Subcooling may also be produced by superheating the gas leaving the evaporator and heading to the gas compressor. These systems withdraw heat from the liquid line and heat up the gas compressor's suction line. This is a very common solution to insure that gas reaches the compressor and liquid reaches the valve. It also allows maximum heat exchanger use as minimizes the portion of the heat exchangers used to change the temperature of the fluid, and maximizes the volume in which the refrigerant changes its phase (phenomena involving much more heat flow, the base principle of vapor-compression refrigeration).