A pressure regulating or pressure relief device comprises an inlet and an outlet chamber with an outlet. The inlet is in fluid communication with the outlet chamber. A valve seat is located between the inlet and the outlet. A valve member is biased to seal against the valve seat, and displaces from the valve seat by an inlet pressure at the inlet increasing above a pressure threshold to allow a flow of gases from the inlet to the outlet via the outlet chamber. The flow of gases through the outlet causes an outlet pressure in the outlet chamber to act on the valve member together with the inlet pressure to displace the valve member from the valve seat.