Fast acting gas valves that operate between two very different pressure environments, which may differ in several orders of magnitude, are not available commercially and, therefore, they must be specifically projected and constructed. For the TCABR impurity pellet injector, under construction, an electromagnetic valve has been built which operates for gas pressure that ranges from 20 to 40 atm at one side of the valve to 10-9atm at the other side. The working principle of the valve is based on the displacement of an aluminum disk (which controls the gas flux) from its closing position by an electromagnetic force, in result to an induced electric current on the disk caused by a magnetic flux variation. Experimental results showed that the electromagnetic impulse on the disk lasts for 200 mus and takes less than 30 ms for the valve to shut up again.
