855 28 Leybold Barrier Gas and Venting Valve

The Inficon / Leybold 855 Series Barrier Gas and Venting Valves are electromagnetically operated. When voltage is applied, the armature is attracted and closes the bypass duct, the throttle orifice remaining always open. The barrier gas enters the pump above the upper bearing and additionally the motor space with its bearings. The barrier gas pressure building up here immediately is distinctly higher than the forevacuum space. The barrier protection gas penetrates further through the gap between bearing cover and drive spindle to the underside of the rotor and thus into the forevacuum space. The gap size between motor space and forevacuum space in TURBOVAC pumps, intended for barrier gas operation has been particularly optimized, as any interruption of the barrier gas flow would entail instantaneous back-diffusion of harmful corrosive media to the bearings. Special attention should, therefore, be given to any kind of pressure fluctuations in the forevacuum region during a process. This concerns particularly the selection of the suitable backing pump and checking of the backing pressure.

A further critical phase follows at the end of the process when the pump is vented. The barrier gas valve is now used as a venting valve. When voltage is no longer applied to the magnetic coil, the released armature opens the bypass duct having a much higher throughput for the admission of venting gas into the TURBOVAC. Venting via the barrier gas valve (bypass duct) must last long enough to ensure that harmful media or reactive gases from the process chamber or the pump rotor blades will not penetrate the forevacuum space and from there to the bearings and motor.