|The piston compressor is the oldest and most common of all compressors. It is available as single or double acting, oil lubricated or oil free with a different number of cylinders in different configurations. With the exception of really small compressors with vertical cylinders, the V configuration is the most common for small compressors. On double acting, large compressors the L-type with vertical low pressure cylinder and horizontal high pressure cylinder, offers immense benefits and is why this is the most common design. Oil lubricated compressors normally work with splash lubrication or pressure lubrication. Most compressors have self-acting valves. A self-acting valve opens and closes through pressure differences on respective sides of the valve disk.