A rotary vane vacuum pump works by using an eccentrically mounted rotor with vanes that slide in and out of slots, creating chambers that expand and contract to draw in, compress, and exhaust gases, ultimately creating a vacuum.
Here's a breakdown of the process:
1. Components:
- Rotor: An off-center (eccentric) rotating component within the pump housing.
- Vanes: Sliding blades or vanes that fit into slots in the rotor. These vanes are typically spring-loaded or rely on centrifugal force to maintain contact with the pump housing wall.
- Housing: The outer casing of the pump, precisely machined to create a sealed chamber.
- Inlet Port: Where the gas to be evacuated enters the pump.
- Outlet Port: Where the compressed gas is expelled.
- Oil (in oil-sealed pumps): Oil is used to seal the clearances between the moving parts, improving vacuum performance and providing lubrication and cooling.
2. Operational Cycle:
a. Intake: As the rotor turns, the vanes extend outwards, creating an expanding chamber on the inlet side of the pump. This expanding volume reduces the pressure, drawing gas into the chamber through the inlet port.
b. Isolation: As the rotor continues to turn, the chamber becomes sealed off from both the inlet and outlet ports.
c. Compression: The rotating rotor reduces the volume of the sealed chamber, compressing the trapped gas.
d. Exhaust: When the compressed gas reaches the outlet port, the pressure forces open an exhaust valve (or in some designs, the pressure simply overcomes the force of the exhaust valve) and the compressed gas is expelled from the pump. In oil-sealed pumps, the oil helps to seal the exhaust valve.
e. Repeat: The cycle repeats with each rotation of the rotor.
3. Key Principles:
- Eccentric Rotor: The off-center rotor is crucial. It's the eccentricity that creates the changing volumes needed for intake and compression.
- Sliding Vanes: The vanes seal against the pump housing, creating distinct chambers that change in volume as the rotor rotates.
- Sealing: Maintaining tight seals between the vanes and the pump housing is essential for achieving a high vacuum. This is often achieved through precise machining and the use of oil in oil-sealed pumps.
4. Types:
- Oil-Sealed Rotary Vane Pumps: These use oil to seal clearances, lubricate, and cool the pump. They can achieve higher vacuums but require oil maintenance.
- Dry Rotary Vane Pumps: These operate without oil, which avoids potential oil contamination issues. They typically achieve lower vacuums than oil-sealed pumps but require less maintenance.
In summary, a rotary vane vacuum pump utilizes a rotating rotor with sliding vanes to create expanding and contracting chambers. These chambers draw in gas, compress it, and expel it, ultimately creating a vacuum by reducing the pressure within a sealed system.
