Today in 1988, US Patent EP 0262762 A1 was issued, an invention of James N. Dewes, James P. Hagan, and Jeffrey W. Gunn, for their “Valve For Beer Keg.” Here’s the Abstract:

A valve (10) for use with a beverage container is fully compatible with, and enhances the utility of, conventional automatic filling equipment. The valve is preferably of formed of plastic components and is therefore can form an economical throw-away unit in combination with a plastic keg. A cylindrical outer cage (18) includes a plurality of lengthwise apertures (20,22,24,26,). A transversely-oriented deflector plate is fixed to an inner cage (30) that is movable with respect to the outer cage. springs (38) urge the inner and outer chambers of the valve to closed positions. The valve is arranged so that both chambers are opened by the insertion of the filling head of a conventional automatic racking machine. The plate deflects a pressurized beverage input, lessening agitation and turbulence, whereby only minimal, if any, foam or head is generated during the filling process.