A pressure regulator, said pressure regulator comprising a housing containing a channel arranged to communicate a fluid from a fluid inlet to a fluid outlet, said channel comprising a valve seat housing, a valve seat and closure member with said closure member operable with the valve seat and valve seat housing to control flow through the channel; wherein the housing comprises a resilient diaphragm in fluid communication with the fluid and in physical communication with the closure member such that the diaphragm is operable to deform in response to a change in pressure of the fluid and such that deformation of the diaphragm causes the closure member to change position, and the section of the diaphragm not in fluid communication with the channel, is in fluid communication with the exterior of the regulator via a vent aperture and; wherein the closure member comprises an upstream valve element and downstream valve element, wherein the downstream valve element is a ridge operable with an aperture in the valve seat housing to at least partially control fluid flow, wherein said ridge of the closure member is partially or fully inside said aperture in the valve seat housing when the upstream valve element of the closure member is at the fully open position or between the fully open position and a predetermined partially open position with the valve seat, to provide a restriction to fluid flow but not to fully obstruct flow; characterised in that, in the event of fluid leakage flow above a predetermined magnitude through the diaphragm to the exterior of the regulator via the vent aperture, the maximum difference between the fluid outlet pressure and the pressure at exterior of regulator is limited to a proportion of the difference between the fluid inlet pressure and the pressure at the exterior of the regulator, the said proportion being substantially determined by a predetermined calculation using; the effective fluid metering area of the restriction defined by the path between the ridge of the downstream valve element of the closure member and the aperture in the valve seat housing when the ridge is fully or partially inside the said aperture and; the effective fluid metering area of the vent aperture. wherein the housing comprises a resilient diaphragm in fluid communication with the fluid and in physical communication with the closure member such that the diaphragm is operable to deform in response to a change in pressure of the fluid and such that deformation of the diaphragm causes the closure member to change position, and the section of the diaphragm not in fluid communication with the channel, is in fluid communication with the exterior of the regulator via a vent aperture and; wherein the closure member comprises an upstream valve element and downstream valve element, wherein the downstream valve element is a ridge operable with an aperture in the valve seat housing to at least partially control fluid flow, wherein said ridge of the closure member is partially or fully inside said aperture in the valve seat housing when the upstream valve element of the closure member is at the fully open position or between the fully open position and a predetermined partially open position with the valve seat, to provide a restriction to fluid flow but not to fully obstruct flow; characterised in that, in the event of fluid leakage flow above a predetermined magnitude through the diaphragm to the exterior of the regulator via the vent aperture, the maximum difference between the fluid outlet pressure and the pressure at exterior of regulator is limited to a proportion of the difference between the fluid inlet pressure and the pressure at the exterior of the regulator, the said proportion being substantially determined by a predetermined calculation using; the effective fluid metering area of the restriction defined by the path between the ridge of the downstream valve element of the closure member and the aperture in the valve seat housing when the ridge is fully or partially inside the said aperture and; the effective fluid metering area of the vent aperture. the effective fluid metering area of the restriction defined by the path between the ridge of the downstream valve element of the closure member and the aperture in the valve seat housing when the ridge is fully or partially inside the said aperture and; the effective fluid metering area of the vent aperture.