GB2031520A - Rotary positive-displacement pump - Google Patents

Abstract

A pump has an eccentric cylindrical rotor (8) in a cylindrical casing (5) with inlet and outlet openings (3 and 4). The rotor is hollow and rotatably mounted on an eccentric member (7) which is fixed to a rotary drive shaft (6). A spring- loaded seal (27) separates the openings (3 and 4). The rotor may have a P.T.F.E. coating (29). <IMAGE>

Description

SPECIFICATION Rotary pump The present invention relates to a rotary pump. There have been various types of rotary pumps such as a cam and piston pump, an external or internal gear pump, a vane pump, a screw pump and so forth. But these types of rotary pumps are complicated in structure and expensive.

The present invention provided an improvement in these respects.

The primary object of the invention is to provide a rotary pump which is very simple in structure, easy to produce and less likely to break down.

The second object of the invention is to provide a rotary pump in which an outer surface of a rotor contacts an inner surface ot a casing at a single position at any one time, the position of contact moving as a shaft revolves, thus reducing wear and improving the sealing capacity.

To achieve the above described objects, the rotary pump is so structured that the outer surface of the rotor and the inner surface of the casing both of which are circular in crosssection and are off-centered relative to each other and contact each other at a single position to define a pump cavity therebetween. The position where the outer surface of the rotor and the inner surface of the casing contact each other follows a round path. The pump cavity is, irrelevant to movement of the rotor, always sealed at a single portion thereof by a seal member, preferably projecting from a cut-out portion of the casing.

The casing has an inlet and an outlet on opposite sides of the seal member respectively, the inlet and the outlet being in communication with the pump cavity.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings.

In the drawings: Figure 1 is a transverse cross-sectional view of the rotary pump; Figure 2 is a vertical cross-sectional view of the pump; and Figures 3 to 14 are vertical cross-sectional schematic views depicting operation of the pump.

A rotary pump 1 comprises, as shown in Fig. 1 and Fig. 2; a casing 5 which encloses a cylindrical cavity 2, an inlet 3 and an outlet 4 through the casing, a shaft 6 being revolved by a prime mover (not shown), an eccentric revolving member 7 which the shaft 6 runs through, a rotor 8 being rotatably mounted on the eccentric revolving member 7 and a seal member 9 which seals a portion of a pump cavity A defined between the casing 5 and the rotor 8.

The casing 5 comprises a main body 10 and a lid 11. The main body 10 has a first axial opening 1 2 through to the cylindrical cavity 2. The central axis of the cylindrical cavity 2 is identified in Fig. 2 by the reference 0.

The curved wall 1 3 of the main body 10 of the casing has an inlet 3 and an outlet 4 which are located circumferentially nearby each other and both in communication with the cavity 2.

In addition, the lid 11 has a circular second opening 1 4 whose central aixs is also the first axis 0.

The main body 10 and the lid 11 are held together by fastening means 1 6 such as bolts with a first seal 1 5 being provided between the main body 10 and the lid 11.

The shaft 6 is rotatably mounted in the second opening 14. There is provided a second seal 1 7 between the shaft 6 and the lid 11.

The eccentric revolving member 7 comprises first, second and third portions 18, 1 9 and 20. The eccentric revolving member 7 has a bore 21 therein which the shaft 6 runs through.

The second portion 1 9 of the revolving member and the bore 21 are coaxially, both sharing the first axis 0 as their central axis.

The central axis of the first portion 1 8 of the revolving member is a second axis 0' shown in Fig. 2. The first axis 0 and the second axis 0' are spaced by a gap As.

The second portion 1 9 is rotatably mounted in the first opening 1 2 in the casing 5, with a third seal 22 being placed between the casing 5 and the portion 1 9.

A securing member 23 is mounted on the third portion 20 of the revolving member. The securing member 23 secures the eccentric revolving member 7 to the shaft 6. The securing member 23 may for example be a wedge but in Fig. 2 is shown as a screw. The eccentric revolving member 7 and the shaft 7 could, of course, be one integral body.

The rotor 8 is mounted rotatably on the first portion 1 8 of the eccentric revolving member 7. Bearings 24, shown in Fig. 2, are mounted between the rotor 8 and the portion 1 8.

The seal member 9 is composed of a groove 25 provided on the curved wall 1 3 of the casing 5 and a fourth seal 27 which is always pressed inwardly by a sheet spring 26 placed in the groove 25. The fourth seal 27 is kept in pressed contact relation with the outer surface of the rotor 8 to give continual sealing. It is also possible that the seal member 9 may be mounted on the rotor 8. The structure of the seal member 9 is not confined to that shown in Fig. 2. Elastic members could be used instead.

It is advisable to use valves 28 at inlet 3 and the outlet 4 which prevent backward flow of liquid to assure that the liquid flow follows the direction of the arrow shown in Fig. 2.

It is also advisable that either the outer surface and the right side and left side surface of the rotor 8 or the inner surface of the hollow 2 is covered with a fifth seal 29 made of a material which stands abrasion and has high sealing capability, for example, Teflon.

The operation of the pump will now be described.

Both the cylindrical cavity 2 and the rotor 8 of the rotary pump 1 are prefectly circular in cross-section, the cavity 2 and the rotor 8 being placed off-centre relative to each other with the gap As being defined between the first axis 0 of the cavity 2 and the second axis O' of the rotor 8. The rotor 8 is so placed in the cavity 2 that the outer surface of the rotor 8 contacts the inner surface of the cavity 2 at P.

The position P moves in a circular path in accordance with revolving movement of the shaft 6.

The seal member 9 contacts the outer surface of the rotor 8 at a second contact position P'. The second contact position P' and the above described first contact position P divide the pump cavity A into two parts. The pump cavity A however is undivided when the first and the second contact positions P and P' are coincident. The relative ratio between the volume of one part of the divided pump cavity A and that of the other changes in accordance with revolving movement of the shaft 6.

Liquid begins to flow in through the inlet 3 when the first contact position P moves to a position as shown in Fig. 4 from the coincidence position shown in Fig. 3. The volume of the pump cavity A' changes as shown in Fig. 5 to Fig. 14 to cause the liquid trapped in the pump cavity A to flow out of the outlet 4 with the pressure in the pump cavity A' being increased.

As the rotor 8 is rotatably mounted on the eccentric revolving member 7, the rotor 8 does not rotate when the shaft 6 rotates.

Instead the rotor 8 is caused to have an eccentric non-rotary movement when the shaft 6 rotates. Consequently wearing is minimized because the outer surface of the rotor 8 does not rub against the inner surface of the hollow 2, but rolls on the inner surface of the hollow 2 with the first contact position P following a round path.

When the contact positions P and P' are coincident as shown in Fig. 9 the inlet 3 is in communication with the outlet 4 through the pump cavity A'.

In this condition the backward flow-stopping valve 28 is preferably provided at least at the outlet 4 in order that the liquid to be pumped out may not flow backwards toward the inlet 3 through the pump cavity A'. However coincidence of the first and second contact positions P and P' is instantaneous. Consequently it will not make a big difference even if no backward flow stopping valve 28 is provided. Backward flow of liquid will never happen if both of the inlet 3 and the outlet 4 have the valves 28, 28 as shown in Fig. 2.

In the embodiment described above, the inner surface of the cavity 2 and the outer surface of the rotor are of a perfectly circular shape, which makes processing easy. This also makes assembling easy because the cavity and the rotor can be positioned off-centered relative to each other by means of the eccentric revolving member only.

The position where the rotor contacts the inner surface of the casing pursues a round path, which makes wearing minimized and therefore sealing good. Sealing capacity is further improved if a seal is provided on either the outer surface of the rotor or the inner surface of the casing.

Consequently the rotary pump is less likely to break down, durable, cheap and requires only a little attention for maintenance.

Claims (4)

1. A rotary pump comprising: a casing enclosing a cylindrical cavity, the casing having an inlet aperture and an outlet aperture to the cavity; a rotatable member mounted eccentrically for rotation about the longitudinal axis of the cavity, a cylindrical rotor disposed non-concentrically within the cylindrical cavity so that the surface of the rotor contacts the inner surface of the casing at one position at any given time, the cylindrical rotor being rotatably mounted on the rotatable member so that as the rotatable member rotates the point of contact between the rotor and casing moves round the casing; and sealing means adapted to seal the space between the rotor and the cavity intermediate the apertures and throughout the change in width of this space during rotation of the rotor.

2. A rotary pump as claimed in claim 1 wherein the rotatable member is mounted on a drive shaft for rotation therewith the drive shaft being co-axial with the cylindrical cavity.

3. A rotary pump as claimed in claim 1 or claim 2 wherein the sealing means comprises a sealing member disposed in a channel on the inner surface of the casing, the sealing member being urged against the rotor by a spring at the base of the channel.

4. A rotary pump substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.