GB2125485A

GB2125485A - Rotary positive-displacement fluid-machines

Info

Publication number: GB2125485A
Application number: GB08314284A
Authority: GB
Inventors: Paul William Nachtrieb
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-10
Filing date: 1983-05-24
Publication date: 1984-03-07
Also published as: GB2125109A; GB8314284D0

Abstract

Each rotor, or "impeller", of an intermeshing pair 14, 16 has four lobes 38...42, or 46...52, each lobe having concavo-convex flanks and two spaced-apart sealing edges 60 on a radially projecting tip 56. The impellers may be incorporated in a pump or a motor comprising a housing 12. The tip on each lobe extends the life of the machine. <IMAGE>

Description

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GB2125 485A 1

SPECIFICATION

Improvements in or relating to positive displacement pumps or motors

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The present invention relates to improvements in positive displacement pumps or motors and in particular to an impeller structure for use as a fluid driver or fluid driven member of such a 10 pump or motor.

For convenience the invention will be described using the word "pump" to include both motor and pump where appropriate.

It is an aim of the present invention to 15 provide a pump having a smooth flow of liquid with a minimum of turbulence and a minimum of "flowback" from the high pressure outlet port to the low-pressure inlet port to ensure a high level of hydraulic and volu-20 metric efficiency.

It is a further aim of the invention to provide a pump which produces a sufficient vacuum at low velocities to impart to the pump effective self-priming capabilities. 25 According to the present invention, there is provided an impeller structure for a pump or motor having a symmetrical cylindrical housing with two arcuate cross-section interior walls separated by an inlet area and an outlet 30 area and accommodating two cylindrical axi-ally symmetric impellers a selected distance apart, each impeller comprising four interior concave arcuate side walls which are disposed 90° apart, and which define inside profiles 35 forming the base of four lobes, which inside profiles flow into and are coupled to exterior convex arc side walls which in turn flow into and connect with two spaced apart edges defining on each lobe an extended tip.' 40 The arcuate cross-section interior wall of the housing extends through 180° of arc. Each impeller is coaxial with the interior wall adjacent thereto, and has a radial dimension slightly less than the radius of the 1 80° arc so 45 that the tips of the impeller come very close to the interior side walls, but do not touch them. The housing is of sufficient size so that the impellers are placed just far enough apart so that the tips of each impeller fail by a small 50 distance to touch the adjacent interior concave arcuate side wall of the opposing impeller during rotation. The impellers are rotated in opposite directions, 45° out of phase by timing gears which are driven by driving means. 55 The interior side walls of the impellers theoretically comprise two offset involute profiles, which in practice have been de-standardised to accommodate volume production assembly techniques, whilst retaining optimum perform-60 ance characteristics. Hereinafter, the shape of the interior side walls is referred to as the inside profile.

The unique structure of the subject invention imparts to a pump the ability to produce 65 sufficient vacuum at relatively low velocity to impart to the pump effective self-priming capabilities. Unlike other self-priming pumps, which depend upon moving parts within their pump chambers which make physical contact 70 and are therefore subject to wear and a gradual deterioration of ability to self-prime, no moving parts touch within the pump chamber, therefore the self-priming ability of the pump is theoretically not affected through extended 75 use. In addition, the tips of the impeller lobes incorporate two tracking edges separated by a relatively wide surface. The edges of the lobe end tip alternate in affecting a sealing surface between the lobe end and the adjacent inside 80 profile of the opposing impeller. Such a structure is more complex than many other impellers, and one of the benefits is that virtually without loss of performance, such impellers will automatically wear incrementally to com-85 pensate for increased backlash in the pump's timing gears which would occur after extensive use. Impellers that incorporate a single tracking point at their impeller tips deteriorate more rapidly in their sealing capabilities since 90 wear to the single-point tips causes a permanent gap between the worn tips and the adjacent pump chamber walls. The dual point tips of the invention's structure allow either, or both, tips to wear without materially effect-95 ing the sealing clearance between the impeller tips and the adjacent pump chamber walls, therefore the structure extends a pump's useful life considerably beyond that possible-to other similar structures.

100 The unique combination of the impeller structure results in a pump capable of performance which sets it apart from other self-priming pumps, resulting in a pump of greater versatility, efficiency and durability than that 105 of other positive-displacement pumps currently being manufactured.

The invention will now be described further, by way of example only, with reference to the accompanying drawings, in which:-110 Figure 1 is a simplified plan view of a pump embodying the invention showing the lobes of the impellers in one position;

Figure 2 is a simplified plan view similar to that shown in Fig. 1, but with the first and 115 second impellers moved to different positions.

Figure 3 is a fragmentary view of part of the impeller to a larger scale;

Figure 4 is a fragmentary plan view showing the contacting relationship between two 1 20 impellers;

Figure 5 is a view similar to that of Fig. 4 but showing the two impellers in different positions; and

Figure 6 is a section through a pump incor-125 porating impellers according to the invention.

Referring more particularly to the drawings, there is shown a pump having a housing 12 in which is formed a chamber 2, having two arcuate cross-section internal walls 68 and are 130 separated by an inlet area 20 and an outlet

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GB2 125 485A

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area 22. The arcuate internal walls have a 180° arc. The chamber accommodates two four-lobe impellers 14, 16. The impellers are driven in synchronism 45° out of phase from 5 drive means generally indicated at 72 in Fig. 6 by way of mating timing gears 78, 80. The gears are disposed in the pump housing and are sealed from the chamber 2 by seals 88. The impellers 14, 16 are secured to respec-10 tive shafts 30, 32 by suitable means and these shafts are journalled for rotation in the pump housing. The gears are in driving engagement with a respective one of the shafts.

Each impeller comprises four interior con-15 cave arcuate side walls 58 disposed 90° apart and forming the base of the four lobes, identified as 38, 40, 42, 44 in the case of impeller 14 and as 46, 48, 50, 52 in the case of impeller 16. Each arcuate side wall 58, here-20 inafter referred to as the inside profile, approximate in shape to two offset involute profiles. In practice each approximate involute profile is formed by three concave arcuate portions. The concave side walls 58 flow into and 25 couple to exterior convex arc side walls 66 which in turn flow into and connect to a slightly extended tip 56. The tip of each lobe has two edges 60, 61 defined by shoulders 64, 65. The two edges of the tip are con-30 nected by a portion 70. The portion 70 has a radius which is slightly smaller than the radius of the interior side walls 68. The construction is shown more clearly in Fig. 3.

Each impeller is coaxially disposed with 35 respect to the associated internal wall 68 of the chamber and runs with slight clearance therein. That is to say, the tip radius is slightly less than the radius of the 180° arcuate interior side wall 68. The impellers rotate 40 together and are spaced apart so that upon rotation the end of one lobe just fails to touch the inside profile by a finely controlled clearance. The inside profile comprises two regions 72, 74 each of which is preferably made up 45 of three concave arcuate portions so as to approximate in shape to an involute profile.

The end surface 20 of the tip may be slightly radiused. Prime seals are generated alternately between the edge 60 and inside 50 profile 72 and between edge 61 and inside profile 74 during rotation of the impellers.

By providing dual edges to the impeller tip and no contact with other pump components, the life of the pump is vastly extended, as the 55 wear of each tip is virtually dependent on the type of fluid pumped.

In operation, the rotating impellers 14, 16 form generally sealed cavities between their lobes and the adjacent 180° arcuate cross-60 section interior walls 68 in which fluid is carried from the inlet area 20 to the outlet area 22 as the impellers are counter-rotated. The shape of the impellers are such as to minimize the amount of flow and vibration 65 caused by fluid flowing back through the small space from the outlet side to the inlet side.

Figs. 4 and 5 show how the edges 60 of the lobe tip of impeller 16 co-operates first 70 with the surface 72 and then the edge 61 cooperates with the surface 74. In the case of the lobe tip of impeller 14 the edge 61 cooperates first with surface 74 and then the edge 60 with surface 72, the impeller 14 75 rotating counter-clockwise and impeller 16 rotating clockwise. Thus there is always at least one edge 60 or 61 of a lobe in contact with a surface 72 or 74 of the other impeller. This ensures that the pump can operate as a 80 self priming pump.

Pumps employing the invention structure combine most of the desirable performance attributes of both centrifugal and positive displacement pumps in one structure, thereby 85 offering to the pumping industry a versatile tool that fills pumping needs with a significant saving in energy consumption.

Claims

90 1. An impeller structure for a pump or motor having a symmetrical cylindrical housing with two arcuate cross-section interior walls separated by an inlet area and an outlet area, and accommodating two identical and 95 perfectly symmetrical impellers a selected distance apart, each impeller comprising four interior concave arcuate sidewalls which are disposed 90° apart and which define inside profiles forming the base of four lobes, which 100 inside profiles flow into and couple to exterior convex arc sidewalls which in turn flow into and connect with two spaced apart edges defining, on each lobe, an extended tip.
2. An impeller structure as claimed in

105 claim 1, in which each impeller is coaxial with the arcuate cross-section interior wall of the housing adjacent to it, and in which said interior walls extend through an arc of 180° and have a radius slightly larger than the 110 radius of the lobe tips, so that the tips of the impellers come very close to the interior side walls, but do not touch them.
3. An impeller structure as claimed in claim 1 or 2, in which the housing is of

115 sufficient size so that the impellers are placed just far enough apart so that the two tips of . each impeller fail by a small distance to touch the corresponding inside profile of the opposing impeller during rotation.

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4. An impeller structure as claimed in claim 1, 2 or 3, in which the impellers are rotated in opposite directions 45° out of phase by timing gears which are driven by driving means.

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5. An impeller structure as claimed in any of claims 1 to 4, in which the interior profile of the impeller comprises two offset profiles which are substantially involute in shape.
6. An impeller structure constructed, ar-130 ranged and adapted to operate substantially

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as hereinbefore described with reference to and as illustrated in the accompanying drawings.

Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd.—1984.

Published at The Patent Office, 25 Southampton Buildings,

London, WC2A 1 AY, from which copies may be obtained.