Interlock for cryogenic liquid off-loading systems

A cryogenic system that off-loads cryogenic liquid from a delivery vehicle and pumps the cryogenic liquid to a storage tank includes an interlock that enables the pneumatic valves which control the flow of the cryogen. The interlock includes a pneumatic relay, a pneumatic line and a pressure sensing line. The pneumatic line transfers pressurized air to the pneumatic relay while the pressure sensing line pressurizes the pneumatic relay when hoses from a delivery truck are connected to the system. The pneumatic relay includes a housing that defines a chamber with a piston having an arcuate passage located therein. When a hose from the delivery truck is connected to the system, the pressure sensing line detects a change in pressure and pressurizes the pneumatic relay. The pressure displaces the piston of the pneumatic relay which aligns the arcuate passage of the relay with the pneumatic valve to allow pressurized air to travel to the pneumatic valve thereby opening the pneumatic valve.