WO1997006050A1

WO1997006050A1 - Cargo discharging pump

Info

Publication number: WO1997006050A1
Application number: PCT/NO1996/000204
Authority: WO
Inventors: Gorm Faerevaag
Original assignee: Frank Mohn Fusa A/S
Priority date: 1995-08-10
Filing date: 1996-08-09
Publication date: 1997-02-20
Also published as: NO953132L; AU6672496A; EP0844961A1; EP0844961B1; NO953132D0; NO300964B1

Abstract

A discharge pump (14) is submersible in the cargo of a cargo tank (10) of a ship via a well (12) at the bottom (11) of the ship's cargo tank (10). A stripping pipe (28) runs from the discharge side of the pump to a delivery location (A, E) via upper deck (22) of the ship. The pump (14) has an impeller (15) which is equipped with opposite pairs of locally defined blades (33, 34), which are disposed downstream just within inlet (13) of the pump (15), the stripping pipe (28) is supplied with pressure medium at a first, lower level and communicates with a pressure medium and/or vacuum source at least at a second, higher lying level of the stripping pipe (28).

Description

Cargo discharging pump.

The present invention relates to a discharge pump arrangement which is submersible in the cargo of the cargo tank of a ship and which has a pump inlet arranged in or at a well at the bottom of the tank.

More specifically the invention relates to an discharge pump arrangement, which is submersible in the cargo of a ship's cargo tank and which has a pump inlet arranged in or at a well at the bottom of the ship's cargo tank, where the impeller of the pump is equipped with an extra pump arrange-ment, which is drive connected to the impeller of the pump, and where the discharge pipe of the discharge pump over the deck of the ship is equipped with a closing valve and beneath the closing valve is coupled via an intake to a supply of compressed air or compressed gas and also between the closing valve and the discharge pump is coupled to an outlet for a stripper pipe having an associated closing valve relative to a delivery location via the upper deck of the ship..

By means of submersible discharge pumps in the form of hydraulic discharge pumps it is possible to unload cargo optimally with a stepless capacity control in all kinds of types of cargo. With pumps of the afore-mentioned kind there is employed for practical reasons a discharge pump in the form of an elongate, rigid pump arrangement, which is readily dis-mountable, that is to say inter alia easily submersible and hoistable relative to the well at the bottom of the cargo tank. There is employed a pump impeller which is driven by a hydraulically driven motor via a short drive shaft, the pump impeller and the pump motor being adapted to be arranged just at the bottom of the ship's cargo tank. In a practical construction the inlet to the pump is bounded between the bottom of the cargo tank and the opposite lower portion of the pump arrangement . The distance between the underside of the pump arrangement and the bottom of the well of the cargo tank is adapted according to the flow cross-section through the pump. Normally the discharge pump can empty the cargo to a level at the under side of the pump arrangement. There will consequently be left behind a first cargo residue in the well, that is to say at the level beneath the under side of the pump arrangement, together with a second cargo residue left behind within the pump itself.

In practice special problems are presented in getting the last residue of the cargo emptied out, which has collected between the under side of the pump arrangement and the bottom of the cargo tank. There have been employed hitherto, for example as is shown in NO Patent application 920380, separate suction arrangements for collecting such residues of the cargo, that is to say special suction arrangements, which operate independently of the discharge pump. Consequently it is possible to suck up the residues by means of a separate suction arrangement with separate driving means, but this requires extra piping and extra cleansing of this additional equipment, something which creates extra complications. In practice such suction arrangements are placed on the outer side of the pump arrangement as a separate unit. With particular types of cargo, for example with especially poisonous cargo types, such as prussic acid, such separate suction arrangements are complicated to use, as a consequence of the special properties of the cargo and the need for protection against poisoning and the need for complete cleansing of the equipment after use.

Alternatively so-called stripping arrangements have been employed in practice for collecting such residues of the cargo, that is to say stripping arrangements, which operate partially together with and partially independently of the discharge pump. By such stripping arrangements it has been possible to effect the cleansing in a controlled accurate and effective manner together with the discharge pump. By means of such stripping arrangements it has been customary, while maintaining the pump's impeller in operation with a certain pump pressure against the residual cargo in the pump, with an extra supplied counter pressure produced by compressed air or compressed gas, to blow the residues of the cargo from the pump pipe via a connected strip conduit to a suitable delivery location via the upper deck of the ship. An objective of the present invention is to use inter alia said stripping technique for removing the residues of cargo from the pump.

It is proposed in NO Patent Application 933729 to suck inwardly into the pump the largest possible amount of the cargo residue which otherwise is left in the tank well, by arranging an extra impeller in drive connection with the impeller of the pump, but then disposed a considerable distance in front, that is to say downstream of the pump's main impeller. By such a solution one is able to fetch up large quantities of cargo residue from the tank well, but a substantial problem is that the stripping equipment has simultaneously conferred an undesired reduced capacity on the pump under normal discharge operations. In order to avoid this problem it has been necessary to increase the distance between the tank well and the pump's inlet and the effect of the solution has therefore not been satisfactory for all purposes . Various proposals are additionally known for feeding pump medium from a feed impeller of a pump to its main impeller. More specifically it is proposed to arrange down-stream of the main impeller a feed impeller, which induces an extra flow of pump medium to the main impeller. Such proposals are evident from DE 1 045 237, DE 2 037 785, DE 2 545 736, US 3 304 877 and US 3 588 280. In all the said publications the flow of pump medium passes the feed impeller first and immediately thereafter passes the main impeller on a continuous course in a coherent flow path. The disposition and the design of the said feed impellers causes however an interference of the pump passage with a significant reduction of the discharge capacity of the pump as the final result. With the present invention the aim is inter alia to be able to solve the last-mentioned problem in a constructionally and operatively simpler manner. In addition the aim is to adjust the conditions so that the largest possible quantity of the cargo residues which necessarily remains in the pump arrangement after the conclusion of a normal discharge operation can be removed. This is solved according to the invention in that an extra pump arrangement is arranged on the pump's impeller in the form of opposite pairs of locally defined blades, which are located downstream just within the inlet of the pump, that the stripping pipe communicates with the pump housing or the lower portion of the discharge pipe at a first height level at the upstream end of the stripping pipe, where the stripping pipe is supplied with extra pressure medium internally via the discharge pipe, and that the stripping pipe communicates at least at a second height level substantially above the first height level with an internal and/or external pressure medium- or vacuum source for the supply of extra pressure medium or vacuum to the stripping pipe.

Without substantially affecting the flow path via the main impeller of the pump and without reducing the capacity of the pump, there is achieved according to the invention an increased sucking in effect in the direction of the cargo residue in the tank well and in addition it is made possible to ensure an effective sucking in and removal of the cargo residue which necessarily is to be found in the pump and its cargo discharge pipe.

By tests carried out with the stripping arrangement according to the invention particularly favourable results are achieved with a construction where a vacuum source is coupled to the downstream end of the stripping pipe, since then there can be utilised in an effective manner the combi-nation of the illustrated impeller with extra pump blades and a displacement of the pump medium by means of extra pressure medium at the upstream end of the stripping pipe together with an additional lifting of the pump medium in the stripping pipe by means of a vacuum source which is coupled to the downstream end of the stripping pipe. Furthermore it has proved favourable to employ a stripping outlet at a level from the discharge pipe, preferably a pair of stripping outlets from one and the same level of the pump housing via two parallel branch pipes . A single stripping outlet from the discharge pipe can alternatively be arranged at a certain height above the pump housing for example in a transition portion between the pump housing and the discharge pipe.

Further features will be evident from the following description having regard to the accompanying drawings, in which :

Fig. 1 shows schematically a pump arrangement according to a known construction which represents the state of the art, illustrated in side view.

Fig. 2 shows in side view a section of a lower portion of the pump arrangement according to Fig. 1.

Fig. 3 shows in vertical section the pump rotor of the pump arrangement and shows in addition a detail according to the present invention. 6

Fig. 3A-3C show an impeller according to the invention illustrated in a perspective view, plan view and in cross-section.

Fig. 4 and 5 show in side view and in section a first and a second construction of the pump arrangement according to he invention.

Fig. 6 shows in a corresponding side view, as shown in Fig. 4, a third construction according to the invention. Fig. 7 shows in a corresponding side view, as shown in Fig. 4, a fourth construction according to the invention.

Fig. 8 shows in a corresponding side view, as shown in Fig. 4, a fifth, modified construction according to the invention.

Fig. 9 shows a side view of the construction according to Fig. 8.

Fig. 10 shows in section and in side view additional equipment for use in the constructions according to Fig. 4-9.

By way of introduction there will be described with reference to Fig. 1 and 2, and also portions of Fig. 3 a known construction of a pump arrangement, which constitutes the state of the art relative to the present invention.

In Fig. 1 there is shown a cargo tank 10 of a ship, where the bottom 11 of the tank 10 is illustrated, which is provided with a locally defined tank well 12, in which there is submerged a lower end of the pump, that is to say an inlet end 13 shown for a pump arrangement 14. The pump arrangement 14 is adapted to function submerged in the cargo in the tank 10 in a relatively free downwardly hanging condition, with local centering side supports, not shown further, disposed at suitable height levels in the cargo tank, for example along the one tank wall.

The tank well 12 is, as shown in Fig. 3, given an optimum design for the sake of the collection and flow of cargo to the pump and is in this connection given a concavely rounded form. If desired in a manner not shown further there can be arranged on the bottom of the tank well 12 just below the inlet end 13 of the pump a cross- shaped portion or another portion which counteracts the flow of the cargo in a rotating manner along the bottom of the tank well 12.

The pump arrangement 14 according to the present invention is of a corresponding submersible type and has a corresponding sealing and a corresponding mode of operation to that which is illustrated and described in NO 123 115. DISCHARGE FUNCTION

In Fig. 1 there is shown a pump means comprising a pump impeller 15, which is received in a snail housing¬ like pump housing 16. The pump housing 16 is freely axially moveable relative to the well 12 and is centered relative to this by means of a combined support/ control and splash shield 16a, which is fastened with lugs 16b to the bottom 11 of the tank just by the tank well 12. At 16c (Fig. 3) there is shown an inverted funnel-shaped guide shield fastened to the pump housing 16 just beneath lower edge 15a of the impeller 15. The impeller 15 is driven via a short drive shaft 17 of a high pressure hydraulic drive motor 18. The drive motor 18 is connected to a remotely disposed source of pressure medium (not shown) via a coupling means 19 on deck 22 of the ship, by means of supply and discharge conduits (not shown further) for hydraulic drive medium. The coupling means 19 is placed on a hatch cover 20, which covers a hatch opening 21 on deck 22 of the ship. The supply and discharge conduits are surrounded in the illustrated embodiment by a common protective pipe 23, while the drive motor 18 is surrounded by an outer protective housing 24, in order to prevent any form of leakage of drive medium into the cargo, and vice versa, as is shown in NO 123 115. From two diametrically opposite sides of the pump housing 16 converge respectively a branch pipe 25a, 25b upwardly towards a transition portion 26a of a common cargo discharge pipe 26. The discharge pipe 26 and the protective pipe 23 for the hydraulic supply and discharge conduits separately pass through the cover 20. The discharge pipe 26 runs further to a suitable discharge location, as shown by an arrow A, on the ship's deck 22. In the upper horizontal portion 26b of the discharge pipe 26 shown in the drawing there is inserted a first closing valve 17, which is closed at the conclusion of the usual discharge operation. There remains hereby a certain amount of cargo in the discharge pipe 26 on the upstream side of the valve 27 and on the downstream side of the pump impeller 15, the pump impeller 15 providing for sufficient pump pressure against the cargo residue in the discharge pipe 26 so as to counteract the exhaust of this cargo residue back to the tank well 12.

FIRST KNOWN PORTION OF STRIPPING FUNCTION:

The cargo residue which remains behind in the discharge pipe 26 below the valve 27, when this is closed, and the cargo residue R (10-12 litres) , which remains behind in the tank well 12, are thereafter removed by means of a stripping function, in which the pump impeller 15 is maintained in continuous operation also after termination of the normal discharge operation. Hereby one can proceed continuously from the normal discharge operation to the subsequent stripping operation, without a break.

According to the invention it is emphasised that a conventional discharge operation shall be conducted under optimum conditions and that the remaining, subsequent functions must be adapted according to existing discharge equipment. Consequently the stripping operation is undertaken in a manner which is adapted according to the equipment and the arrangement which is used in the foregoing discharge operation.

In Fig. 1 a stripping pipe 28 is shown, which has an intake opening 29 connected to the discharge pipe 26 a distance below the valve 27. In the illustrated embodiment the opening 29 is connected to the transition portion 26a of the discharge pipe 26, that is to say connected downstream of the adjacent discharge branch conduits 25a, 25b. The stripping pipe 28 has a discharge opening 30 connected to the discharge pipe 26 in a portion 26b at the rear, that is to say downstream of the valve 27. Upstream just in front of the opening 30 a second closing valve 31 is inserted.

When the valve 31 is opened in the stripping pipe 28 for the discharge pipe 26 the cargo residue in the discharge pipe 26 can be emptied round the valve 27 to the exhaust as shown by the arrow A. This occurs on an extra pressure loading with compressed air or for example inert compressed gas. In an upper portion 26c of the discharge pipe 26, upstream just in front of the valve 27, there is connected via a connecting branch 26 a compressed air/compressed gas conduit, as is shown by the arrow 33 and which impresses air or inert gas under pressure to the discharge pipe 26 against the pump pressure which prevails in the pump housing and which is produced by the impeller 15 when this is in operation. Consequently residues of the cargo in the discharge pipe 26 are first pressed over the transition portion 26a, by means of the compressed air or the compressed gas, upwardly through the stripping pipe 28 and further to the discharge pipe 26 on the rear side of the valve 27. The cargo which is present in the discharge pipe 26 below the transition portion 26a can to a certain degree be pressed upwardly through the discharge pipe 26 and further into the stripping pipe 28 by means of the pump pressure. However there is a need in practice for a more effective lifting of the last-mentioned cargo upwardly in the stripping pipe 28. A SECOND STRIPPING OPERATION ACCORDING TO THE INVENTION. The afore-mentioned stripping operation removes in practice the major portion of the cargo in the discharge pipe 26, but hitherto it has been difficult to get removed the last residues of the cargo in the well 12 and that portion, which is still to be found in lower branch pipes 25a,25b of the discharge system as a result of static pressure from such cargo residues. There will be described in what follows various solutions one after the other for the optimal removal of the afore-mentioned cargo residues, during use of at least portions of the afore-mentioned arrangement, at the same time taking into account the desire for optimal operating condi-tions in the normal discharge operation. The various embodiments, which are illustrated herein according to Fig. 4-10, are based on different principles. Generally the principles can be used singly separately or in combination.

As mentioned, the present invention aims especially at removing the said cargo residue during the utilisation of at least certain components and certain main functions of the pump arrangement 14, as shown and described with reference to Fig. 1-2.

In connection with a first part solution according to the present invention additional reference is made to Fig. 3 and Fig. 3A-3C, in which in connection with the known pump impeller 15 there is drawn in an extra pump arrangement 33,34. There is secured to impeller 15 of the pump arrange-ment 14 an extra pump arrangement in the form of a pair of relatively small, mutually separated, that is to say opposite blades 33,34, which are fastened each on its diametrically opposite side of the impeller 15 just by its lower edge 15a. The blades project slightly outwards in a radial direction by an order of magnitude of 1/5 to 1/15 of the radius of the pump inlet and has a limited dimension along the periphery of the pump inlet of an order of magnitude of 1/10-1/20 of the dimension of the periphery.

The blades 33,34 are designated herein as an extra pump arrangement, while it is apparent that this extra pump arrangement, which is fastened to the impeller 15, is driven by the impeller 15 and besides as to flow cooperates intimately with the impeller 15. The extra pump arrangement is particularly effective in connection with the stripping phase according to the present invention, that is to say in the stripping phase which will be described in what follows, but is necessarily also active in the discharge operation itself.

In a typical ship's cargo tank the pump arrangement has a height from the bottom 11 of the tank 10 to just above the hatch cover 20 on top of the tank of about 20 metres, while the remaining discharge equipment at the discharge location requires an additional lifting height of an order of magnitude of 10 metres. In other words the impeller 15 of the pump arrangement normally has a counter pressure of 30 metres liquid height, and then with a pump pressure of about 30 bars. It is usual in submersible pump arrangements of known construction that at pump pressures of said order of magnitude a significant out flow (leakage) of pump medium takes place via upper and lower gaps in the pump housing 16 of the pump arrangement between the impeller 15 and sealing arrangements not shown further in the pump housing 16.

In practice it has been found that even small changes in the progress of the flow of the cargo through the impeller 15 can act negatively on the desire for an optimally arranged discharge operation.

Furthermore in practical experiments it has been found that the extra pump arrangement shown herein, based on the said relatively small blades 33,34, provide an effective fetching up of the residues of cargo from the tank well 12 so as to be intercepted by the normal main blades 15b of the impeller 15. A FIRST CONSTRUCTION ACCORDING TO FIG. 4

According to a first construction of the pump arrangement, as shown in Fig. 4, a branch conduit 35a is employed from a diffuser portion 36 in a respective one of the branch pipes 25a (25b) to a common transition portion 37 of the dis-charge pipe 26. In Fig. 4 only the one branch conduit 35a from the one branch pipe 25a is shown, the remaining branch conduit passing hidden behind the illustrated branch conduit. By means of the afore-mentioned arrangement an effective air-lifting effect (airlift effect) can be obtained on the cargo or the cargo/air mixture in the lower portions of the branch pipes 25a (25b) , due to compressed air or inert gas under pressure, which is supplied from the cargo pipe 26 to the stripping pipe 28 via the inlet opening 29 producing a first pulling along effect against the cargo or cargo/air mixture in the upper portion of the branch pipes 25a (25b) and an extra pulling along effect at the lower end of the branch conduit 35a against cargo or cargo/air mixture in the lower portion of the branch pipes 25a (25b) , based on the pump pressure which is produced by the impeller 15 and the pulling along effect in the transition between the stripping pipe 28 and the associated branch conduit 25a (25b) .

A SECOND CONSTRUCTION ACCORDING TO FIG. 5.

According to a second construction, as shown in Fig. 5, a pair of branch conduits 35b are employed which extend from their respective suitable locations on the pump housing 16, for example downstream in the snail housing- shaped pump hous-ing 16, to the transition portion 37 of the stripping pipe 28. In this instance also an effective air-lifting effect is obtained, based on an extra discharge upstream of the dis-charge pipe 26, in addition to the discharge via the opening 29 in the discharge pipe 26. A THIRD CONSTRUCTION ACCORDING TO FIG. 6.

According to a third construction, as shown in Fig.

6, there is inserted in the transition portion 37 of the stripping pipe 28 an ejector or air siphon 38, which is operated as is shown by an arrow C, with internal drive medium, that is to say is operated with air or inert gas which is supplied under pressure from the upper portion 26c of the discharge pipe 26 via the transition portion 26a of the discharge pipe 26 to the stripping pipe 28. The ejector 38 is shown connected to the branch conduits 35a according to the first construction of Fig. 4, but the ejector 38 can just as well be connected to the branch conduit 35b, according to the second construction of Fig. 5 in a manner not shown further.

A FOURTH CONSTRUCTION ACCORDING TO FIG. 7.

According to a fourth construction, as shown in Fig.

7, operation of the ejector 38 is employed with an external drive medium, as shown by an arrow D, instead of operating the ejector 38 with internal drive medium. In this connection pipe connection 28a (Fig. 6) of the stripping pipe 28 via the intake opening 29 to the discharge pipe 26 is omitted. From the drawing it should be evident that the internal drive medium is forced via the discharge branch pipes 25a,25b from below and upwards through the branch pipes 35a. At the same time there is provision to press the cargo or the cargo/air mixture by means of the pump pressure and the internal air supply to the discharge pipe 26 via the branch pipes 25a and 26a to the branch conduits 35a. In addition the cargo or the cargo/air mixture is pulled along from the diffuser portion 36 in the branch pipes 25a,25b via the branch conduits 35a and the ejector 38 inwardly into the stripping pipe 28. In Fig. 7 the ejector 38 is shown connected to the branch conduits 35a according to the first construction of Fig. 4, but the ejector 38 can just as well be connected jointly to a pair of branch conduits 35b as shown in Fig.

5.

A FIFTH CONSTRUCTION ACCORDING TO FIG. 8 AND 9.

In Fig. 8 and 9 a fifth construction is shown, in which air-lifting ("air lifting") is employed with an external air injection via a supply conduit 39, which has a nozzle 40 directed axially upwards through the stripping pipe 28. In the illustrated embodiment the solution is adapted for two stripping outlets 41a,41b via their respective branch conduits 35b' and 35c' with each stripping outlet arranged in each respective branch pipe 25a, 25b.

EXTRA EQUIPMENT ACCORDING TO FIG. 10.

In Fig. 10 equipment is shown which can be connected up at the upper end of the stripping pipe 28 in combina¬ tion with an arbitrary one of the constructions according to Fig. 3 - 9. A branch conduit 42 is shown, one end 42a of which is coupled to the stripping pipe 28 between the inlet 29 (Figs. 4 and 5) and the closing valve 30. At said one end 42a of the branch conduit 42 a closing valve 43 is inserted together with an ejector 44 or second vacuum source which is supplied drive air/drive gas, as shown by the arrow D. The said second vacuum source can for example be formed by a vacuum tank. The vacuum tank can by way of example be formed in the discharge conduit itself between the valve 27 and a manifold not shown further. From the ejector 44 the mixture of drive gas and cargo or cargo/air mixture is delivered to a discharge tank not shown further, as indicated by an arrow E or alternatively via a branch conduit 45 to the discharge pipe 26 downstream of the valve 27, controlled via a three-way valve 46. By adjusting the three-way valve 46 the afore-mentioned mixture can be delivered as required directly to the discharge pipe 26 downstream of the closing valve 27 or to the discharge tank as indicated by the arrow E. In practice during operation of the ejector 44 one can open the valves 43 and 46 and close the valve 31, by way of example in a final phase of the stripping operation in order to remove the last residues of cargo to the greatest extent possible from the interiors of the discharge and stripping equipment .

The best practical results hitherto achieved by means of stripping controlled by pump pressure and compressed gas are that approximately 12 litres remains behind in the tank well, while in practical experiments according to the present invention the cargo residue in the tank well can be reduced to 4 - 5 litres on completely emptying the discharge and stripping equipment.

Claims

Patent Claims

1. Discharge pump (14) arrangement, which is submersible in the cargo of a cargo tank (10) of a ship and which has a pump inlet (13) arranged in or by a well

(12) of the ship's cargo tank (10), where impeller (15) of the pump is equipped with an extra pump arrangement (33,34) , which is operatively connected to impeller (15) of the pump (14) , and where discharge pipe (26) of the discharge pump (14) over deck (22) of the ship is equipped with a closing valve (27) and below the closing valve (27) via an intake (32) a compressed air or compressed gas supply (33) is coupled and also between the closing valve (27) and the discharge pump (14) an outlet (29,-41a, 41b) is coupled to a stripping pipe (28) having an associated closing valve (31) relative to a delivery location (A,E) via upper deck (22) of the ship, characterised in that an extra pump arrangement is arranged on impeller (15) of the pump (14) in the form of opposite pairs of locally defined blades (33,34) , which are disposed downstream just within inlet (13) of the pump (15) , that the stripping pipe (28) communicates with the pump housing (16) or the lower portion of the discharge pipe (26) at a first height level at the upstream end of the stripping pipe (28) , where the stripping pipe (28) is supplied with extra pressure medium internally via the discharge pipe (26) , and the stripping pipe (28) communicates at least at a second height level substantially above the first height level with an internal and/or external pressure medium or vacuum source for the supply of extra pressure medium or vacuum to the stripping pipe (28) .

2. Arrangement in accordance with claim 1, characterised in that at its upstream end the stripping pipe (28) is branched via two separate stripping branch conduits (35a;36b) , which communicate via their respective lower intake openings directly with pump housing (16) of the pump (14) , the intake openings from the pump housing having in part applied thereon the pressure from impeller (15) of the pump (14) and in part applied thereon the pressure from the pressure medium, which is supplied from the discharge pipe (26) via branch pipes (25a, 25b) to the pump housing (16) , while the stripping branch conduits (35a;35b) are subjected via a branching point for the stripping pipe (28) to a suction effect or pulling along effect produced by the internal and/or the external supply of pressure medium.

3. Arrangement in accordance with claim 1, characterised in that at its upstream end the stripping pipe (28) is branched via two separate stripping branch conduits (35a,-36b) , which communicate with pump housing (16) of the pump (14) via their respective lower intake openings in their respective branch pipes (25a, 25b) which connect the pump housing (16) to the discharge pipe (28) , the intake openings having in part applied thereon the pressure from impeller (15) of the pump (14) and in part applied thereon the pressure from the pressure medium, which is supplied from the discharge pipe (26) via the branch pipes (25a, 25b) to the pump housing (16) , while the branch conduits (35a;35b) are subjected via a branching point for the stripping pipe (28) to a suction effect or pulling along effect produced by an internal and/or external supply of pressure medium.

4. Arrangement in accordance with claim 2 or 3 , characterised in that the stripping pipe (28) is connected to the branch conduits (35a;35b) downstream of a separate conduit connection (28a) between the discharge pipe (26) and the stripping pipe (28) , the separate conduit connection (28a) having an intake opening connected to a transition portion (26a) between the discharge pipe (26) and its branch pipes (25a, 25b) .

5. Arrangement in accordance with claim 2 or 3, characterised in that the stripping pipe (28) is connected to the discharge pipe (26) via two parallel branch pipes via a respective one branch pipe (25a, 25b) and a respective one branch conduit (35a;35b) .

6. Arrangement in accordance with claim 4 or 5, characterised in that the branch conduits (35a, 35b) are connected at their downstream end, that is to say at their transition to the common stripping pipe (28) , to a common suction path in an ejector (air-siphon 38) , the exhaust of which empties directly into the stripping pipe (28) , the drive medium path of the ejector (38) being connected to the internal or the external supply of pressure medium.

7. Arrangement in accordance with claim 4 or 5, characterised in that an air lifting arrangement in the form of a co- current directed nozzle having an external supply of pressure medium is inserted in the stripping pipe (28) , in or downstream of the transition portion between the branch conduits (35a, 35b) and the common stripping pipe (28) .

8. Arrangement in accordance with one of the claims 1 - 7, characterised in that the stripping pipe (28) communicates with a vacuum source at the downstream end of the stripping pipe (28) .