CENTRIFUGAL PUMP

Abstract: A centrifugal slurry pump has a vaneless impeller (30) with a smooth concave annular face (31) opposed to a smooth front plate (11) of the pump across the pumping chamber in the flow path between the inlet (37) and outlet (17). The flow path is thus smooth and is of constant effective cross-section between the inlet through the pumping chamber to the outlet to induce laminar flow through the pump.

Description: This invention relates to pumps and particularly to centri­ fugal pumps for moving fluids or slurries of varying viscosities. Most impellers for centrifugal pumps have some type of vane to impart movement to the contained fluid or slurry through the pump. These vane-type impellers have limited life because of the problem of cavitation which causes the gradual deterioration or erosion of the surfaces of the vanes over time due to the movement of the materials in and around the vanes, creating pockets of vapor which explode causing damage. In addition, the typical vane-type impeller offers a very high starting torque under loaded conditions. Also, many pumps designed for the movement of high viscosity slurries are limited as to the particulate size that can be safely transited through the pump without unduly eroding the pump parts. Because of these problems, most pump parts must be manufactured of highly durable, and therefore expensive, materials. Also such pumps have relatively high operating costs. For optimum operation these known pumps are designed to operate with a particular specified material of defined viscosity and other characteristics and at a specified rotational speed. The shape of the vanes must be different when different pumping conditions are encountered. One of the earlier "Rotary Pumps" is typified by U.S. patent 651,400 of Trouve and Bellot (1900) in which the impeller was two conoidal shells with generatrixes which may be convergent, divergent or curvilinear and connected by rectilinear or helical ribs. There were a number of attempts in later years to improve the efficiency of impellers. Denys, in 1946 (U.S. Patent 2,392,124) designed a disc of concave-convex profile, a disc of uniform strength, in which the stress at any point between the centre and the rim was constant. His operating principle was that ligher molecular weight gases impinge more frequently on the rotating disk from left to right. The tangential component of rotation propels heavier molecules towards the outer periphery from where they are scavenged; lighter gas molecules are scavenged from the central outlet. Later Grantham (1951) in U.S. Patent 2,569,563 developed a centrifugal pump in which the impeller (frusto-conical) had a conical liquid-engaging surface with spiral grooves cut therein. Pumping space was adjustable to vary the volume of liquid pumped. A modification of the invention had a multi-cone impeller. Kletschka et al (1975) described in U.S. Patent 3,864,055 pumps which were capable of use as heart pumps and blood pumps. Circular fluid rotators (accelerators) were outwardly convergent and rotated to impel the fluid circularly at substantially the speed of the rotators. Angular velocity of the rotator increased as the radial distance from the axis increased. The pumping action was radially increasing pressure gradient pumping or more specifically, it was constrained force-vortex radially increasing pressure gradient pumping. The rotators were of hollow frusto-conical form, convergent at the peripherals. These same inventors designed similar devices, apparently with the primary objective of developing apparatus for use with delicate fluids. U.S. Patent 4,036,584 to Glass describes a "turbine" which is a multi-disk plate turbine reminiscent of Tesla. The turbine had tangential nozzle delivery to peripheral portions of the plates to impart motion. Discharge was through the centre. Spiral-like fencing was found between adjacent plates. Recent tangential art known to these inventors in U.S. patent 4,239,453 of Hergt et al (1980) which pump was designed for reducing cavitation-induced erosion of centrifugal pumps. A conical or stepped intake diffuser directs flow of part-load eddy from impeller back into intake fluid pulse flow. Downstream portion of the diffuser constitutes an integral part of the impeller. Pumps operating on the centrifugal principle which need not have vanes have been proposed in U.S. Patent 1,934,013 to Sim and Swiss Patent 393,092 inventor Helfer, but we have appreciated that these pumps will also cavitate and the impellers will suffer the same deterioration as the vaned pumps discussed above. The present invention is designed to overcome the drawbacks of prior art impellers that are subject to cavitation and to solve other problems associated with pumps, particularly centrifugal pumps, designed primarily for pumping slurries. The present invention in its various aspects is defined in the appended claims to which reference should now be made. A preferred embodiment of the invention is described below in detail with reference to the drawings. The preferred embodiment is a vaneless centrifugal pump designed to overcome the cavitation and maceration found in conventional centrifugal pumps by utilising design principles derived from aerodynamics. The impeller of the pump has a concave face configured from the centre of the impeller to the outer perimeter of the impeller, as shown in the accompanying drawings. The surface of the impeller is very smooth. The impeller is fastened to a shaft which is supported by a back plate. The back plate is configured to support the impeller and has a profile conforming to the rear surface of the impeller, permitting the impeller to nestle inside the back plate yet providing clearance between the impeller and the back plate. The back plate has an opening to receive the shaft mounted therethrough and to support the sealing housing containing the seal which surrounds the shaft. The back plate is coupled to a power frame or to an electric motor by means of an interconnecting frame adapter. Beyond the frame adapter the shaft is mechanically connected to a driving motor, not shown in the accompanying drawings, because suitable driving motors are well known in the art. A front plate is provided which, in conjunction with back plate and impeller, forms a pumping chamber. The front plate and back plate are attached together by mounting flanges, capscrews and nuts, proving a water tight seal. The front plate has input port, and provides an output housing and a discharge port. The front plate has a smooth interior surface configured, as shown in the accompanying drawings, to present minimal drag to the movement of materials pumped therethrough. The output housing joins the front plate at the discharge port and the upper end of the output housing connects to an output distribution system, not shown in the accompanying drawings. The interior surface of the front plate contributes to the efficiency of the vaneless centrifugal pump by the configuration of the interior surface, in accordance with the principles of the present invention, to present minimal drag to the movement of materials, such as fluids and slurries, passing by the interior surface on the way through the pumping chamber to the discharge port during the pumping operation. The shape of the impeller is such as to provide a concave annular surface the curvature of which gradually decreases as seen in radial section going outwardly from the centre. This is because the centrifugal force on the fluid increases towards the periphery. The front plate is carefully shaped relative to the impeller profile. The axial space between the front plate and the impeller decreases outwardly so that the effective flow cross-section is substantially constant from the intake port through the pumping chamber to the discharge port. More precisely, the pump provides for a constant volumetric flow rate right through the pump. Material entering the intake port of the front plate is diverted about the rotating impeller and redirected in an outward direction along the minimal drag interior surface of the front plate to the discharge port and the adjacent output housing. The incoming material stream follows an approximate Archimedian spiral, as seen axially of the fixed front plate, due to the fact that laminar flow is induced within the pumping chamber with substantially no cavitation whatsoever. The pressure applied against the impeller and the forces acting centrifugally on the material stream, join to produce the optimum imparting of kinetic energy to the material stream for the particular impeller speed. As a slurry pump, the vaneless design permits any particulate size of material which can clear the discharge port of the pump to safely pass through the pump without maceration or undue agitation. As cavitation is totally absent, the pump can easily handle the movement of fragile, volatile or gaseous materials. Lacking cavitation, the pump can be operated over a wide range of speeds, matching desired feed without undue loss of efficiency. Lacking vanes, the impeller offers very low starting torque under a loaded condition and thus obvious savings in operating and maintenance costs. The variable delivery of the pump and its ability to handle slurries of various densities, without cavitation, presents a significant advance in the art. The preferred embodiment of the invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a front view of a vaneless centrifugal pump, constructed in accordance with the principles of the present invention, showing the front plate and the output housing; Figure 2 is a fragmentary side sectional view of the vaneless centrifugal pump taken along line 2-2 of Figure 1 showing the front plate, the back plate, the impeller, and the design of the pumping chamber formed by the concave face of the impeller and the interior surface of the front plate; and Figure 3 is a perspective view from the left front of the impeller, showing the concave face of the impeller. The vaneless centrifugal pump illustrated is a compact, relatively small unit, which is easily and quickly installed at a site where the pumping of fluids or slurries is desired. Throughout the following detailed description of the pump like reference numerals are used to denote like parts disclosed in the accompanying drawings. The pump has a circular shaped housing, indicated generally at reference numeral 10, composed of a front plate 11 and back plate 12, which are held together by a mounting flange 13 along the outer perimeter of the front plate 11 and a mounting flange 14 about the outer perimeter of the back plate 12. Mounting flange 13 and mounting flange 14 are secured to one another by cap screws 15 and nuts 16. Optionally, mounting flange 13 and mounting flange 14 could be secured to one another by cap screws 15 and retaining threads (not shown) tapped into either of the mounting flanges. Extending upwardly from the right side of the front plate 11 (as seen in Figure 1) as an integral part thereof, is an output housing 17 which in turn fastens at its upper end to an output distribution system, not shown. Output housing 17 communicates with the front plate 11 through a discharge port 18, located at the junction of the front plate 11 and the output housing 17. Back plate 12 is configured to support an impeller 30 and has a profile conforming to the profile of the rear surface of the impeller 30. The back plate 12 has a vertical centre portion 19 and an extension portion 20 which flares inwardly, at approximately 35 degrees to the vertical, to join the front plate 11 at the mounting flange 13 and mounting flange 14. At the centre of the back plate 12, an opening 21 is provided to receive a shaft 22 and shaft sleeve 23. The shaft sleeve 23 is surrounded by a seal 24 which is held in place and kept moist by a seal housing 25, thus providing a waterproof juncture. Shaft 22 is secured to the impeller 30 by key 26. The back plate 12 is connected to a power frame 27 by a frame adapter 28 which bolts to the centre portion 19 of the back plate 12 by a plurality of mounting cap screws 29 spaced and tapped at equal intervals around the periphery of the centre portion 19 of the back plate 12. Shaft 22 is mechanically connected to a suitable driving motor, not shown. The impeller 30 is a circular rotor. The impeller 30 has a concave face 31 whose smooth surface is curved, from its centre 32 to its outer perimeter 33, as shown in Figures 2 and 3. The curvature gradually decreases over its outer peripheral portion. The rear surface 34 of the impeller 30 is shaped to conform to the dimensions of, and the enclosure formed by, the centre portion 19 and extension portion 20 of the back plate 12. The impeller 30 is fastened to shaft 22 by a capscrew 35, threaded into the end of shaft 22 and by key 26. A nose piece 36 is threaded or snapped onto the centre 32 of the impeller 30 to cover the attachment means just described and to preserve the curve of concave face 31. With an alternative form of fixing, a threaded fitment can be moulded into the rear of the impeller so that the nose portion can be part of the same integral moulding and a separate nose piece is not then necessary. The front plate 11 has an input port 37, and output housing 17 and discharge port 18. The front plate has an interior surface 38 configured to present minimal drag to the movement of materials pumped therethrough. The front plate 11 has input port 37 to access the concave face 31 of the impeller 30 designed and positioned to direct the incoming fluids or slurries in and around the centre 32 of the impeller 30, striking the smooth surface of the concave face 31 as the impeller 30 rotates, and inducing the laminar action effect observed in the art in stationary conduits. The combined forces, from the friction effect of the rotating impeller 30 and the centrifugal action of the moving material, accelerates the material rapidly, but smoothly, to discharge port 18 of output housing 17 and thence on into the output distribution system, not shown. The interior surface 38 of the front plate 11 is configured, in co-operation with the curve of the impeller 30, to present minimal pressure, and thus minimal drag, to the movement of the fluid or slurry as these materials move through the pumping chamber 39, to the discharge port 18. As best illustrated by Figure 2, the material stream to be pumped enters the pump through input port 37 where the stream strikes concave face 31 of impeller means 30 at approximately a right angle to the mean plane of the impeller 30. As the impeller 30 rotates, the material stream is redirected by the friction effect of the spinning impeller 30 outwardly towards the outer perimeter of the impeller 30, setting up laminar action along concave face 31 and increasing the angular velocity of the stream as it is diverted to the outer perimeter of the impeller 30 through pumping chamber 39 to the discharge port 18. The interior surface 38 of the front plate 11 is configured to present minimal pressure, and thus minimal drag, to the material stream as it is redirected by the impeller 30. The combination of the design of concave face 31 of the impeller 30, and the minimal pressure, minimal drag configuration of interior surface 38 of the front plate 11, together provide an environment in which laminar flow is set up, contrary to the situation in known pumps. Such non-turbulent fluid flow with a low Reynolds number is found to provide an optimum efficient environment for pumping materials of nearly all types, including slurries which have high viscosities. The absence of the usual gaseous bubbles generated by vane-type centrifugal pumps, overcomes the problem of cavitation which causes the gradual deterioration of the vanes, usually accompanied by a rattling noise and vibration of the pumping mechanisms. The absence of the vanes also permits the pumping of material of any particulate size, without maceration or undue agitation, which will clear the discharge port 18 of the vaneless centrifugal pump illustrated. Because of the laminar flow, the wear on the pump with slurries containing particles of a wide range of sizes is insignificant compared with known pumps. The absence of cavitation also permits the use of less expensive materials for casting the impeller 30, such as plastic, whereas vane-type impellers are normally constructed of highly durable metals to combat cavitation. Of course, vane-type impellers are by design more complicated and thus more expensive to manufacture than impeller 30. Being more complicated, centrifugal pumps having vane-type impellers are necessarily more expensive to manufacture and more difficult to balance than the vaneless centrifugal pump illustrated. The impeller 30, by its configuration having a reverse surface plane greater than 90 degrees of the horizontal axis of the inflowing material, automatically is exercising boundary layer control similar to that observed in aerodynamics. The shape of the impeller 30 controls the pressure by establishing a predetermined path for the material being pumped. The control is automatic because the pumped material follows the point of least pressure across the concave face 31 which is the path of least resistance. Graphically the material describes a streamline in the shape of an Archimedian spiral as the impeller 30 rotates, the streamline being similar to the upper surface of an aircraft wing. It is important that all irregularities on the opposed surface 31 of the impeller 30 and 38 of the front plate 11 are avoided, as even very small irregularities can upset the laminar flow and cause cavitation, thus destroying the pump efficiency. The curvature of the interior surface 38 of the front plate 11 is designed to complement and not to interfere with the laminar induced movement of the material as it heads for the discharge port 18. Trial and error observations during development by these inventors has established minimal drag to be evident when the chord of the Archimedian spiral described on the impeller 30 is exactly parallel with the chord of the streamline described by the movement of the pumped material along interior surface 38 of the front plate 11 between reference point 37 (input port) and point 11, where the front plate 11 joins the back plate 12. This appears to be achieved when the pumping chamber provides for a constant volumetric rate of flow through the pump, and the surface 38 of the front plate is shaped so as to produce this effect. It should also be noted that the cross-sectional areas of the intake and outlet ports will be the same as each other and as the effective annular cross-section through the pumping chamber. The precise shape of the outlet port may not be that important provided that it is smooth and does not upset the laminar flow through the pump. The efficient design of the pump reduces operating costs by requiring less torque to start the driving motors under load conditions. The pump will start even when full of, for example, wet sand, a condition that would normally cause known pumps to fail and burn out the motor or break the impeller. Similarly if flow through the pump stops for any external reason the impeller rotates freely without damage. There are no vanes to clog or present obstructions to the free flow of the material being pumped, thus minimizing wear and tear on the pump and reducing maintenance costs. Although the curve shown in the accompanying drawings is the preferred embodiment, the impeller 30 could be configured with concave face 31 ranging from 91 degrees to 135 degrees to the horizontal axis of the inflowing material. The manufacture of impellers and centrifugal pumps is well known in the art. The variables are the viscosity and specific gravity of the material being pumped, the RPM (revolutions per minute) of the pump motor, and the temperature of the pumped material. Impellers can be molded or turned on a lathe. The preferred embodiment of the vaneless centrifugal pump, shown in the drawings, could be manufactured by merely templating the curvatures of the impeller 30, the front plate 11 and the back plate 12, as shown, or as would show on a proportional enlargement of the drawings. Example I A pump with a 12 inch (30 cm) diameter impeller has a 2 inch (5 cm) diameter inlet and outlet. A valve is located in the outlet line. With the valve wide open and the impeller rotating a 3551 RPM, the pump passes 131.5 gallons (600 litres) per minute of water at an outlet pressure of 29.2 feet (8.9 metres) of head. Closing the valve to give zero flow rate causes the impeller speed to change only to 3556 RPM. The pressure at the outlet is 71.4 feet (22.7 metres) of water head. That is, as the valve closes the head pressure increases from 29.2 feet to 71.4 feet with no significant drop in RPM. In fact, there is a slight increase in RPM. Normally a test such as this would stall a pump or motor. The present pump just slips under this closed-valve condition. Example 2 Assume delivery requirement of 50 feet (15.2 metres) of head and 100 gallons (454 litres) per minute with 3 inch (7.5 cm) diameter pipework. Pick an off-the-shelf pump with 1800 RPM and 7½ HP. With a conventional pump designed to operate at a constant speed and a constant delivery, if you varied the speed to vary the delivery, you would get cavitation and rapidly erode the pump parts. The present pump avoids this problem by sizing the pump to use a 12 inch (30 cm) impeller. To vary the delivery from 1 gallon (5 litres) to 5000 gallons (22,700 litres) per minute, in principle we need only to vary the RPM from 500 to 3500, getting a head varying from zero to 150 feet (45 metres). The entering material finds its natural inflow path along the points of minimal pressure on concave face 31. The user can vary the speed to alter the delivery rate with no adverse effects on the pump. It should be noted that efficiencies of the order of 70% are obtained with such pumps. Other pumps depend on paddles or vanes to move fluids, not on the surface of the impeller, which is at a neutral angle of 90 degrees to the horizontal on most pumps. The present pump relies entirely on the concave face 31 of the impeller 30 to impart movement to the pumped material. The present pump has one design for one delivery, varying in size only to fit different diameters of input. The reverse plane of concave face 31 produces the laminar action describing an Archimedian spiral as the particles of pumped material pass from the centre to the outer edge of the revolving concave face 31. In summary, the slurry pump illustrated has many advantages, including the following, namely it is: 1) not subject to the cavitation or agitation found in conventional centrifugal pumps; 2) more simple and inexpensive to manufacture than pumps known in the prior art designed to perform the same function; 3) compact in size and unitary in design, to permit less costly installation and maintenance; and 4) more efficient to operate, presenting lower starting torque under loaded conditions. It will be appreciated from the above discussion that the invention provides a pump which has a smooth fluid flow path from the inlet past the impeller to the outlet. To this end the impeller is not required to have vanes, because the vanes can cause cavitation and upset the laminar flow. Furthermore, in vaned pumps the flow rate, viscosity and motor speed have to be specified for optimum operation. There may, however, be some circumstances where the inclusion of vanes is nevertheless appropriate, providing that the vanes are shaped to be strictly parallel to the local fluid flow path so as not to upset the laminar flow. In this instance the pump would be application-specific and would not have the advantage of being adaptable to different conditions as is the pump illustrated.

Claims: 1. A pump comprising an inlet port, an outlet port, a continuously movable impeller, and a flow path defined through the pump between the inlet port and the outlet port passing over the surface of the impeller, characterised in that the flow path is smooth throughout its length and in that the flow path and ports are of constant and equal effective cross-section such that laminar flow is maintained through the pump. 2. A centrifugal pump comprising a housing defining a circular pumping chamber, and an inlet port on the circular axis of the housing, an outlet port on the periphery of the housing, the pump chamber containing an impeller continuously rotatable about the said axis, and against which the pumped material passes, characterised in that the flow path from the inlet port through the pumping chamber to the outlet port is smooth throughout its length, and in that the cross-section of the flow path through the pumping chamber is constant and equal to the cross-section of the inlet and outlet ports, such that laminar flow is maintained through the pump. 3. A pump according to claim 2, in which the pumping chamber is effectively formed between a fixed plate about the inlet port and the impeller, the face of which is opposed to the fixed plate and the inlet port, the impeller face being of concave annular shape, the central portion on the said axis pointing at the inlet port and the peripheral portion being at greater than 90° to the said axis. 4. A pump according to claim 2 or 3, in which the impeller is vaneless. 5. A vaneless centrifugal pump, in combination with a driving motor, which comprises: a circular rotor to impart laminar movement to materials being pumped thereby, and having a concave face ranging at an angle from 91 degrees to 135 degrees in relation to the horizontal axis of the inflowing materials pumped therethough, a back plate for mounting said circular rotor thereon, and having a profile conforming to the profile of the rear surface of said circular rotor, and a front plate, in conjunction with said back plate and said circular rotor forming a pumping chamber, said front plate having input port, output housing and discharge port, which front plate has an interior surface configured to present minimal drag by narrowing in a radially outward direction with respect to said concave face of said circular rotor, to maintain the volume, and thus constant pressure, of said inflowing materials, and directing the movement of said inflowing material in a streamline, the chord of which streamline is parallel to the chord of an Archimedian spiral described by said inflowing material on said circular rotor.

Inventors: BROWN, CHARLES WILFRED, MANN, GEORGE ZEPHFUSS
Applicants: BROWN, CHARLES WILFRED, MANN, GEORGE ZEPHFUSS
Application year: 1985
Main classification: F04D5
IPC codes: F04D29, F04D5