A pressure regulating device for regulating pressure in a pressurized dispensing vessel, the device comprising a cartridge for storing pressurized fluid； the cartridge being sealed by a cap assembly having an expandable chamber and a flow passage for communicating fluid from the cartridge to the interior of the dispensing vessel； a closure member in the cap assembly to open and close the flow passage and an actuation means in the cap assembly to actuate the closure member, wherein the actuation means operates in response to expansion of the expandable chamber； and a one-way valve communicating the expandable chamber with the interior of the dispensing vessel via an aperture in the cap assembly, the valve having a resilient chamber seal in the expandable chamber extending across the aperture and restrained by chamber wall so to allow fluid to enter through the aperture and past the seal to charge the chamber to a predetermined pressure difference below the pressure in the dispensing vessel, and wherein expansion of the chamber occurs when the pressure in the dispensing vessel is lower than the pressure in the chamber.
