How it works
The most common kind of vacuum pump is the rotary vane pump. In the oil-sealed type a rotor with sliding vanes turns in a bath of oil. The drawing shows one from the side, then cut open.
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How the vanes pump
The rotor sits off-center in the round bore of the stator. As it turns, its vanes slide out against the wall of the bore. Gas from the inlet fills the growing pocket behind a vane, is swept round, squeezed, and pushed out past the exhaust valve into the oil case and away through the exhaust port. Numbers 1 to 10 are on the outside of the pump. Numbers 11 to 17 are the pumping part, cut across. Numbers 18 and 19 are on the shaft between motor and pump.
- The oil does three jobs: it seals the pump, lubricates it and cools it.
- Other vacuum pumps are built differently: a diaphragm pump, for one, uses no oil.
Questions and answers
What are the main parts of a rotary vane vacuum pump?
A stator with a round bore, a rotor set off-center in it, and vanes that slide in the rotor. Round them are the oil case, an inlet port, an exhaust valve and exhaust port, and a motor joined to the rotor by a coupling.
What does the gas ballast valve do on a vacuum pump?
It lets a small amount of air into the pump while the gas is being compressed. That keeps vapors, such as water vapor, from condensing inside the pump and getting into the oil.
Why does a vacuum pump have oil in it?
In an oil-sealed pump the oil seals the small gaps between the vanes, the rotor and the stator, and it lubricates and cools the moving parts. The level shows in the sight glass.
What is the sight glass on a vacuum pump for?
It is a window on the oil case that shows the oil level, so the level can be checked when oil is added and while the pump is running.