Title:
WATER JET PROPULSION UNIT
United States Patent 3824946


Abstract:
A water jet propulsion unit including two deflector blades which are located in the pressurized water stream emanating from a rotatable impeller and being movable about respective pivots by steering means so as to deflect the water stream to give directional control to an associated craft. The blades are moved in the same directin of rotation by the sterring means so as to emanate a parallel relationship. Actuating means are also connected to the blades and are operative to move the blades in opposite directions about their pivots so as to locate them in a position such as to direct the stream of water forwardly of the craft and thereby create rearward propulsion. The impeller is mounted in the housing which also carries the deflector blades and is arranged for attachment to the outside of the rear wall of the craft, and water is fed into that housing through a tunnel member secured within the craft and extending between the rear and bottom walls thereof.



Inventors:
Macardy, Douglas (Victoria, AU)
Kelly, Ian William (Victoria, AU)
Application Number:
05/284913
Publication Date:
07/23/1974
Filing Date:
08/30/1972
Assignee:
MACARDY D,AU
KELLY I,AU
Primary Class:
International Classes:
B63H11/117; (IPC1-7): B63H11/10
Field of Search:
115/11,12R,13,14,35R 244
View Patent Images:
US Patent References:
3570247N/A1971-03-16Denning et al.
3561392UNIT OF PROPULSION BY HYDRODYNAMIC REACTION1971-02-09Baez
3283737Jet propulsion device for water vehicle1966-11-08Gongwer
3187708Propulsion device1965-06-08Fox
2460374Aircraft flight control system1949-02-01Walls
1670622Boat1928-05-22Hickman



Primary Examiner:
Reger, Duane A.
Assistant Examiner:
Sotelo, Jesus D.
Attorney, Agent or Firm:
Lerner, David, Littenberg & Samuel
Claims:
Having now described our invention, what we claim as new and desire to secure by Letters Patent is

1. A water jet propulsion unit including an open-ended tunnel arranged to be secured to a water-borne craft; an impeller rotatably mounted adjacent a rear end of said tunnel, operative to pressurize water passing through or received from said tunnel and project same towards an outlet opening of said unit; two deflector blades pivotally mounted adjacent said opening for movement between an open position in which they do not substantially effect the direction of emergence of said pressurized water from said opening, and a closed position in which they cooperate with each other to substantially prevent passage of said pressurized water through said opening; steering means for moving said blades about their respective pivots in the same direction of rotation through a range of steering positions in which each said blade is operable to deflect said pressurized water and thereby control the direction of emergence of same from said opening; said blades being mounted in side-by-side relationship and each having its pivotal axis located so that in a said steering position said pressurized water impinges on each of two sections of the said blade which are disposed on respective opposite sides of said axis; and an actuator is connected to said blades and is operable to move them between said open and closed positions by causing said blades to simultaneously rotate about their pivots in opposite directions respectively.

2. A unit according to claim 1, wherein said actuator includes a slidably mounted rod which is connected to links which interconnect said blades and are pivotally connected to one another; said actuator retaining said links against relative movement when in a forward drive position, and causing relative movement of said links when moved between said forward drive position and a reverse drive position.

3. A unit according to claim 2, wherein said steering means includes a rack and pinion assembly which is operable to move said blades in the same direction of rotation and maintain them in substantially parallel relationship in said steering positions, and said actuator rod is slidably mounted within a shaft to which said pinion is secured.

4. A unit according to claim 1, wherein at least one reverse drive opening is provided in a housing containing said impeller and secured to the rear end of said tunnel, said reverse drive opening being located forwardly of said outlet opening so as to allow escape of said pressurized water from said unit in one or more streams when each said blade is in the closed position, the said reverse drive opening being arranged so that a said stream emerges therefrom in a direction substantially opposite to that in which water emerges from said outlet opening when each said blade is in the open position.

5. A unit according to claim 1, wherein a series of water straightening vanes are located intermediate said impeller and said deflector blades.

6. A unit according to claim 5, wherein said vanes extend radially outwards from a conical hub member arranged coaxial with said impeller and diverging away from said impeller, and an annular discharge orifice is defined between the large diameter end of said hub and the surrounding surface of the housing containing said impeller.

7. A housing for a water jet propulsion unit, said housing being open ended and including a forward compartment for receiving an impeller, an outlet opening defined at a rear end, a conical boss located axially of said housing intermediate said compartment and said outlet opening and diverging away from said compartment, a series of water straightening vanes extending radially from said boss and connected to the surrounding wall of said housing, an axial bore formed in said boss for receiving portion of an impeller shaft, and two deflector blades arranged in side-by-side relationship and pivotally connected to said housing adjacent said outlet opening for movement about respective axes extended transverse to the longitudinal axis of said housing, each said blade being elongated in a direction of its pivotal axis and the said axis being located intermediate the longitudinal edges thereof.

8. A water jet propulsion unit including, an open-ended tunnel arranged to be secured to a water-borne craft; an impeller rotatably mounted adjacent a rear end of said tunnel and operative to pressurize water passing through or received from said tunnel and project same towards an outlet opening of said unit; two deflector blades pivotally mounted adjacent said opening for movement between an open position in which they do not substantially effect the direction of emergence of said pressurized water from said housing, and a closed position in which they cooperate with each other to substantially prevent passage of said pressurized water through said opening; steering means for moving said blade about their respective pivots in the same direction of rotation through a range of steering positions in which each said blade is operable to deflect said pressurized water and thereby control the direction of emergence of same from said opening; and an actuator is connected to said blade and is operable to move them between said open and closed positions by causing said blades to simultaneously rotate about their pivots in opposite directions respectively, said steering means including a cam mechanism operable to move a selected one of said blades through a limited distance from its closed position towards the open position when said actuator is arranged to locate said blades in their closed position, and thereby enable directional control in the reverse condition of said unit.

Description:
This invention relates to water jet propulsion units of the kind used in boats and other marine craft. For convenience, the invention will be hereinafter described in relation to boats, but it will be appreciated that the invention is applicable to other marine or water-borne craft not generally designated as "boats".

Water jet propulsion units generally include an open-ended tunnel which is arranged to be mounted in a boat so that the opposite ends thereof open through the base and stern of the boat respectively. Means is provided within the tunnel to draw water through the base opening, pressurize that water and discharge it through the stern opening as a pressurized stream or jet. The reaction between the stream or jet and the body of water supporting the boat, provides the propulsion effect.

The pressurizing means usually includes at least one impeller, and the section of the tunnel containing that impeller must be relatively straight so as to enable mounting of the impeller and minimize fluid leakage radially of the impeller, and also must be formed of a relatively hard material such as metal in order to keep wear within acceptable limits and obtain a reasonable operational life. As the impeller is generally mounted intermediate the length of the tunnel, the entire tunnel is usually made of metal. Because of the foregoing requirements, manufacture of the tunnel is complex and expensive, accurate mounting of the tunnel is difficult, and maintenance is complicated by the location of the impeller.

A further disadvantage of prior constructions is that directional control of the jet is normally effected by a nozzle or similar deflector which at least partially surrounds the ejected stream of water and is pivotally mounted so as to enable the direction of that stream to be changed. Such an arrangement is rather complicated, and the nozzle is difficult to turn because the contained stream always tends to return the nozzle to its neutral position. In addition, that arrangement makes it difficult to incorporate means whereby reverse movement of the boat can be effected. Such reversing means normally includes a pivotal shroud or chute, and is complicated even under favourable circumstances.

It is a principal object of the present invention to provide a propulsion unit of the kind indicated which is relatively simple and economic in construction and presents minimum difficulties in mounting within a boat. A further object of the invention in a preferred form is to provide such a unit which requires comparatively little effort to effect a change in direction, and which is able to effect reverse movement of the associated boat.

According to one aspect of the present invention, there is provided a water jet propulsion unit including, an open-ended tunnel arranged to be secured to a boat or other water-borne craft, a housing formed separate from and releasably securable across or to a rear end of said tunnel so as to receive water from said tunnel, and water pressurizing means mounted within said housing.

According to a further aspect of the invention, there is provided a water jet propulsion unit including, an open ended tunnel arranged to be secured to a boat or other water-borne craft, an impeller rotatably mounted at or adjacent a rear end of said tunnel and operative to pressurize water passing through or received from said tunnel and project same towards an outlet opening of said unit, at least one deflector blade pivotally mounted at or adjacent said opening for movement between an open position in which it does not substantially affect the direction of emergence of said pressurized water from said opening, and a closed position in which it substantially prevents, or it cooperates with a further said blade or blades to substantially prevent, passage of said pressurized water through said opening, and steering means for moving said blade about its pivot through a range of steering positions in which the blade is operable to deflect said pressurized water and thereby control the direction of emergence of same from said opening.

In a preferred form of the invention two blades are provided with their pivotal axes on opposite sides respectively of the centre of the outlet opening, and steering means is connected to both said blades and operative to cause the blades to move in the same direction of rotation and maintain them substantially parallel in their steering positions. It is further preferred that an actuator or selector be connected to the blades so as to enable rapid movement of same between their open and closed positions, and that actuator is preferably arranged so as to cause the blades to move in opposite directions of rotation.

The following description refers in more detail to these essential features and further optional features of the invention. To facilitate an understanding of the invention, reference is made to the accompanying drawings where these features are illustrated in preferred form. It is to be understood however, that the essential and optional features of the invention are not limited to the specific forms of these features as shown in the drawings.

In the drawings:

FIG. 1 is a side elevational view of one particular jet propulsion unit made in accordance with the invention, parts being broken away for convenience of illustration;

FIG. 2 is a transverse cross-sectional view taken along line II--II of FIG. 1;

FIG. 3 is a plan view looking in the direction of arrows III--III of FIG. 1, and showing the deflector blades in the open position;

FIG. 4 shows the blades in the same position as FIG. 3, but part of the actuator mechanism has been omitted to show the interconnection between the blades;

FIG. 5 is a view similar to FIG. 3 but showing the blades located in a selected steering position;

FIG. 6 shows the blades in the same position as FIG. 5, but part of the actuator mechanism has been omitted to show the connection between the blades;

FIG. 7 is a view similar to FIG. 3, but showing the actuator at a position intermediate the forward drive and reverse drive positions;

FIG. 8 is a view similar to FIG. 7 but showing the actuator moved fully in the reversed drive position;

FIG. 9 is a cross-sectional view taken along line IX--IX of FIG. 8;

FIG. 10 is a view similar to FIG. 8 but showing the steering mechanism operated to cause slight opening of one deflector blade;

FIG. 11 is an end elevational unit looking in the direction of arrows XI--XI of FIG. 1; and

FIG. 12 is a longitudinal sectional view of part of the housing showing pump or water cooling connections.

A propulsion unit according to the invention is shown in FIG. 1 and includes the usual open-ended tunnel 2 arranged to provide a communication between openings in the base 3 and rear wall or transom 4 of a boat. In contradistinction to prior units however, the pressurizing means 5 is not located within the body of the tunnel 2 so that the tunnel 2 can be manufactured with less concern for tolerances and wear-resistance. With regard to the last point, the pressurizing means 5 is located rearwardly of the stern end 6 of the tunnel 2 so that in use the tunnel 2 is subjected to lower internal pressure than is the case in prior constructions. Because of this novel arrangement the tunnel 2 can be manufactured of fiberglass, other reinforced plastics materials, or any other relatively inexpensive and easily workable material having sufficient rigidity to support the working pressures to which the tunnel 2 will be subjected.

Mounting of the tunnel 2 within a boat is greatly simplified with this construction since it is much easier to cut and shape the ends of the tunnel 2 to suit a particular boat. In addition, a tunnel 2 made of a plastics material can be easily bonded in place so as to form an integral part of the boat.

Yet another advantage arising out of this novel tunnel construction is that it does not require a straight section to contain the pressurizing means, and consequently water within the tunnel 2 is not subjected to sudden changes in direction. The longitudinal axis of the tunnel 2 can be formed as part of a circle, or it may follow the path of several merging arcs, or any other suitable path such as to effect desirable flow characteristics within the tunnel 2. Cavitation problems may be minimized by forming the tunnel 2 so that it gradually increases in diameter (the tunnel is usually circular in cross-sectional shape) towards the stern end 6, whereas the reverse generally applies in prior constructions, and such an increase need only be affected over an end portion of the tunnel as distinct from the entire length thereof.

As previously mentioned, the pressurizing means 5 is located rearwardly of the stern end 6 of the tunnel 2, and in the preferred construction shown it is arranged to be mounted externally of the rear wall or transom 4 of a boat so as to facilitate maintenance. In the construction shown, the pressurizing means includes an impeller 7 which is rotatably mounted within a housing 8. The impeller 7 may be of any suitable construction to produce a satisfactory pressure gradient, and if desired more than one impeller can be used. The housing 8 can be formed of metal or other wear-resistant material and is preferably arranged as shown to be bolted or otherwise releasably secured to the stern wall or transom 4 of a boat. As shown, the tunnel 2 and housing 8 cooperate through a spigot 9 and recess 11 provided on the stern end 6 of the tunnel 2 and the housing 8 respectively, so as to enable convenient and accurate location of the impeller housing 8 relative to the tunnel 2.

Drive means for the impeller may take any appropriate form, but in the preferred embodiment shown includes an internal combustion or compression ignition engine (not shown) having a drive shaft 12 which, in the assembled condition of the unit, connects with a further shaft 13 through an appropriate universal joint or coupling 14, which shaft 13 extends through a bearing part 15 of the tunnel 2 and has the impeller 7 mounted thereon. The impeller 7 is screwed or otherwise secured to the shaft 13 so as to rotate therewith, and an end portion 16 of the shaft 13 is rotatably supported within a bearing 17 secured to the housing 8 as hereinafter described. If desired that bearing may be located within a separately formed rear extension which is removably attached to the housing 8.

Water straightening vanes 18 are located directly behind the impeller 7 of the preferred embodiment shown to ensure that a maximum thrust effect is obtained from the pressurized stream of water emanating from the impeller 7. The vanes 18 may be of any known construction and as shown in FIGS. 1 and 2, are preferably secured within the impeller housing 8 so as to extend between the bearing 17 and the housing wall, and thereby provide a support for the bearing 17.

In the preferred construction shown, means is provided to form the pressurized stream so that it is substantially annular in transverse cross-section at the zone of ejection from the unit. Such means includes a cone or cone-like member 19 which is secured to the impeller housing 8 and is arranged to diverse rearwardly as shown in FIG. 1. Part of the impeller housing 8 surrounds the cone member 19 in radially spaced relationship so as to define an annular discharge orifice 21, which is more clearly shown in FIG. 9. In the form shown, the cone member 19 provides a hub or boss for the water straightening vanes 18, and also contains the rear bearing 17 for the shaft 13, which bearing can be water lubricated.

Steering of a boat powered by a unit according to the invention may be effected through a conventional rudder system, but in the preferred embodiment illustrated, the unit incorporates its own directional control means whereby the direction of emergence of the pressurized stream or jet can be regulated. Such control means preferably includes at least one blade located in the path of the merging stream and mounted for pivotal movement about an upright axis. The blade acts as a deflector when disposed angularly relative to the normal direction of emergence of the pressurized stream, and may be arranged to enable deflection of the stream through substantially 180° and thereby cause reverse movement of the associated boat. Ideally, the blade is elongated in the direction of its pivotal axis.

In the preferred construction shown, two deflector blades 22 and 23 are provided, although a greater number can be used if desired, and the blades are pivotally mounted at 24 and 25 respectively (see FIG. 5) on a shroud element 26 projecting rearwardly of the impeller housing 8. The blades 22 and 23 are mounted with their pivotal axes on opposite sides respectively of the centre of the annular discharge orifice 21, and the leading and trailing edges of each blade may be spaced a substantially equal distance from their respective pivot axes for a reason hereinafter made clear. Also, each pivotal axis 24 and 25 is preferably laterally spaced from the centre of the discharge orifice 21 by a distance substantially equal to the distance between that axis and the leading or trailing edge of the associated deflector blade.

The blades 22 and 23 are arranged and formed to be capable of closing the outlet end of the shroud 26 so as to effectively bar discharge of the pressurized stream rearwardly of the shroud 26. In practice some leakage may occur through that barrier, but the bulk of the stream will be deflected back towards the bow of the associated boat. The forwardly deflected stream escapes from the housing 8 through at least one opening 27 (see FIGS. 1, 2 and 9) defined between a front end portion of the shroud 26 and a part of the body of housing 8 located within that front end portion, but the openings 27 may be formed by any other suitable arrangement. For best results the escape openings 27 are located forwardly of the main discharge orifice 21.

Movement of the deflector blades may be effected through any appropriate steering means, and in the preferred form shown that means includes a rack and pinion assembly. The rack 28 is mounted to slide within guides (not shown) and is operatively connected to each blade 22 and 23 so that the pivotal position of each blade is determined by the position of the rack 28 within its guides. Linear movement of the rack 28 is effected by rotation of the cooperating pinion 29 which may be connected by means of a shaft 31 to a wheel, handle, or other manually operable device (not shown). The arrangement is preferably such that both blades 22 and 23 move in unison and always have the same position relative to the normal direction of discharge of the pressurized stream -- i.e., they are retained substantially parallel.

In the particular form of the invention illustrated, the rack 28 is operatively connected to the deflector blades 22 and 23 through opposed abutment surfaces 32 on the rack 28, each of which abutment surfaces 32 is engageable with a cooperable element attached to a respective one of the blades 22 and 23. The abutment surfaces 32 are formed on rearwardly directed projections 33 provided at each end of the rack 28, and each cooperable element is formed by an extension of a pivot pin 34 (see FIG. 11) associated with the respective deflector blade 22 or 23. Each pin 34 is connected to an end portion of a respective arm 35, one of which is secured to the pivot spindle 24 and the other is secured to the pivot spindle 25. Thus, the arms 35 move with the blades 22 and 23, and those arms are arranged so that the extensions of pins 34 are disposed between the opposed abutment surfaces 32 of the rack 28. The arms 35 are connected at their outer ends by two pivotally connected links 36 so that movement of one arm 35 causes corresponding movement of the other, and consequently the associated blade. That is, each arm 35 is pivotally connected by one of the pins 34 to an end portion of a respective one of the links 36.

Adjusting means may be provided to enable variation of the amount of free movement of the rack relative to the blade arms. In an arrangement not shown, such means may include an adjusting screw threadably mounted in the outer end portion of each arm and projecting therethrough so that a conical nose section of the screw depends from the arm and is engageable by the adjacent abutment surface of the rack. Each such abutment surface may be provided with a slope corresponding substantially to the taper of the aforementioned nose section, and the maximum clearance between each nose section and associated abutment surface is determined by the axial position of the screw relative to its arm.

The steering means described above may be used to turn the blades 22 and 23 into the position in which they close the shroud outlet and cause reverse movement of the associated boat. It is preferred however, that a separate reverse actuator is provided to enable positive and rapid movement of the blades into their reverse position. One such actuator, as shown in the drawings, includes an actuator rod 37 slidably mounted within an axial bore of the pinion 29 for operative connection to the blade steering arms 35. That connection is effected through a plate 38 secured to the rod 37 and having an aperture or recess 39 therein which defines opposed cam surfaces 41 (see FIG. 10) cooperating with a cam follower 42 attached to the steering arm links 36, which for this particular arrangement is formed by the pivot pin connecting the links 36. The link pivot pin 42 has its axis substantially parallel to the pivotal axes of the deflector blades 22 and 23, and if desired a roller may be mounted on that pin for engagement with the cam surfaces 41. The cam surfaces 41 are arranged so that longitudinal movement of the actuator rod 37 in a rearward direction (or a forward direction if preferred) causes the links 36 to collapse (see FIGS. 7, 8 and 10) about the central pivot 42 so that the two links 36 swing inwardly towards each other. Such relative movement of the links 36 causes the deflector blades 22 and 23 to move about their respective pivots 24 and 25, and relatively little movement of the actuator rod 37 is required to bring the blades 22 and 23 into a position in which they effectively close the shroud outlet as shown in FIG 8. A handle or other manually operable means (not shown) may be attached to the forward end of the rod 37 to facilitate operation thereof.

In the normal or forward position of the actuator rod 37, the plate 38 is arranged so that the two links 36 are retained in substantial alignment as shown in FIG. 4 so that the links 36 functions as a single rigid body. Each cam surface 41 is shaped to retain the links 36 in that position as the rack 28 and links 36 are moved endwise during steering operations. It will be appreciated however, that the actuator rod 37 can be moved to place the deflector blades 22 and 23 in their reverse position, regardless of the steering position of the rack 28 and links 36. Furthermore, when the deflector blades 22 and 23 are in the reverse or closed position it is preferred that they are disengaged from the steering means, and that may be achieved by having the blade arms 35 located so that the pins 34 are not engageable by the rack abutment surfaces 32, as shown in FIG. 10.

Steering during reverse operation of the unit may be effected in any appropriate manner, and according to the preferred arrangement the rearward projections 33 associated with the rack 28 each have a cam surface 43 which is cooperable with a cam surface 44 formed on the adjacent steering arm 35. The arrangement is such that, when the baldes 22 and 23 are in the closed position as shown in FIG. 8, each cam surface 44 is engageable by the adjacent cam surface 43 when the rack 28 is moved endwise in either of the two directions allowed by its associated guide. FIG. 10 shows the rack 28 moved in one direction so that the cam surfaces 43 and 44 shown at the lower part of the figure engage and cause the blade 23 to be moved slighty towards the open position such as to allow lateral escape of water from the housing 8. That lateral discharge will have a steering effect on the unit, and it will be appreciated that either blade 22 or 23 may be manipulated in this way to effect a desired direction of steering.

In an alternative arrangement not shown, a steering nozzle may be operatively connected to the reversing mechanism described. Preferably, two such nozzles are provided at the front region of the shroud on opposite sides thereof, and each may extend laterally from an upstanding receiver tube rotatably mounted in the shroud or some other part of the unit. Each receiver tube has a slot or other shaped port formed therein which communicates with the or a respective escape opening of the shroud when the reverse mechanism is positioned to locate the deflector blades 22 and 23 across the rear outlet of the shroud 26. The receiver tubes are also operatively connected to the steering means, at least in the reverse position of the actuator rod 37, so that steering is effected through movement of the rack which causes rotation of the receiver tubes with consequent change in the direction of discharge of the nozzles.

If desired, the nozzles may remain connected to the steering means in all positions of the actuator rod so that they extend rearwardly when the deflector blades are positioned for normal forward movement.

Retaining means (not shown) such as a springloaded ball detent and cooperable recesses, may be provided to releasably retain the actuator rod 37 in its forward, neutral and reverse movement positions. Preferably, the deflector blades 22 and 23 are operatively connected to the steering means in the forward position only of the actuator rod 37, which is shown in FIGS. 3 to 6. In the netural position of the rod 37 (shown in FIG. 7) the blades 22 and 23 are positioned so that they deflect the ejected water stream laterally in substantially opposite directions so that each part of the ejected stream counteracts the other, and the precise location of the neutral position may vary with conditions of use. In the neutral position, there is little or no tendency for the unit to drive an associated boat in a forward or reverse direction.

A cover (not shown) of reinforced plastics or other suitable material may be located over the steering and reverse mechanisms for protection of same, and provision is made to allow easy removal of that cover for maintenance purposes.

When a unit according to the invention is mounted on a boat, it is preferably arranged so that the normal direction of discharge of the pressurized stream is in substantial alignment with the longitudinal axis of the boat. Thus, the boat is caused to follow a straight line in the forward direction when the control blades 22 and 23 have their deflection surfaces, which are preferably flat, arranged parallel to the normal direction of discharge. When it is desired to turn the boat, the blades 22 and 23 are moved through an appropriate angle (FIGS. 5 and 6) by means of the steering mechanism and such movement encounters minimum resistance by the pressurized stream because that stream impinges against substantially equal areas of each blade 22 and 23 on both sides of the respective blade pivot. Thus, the forces acting on each blade 22 and 23 are substantially balanced in all blade positions.

Reverse movement of the boat can be rapidly effected by pushing the actuator rod 37 into its reverse position as shown in FIGS. 8 and 9, and in that position the outlet of the shroud 26 is completely closed. Steering of the boat when reversing is effected by moving the rack 28 into a position such that one of the cam surfaces 44 engages its adjacent cam 43 and thereby cause opening movement of the associated blade 22 or 23. Such movement does not detract significantly from the reverse drive force of the unit, but permits a lateral discharge as shown in FIG. 10, which is sufficient for steering.

It will be appreciated that a propulsion unit as described possesses numerous advantages over prior water jet units. The advantages arising out of the particular tunnel and impeller housing arrangement have already been discussed. Another important advantage is that reverse movement of an associated boat can be effected in a simple and positive manner. Still further, the use of an annular discharge orifice permits the size of the unit to be condensed and also enables production of lower discharge velocities and a greater volume in the pressurized stream ejected by the unit. Reduction in size of the unit as compared with prior constructions permits the use of heavy materials such as bronze, for the impeller housing without resulting in an excessively heavy unit.

Finally, it is to be understood that various alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the spirit or ambit of the invention.