HELICAL GEAR PUMP

Abstract: A helical gear pump 18 has a rotor 44 rotatably mounted about the axis, the drive shaft 22, and at least two stators 42.1, 42.2, 42.3 of resilient material mounted operatively in series around the rotor 44, at least one of the stators 42.2 having an outer wall which is unconstrained against radial inward movement along a portion of its length. Delivery pressure in a clearance space 48 around the outside of such unconstrained wall of the stator 42.2, compensates at least in part for the internal pressure exerted radially outwardly tending to expand the stator 42.2. Such an arrangement, makes it possible the provision of less initial interference between rotor 44 and stator 42.2 thereby resulting in the use of a lower starting torque and making it possible for such pumps when fitted in boreholes, to be hand driven or to be driven by a windmill. Such an arrangement also makes possible the effective pumping of hot liquids, by having initial interference between the rotor 44 and the stator 42.2 than would have been necessary with a conventional rotor.

Description: THIS INVENTION relates to a helical gear pump. The Applicants are aware of different types of helical gear pumps. Each of these types includes an inner member, usually a rotor, and an outer member, which is usually in the form of a stator. The rotor has an external helical gear form with n starts. The stator has a complementary internal helical gear form with n + 1 starts. One of the said members, usually the stator, is of resilient material. In use, when rotary power is applied to the rotor, it rotates and orbits within the stator and, in engaging sealingly with the inner surface of the stator, causes pumping to take place by postive displacement of the rotor in the stator. Such pumps are capable of delivering against high delivery pressures, and are suitable for borehole pumps. They require good sealing and hence adequate initial interference between inner and outer members, so that interference and hence sealing will not be lost completely when the resilient member deforms under pump delivery pressure. However, such adequate initial interference may result in a high starting torque being required. Such a high starting torque may be a drawback when the pump is to be hand-operated. It is an object of this invention to provide a pump of this type, having a low starting torque, and thereby making it suitable-for use as a hand pump, capable of pumping from a deep well or borehole. Accordingly, the invention, according to one aspect, provides a helical gear pump having an inlet and an outlet, and which includes a rotor rotatably mounted about a longitudinal axis; and at least two stators of resilient material mounted operatively in series around the rotor, at least one of the stators having an outer wall which is unconstrained against radial inward movement along a portion of its length. The stators may be mounted in an outer sleeve having connecting means for connection to a delivery outlet. It may be a stator remote from the connecting means which has its outer wall unconstrained along a portion of its length. There may be provided a plurality of stators which have their outer walls unconstrained against radial inward movement along portions of their lengths. The invention, according to another aspect, extends to a borehole pump installation, which includes a rising main in a borehole and extending from a low level upwardly to a level above the mouth of the borehole; a helical gear pump as described, having its outlet connected to the lower end of the rising main; and a shaft inside the rising main, and connected to and extending upwardly from the rotor to a level above the upper end of the rising main; the rising main having an outlet opening opening at a high level, and the shaft at a level above the outlet opening being adapted for connection to a source of rotary power so as, in use, to cause rotation and orbiting of the rotor within the stators, and to cause water to be pumped from the borehole for delivery out of the outlet opening. The source of rotary power may be provided by manually-operable means which includes an arm operatively connected to the shaft, the arm having a handle whereby the shaft may be rotated about its axis relative to the rising main. The manually-operable means may include a pedestal mounted over and connected to the upper end of the rising main, the upper end of the pedestal supporting a bearing for the arm and having a clutch device to permit rotation of the arm in one direction only, about the rotational axis of the rotor. The pedestal may have a water outlet below the level of the bearing, and a sealing gland below the bearing, but above the water outlet, the shaft being adapted to pass sealingly through the sealing gland. The water outlet may be in the form of a spout directed downwardly from the pedestal. An upwardly directed baffle may be provided at the inner end of the spout. The invention, according to yet another aspect, extends to manually-operable means which includes a pedestal having mounting means for mounting it over the mouth of a borehole, and over the upper end of the rising main of an installation as described, and which has an arm operatively connectable via the connecting means to the shaft of the said installation, the arm being rotatably supported at the upper end of the pedestal about an axis which in use is co-axial with the shaft of the said installation. The rotational support of the arm by the pedestal may be provided by a bearing, and the pedestal may have a sealing gland below the bearing to permit the shaft to pass sealingly therethrough. The arm may be provided with gripping means for co- operating with the connecting means, the gripping means including two bushes in a transverse bore intersected by a longitudinal bore to accommodate the shaft, and the two bushes in use being urged together by a bolt passing through them to grip the shaft where it intersects the transverse bore. Instead of manually-operable means, the source of rotary power may be provided by a windmill-operated rotary drive having its output operatively connected to the shaft. According to another aspect of the invention, in the pumping of a fluid by a helical gear pump, which includes at least two resilient outer members arranged in series around an inner member, the inner and outer members being adapted to rotate and orbit relative to each other about a longitudinal axis, there is provided the method of using the delivery pressure of the fluid to exert external pressure on at least one of the outer members to balance at least to some degree the internal fluid pressure directed outwardly against the inner surface of the said outer member during pumping. The outer members may be stators and the inner member may be a rotor, the rotor being adapted to rotate and orbit inside the stators. The invention will now be described by way of example with reference to the accompanying diagrammatic drawings. In the drawings, Figure 1 shows a part-axial section through a borehole pump installation in accordance with the invention; Figure 2 shows a part-axial section of a stator-rotor combination mounted according to the invention; Figure 3 shows a part-axial section through an alternative stator-rotor combination according to the invention; Figure 4 shows a part-axial section through the upper end of a borehole hand pump installation according to the invention; and Figure 5 shows a part-sectional plan at V-V in Figure 4. Referring to Figure 1 of the drawings, there is shown a borehole, generally indicated by reference numeral 10. It has a borehole casing 12 within which a rising main 14 is centrally located by stabilizers 16 arranged at axially spaced intervals within the casing 12. A helical gear pump 18, according to the invention, is mounted at the lower end of the rising main 14. A foot valve and strainer 20 is provided below the pump 18. The pump 18 has a shaft 22 located centrally within the rising main 14 by bobbin bearings 24. Rotary power is applied to the shaft 22 by means of manually-operable means in the form of a hand pump arm 26 of a hand pump head, generally indicated by reference numeral 27. The hand pump arm 26 is rotatably mounted on pedestal 28 which is mounted by means of a base member 30 over the borehole 10. The pedestal 28 has a delivery or outlet pipe 32 which is provided with a baffle 34 on the inside of the pedestal so as to prevent the introduction of foreign matter into the pedestal 28 from outside, via the outlet pipe 32. The base member 30 is mounted on a concrete block 36 cast into the soil 38 around the mouth of the borehole 10. Referring to Figure 2 of the drawings, the pump 18 comprises a cylindrical casing 40 connected to the lower end of the rising main 14 (not shown). within the casing 40, stators 42.1 and 42.2 are mounted sealingly in tandem around the rotor 44. The ring 45 is arranged at the suction end of the stator 42.2. The rotor 44 is connected to the lower end of the shaft 22. The stator 42.1 is moulded into casing 42.11 which is attached to the casing 40. The stator 42.2 is moulded into ring 45 which is attached to the casing. A clearance space 48 is provided around the upper end of the stator 42.2. The rotor 44 will be arranged to have conventional radial interference with the stator 42.1, and little radial interference with the stator 42.2. The stators 42.1 and 42.2 are also arranged in timed relationship with each other relative to the rotor 44 and are held in position in the casing 40. Under no load, the radial interference between the rotor 44 and the inner surface of the stator 42.2 will be less than the radial interference between the rotor 44 and the inner surface of the stator 42.1. The shaft 22 is sufficiently flexible to take up the eccentricity of the rotor orbiting within the stator. It is therefore not necessary to have flexible connectors, such as universal joints and so on, in line with shaft 22. The shaft 22 is made up of a number of sections joined end-to-end. In use, there will be such interference between the rotor 44 and the inner surfaces of the stators 42.1 and 42.2 at start-up as can be tolerated. The interference provided by the stator 42.1 will be within a predetermined tolerance for start- up purposes, so that the starting torque will not be excessive. Referring to Figure 3 of the drawings, the arrangement is similar to that shown in Figure 2. The upper stator 42.3 is also sealingly mounted in similar fashion to the stator 42.2 within the casing 40. Rotor 44 and stator 42.2 of Figure 3 operate in the same way as described for the stator 42.2 and the rotor 44 of Figure 2. The stators 42.2 and 42.3 of Figure 3 are also arranged in timed relationship relative to each other and relative to the rotor 44, and are held in position in the casing 40. The delivery pressure at the outlet from the stator 42.3 will act on the outside of the stator in the clearance space 48 and will balance to some degree the internal pressure inside the stator 42.3. Thus, sealing interference between the stator 42.3 and the rotor 44 will be substantially maintained so that delivery can take place even under a high head. Referring now to Figures 4 and 5 of the drawings, there are shown details of manually-operable means in the form of a hand pump head 27, which includes the pedestal 28 rotatably supporting the arm 26 via anti-friction bearing 60. The arm 26 has a ratchet device 62 to prevent it from being turned in the wrong direction. The teeth for the ratchet device 62 and bearing 60 are mounted in a plug 64 which is located in the upper end of the pedestal 28. The shaft 22 passes through seals 66 which engage sealingly with the shaft 22 along its outer surface. The shaft 22 is locked in relation to. the arm 26 by gripping means which includes bushes 68 and 70 urged together by a bolt 72 passing with clearance through them. The bushes have faces 68.1 and 70.1 urged into gripping relationship with the shaft 22 by means of the bolt 72. The bushes are located axially in a bore 74 which is intersected by the shaft 22. If desired, the ends of the bore 72 are closed off by plugs 76 and 78 to prevent tampering with the locking arrangement on the shaft 22. The bolt 72 is provided with a socket head 72.1, further to discourage tampering if the cover 76 should be removed. In Figure 4 the plug 78 is shown removed. In a preferred configuration of the helical gear pump, the stator has three starts and the rotor has two starts. The lower ends of the casing is conveniently threaded to engage with a foot valve or a foot valve and strainer 20. In use, the direction of rotation of the rotor is arranged to take place in such a direction that water will be pumped upwardly. The upper ends of the stators 42.2 will be subjected to partial delivery pressure. The upper ends of the stators 42.1 and 42.3 will, on the other hand, be subjected to full delivery pressure. This is the pressure which is applied to the clearance spaces 48. During start-up, the interference between the rotor and the stators 42.2 and 42.3 can be minimal. As pressure builds up, however, a tendency for the stators to expand under internal pressure can be cancelled or counteracted or compensated for by the external pressure around the outside of the stators, in the clearance spaces mentioned. It is thus possible to start with minimal interference between the rotor and the stators, yet without the danger of losing necessary sealing interference, as pressure builds up inside the stators. Because of the compensating effect which the delivery pressure has on the outer surfaces of the stators 42.2 and 42.3, they may for brevity be referred to as compensating stators. The hand pump embodiment shown in the drawings, shows the handle connected directly to the pump shaft without an intermediate gear ratio. It is possible to have the pump shaft driven via a step-down or step-up drive to drive it slower or faster than the handle. Such a drive may be provided by chain and sprockets, V-belts and pulleys, or a gear drive with toothed gearwheels. The pump shaft may also be driven by a rotary windmill-driven shaft directly or via a step-up or step- down drive. A pump according to the invention, having a compensating stator, also has advantages in pumping hot liquids or in pumping cold liquids which later become hot. In order to allow for temperature, the moulded-to metal stator 42.1 must have greater initial clearance at low temperature. This would result in poor performance in the cold condition, if used alone, because of excessive clearance. The addition of a compensating stator 42.2 ensures adequate performance in the cold condition. As temperature rises, so the stator 42.1 expands, thereby taking up the greater initial clearance and providing required interference and hence good sealing at the final operating temperature. The Applicants have found that helical gear pumps having stators arranged in series in accordance with the invention, have low starting torques in practice yet have adequate deliveries even at high heads and at low speeds, without excessive torque requirements. Thus, such pumps are very suitable for use as hand pumps on boreholes. The Applicants have found that in order to pump at high heads an increase in length of a compensating stator will lead to an unacceptably high load torque and low delivery rate. They have found that this drawback can be overcome by mounting an equivalent length of compensating stators in series around a rotor. Such a pump does not have an unacceptably high load torque, and yet has an adequate delivery rate. In other words, a pump having a series mounting of compensating stators has an increased efficiency over a pump having a single compensating stator of a length equivalent to the series-mounted compensating stators.

Claims: CLAIMS 1. A helical gear pump having an inlet (20) and an outlet (32), a rotor (44) rotatably mounted about a longitudinal axis and a stator (42) of resilient material mounted around said rotor, characterised in that said stator comprises at least two stators (42.1, 42.2 or 42.3, 42.2) mounted operatively in series around said rotor and in that at least one of said stators (42.2) has a radially outer wall which is unconstrained against radial inward movement along a portion of its length. 2. A pump according to claim 1, characterised in that the stators (42.1, 42.2, 42.3) are mounted in an outer casing (40) having connecting means (14) for connection to said outlet (32). 3. A pump according to claim 2, characterised in that it is a stator (42.2) remote from said connecting means which is unconstrained along a portion of its length. 4. A pump according to claim 1 or 2, characterised in that a plurality of stators are provided which have their outer walls unconstrained against radial inward movement along portions of their lengths. 5. A pump according to claim 2 or 3, characterised in that it is mounted in a bore-hole pumping installation comprising a rising main forming said connecting means (14) which the pump at the lower end of the rising main which extends from a lower level upwardly to a level above the mouth of the bore-hole, in that a shaft (22) inside the rising main is connected to, and extends upwardly from the rotor to a level above the upper end of the rising main, in that the shaft has at a level above the outlet opening (32) means (26) to rotate the shaft whereby, in use, the rotor is caused to rotate and orbit within the stators to cause water to be pumped from the bore-hole for delivery out of the outlet opening. 6. A pump according to claim 5, characterised in that the rotating means is provided by a manually operated device including an arm connected to the shaft, said arm having a handle (26.1) whereby the shaft may be rotated manually about its axis. 7. A pump as claimed in claim 6, characterised in that the manually operable means includes a pedestal (28) mounted over and connected to the upper end of the rising main (14), the upper end of the pedestal supporting a bearing (60) and in that a ratchet (62) is provided to permit rotation of the arm in one direction only about the rotational axis of the shaft. 8. A pump as claimed in claim 7, characterised in that the pedestal (28) has the water outlet (32) below the level of the bearing (60). 9. A pump as claimed in claim 8, characterised in that the pedestal (28) has a sealing gland (66) below the bearing (60), but above the water outlet (32), said shaft being adapted to pass sealingly through the sealing gland. 10. A pump as claimed in claim 8 or 9, characterised in that the water outlet is in the form of a spout directed downwardly from the pedestal and in that a baffle (34) extends upwardly at the inner end of the spout.

Inventors: PAYNE, STANLEY ASHBOURNE EATON
Applicants: MONO PUMPS LIMITED
Application year: 1983
Main classification: F04C2
IPC codes: F04C2, E21B43