[en] A new type of driving mechanism suitable for fast U.H.V. valves is presented, based on the electrodynamic forces exerted between closely spaced current carrying conductors. The valve is forced at its maximum throughput within some fractions of a millisecond and it is kept open for some milliseconds, depending on the type of circuit used to excite the coils. A capacitor is used as energy storer and as the source of the fairly large currents required to deliver the necessary acceleration to the sealing needle. Owing to its good timing properties the valve is used for the gas puffing in the Tokamak THOR, while an improved version is under development in order to achieve a faster aperture and a better control of the time the valve stays open