1. Field of the Invention
The present invention generally relates to pumps, and more particularly to positive-displacement rotary pumps.
2. Description of the Related Art
Positive displacement pumps displace a known quantity of liquid with each revolution of the pumping elements (e.g., vanes). Positive displacement pumps displace liquid or gas by creating a space between the pumping elements and trapping the liquid or gas within the space. Rotation of the pumping elements then reduces the volume of the space and moves the liquid out of the pump. A rotary vane pump is an example of a positive-displacement pump.
Rotary vane pumps operate through the action of a number of rotating vanes or blades. A conventional rotary vane pump includes a rotor assembly eccentrically positioned within a pumping chamber. The number of vanes are spaced around the rotor to divide the pumping chamber into a series of cavities. As the rotor rotates, these cavities rotate around the pumping chamber continually changing in volume due to movement of the vanes and the eccentric alignment of the rotor and pumping chamber. An inlet communicates with the pumping chamber on the side of the pump where the volume of the cavities expand. Similarly, an outlet communicates with the pumping chamber on the side of the pump where the volume of the cavities contract. As each cavity expands, a partial vacuum is created to draw fluid into the pump through the inlet. As the cavity contracts, the pressure within the cavity increases forcing the fluid out of the pump through the outlet. This expansion and contraction process continues for each cavity to provide a continuous pumping action.
There is a desire to improve upon the currently available rotary pumps. For example, there is a desire to reduce the cost of manufacturing rotary pumps while maintaining (and possible increasing) the vacuum level produced by a pump of specific dimensions. There is also the desire to increase the volume of fluid that can be displaced during a period of time by a pump of specific dimensions (i.e., without increasing the overall dimensions of the pump). Further, there is the desire to simplify the manufacturing and assembly required for producing rotary pumps.
The present invention is directed to a dual chamber or double sided rotary pump that includes a stator housing and a rotor.
In accordance with an embodiment, the stator housing has an oblong inner surface. The rotor, which is disposed in the stator housing, has a substantially circular outer surface within which a plurality of vane slots are defined. A first chamber is defined between a first half of the oblong inner surface and the outer surface of the rotor. Similarly, a second chamber is defined between a second half of the oblong inner surface, diametrically opposite the first half, and the outer surface of the rotor. Resting within each of the plurality of vane slots is a corresponding sliding vane. A first inlet port and a first outlet port provide access to the first chamber. Similarly, a second inlet port and a second outlet port provide access to the second chamber. The vane slots are arranged about the outer surface of the rotor such that there is always at least one of the vanes separating each of the first inlet port, the first outlet port, the second inlet port and the second outlet port from one another.
As the rotor is rotated within the stator housing, centrifugal force pushes or urges the vanes radially outward against the inner surface of the stator housing. As this occurs, each of the first and second inlet ports draws in fluid (i.e., gas and/or liquid), and each of the first and second outlet ports expels fluid. More specifically, fluid drawn into the first inlet port is expelled out of the first outlet. Similarly, fluid drawn into the second inlet port is expelled out of the second outlet port. This occurs as described below.
At any given time there exists multiple cavities formed between adjacent pairs of the vanes. For example, there are eight cavities in the embodiment of the present invention where there are eight vane slots and eight vanes. During each full rotation of the rotor, each formed cavity expands and contracts in volume twice. More specifically, each cavity expands in volume as it passes the first inlet port, shrinks in volume as it passes the first outlet port, expands in volume as it passes the second inlet port, and shrinks in volume as it passes the second outlet port. When a cavity expands in volume it creates a partial vacuum, as it passes one of the inlets ports, and thereby draws fluid into the cavity. When the same fluid filled cavity shrinks in volume, as it passed one of the outlet ports, it expels that fluid. Thus, at any given time (while the rotor is rotating at a sufficient speed) two chambers are drawing fluid in and two other chambers are expelling fluid. The remaining chambers are in the process of transferring fluid that has just be drawn in (by one of the input ports) toward one of the outlet ports, so that the fluid can be expelled.
The rotary pump further includes first and second side plates (also referred to as end caps) located opposite one another at axial ends of the stator housing. The first and second side plates together with the stator housing form a hollow oblong cylinder within which the rotor is disposed. One of the side plates may be integrally formed with the stator housing.
In accordance with an embodiment of the present invention, most or all of the rotary pump is manufactured out of plastic. This can significantly reduce the cost and weight of the rotary pump. In accordance with an embodiment, the stator housing and side plates are manufactured from polyetherimide, the rotor is manufactured from polyphenylene sulfide, and the vanes are manufactured from thermoplastic polyimide. For strength, durability and lubrication: the polyethermide can include a carbon fill of about 25-35 percent and a polytetrafluoro ethylene fill of about 10 to 20 percent; the polyphenylene sulfide can include a carbon fill of about 35-45 percent; and the polyimide can include a carbon fill of about 25-35 percent and a polytetrafluoro ethylene fill of about 10 to 20 percent.
Further embodiments, features and advantages of the present invention may be more readily understood by reference to the following description taken in conjunction with the accompanying drawings and claims.