Abstract: A pressure regulator-reducer in a first embodiment comprises two pistons (6, 7) provided with elastically deformable rings (9, 10) mounted in a bore (5) and held by a spring (12) bearing against a bulkhead packing (13) surrounding an outlet orifice (16). The double piston defines three chambers (19, 20, 21) respectively in communication with the product under pressure, the atmospheric pressure and the outlet. Facing the ring of the piston (6) on the outlet side there is provided a narrow longitudinal slot (24). A second pressure regulator-reducer is also disclosed that uses a slide mounted in a bore. The side has a piston and a spaced shoulder. The shoulder and piston controls flow along the bore to a dispensing orifice. A spring, mounted in the bore, controls the movement of the side in response to fluid flow.