Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
  • F04C13/00—Adaptations of machines or pumps for special use, e.g. for extremely high pressures
  • F04C13/001—Pumps for particular liquids
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
  • F16J—PISTONS; CYLINDERS; SEALINGS
  • F16J15/00—Sealings
  • F16J15/16—Sealings between relatively-moving surfaces
  • F16J15/34—Sealings between relatively-moving surfaces with slip-ring pressed against a more or less radial face on one member
  • F16J15/3464—Mounting of the seal
  • F16J15/348—Pre-assembled seals, e.g. cartridge seals

Definitions

• This invention relates to pumps, and espe ⁇ cially, but not necessarily exclusively to positive displacement pumps suitable for use, for example, in the food processing, pharmaceutical and chemical industries, where high standards of sanitation are demanded.
• a known form of sanitary positive displacement pump comprises a pump housing enclosing a pump cham ⁇ ber, and two rotors each having a plurality of lobes and mounted on respective shafts to be rotated in opposite directions for pumping fluid from an inlet to an outlet of the pump housing.
• the known pumps sometimes called lobe pumps, can be used for pumping liquids having a wide range of viscosities and are suitable for homogeneous liquids and liquids with particles and solids in suspension.
• a known seal arrangement is mounted externally of the pump housing and includes a pair of sealing rings urged into axial abutment, one ring being fast for rotation with and sealed to the shaft, and other ring being sealed to the pump housing and held against rotation. O-rings are employed to seal between the sealing rings and the shaft and housing respectively. A collar is clamped to the shaft by a grub screw and provides axial support for the rotating sealing ring which is 8798 '
• the latter ring is capable of moving axially to increase the contact pressure between the sealing rings, the spring being caused to be compressed, under the influence of liquid being pumped and under pressure penetrating into the seal arrangement and acting between the housing and stationary sealing ring. This movement ensures that the sealing force increases as the operating pressure of the pump rises so that the sealing rings do not become pushed apart by liquid becoming forced between them.
• the known seal arrangement performs satisfactorily, but it is not without its drawbacks and limitations. Because of the necessary working clearances there are gaps or voids into which the liquid being pumped penetrates and in which the liquid can stagnate or even crystallise or solidify depending on the nature of the liquid. As a result, frequent cleaning operations are necessary and since effective flushing of the spaces in question cannot be ensured by passing washing solutions through the pump it is essential for manual cleaning to be carried out, which involves the cover of the pump housing and the rotors being removed. These cleaning operations are obviously inconvenient and mean significant down time of the pump and the processing plant of which it forms part.
• a seal arrangement for sealing a rotor shaft to a pump housing comprising a first sealing ring carried on the shaft for rotation therewith, and a second sealing ring in axial abutment with the first sealing ring and non-rotatable relative to the pump housing, the second ring having an inner surface tapering towards the shaft in the axial direction away from the pump chamber.
• the seal arrangement of the invention marks a significant departure from conventional thinking. Instead of trying to keep spaces within the arrangement to a minimum, the stationary sealing ring defines an annular cavity of significant volume around the shaft, the cavity being so shaped that circulation of liquid within this spaced is produced under the effect of the rotating shaft. Due to friction, liquid in the seal cavity tends to rotate with the shaft.
• the pump can be cleaned well enough to meet sanitation regulations by washing through with cleaning solutions and without need for the pump to be disassembled.
• Another disadvantage of the known seal arrangement described above is that the grub screw locking the collar to the shaft can loosen and/or slip with the result that the seal leaks.
• accurate setting up is necessary to ensure correct location of the collar along the shaft when the seal arrangement is installed, the preload of the spring being determined by the collar position.
• a seal arrangement for sealing a rotor shaft to a pump housing comprising a first sealing ring carried on the shaft for rotation therewith, and a second sealing ring in axial abutment with the first sealing ring and non-rotatable relative to the housing, the first ring having a shoulder axially supported by a confronting shoulder formed on the shaft facing the second sealing ring.
• the first sealing ring is sealed to the shaft by a cylindrical seal element having an external flange portion engaged between the shoulders to be compressed therebetween.
• a seal arrangement for sealing a rotor shaft to a pump housing comprising a first sealing ring carried on the shaft for rotation therewith, and a second sealing ring in axial abutment with the first sealing ring and non-rotatable relative to the housing, the second sealing ring being received in a seal housing member mounted to the pump housing, and a single sealing element being arranged to seal the housing member to the pump housing and to the second sealing ring.
• the sealing element can conveniently take the form of an O-ring seal or other similar elastomeric sealing member.
• the seal housing member has a rebate in the inner surface thereof and arranged to define an inwardly opening groove with the outer surface of the pump housing, the O-ring being received in the groove and projecting therefrom into sealing contact with an outer surface of the second sealing ring.
• the sealing ring has at least one notch in its outer periphery and the housing has an integral dog which engages in each notch.
• the dogs can serve to retain a spring which urges the second sealing ring axially into abutment with the first sealing ring, which facilitates assembly of the seal arrangement.
• a construction in which an enclosure defines a chamber surrounding the seal arrangement and into which a barrier fluid can be introduced through a port in the enclosure.
• the enclosure is sealed to the pump housing and at the other end it is sealed to the shaft by a lip seal which contacts the rotating shaft.
• This arrangement is inconvenient because the lip seal can wear the shaft over the long term use, and disassembly of the seal arrangement is complicated.
• a seal arrangement for sealing between a rotor shaft and a pump housing comprising a first sealing ring carried on the shaft for rotation therewith, a second sealing ring in axial abutment with the first sealing ring and non-rotatable relative to the housing, an enclosure defining a chamber surrounding the sealing rings and including a port for supplying a barrier fluid to the chamber, the enclosure being sealed to the pump housing at one end and being sealed to the outer surface of the first sealing ring at the other end.
• a lip seal can be used to seal between the enclosure and the first sealing ring.
• the sealing ring is relatively simple and cheap to replace should it become worn by the seal.
• disassembly is facilitated by this sealing arrangement.
• the enclosure can be constituted by the aforementioned seal housing member whereby the manufacture and assembly may be facilitated.
• the rotors are fastened to their shafts so as to enable easy removal for cleaning purposes.
• the rotors are splined on the shafts and are fixed axially by nuts which screw onto threaded end portions of the shafts.
• a pump having a rotor removably mounted on a shaft and secured thereto by a threaded connector engaged with an end of the shaft, said connector having an integral external flange received in a counterbore of the rotor, and a sealing means being received between the peripheral surface of the flange and the counterbore.
• the sealing means may be an O-ring and apart from providing an effective seal between the connector, and hence the shaft, and the rotor it also acts as a friction device to resist unintentional loosening of the connector due to vibrations and the like occurring during operation of the pump.
• Another disadvantage associated with the known lobe pumps and connected with the problems of cleaning stems from the fact that a seal located between the end face of the pump housing and the detachable cover is at least at some locations spaced at an appreciable distance from the inner edge of the housing end face. As a consequence small gaps can occur between the cover and housing which are open to the pump chamber and into which liquid being pumped can enter and remain. Once again these dead spaces cannot be effectively cleaned by so-called cleaning in place, i.e.
• the pump chamber has two portions of part circular configuration and each extending through more than 180° about the axis of a respective rotor. At each side these portions are connected by wall portions made slightly concave.
• the present invention provides a pump comprising a pair of rotors with lobes and arranged to cooperate with each other and with a pump housing to pump fluid from an inlet to an outlet upon rotation of the rotors in opposite directions, the pump housing defining a chamber including a pair of opposed straight parallel wall portions interconnected at opposite ends by substantially semi-cylindrical wall portions generally centred on the axes of the respective rotors, the housing having a cover attached thereto and closing the chamber, and an annular seal interposed between the housing and the cover and following in close proximity the edge of the pump chamber around the entire periphery thereof.
• the seal can follow very closely the inner edge of the end face of the housing and as a result dead spaces between the housing and the end cover are precluded.
• a pump having several benefits over the prior art can be obtained especially regarding the ability to be cleaned efficiently enough to meet sanitary regulations without need to disassemble any parts of the pump.
• cleaning operations are further facilitated by the pump being self draining, which is achieved, firstly by the inlet and outlet ports being located at the top and the bottom (rather than at the sides which is conventional) so that liquid can drain under gravity through the lower port when the pump is not operating, and secondly by liquid being free to flow under gravity out of the annular cavity of each shaft seal arrangement.
• Figure 1 is a side view of a positive displacement pump in accordance with the invention.
• Figure 2 is a top plan view of the pump shown partly in cross-section taken along the line x-x of Figure 1 ;
• Figure 3 is a sectional view showing one seal arrangement of the pump on an enlarged scale
• Figure 4 is a cross-section taken along the line A-A of Figure 3;
• Figure 5 is an enlarged schematic sectional view illustrating the liquid movement within the seal arrangement;
• Figure 6 is a view corresponding to Fig. 3 but showing a modified construction
• Figure 7 is a front view of the pump with the cover of the pump housing detached.
• FIG. 1 Illustrated in Figure 1 is a positive displacement pump of the so-called lobe pump type.
• the pump has a timing gearbox 1 with a single input shaft 2, and twin, parallel output shafts 3 which are driven at equal speeds, but in opposite directions, when the input shaft is rotated.
• a pump housing 5 and a front end cover 6 Secured to the forward end of the gearbox housing by bolts 4 is a pump housing 5 and a front end cover 6 which closes the pump chamber 7 defined within the pump housing.
• the pump chamber has integral connections 8, 9 for pipes to conduct liquid being pumped to and from inlet and discharge ports of the pump.
• the two output shafts 3 are journalled in the gearbox housing by bearings 10 (Fig. 2) and extend through seals 11 fitted to an end plate 12 which is bolted to the gearbox housing and closes its front end.
• the rear wa il of the pump housing 5 includes a flange 13 which locates within a rim 14 of the gearbox housing to ensure correct alignment between the pump chamber 7 and the axes of the shafts 3, which is important -te ensure that the rotors 16 attached to the shafts (as described in more detail below) do not come into contact with the wall of the pump chamber during operation of the pump.
• the rim 14 of the gearbox housing is machined, at its opposite sides, about respective centres coincident with the axes of the shafts 3. Hitherto, it has been normal to machine the rim about one centre, which is the centre line of the pump, i.e. midway between the axis of shafts 3.
• the shafts 3 project through respective openings in rear wall of the pump housing 5, to which wall the shafts are sealed by sealing arrangements 18.
• the ends of the shafts 3 received in the pump chamber are splined and receive the respective rotors 16, each of which has a plurality of lobes 19, which are four in number in the illustrated embodiment as best seen in Fig. 7.
• the rotors 16 cooperate, without coming into direct contact with each other or with the pump housing, to cause liquid to be transferred from the inlet port to the discharge port, when the rotors are contra-rotated by the shafts 3. To prevent any of the liquid entering the interstices of the rotors each is sealed to its shaft.
• one O-ring seal 22 is positioned between the rear face of the rotor 16 and a radial shoulder on the shaft 3, and a second O-ring 23 is located between the periphery of a_flange 20 and a surrounding surface of the rotor adjacent its front face.
• the flange 20 is integral with a front bolt 21 which screws into a tapped blind hole -provided in the end of the shaft 3 to secure the rotor 16 on the shaft.
• the rotor has a shallow counterbore for accommodating the flange and in addition to sealing between the flange and counterbore the O-ring 23 serves as a friction device to resist rotation of the bolt 21 to help prevent it undoing because of vibrations occurring within the pump. It will be appreciated that by virtue of the seals 22, 23 liquid is prevented from penetrating into and occupying any dead spaces within the rotors 16.
• the seal arrangements 18 are the same for each shaft 3 and one will now be described in detail making particular reference to Figs 3 and 4.
• the shaft is stepped with two cylindrical portions 30,31 separated by a radial shoulder 32, and the opening in the rear wall of the pump housing 5 is of sufficient diameter to define a substantial clearance with the portion 31 of smaller diameter. As shown, the opening is slightly smaller in diameter than the hub of the rotor 16.
• a pair of sealing rings 34, 35 are provided and have opposed plain faces adapted to abut in sealing cooperation with each other.
• One sealing ring 34 is carried on the shaft 3 and is fast for rotation with the shaft.
• the sealing ring 34 has stepped internal surface with smaller and larger diameter surface portions separated by a radial shoulder which is axially.supported by the shoulder 32 of the shaft 3.
• a sealing element 36 is interposed between the ring 34 and the shaft, the element having the form of a cylindrical sleeve with an external flange which is held between the confronting shoulders.
• a short axial slot 38 is provided in the ring at the end opposite the sealing face, and a pin 39 fixed into a hole in the shaft engages in this slot so that the ring 34 rotates with the shaft 3 b t-is not held against axial displacement.
• the second sealing ring 35 is mounted in a seal housing 40 which has a central boss received in a recess of the pump housing wall, and a peripheral flange which is fastened to the pump housing wall by the bolts 41.
• the boss has a stepped bore defining a radial shoulder facing away from the pump housing and a wave spring 42 is inserted between this shoulder and an external flange formed on the sealing ring 35 for urging the rinq 35 towards the first sealing ring 34, and hence biasing the sealing faces of these rings into sealing abutment.
• the housing 40 is formed with a plurality (three as seen in Fig. 5) of dogs 44 which engage in complementary notches provided in the flange of ring 35.
• the seal housing 40 is sealed to both the wall of the pump housing and the sealing ring 35 by a single O-ring seal 46.
• the central boss of the seal housing has a rebate which defines with the outer surface of the pump housing wall a groove of rectangular cross- section in which the 0-ring 46 is received.
• the O-ring is compressed between the bottom wall of the groove and the outer surface of the sealing ring 35 adjacent the end of the sealing ring nearest the pump chamber.
• the internal surface of the--sealing ring 35 is made frusto-conical so that it tapers inwardly in the axial direction towards the first sealing ring.
• the ring 35 defines with " the shaft 3 an annular cavity 48 of generally triangular cross-section. In operation of the pump, this cavity fills with liquid and, due to friction, is caused to be rotated by the shaft. Under the effect of the resultant centrifugal forces the liquid moves radially outwards and impinges against the inclined surface of the sealing ring 35 which directs the liquid back towards the pump chamber.
• the direction of liquid flow is illustrated by the arrows in Figure 5.
• the space 50 surrounding the sealing arrangements 18, between the gearbox and the pump head is connected to atmosphere via openings defined between the housings at the top and bottom of the pump.
• the modified seal arrangement depicted in Figure 6 is suitable for such applications.
• Most of the compo ⁇ nents are identical to those of the previous embodi ⁇ ment and are designated with the -same reference numer- als in the drawing.
• the seal housing 40 is in this case arranged to enclose a fluid compartment 55 around the sealing rings 34, 35, and has a port 56 for sup ⁇ plying barrier fluid to this compartment.
• the forward end of the housing 40 is sealed to the pump housing 5 and the ring 35 by the O-ring 46.
• the housing 40 carries a lip seal assem ⁇ bly comprising an annular sealing lip 52 which is in contact with the outer surface of ring 34.
• the ring 34 is of wear resistant material and is relatively cheap to replace.
• the cooperation of the lip seal with the ring 34 instead of with the shaft 3 as in prior art constructions, has a significant advan ⁇ tage.
• assembly and disassembly of the seal arrangement are much more convenient.
• the described pump is entirely self-draining.
• the inlet and outlet ports With lobe pumps it is usual for the inlet and outlet ports to be positioned horizontally, i.e. at opposite sides of the pump housing.
• the embodiment of the present invention has ports 8, 9 located at the top and bottom of the pump housing, as shown in Figure 1 , so that liquid can drain from the pump chamber and out through the port 8 when the pump is not operating.
• the cavity 48 of each seal arrangement (see Figs 3 and 6) is open to the pump chamber so that liquid drains from this cavity under the influence of gravity and will pass out through the port 8 with the other liquid when the pump operation is interrupted.
• the inner edge of the rear wall of the pump housing 5 does not extend inwardly beyond the seal 46 and as a result it is without any lip directed inwardly towards the shaft (a commonfeature of prior art seal arrangements) and forming a weir preventing liquid within the seal arrangement from draining back into the pump chamber. It will be understood that the self- draining characteristics contribute significantly to the ease of cleaning the pump.
• cover to the pump housing follows the line 63 and, as can be seen, is spaced at a significant distance from the edge of the pump chamber, especially at the interconnections between the part cylindrical portions 60 and the concave portions 61.
• the pump of the invention has a chamber with semi-cylindrical portions 65 connected together by straight parallel portions 66.
• the O-ring seal 67 which seals the cover 6 to the pump housing follows a line 68 which is closely adjacent the edge of the chamber around its entire periphery. Small dead spaces between the cover and housing in which liquid may collect are thereby obviated.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Details And Applications Of Rotary Liquid Pumps (AREA)
• Rotary Pumps (AREA)

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• 1988
  • 1988-03-16 GB GB888806242A patent/GB8806242D0/en active Pending
• 1989
  • 1989-03-16 EP EP19890904147 patent/EP0440622A1/de not_active Withdrawn
  • 1989-03-16 WO PCT/GB1989/000281 patent/WO1989008798A1/en not_active Ceased

Non-Patent Citations (1)

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