US3367274A

US3367274A - Rotary pump

Info

Publication number: US3367274A
Application number: US575322A
Authority: US
Inventors: Ralph S Lombard
Original assignee: Textron Inc
Current assignee: Textron Inc
Priority date: 1966-08-26
Filing date: 1966-08-26
Publication date: 1968-02-06
Anticipated expiration: 1985-02-06

Description

Feb. 6, 1968 R- S. LOMBARD ROTARY PUMP Filed Aug. 26, 196

3,367,274 ROTARY PUMP Ralph S. Lombard, Stamford, Conn, assignor to Textron, Inc, Providence, ILL, a corporation of Rhode Island Filed Aug. 26, 1966, Ser. No. 575,322 6 Claims. (Cl. 103-103) The present invention relates to rotary pumps and particularly to self priming pumps capable of handling liquids containing solid pieces or particles. Such pumps are useful, for example, in pumping water from ditches or excavations where stones or other solid objects may be drawn in through the suction line of the pump.

A rotary pump of the kind of which the invention relates comprises an impeller rotating in a housing or casing having inlet and discharge passages. The impeller is mounted on a shaft driven by a suitable motor, for example an internal combustion engine.

When a pump of this kind is used to pump water or other liquid containing solids, for example sticks or stones, considerable damage may be done in the event a solid object jams or wedges between the impeller and the housing. Since the driving motor has a considerable amount of rotational inertia, high forces are generated when the impeller is suddenly jammed or blocked. This may result in breaking the impeller or housing or other serious damage to the pump or to the engine driving the pump.

The present invention is directed to the problem of overcoming this difficulty and protecting the pump and engine from damage when such blocking or jamming by a solid object occurs. The problem is complicated by the fact that in order to provide good self-priming characteristics, the radial and axial clearances between the rotor and portions of the housing must be carefully selected and rigidly maintained. Hence, conventional flexible connections permitting considerable relative movement are not satisfactory. Moreover, in order to maintain high vacuum in the final stages of priming, the impeller must be mounted on the shaft in such a way as to avoid any air leakage that would dissipate the vacuum.

In accordance with the invention, there is provided a novel rotary pump, and in particular a novel mounting of the pump impeller on the drive shaft, which makes it possible for the pump to be blocked or jammed repeatedly by solid objects drawn in through the pump intake without material damage to the pump or to the impeller mounting or engine. For example in tests, pumps in accordance with the invention have been found capable of withstanding repeated jamming by used spark plugs fed into the liquid intake of the pump.

The nature and characteristics of the invention will be more fully understood from the following description of a preferred embodiment shown by way of example in the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view of a pump and a portion of an engine by which the pump is driven.

FIG. 2 is an enlargement of a portion of FIG. 1 showing in more detail the mounting of the impeller on the drive shaft and,

FIG. 3 is a perspective view of a bushing incorporated in the impeller mount.

In the drawings, a pump P in accordance with the invention is shown mounted on an internal combustion engine E by which the pump is driven. The engine B (only a portion of which is shown in the drawing) comprises a housing or casing 10 with a cylinder 11. A crankshaft 12 is rotatably mounted in the housing by suitable bearings of which two are shown at 13 and 14 as ball bearings having inner and outer raceways. The bearings rotatably supoprt the shaft radially and also position it in an axial direction. The housing includes a crankcase portion 15 containing a crankpin 16 on a counter-weighted States Patent f 3,367,274 Patented Feb. 6, 1968 crank disc 17 which is integral with, or fixed on, the shaft 12. The crankpin 16 is connected by a suitable connecting rod .(not shown) to a piston (not shown) reciprocating in the cylinder 11. A fan 18 having a hub portion 19 is keyed on the shaft 12 and is secured by a nut 21 screwed onto a threaded portion 12a of the shaft 12. The hub portion of the fan bears on the inner race of the hearing 13 which is spaced by a sleeve 22 from the inner race of bearing 14 which in turn abuts the crank disc 17 so as to position the assembly in fixed position on the shaft 12. The nut 21 provides a shoulder on the shaft for positioning the impeller of the pump as will appear below. A shim or washer 23 is shown interposed between the nut 21 and the hub portion 19 of the fan. The shaft 12 is provided with suitable oil seals of which one is shown at 24. Other portions of the engine which are not needed for an understanding of the present invention are not shown or described.

The pump P has a casing or housing 25 which is shown as comprising a back plate 25a including a housing for the fan 18, an impeller chamber 25b having a suitable volute passage and an end plate 25c. The several parts of the housing are assembled and secured together by suitable means such as screws or bolts (not shown). Fluid tight seals between the portions of the housing are provided by O-

rings

26, 27 and 28 and by a Neoprene washer 29. The pump casing is likewise mounted on the engine E by suitable bolts or other means not shown. The pump housing is provided with a suitable intake or inlet opening 31, discharge opening 32 and drainage opening 33, normally closed by a suitable plug.

The pump P further comprises an impeller 35 which is mounted on and driven by the shaft 12 and is rotatable in the impeller chamber 25b of the pump housing. The impeller 35 comprises a hub portion 35a, a back plate or body portion 35b, and one or more vanes 350 of generally spiral configuration. In order to assure efficient operation of the pump and achieve effective priming, it is important to provide close clearances between the impeller and the wall of the impeller chamber as indicated at 36 and also between the periphery of the impeller and the cutoff or breakwater (not shown) of the volute portion of the impeller chamber.

A fluid tight seal between the hub portion of the impeller and the housing is provided by a sealing ring 41 carried on and rotating with the impeller hub and pressed by a spring 42 against a stationary ring 43 set into an annular recess in the housing. An O-ring 44 provides a seal between the housing and the ring 43. A bellows-like diaphragm 45 provides a seal between the sealing ring 41 and the hub portion of the impeller while permitting axial movement of the ring 41 under pressure of the spring 42.

The hub 35a of the impeller 35 has a central bore comprising a cylindrical portion 46a which receives and closely fits an end portion of the shaft 12, an intermediate cylindrical portion 46b of small diameter and a fursto conical or tapered portion 460 which increases in diameter in a direction toward the outer end of the impeller hub. Beyond the tapered bore portion 46c there is a counter bore or recess 46d of larger diameter than the maximum diameter of the tapered bore. An annular bushing 47 fits into the tapered bore 460 and has an inner diameter approximately equal to that of the intermediate bore portion 46b.

The impeller 35 is secured on the shaft 12 by a stud bolt or screw 50 which extends through the bore of the impeller and through bushing 47 and is screwed into a tapped hole 51 in the end of the shaft 12. The screw 50 has a head portion 50a, a smooth cylindrical shank portion 50b having a diameter fitting the inner diameter of the bushing 47 and a threaded portion 500 having threads matching those of the tapped hole 51. A washer 52 of hard durable material such as stainless steel is interposed between the head 50a of screw 50 and the outer end of the bushing 47. The washer 52 is of substantial thickness in an axial direction and has an inner diameter closely fitting the shank portion of the screw and an outer diameter substantially equal to the diameter of the outer end portion of the bushing 47. The direction of the threads of the screw 50 and of the mating threads of the tapped hole 51 in the end of the shaft 12 is such that rotation of the shaft 12 in the direction in which it is normally driven tends to tighten the screw.

The cylindrical bore 46a of the impeller hub closely fits the end portion of shaft 12 so as to center the impeller accurately with respect to the shaft, but it does not fit sulficiently tightly to provide a driving connection between the shaft and impeller or to prevent movement of the impeller relative to the shaft in an axial direction. The axial position of the impeller relative to the shaft so as to provide and maintain close tolerances of the clearance 36 is provided by shimming between the inner end of the propeller hub and the nut 21 screwed onto a threaded portion 12a of the shaft to secure the fan 18 in assembled position as described above. Accordingly one or more shims 53 are interposed as required between the nut 21 and the inner end of the impeller hub to achieve the desired clearance. The impeller hub is secured on the shaft 12 and pressed tightly toward the nut 21 by the screw 5% Because of high pressures generated when the impeller strikes a solid object, the shim 53 should be of hard durable material such as stainless steel rather than softer material such as brass.

A driving connection between the shaft 12 and the impeller of the pump is provided by the bushing 47 and screw 50. The bushing 47 is formed of elastomeric material which is hard and yet capable of flow and elastic deformation under sumciently high forces. When the screw 5-) is tightened, the pressure applied through the washer 52 wedges the bushing 47 tightly in the tapered bore portion 460 of the impeller hub and causes the bushing to grip tightly the shank portion of the screw. The bushing is substantially fully confined by the impeller hub, screw and washer 52 so as to prevent extrusion of the bushing material.

The bushing also provides an air-tight seal between the impeller hub and the screw 50 to prevent the ingress of any air between the impeller and the shaft during priming. In the final stages of priming there is a high vacuum in the impeller chamber and anything less than a completely gas-tight seal would permit air to enter and impair the priming characteristics of the pump.

The bushing 47 has an axial length approximately equal 1 to that of the tapered portion 460 of the bore in the impeller hub. The inner bore 47a of the bushing is cylindrical and of substantially the same diameter as the shank of the screw 50. The outer periphery 47b of the bushing is tapered to conform substantially with the taper of the bore portion 460 of the impeller hub. The taper is preferably of the order of 5 to degrees relative to the axis of the bushing, and preferably about 6 or 7 degrees. While the size and proportions of the bushing depend on the design of the particular pump in which it is used, it will usually have an axial length somewhat less than the inside diameter, but at least 50% of the diameter, and an outside diameter at the smaller end of the order of 30% to 50% greater than the inside diameter. As an example, a bushing for a 3 pump has an inside diameter of approximately 0.56 inch, a minimum outside diameter of approximately 0.77 inch, and a length of inch with a taperrelative to the axis of approximately 6.5 degrees.

An elastomeric material suitable for the bushing 47 has the characteristics of being hard, tough, resilient, abrasion resistant, oil resistant, and air resistant, with a high load bearing capacity in compression and a high shear strength. It should preferably be free of fillers which tend to restrict elastic strain. The material should also preferably have a sufficiently high co-etficient of friction with respect 4 to the surfaces engaged by the bushing to inhibit slipping. It has been found that the bore of the impeller can have a conventionally machined surface. Steel, stainless steel and chromium plated bolts have been found satisfactory for use as the screw 50.

It has been found that urethane compounds which have been compounded to provide a high durc-meter are satisfactory for use as the bushing 47. As an example, a urethane compound having the following characteristics has been satisfactorily used:

Durometer (Shore A or D) D Tensile strength, p.s.i 6500 Elongation, percent 250 Modulus, L-lOO 4700 Impact resistance, ft.-lb./in 1.2 Tear strength, lbs/in 1400 Compressive set (percent in 22 hrs. at 158 F.) 9

A pump having an impeller mounted in the manner shown and described has been found to withstand repeated jamming by solid articles such as spark plugs without material damage to the pump or engine. The elastic properties of the bushing 47, despite the high durometer of the material used, appear to cushion the impact sufficiently to avoid damage. There is no evidence of material abrasion or wear of the bushing indicative of excessive slipping. After repeated jamming tests, it appears that there has been slight further tightening of the screw 50. A small amount of extrusion of the bushing material may occur around the washer 52 despite the hardness of the bushing and its almost complete confinement. The driving connection between the screw 50 and the impeller provided by the bushing 47 is sufficiently positive not only to prevent any slippage of the impeller in normal use, but also to permit unscrewing the screw 5lleven after repeated jammingsby cushioned tangential hammer blows on the impeller.

While the invention has been described with reference to a preferred embodiment shown by way of example in the drawing, it will be understood that the invention is in no way limited to the precise details of construction shown and described, but may be modified within the scope of the appended claims.

What I claim is:

1. A rotary pump for liquids which may contain solids, said pump comprising a casing having an impeller chamoer with intake and discharge passages and a bore extending into said chamber, a shaft extending through said bore and adapted to be driven, said shaft having a tapped axial hole in its end and a shoulder spaced from the end, an impeller accommodated in said chamber and having a hub portion with a bore including an inner cylindrical portion fitting the portion of said shaft between said end and said shoulder and a tapered outer portion extending beyond the end of said shaft, a tapered bushing of hard elastomeric material seated in said tapered bore portion and having a central hole, a screw extending through said bushing into said threaded hole in the shaft, said screw having a head portion bearing on an outer end of said bushing to press said bushing axially inwardly in said tapered bore of said impeller hub and thereby provide a driving connection between said rotor and sltaft through said bushing, said driving connection being normally positive but permitting limited yielding to cushion the impact and avoid the breakage of parts in the event of a solid wedging between said impeller and easing.

2. A rotary pump according to claim 1, in which said bore in said impeller hub has an intermediate cylindr cal portion of a diameter to closely fit said screw and inhlbtt extrusion of the material of said bushing axially inwardly along said bolt.

3. A rotary pump according to claim 1, further comprising means for accurately positioning said impeller with espect to said shoulder on said shaft and for varying said 5 position selectively to locate said impeller with close clearances with respect to said casing.

4. A rotary pump according to claim 1, further comprising an annular washer between said screw head and the outer end of said bushing, said washer having an inner diameter to closely fit said screw and an outer diameter substantially equal to the diameter of the larger end of said bushing, said Washer substantially confining the outer end of said bushing against extrusion.

5. A rotary pump according to claim 1, in which said bushing has a durometer of the order of 75 on the Shore D scale.

6. A rotary pump according to claim 1, in which said bushing is formed of a hard, elastic urethane compound.

References Cited UNITED STATES PATENTS 2,669,938 2/1954 La Bour 103-111 3,253,136 5/1966 Faul 287-5206 FOREIGN PATENTS 535,747 4/ 1941 Great Britain. 329,480 6/ 1958 Switzerland.

HENRY F. RADUAZO, Primary Examiner.

Claims

1. A ROTARY PUMP FOR LIQUIDS WHICH MAY CONTAIN SOLIDS, SAID PUMP COMPRISING A CASING BETWEEN AN IMPELLER CHAMBER WITH INTAKE AND DISCHARGE PASSAGES AND A BORE EXTENDING INTO SAID CHAMBER, A SHAFT EXTENDING THROUGH SAID BORE AND ADAPTED TO BE DRIVEN, SAID SHAFT HAVING A TAPPED AXIAL HOLE IN ITS END AND A SHOULDER SPACED FROM THE END, AN IMPELLER ACCOMMODATED IN SAID CHAMBER AND HAVING A HUB PORTION WITH A BORE INCLUDING AN INNER CYLINDRICAL PORTION FITTING THE PORTION OF SAID SHAFT BETWEEN SAID END AND SAID SHOULDER AND A TAPPERED OUTER PORTION EXTENDING BEYOND THE END OF SAID SHAFT, A TAPERED BUSHING OF HARD ELASTOMERIC MATERIAL SEATED IN SAID TAPERED BORE PORTION AND HAVING A CENTRAL HOLE, A SCREW EXTENDING THROUGH SAID