Abstract: A pressure regulator having a valve cartridge adapted to be removably held within its housing, said cartridge having a frame carrying and positioning a valve seat, a valve member, a valve stem, and a spring. The valve cartridge ensures correct spacing between the valve member and the valve seat. Difficulties in pressure regulation may be quickly rectified and pressure flow characteristics may be altered by removing and replacing the valve cartridge. Another aspect of the invention discloses a multiple pressure regulator comprising: a housing adapted to removably house two valve cartridges; an inlet opening into the housing; an outlet opening from the housing; and two valve cartridges adapted to be removably held within the housing. Each of said cartridges similar to those described above.