A pressure regulator valve adapted to be secured within a container housing a beverage to be dispensed through the aid of pressure within the headspace (11) above the beverage, the regulator valve includes a housing (16) containing a piston (26) having one surface exposed continuously to the pressure in the headspace and the other surface being engaged by a spring (44), a source of pressurized gas (14) such as carbon dioxide is secured to the housing and includes a valve (60) which is activated by the piston which moves responsive to a differential between the spring force and the headspace pressure to open the valve (60) when the headspace pressure falls below a predetermined level to insert the carbon dioxide into the headspace to maintain the headspace pressure sufficient to dispense the beverage.