Counterpressure valves for filling cans with liquids under pressure such as carbonated beverages are disclosed. In a preferred embodiment, the present invention provides a filling valve in which the seal between the valve and a can is created by an O-ring seal disposed about a valve member. Preferably, two concentric, axially-spaced O-rings are used; a first O-ring serves as a guide, while the second, slightly larger O-ring creates a seal. Since the sealing O-ring may be moved axially along the can to permit the head space volume to expand, the need for a shift valve or similar relief valve is eliminated. Sealing valves utilizing radially expandable gaskets are also disclosed. In these embodiments, the gaskets expand radially under counterpressure to form a seal with the inner surface of the can.

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