertical cylinders, the V-configuration is the most common for small compressors. On double-acting, large compressors the L-configuration with a vertical low pressure cylinder and horizontal high pressure cylinder offers immense benefits and has become the most common design.