A rotary vane vacuum pump relies on a rotating mechanism with sliding vanes that direct vapor flow through the pump. These pumps are available in a wide range of pumping speeds, and multistage vacuum pumps are able to attain ultimate pressure values that are quite low. Most rotary vane pumps, whether belt driven or directly driven by a shaft from the motor, use oil that lubricates the mechanism and provides a seal that permits the pumps to reach the design vacuum levels.
Because chemical vapors common in laboratories eventually contaminate the pump oil, hybrid pumps (combining rotary vane and diaphragm pump components) and oil-less rotary vane pumps have been introduced in recent years to reduce service demands. The pump’s performance can also be extended with products that employ fluoropolymer or nitrogen plasma-treated components for corrosion resistance.
Design of A rotary vane vacuum pump
A rotary vane vacuum pump is an oil-sealed rotary displacement pump. The pumping system consists of a housing(1), an eccentrically installed rotor (2), vanes (3) that move radially under centrifugal and resilient forces and the inlet and outlet (4). The inlet valve, if available, is designed as a vacuum safety valve that is always open during operation. The working chamber (5) is located inside the housing and is restricted by the stator, rotor and the vanes. The eccentrically installed rotor and vanes divide the working chamber into two separate compartments with variable volumes. As the rotor turns, gas flows into the enlarging suction chamber until it is sealed off by the second vane. The enclosed gas is then compressed until the outlet valve opens against atmospheric pressure. The outlet valve is oil-sealed. When the valve is open, a small amount of oil enters the suction chamber and not only lubricates it but also seals the vanes against the housing (stator).
Advantage of rotary vane vacuum pump
Oil sealed rotary vane pumps are compact and quiet in operation, with exceptionally high water vapor tolerance. New side mounted catch-pot and oil mist filter designs enhance these design qualities while extending the range of application. The pressurised oil circulation ensures stable, low ultimate vacuum and an integrated shut off valve on most models prevents oil migration when switched off. A wide range of pumping speeds and final vacuum specifications are available to suit a variety of applications.
Usage of rotary vane vacuum pump
Vane pumps are commonly used as high-pressure hydraulic pumps and in automobiles, including supercharging, power-steering, air conditioning and automatic-transmission pumps. Pumps for mid-range pressures include applications such as carbonators for fountain soft-drink dispensers and espresso coffee machines. Furthermore, vane pumps can be used in low-pressure gas applications such as secondary air injection for auto exhaust emission control, or in low-pressure chemical vapor deposition systems.
Rotary-vane pumps are also a common type of vacuum pump, with two-stage pumps able to reach pressures well below 10−6 bar. These vacuum pumps are found in numerous applications, such as providing braking assistance in large trucks and diesel-powered passenger cars (whose engines do not generate intake vacuum) through a braking booster, in most light aircraft to drive gyroscopic flight instruments, in evacuating refrigerant lines during installation of air conditioners, in laboratory freeze dryers, and vacuum experiments in physics. In the vane pump, the pumped gas and the oil are mixed within the pump, and so they must be separated externally. Therefore, the inlet and the outlet have a large chamber, maybe with swirl, where the oil drops fall out of the gas. Sometimes the inlet has a venetian blind cooled by the room air (the pump is usually 40 K hotter) to condense cracked pumping oil and water, and let it drop back into the inlet. When these pumps are used in high-vacuum systems (where the inflow of gas into the pump becomes very low), a significant concern is contamination of the entire system by molecular oil backstreaming.