One of the important parts of an air compressor is the air-regulator unit. When you obtain a new air compressor that is regularly used in portable pneumatic or air tools, a filter-regulator unit is already installed on it. Typically, some cheap air compressors only mount an air-regulator without the filter to regulate the price, but in certain reputable companies like Ingersoll Rand Air Compressors. They are actually furnished with modular air filter-regulator unit as standard accessory.