An eccentric rotary-vane pump. Note that modern pumps have an area contact between rotor
and stator (and not a line contact).
1. pump housing
2. rotor
3. vanes
4. spring
A rotary vane
pump is a positive-displacement
pump that consists of vanes mounted to
a rotor that rotates inside of 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. It was
invented by Charles C. Barnes of Sackville, New Brunswick, who patented
it on June 16, 1874.[1][2] There have been various improvements, including a variable vane
pump for gases (1909)[3]
The simplest vane pump has a circular rotor rotating inside a larger circular
cavity. The centers of these two circles are offset, causing eccentricity. Vanes are allowed to slide into
and out of the rotor and seal on all edges, creating vane chambers that do the pumping work. On the intake
side of the pump, the vane chambers are increasing in volume. These increasing-volume vane chambers are
filled with fluid forced in by the inlet pressure. Inlet pressure is actually the pressure from the system
being pumped, often just the atmosphere. On the discharge side of the pump, the vane chambers are
decreasing in volume, forcing fluid out of the pump. The action of the vane drives out the same volume of
fluid with each rotation. Multistage rotary-vane vacuum pumps can attain pressures as low as
10−6 mbar (0.0001 Pa).
Vane pumps are commonly used as high-pressure hydraulic pumps and in automobiles, including supercharging, power-steering 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 depositionsystems.
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.[4]
Variable-displacement vane pump[edit]
One of the major advantages of the vane pump is that the design readily lends
itself to become a variable-displacement pump, rather than a fixed-displacement pump such as
a spur-gear (X-X) or a gerotor (I-X) pump. The centerline distance from the rotor to the eccentric
ring is used to determine the pump's displacement. By allowing the eccentric ring to pivot or translate
relative to the rotor, the displacement can be varied. It is even possible for a vane pump to pump in
reverse if the eccentric ring moves far enough. However, performance cannot be optimized to pump in both
directions. This can make for a very interesting hydraulic-control oil pump.
A variable-displacement vane pump is used as an energy-savings device and has
been used in many applications, including automotive transmissions, for over 30 years.