Complex sentence: For larger valves, a metal tank with ceramic insulators for the electrodes is used, sometimes with a vacuum pump system to counteract slight leakage of air into the tank around imperfect seals.
Split into simpler sentences: For larger valves, a metal tank with ceramic insulators for the electrodes is used. Metal-tank valves may have vacuum pump systems to counteract slight leakage of air into the tank around imperfect seals.