GB2125109A - Rotary positive-displacement fluid-machines - Google Patents

Abstract

A rotor, or "impeller", for a motor or a pump having in housing 12 a pair of such impellers 14, 16, which intermesh and revolve in synchronism 45 DEG out of phase, comprises four lobes furnished with tips 54, 56 separated from each other by an arcuate indentation 70. This provision reduces leakage between the lobes and the housing walls. The flanks of each lobe comprise concave and convex portions 58, 60 and 64, 66. The working fluid may be a liquid. <IMAGE>

Description

SPECIFICATION Improvements in or relating to positive displacement pumps or motors The present invention relates to improvements in positive displacement pumps or motors and in particular to an impeller structure for use as a fluid driving or fluid driven member of such a 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 provide a pump having a smooth flow of liquid with a minimum of turbulence and a minimum of "flowback" from the high pressure outlet part to the low-pressure inlet part to ensure a high level of hydraulic and volumetric efficiency.

It is a further aim of the invention to provide a pump which produces sufficient vacuum at low velocities to impart to the pump effective selfpriming capabilities.

According to the present invention, there is provided an impeller structure for a pump or motor having a symmetrical cylindrical housing with two 1 900 arc cross-section interior walls separated by an inlet area and an outlet area and accommodating two cylindrical axially symmetric identical impellers a selected distance apart, each impeller comprising four interior concave arc side walls which are disposed 900 apart, and which form the base of four lobes and which flow into and are coupled to exterior convex arc side walls which in turn flow into and connect to dual slightly extended tips, each of the tips being separated from the opposite tip on the end of the lobe by an arc tip indentation.

Each impeller is coaxial with the 1 900 arc cross-section interior wall of the housing adjacent to it and has a radial dimension slightly less than the radius of the 1 900 arc so 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 piaced just far enough apart so that the tips of each impeller fail by a small distance to touch the adjacent interior concave arc side wall of the opposing impeller during rotation. The impellers are rotated in opposite directions, 450 out of phase by timing gears which are driven by driving means.

The interior side walls of the impellers comprise two arcs of identical radius having centres slightly disposed from each other, the adjoining portions of the arc being smoothed out over slightly less than 470 so as to give the interior arc side walls a generally circular but slightly elliptical crosssection.

The unique structure of the subject invention imparts to a pump structure the ability for such a pump to produce sufficient vacuum at relatively low velocity to impart to the pump effective selfpriming capabilities. In fact, it has been found that pumps which use the new improved impellers have developed a vacuum of 1 5" Hg at 3,000 RPM operated without a wetting agent.

Utilizing a wetting agent of low viscosity, such as water or alcohol, the pumps develop a vacuum of 20" Hg at 3,000 RPM, and using wetting agents of higher viscosity would produce even higher vacuums. Unlike other self-priming pumps, which depend upon moving parts within their pump chambers which make physical contact 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 not affected through extended use.In addition, the tips of the impeller lobes incorporate a spoiler and two tracking tips separated by relatively wide surfaces which have a radius slightly less than the radius of the pump chamber in which the impeller revolves, the tips of which alternate in affecting a sealing surface between the lobe ends and the adjacent interior compound curves of the opposing impeller. Such a structure, although appearing to be more complex than many other impellers, is actually simpler, easier and less expensive to fabricate than impellers having a single radiused tip, also such impellers will automatically wear incrementally to compensate 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 wear to the single-point tips causes a permanent gap between the worm 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 effecting the sealing clearance between the impeller ends and the adjacent pump chamber walls, therefore the structure extends a pump's useful life considerabiy beyond that possible to other similar structures.

The unique combination of the impeller structure results in a pump capable of performance which sets it apart from other selfpriming pumps, resulting in a pump of greater versatility, efficiency and durability than that 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: Figure 1 is a transverse cross-sectional view of a pump embodying the invention; Figure 2 is the same transverse cross-sectional view shown in Figure 1, but with the first and second impellers moved to different positions; Figure 3 is a fragmentary view showing a tip of the impeller to an enlarged scale; Figure 4 is a partially diagrammatic sectional view of a pump taken on line 4-4 of Figure 1; Figure 5 is an end view of an impeller; Figure 6 is a fragmentary view showing the co operating engagement between the two impellers; and Figure 7 is the same view as Figure 6, with the impellers in different relative angular positions.

Referring more particularly to the drawings, there is shown a pump having a housing 12 in which are formed two chambers 2, 4. The chambers are formed by 1 900 arc cross-section internal walls 68 and are separated by an inlet area 20 and an outlet area 22. Disposed within each chamber is a respective four lobe impeller 14, 1 6. The impellers are driven in synchronism 450 out of phase from drive means 72 by way of mating timing gears 78, 80. The gears are disposed in the pump housing and are sealed from the chambers 2 and 4 by seals 88. The impellers 14, 1 6 are secured to respective 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 concave arc side walls 58, 60 disposed 900 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 56. The concave side walls 58, 60 flow into and couple to exterior convex arc side walls 66, 64 which in turn flow into and connect to dual slightly extended tips 56, 54. Each of said tips is separated from the opposite tip on the end of the lobe by an arcuate tip indentation 70.

Each impeller is coaxially disposed in its respective chamber and runs with slight clearance therein. That is to say, the tip radius is slightly less than the radius of the 1900 arc interior side wall 68. The impellers rotate together and are spaced apart so that upon rotation the tip of one lobe just fails to touch the concave arc side wall of the opposing rotation by a small distance. The interior side walls of the impellers comprise two arcs 58, 60 of identical radius having centres slightly disposed from one another, the adjoining portions of the arcs being smoothed out over a distance of slightly less than 470 so as to give the interior side walls a generally circular but slightly elliptical cross-section.

The dual tips 54, 56 of the impeller lobes have wide surfaces 62 which are slightly radiused.

Contact is made alternately between the tip 54 and concave surface 58 and between tip 56 and concave surface 60 during rotation of the impellers. A structure of this type is more easy to fabricate and less expensive than impellers having a single radiused tip.

By providing dual tips the life of the pump is extended, as the wear of each tip is approximately half that of the wear on a single radius tip.

In operation, the rotating impellers 14, 1 6 form generally sealed spaces between their lobes and the adjacent 1 900 arc cross-section interior walls 60 through which fluid is pumped from the inlet area or chamber 20 to the outlet area or chamber 22 as the impellers are counter-rotated. A space is formed between the tips 62 of one impeller and the adjacent interior concave arc side wall 58, 60 of the opposite impeller during operation which is less than ten percent the size of the space formed between adjacent lobes and the 1 900 arc interior wall of the housing and through a smaller space fluid flows back from the outlet side to the inlet side. The shape of the impellers are such as to minimize the amount of flow and vibration caused by fluid flowing back through the smaller space from the outlet side to the inlet side.

Field tests have shown the pump, utilizing the improved impeller structure of the invention, at least in its present production model having a net displacement of 19 Cu. In., requires only 50% of the input energy required by centrifugal pumps of identical capacity. Pumps employing the invention structure combine most of the desirable performance attributes of both centrifugal and positive displacement pumps in one structure, thereby offering to the pumping industry a versatile tool that fills pumping needs with a significant saving in energy consumption.

Claims (6)

1. An impeller structure for a pump or motor having a symmetrical cylindrical housing with two 1900 arc cross-section interior walls separated by an inlet area and an outlet area, and accommodating two cylindrical axially symmetric identical impellers a selected distance apart, each impeller comprising four interior concave arc sidewalls which are disposed 900 apart and which form the base of four lobes, and which flow into and couple to exterior convex arc sidewalls which in turn flow into and connect to dual slightly extended tips, each of said tips being separated from the opposite tip on the end of the lobe by an arc tip indentation.

2. An impeller structure as claimed in claim 1, in which each impeller is coaxial with the 1 900 arc cross-section interior wall of the housing adjacent to it and has a radius very slightly less than the radius of the 1 900 arc, 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 sufficient size so that the impellers are placed just far enough apart so that the tips of each impeller fail by a small distance to touch the adjacent interior conave arc side wall of the opposing impeller during rotation.

4. An impeller structure as claimed in claim 1, 2 or 3 in which the impellers are rotated in opposite directions 450 out of phase by timing gears which are driven by driving means.

5. An impeller structure as claimed in any of claims 1 to 4, in which the interior side walls of the impellers comprise two arcs of identical radius having centres slightly disposed from each other, the adjoining portions of the two arcs being smoothed out over a distance of slightly less than 47 so as to give the interior arc side walls a generally circular but slight elliptical cross-section.

6. An impeller structure constructed and arranged and adapted to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.