GB2282853A - Rotary positive displacement pump. - Google Patents

Abstract

A rotary pump has a cylindrical cavity 48 in a housing 46 and a rotor 60 rotatable therein. The rotor 60 has vanes 70 which pump liquid from an inlet 50 in an anti-clockwise direction (relative to the drawing) to an outlet 52. Switching means, which effect sealing between the outlet 52 and the inlet 50, include a part round cylindrical surface 76 and a recess 78. The surface 76 is rotated close to a periphery of the rotor between vanes 70 to effect sealing. The recess 78, which allows the vanes 70 to pass, has an operative surface with a large radius of curvature, and is preferably flat, so as not to interengage with the vanes. Substantial sealing is effected across small clearance spaces to avoid rubbing and to enhance smooth and quiet operation. The pump can be applied in the food industry. <IMAGE>

Description

THIS INVENTION relates to a positive displacement rotary pump.

In accordance with the invention, there is provided a positive displacement rotary pump including a housing defining a circular stator cavity having an axis; an inlet into atd an outlet out of the circular stator cavity; a rotor rotatable in the stator cavity about said axis, the rotor having a generally periphery cf predetermined diameter to form an annular cavity within the stator cavity; drive means for driving the rotor in a predetermined pumping direction;; a plurality of outwardly proJecting vanes arranged at regular circumferential spacings on the rotor and forming past of the rotor, the extremities of the vanes being arranged to be at a major diameter of the rotor to be movable with little clearance along an inner periphery of the stator cavity, the general periphery of the rotor being t a minor rotor diameter, the vanes compartmentalizing the annular cavity in a corresponding plurality of part annular pumping chambers, the arrangement of the inlet and the outlet being such that, from the inlet, a first passage or pumping passage leads in said pumping direction to the outlet, and, from the outlet, a second passage or blind passage leads in said pumping direction to the inlet, in which arrangement the pumping passage is at least longer than the effective spacing between vanes, the pump including switching means operative in the blind passage to seal the blind passage and to pass the respective vanes in use, the switching means including a lay shaft, drive means for driving the lay shaft in counter rotation to the rotor and in synchronism with the vanes of the rotor, and a switching formation on the lay shaft, the switching formation including a part cylindrical surface arrange to move generally tangentially with and at little clearance adjacent the minor rotor periphery in between vanes, and a switching recess interrupting the part cylindrical surface to pass the respective vanes with little clearance, the switching recess having an operative surface with a radius of curvature between a minimum value equal to the effective radius of the extremity of the vane, and a maximum value of infinity.

In a preferred embodiment, the operative surface may be planar, I.e. having a radius of curvature of infinity.

The rotary speed of the lay shaft in use may be equal to the rotary speed of the rotor times the number of vanes. The effective diameter of the part cylindrical surface in relation to the minor diameter of the rotor, i.e. the periphery between vanes, may be in inverse relationship to the respective rotary speeds to equalize their tangential speeds.

The invention is now described by way of example with reference to the accompanying diagrammatic drawings. In the drawings Figure 1 shows, in axial section taken at I-I in Figure 2, a positive displacement rotary pump in accordance with the invention; Figure 2 shows an axial view taken at II-II in Figure 1; and Figures 3 to 5 show axial sectional views taken at III-III in Figure 1, but with the rotor in different orientations.

With reference to the drawings, a positive displacement rotary pump in accordance with the invention is generally indicated by reference numeral 10. The pump 10 is intended to pump a liquid.

The pump 10 comprises a housing generally indicated by reference numeral 12 which defines a central passage 14 having a centre line 16 on which a pump shaft 18 is mounted for rotation in sets of bearings 20, 22. An oil seal 24 seals the central passage 14 off toward its inner end.

The housing 12 comprises also a lay shaft passage 26 adjacent and underneath (as shown in the drawings) the central passage 14. It defines a centre line 28, parallel to the centre line 16, and on which a lay shaft 30 is mounted for rotation by means of bearings 32, 34. An oil seal 36 seals an inner end of the lay shaft passage 26.

At one end, as shown at 38, the pump shaft 18 projects beyond the housing 12 to provide connection means including a key-way in which a key is shown for connecting the pump shaft to a source of rotary power.

Inward of the end 38 and accommodated within a cavity 39 in the housing 12, a gear wheel 40 is mounted on the pump shaft 18. A complemental pinion 42 is mounted in alignment on the lay shaft 30 to mesh with the gear wheel 40 as indicated by reference numeral 44. The effective pitch circle diameter of the gear wheel 40 is three times that of the pinion 42 such that the lay shaft 30 is rotated at exactly three times the speed of the pump shaft 18, and in the opposite direction.

The cavity 39 is closed off by means of a cover 41.

A seal 25 is provided between the stationary cover 41 and the rotary pump shaft 18.

The pump 10 comprises a stator housing 46 mounted on the main housing 12. The stator housing 46 defines a round cylindrical stator cavity 48 concentric with the centre line 16.

A switching cavity 49, which is part-cylindrical and which intersects the stator cavity 48, is defined parallel to and underneath the stator cavity. The switching cavity 49 is coaxial with or concentric with the centre line 28.

An inlet 50 leads into the stator cavity 48 from one side of the pump 10. Aligned therewith and diametrically opposed thereto, there is provided an outlet 52. The inlet 50 and outlet 52 are co-axial about a centre line 5. The centre line 54 is perpendicular to the centre lines 16 and 28.

An end cover 56 covers the stator cavity 48 and the switching cavity 49 and is mounted on the stator housing 46 by means of stud and nut arrangements generally indicated by reference numerals 58. An "O"-ring is provided as a seal.

A rotor generally indicated by reference numeral 60 is rotatable within the stator cavity 48. From one end of the rotor which is an inner end in use, there is formed a concentric socket 66 within which an end portion of the pump shaft 18 is received.

In series therewith, and from the other end of the rotor 60 which is an outer end in use, there is provided an eccentric socket of smaller diameter generally indicated by reference numeral 62.

A stud-formation 64, integral with the pump shaft 18, is snugly received within the socket 62. In this manner, the rotor 60 is drivingly connected to the pump shaft 18.

As can best be perceived from Figure 2, the rotor 60 further comprises three vanes in the form of protrusions 70 which are integral with the rest of the rotor 60. The protrusions 70 have outer extremities indicated by reference numeral 72 which are concentric about the centre line 16. The extremities lie on a major diameter such that the rotor 60 can rotate with little clearance within the stator cavity 48.

In between the vanes 70, the rotor 60 has a general periphery at a minor diameter generally indicated by reference numeral 74. The diameter at 74 is substantially smaller than the effective diameter of the stator cavity 48 such that an annular chamber is formed intermediate the rotor 60 and the stator housing 46. Said annular chamber is sub-divided in three subchambers or pumping chambers by the vanes 70.

The lay shaft 30 forms part of switching means in accordance with the invention. The switching means is completed by having, at an end of the lay shaft 30 corresponding to the axial position of the rotor 60, a part-cyiindrical surface 76 interrupted by a recess 78 indicated in the drawings at a bottom or floor thereof. In this embodiment, a floor of the recess 78 is flat and is parallel to a geometric diameter of the lay shaft 30 such that the recess is slightly deeper than the diameter of the lay shaft i.e. the part-cylindrical surface subtends an angle slightly less than 180 .

The arrangement of the lay shaft 30 including the position of the centre line 28 and the effective diameter of the part-cylindrical surface 76 are such that the part-cylindrical surface 76 and the minor periphery 74 move closely adjacent each other at one point on a centre line intersecting the centre lines 16 and 28. In this embodiment, as can best be seen in Figures 3 to 5, a slight clearance space 80 is provided at that point.

The significance of this will become apparent hereinafter.

As can also better be seen in Figures 3 to 5, the lay shaft 30 is rotated such that the timing at which the recess 78 faces toward the rotor 60 co-incides with the timing when the vanes 70 move passed the position 79 such that the recess 78, in turn, passes the vanes 70. In this regard, it is to be appreciated that the la shaft is rotated at exactly three times the rotation speed of the rotor 60.

With reference now more specifically to Figures 3, 4 and 5, operation of the pump 10 is now described.

In Figure 3, the vane 70.1 is shown passing the'point 79 as allowed by the recess 78 in the switching cylinder. At that point, the pumping cavity 74.1 immediately ahead of the vane 70.1 is fully exposed to the inlet 50 and flow of liquid takes place as shown at 82 via the inlet 50 into the pumping cavity 74.1. Emphasis is placed on the existence of the clearance space 80. Substantial sealing takes place between, on the one hand, the inlet 50 and the pumping cavity 74.1, and, on the other hand, the outlet 52 and the pumping cavity 74.3, by providing a small clearance only at the position 81 indicated in Figure 3.

As the rotor 60 advances to the position shown in Figure 4, the vane 70.1 is on the point of moving beyond the inlet 50 to compartmentalize the pumping cavity 74.1. The pumping cavity 74.1 will then be sealed by vane 70.2 and the vane 70.1 substantially sealing against the inner periphery 48 of the pumping cavity. Thus, the liquid trapped in the pumping cavity 74.1 moves with the rotor in the pumping direction shown at 8 to the outlet 52.

Simultaneously, a lead portion of the succeeding pumping cavity 74.3 commences being exposed to the inlet 50 and commences collecting liquid flowing through the inlet 50. It is to be appreciated that the volume of the pumping cavity 74.3 enlarges thus causing a suction effect to enhance filling thereof. It is to be appreciated that the part cylindrical surface 76 of the switching cylinder is rotated at equal tangential speeds with little clearance passed the minor diameter of the rotor 60 to provide substantial sealing between the portion of the pumping cavity downstream of and the portion of the pumping cavity upstream of the point of sealing 79.

In Figure 5 it is shown that the pumping cavity 74.1 and its charge of liquid have progressed in the direction 84.

The pumping cavity 74.3 is still being filled via the inlet 50.

The switching cylinder rotates to such an extent that the recess 78 is on the point of being offered to pass the vane 70.3 with little clearance.

Referring again to Figure 3, it is shown that the pumping cavity 74.3 is being exposed to the outlet 52, more specifically that the whole of the pumping cavity is exposed to the outlet 52. The portion of the volume of the pumping cavity 74.3 exposed to the outlet 52 decreases as the rotor advances as can be seen from Figures 4 and 5. Thus, the volume of liquid contained in the pumping cavity 74.3 is forced through the outlet 54 thus pumping takes place as shown at 86.

It is to be appreciated that the outer extremities of the vanes do not actually rub against the inner periphery of the stator cavity, but passes with little clearance, thus substantial sealing takes place. Also, extremities of the vanes pass the recess 78 of the switching cylinder with clearance on account of the clearance space 80.

The Applicant believes that it is an advantage that slight clearance spaces are provided at the points of sealing, and that rubbing does not take place. Thus, it is believed that a pump in accordance with the invention will be quiet, will be less prone to vibration and will be operable at relatively high speeds. Thus, it is also of importance that interlocking between the switching means and the vanes does not take place thus making exact synchronization non-critical.

It is further an advantage that the design of the pump in accordance with the invention allows it to be used with foodstuffs. It is envisaged that the components of the pump which will be exposed to the foodstuffs will be of a suitable material such as stainless steel or the like.

Claims (5)

1. A positive displacement rotary pump including a housing defining a circular stator cavity having an axis; an inlet into and an outlet out of the circular stator cavity; a rotor rotatable in the stator cavity about said axis, the rotor having a generally periphery of predetermined diameter to form an annular cavity within the stator cavity; drive means for driving the rotor in a predetermined pumping direction;; a plurality of outwardly projecting vanes arranged at regular circumferential spacings on the rotor and forming part of the rotor, the extremities of the vases being arranged to be at a major diameter of the rotor to be movable with little clearance along an inner periphery of the stator cavity, the general periphery of the rotor being at a minor rotor diameter, the vanes compartmentalizing the annular cavity in a corresponding plurality of part annular pumping chambers, the arrangement of the inlet and the outlet being such that, from the inlet, a first passage or pumping passage leads in said pumping direction to the outlet, and, from the outlet, a second passage or blind passage leads in said pumping direction to the inlet, in which arrangement the pumping passage is at least longer than the effective spacing between vanes, the pump including switching means operative in the blind passage to seal the blind passage and to pass the respective vanes in use, the switching means including a lay shaft, drive means for driving the lay shaft in counter rotation to the rotor and in synchronism with the vanes of the rotor, and a switching formation on the lay shaft, the switching formation including a part cylindrical surface arranged to move generally tangentially with and at little clearance adjacent the minor rotor periphery in between vanes, and a switching recess interrupting the part cylindrical surface to pass the respective vanes with little clearance, the switching recess having an operative surface with a radius of curvature between a minimum value equal to the effective radius of the extremity of the vane, and a maximum value of infinity.

2. A positive displacement rotary pump as claimed in Claim 1 in which the operative surface of the switching rece s is planar.

3. A positive displacement rotary pump as claimed in Claim 1 or Claim 2 in which the rotary speed of the lay shaft in use is equal to the rotary speed of the rotor times the number of vanes.

4. A positive displacement rotary pump as claimed in Claim 3 in which the effective diameter of the part cylindrical surface of the switching formation in relation to the minor diameter of the rotor is in inverse relationship to the respective rotary speeds to equalize their tangential speeds.

5. A positive displacement rotary pump substantially as herein described and illustrated.