Safety device for a liquid-dispensing nozzle for fuel

Claim 1

In a liquid-dispensing nozzle comprising: a valve housing having an upstream end with a spigot, a filling hose connector and a connected fuel duct, an operating mechanism with a pistol-grip handle, automatic shut off device and a safety device having a locking mechanism; a valve seat being located near said upstream end of said valve housing and an associated valve body loaded by a closing spring mounted in said valve housing with an axially slidable valve stem, said valve stem being a hollow spindle, in which a pull rod connected with said pistol-grip handle is guided, said valve stem and said pull rod being couplable and uncouplable by said locking mechanism of said automatic shut off device; and said automatic shut off device having a pressure equalizing chamber, a vacuum chamber with a filling state sensing duct and with a vacuum duct open near said valve seat and a chamber-separating control membrane which operates said locking mechanism, said control membrane having a control membrane spring with which is set a below atmospheric pressure limit that when reached shuts off said automatic shut off device, and a hollow piston shaft of a safety piston guided in said valve housing which is movable between a locked in position and a locked out position and further said control membrane being connected with flexible free play to said hollow piston shaft of said piston and said piston having a side facing away from said control membrane is acted upon by pressure in said filling hose connector communicated thereto by a pressure duct and which is supported with a safety piston spring in said valve hosuing, said spring being attached to said control membrane, the improvment wherein said safety piston is a differential piston with a small effective piston surface and a large effective piston surface, said safety piston being acted upon in said locked out position with said small effective piston surface by said pressure in said filling hose connector and said safety piston after overcoming the compressive force of said safety piston spring in said locked in position with said large effective piston surface being acted upon by said pressure in said filling hose connector; and an upper chamber in said valve housing in which is guided said safety piston, said upper chamber communicating with said vacuum chamber through a gap means for equalizing pressure, said gap means being an effective seal when said pressure acts on said small piston surface until in said locked in position where said safety piston can be acted on with said large piston surface by said pressure in said filling hose connector.