Rotary vane pump

A rotary vane pump is a type of positive-displacement pump that consists of vanes mounted to a rotor that rotates inside a cavity. In some cases these vanes can have variable length and/or be tensioned to maintain contact with the walls as the pump rotates. This type of pump was invented by Charles C. Barnes of Sackville, New Brunswick, who patented it on June 16, 1874. There have been various improvements since, including a variable vane pump for gases (1909). This type of pump is considered less suitable than other vacuum pumps for high-viscosity and high-pressure fluids, and is . They can endure short periods of dry operation, and are considered good for low-viscosity fluids. The simplest vane pump has a circular rotor rotating inside a larger circular cavity. The centres of these two circles are offset, causing eccentricity. Vanes are mounted in slots cut into the rotor. The vanes are allowed a certain limited range of movement within these slots such that they can maintain contact with the wall of the cavity as the rotor rotates. The vanes may be encouraged to maintain such contact through means such as springs, gravity, or centrifugal force. A small amount of oil may be present within the mechanism to help create a better seal between the tips of the vanes and the cavity's wall. The contact between the vanes and the cavity wall divides up the cavity into "vane chambers" that do the pumping work. On the suction side of the pump the vane chambers are increased in volume and are thus filled with fluid forced in by the inlet vacuum pressure, which is the pressure from the system being pumped, sometimes just the atmosphere. On the discharge side of the pump the vane chambers decrease in volume, compressing the fluid and thus forcing it out of the outlet. The action of the vanes pulls through the same volume of fluid with each rotation. Multi-stage rotary-vane vacuum pumps, which force the fluid through a series of two or more rotary-vane pump mechanisms to enhance the pressure, can attain vacuum pressures as low as 10−6 mbar (0.