ABSTRACT
Displacement pumps belong to a subcategory of transfer pumps. The general characteristic of these pumps is continuous displacement of gases from a vacuum system via the pump interior to discharge them into the atmosphere or to a higher-pressure zone, from where they are removed by another pump. Commercial piston pumps are similar in physical principle, but their construction is more sophisticated. Historically, the rotary vane oil pumps used to work at lower revolution speeds. The older systems of rotary oil pumps had to be vented manually after their stopping because the pressure difference across the rotor-vane system draws oil into the vacuum system. Some constructions of these pumps prevent the leaking of oil into the pump interiors by lubricating oil ways using special valves at the oil way inlets. The force-sealed construction of rotary vane pumps is adopted for lower pumping speeds because of vane friction and consequent oil degradation.
