A safety valve (1) for retaining liquid in an inverted, liquid-filled canister (5a) inserted within a receptacle (5) having an outlet, includes a valve (2) having a base (7) and a head (8), a retainer (4) attached to the receptacle, the retainer having a compartment (10) for receiving the valve base and at least one passage (11) for allowing the liquid to flow through at least one passage when the valve is disengaged, and a spring (3) positioned within the compartment, telescopically engaging the valve base, for providing a sealing force on the valve, wherein the valve head engages the outlet of the receptacle for retaining the liquid within the canister when the spring force exceeds the hydrostatic force of the liquid within the canister and the weight of the valve.