US3574487A

US3574487A - Pump means

Info

Publication number: US3574487A
Application number: US776826A
Authority: US
Inventors: Frank Mohn
Original assignee: Patents and Development AS
Current assignee: Patents and Development AS
Priority date: 1967-10-18
Filing date: 1968-10-14
Publication date: 1971-04-13
Anticipated expiration: 1988-04-13
Also published as: DK141382B; SE350308B; FI48912B; IE32424L; NL158263B; FR1587994A; DE1803293B2; PL71362B1; BE722565A; DE1803293A1; AT302177B; GB1238208A; DE1803293C3; FI48912C; NL6814956A; NO123115B; IE32424B1; ES359260A1; CH488113A

Abstract

A pump means for submersion in and transfer of fluid ship''s cargo, having a zone between the driving system of the pump and said fluid cargo to receive any leakage of driving medium and fluid cargo and means for controlling the pressure and regulating the thermal conditions in said zone and for remote controlling the removal of leakage from said zone. A pump unit comprising said pump means received in a protective rigid casing.

Description

United States Patent Frank Mohn Krakenes, Fana, Norway 776,826

Oct. 14, 1968 Apr. 13, 1971 Patents and Developments A/S Helldal, Norway Oct. 18, 1967 Norway Inventor Appl. No. Filed Patented Assignee Priority PUMP MEANS 12 Claims, 5 Drawing Figs.

US. Cl

1nt. C1 Field of Search (E), 111 (D) (D1) (C)8; 417/375, 405, 409

Primary Examiner-Robert M. Walker Attorney-Bierman and Bierman ABSTRACT: A pump means for submersion in and transfer of fluid ship's cargo, having a zone between the driving system of the pump and said fluid cargo to receive any leakage of driving medium and fluid cargo and means for controlling the pressure and regulating the thermal conditions in said zone and for remote controlling the removal of leakage from said zone. A pump unit comprising said pump means received in a protective rigid casing.

7o 17 5 2 53a 55b 16 55a Q 170 51 17b 0 11 12 PUMP MEANS This invention relates to pump assemblies and, in particular, to pump assemblies for submersion in and the transfer of fluid ships cargoes, operated by hydraulic prime mover means via a driving shaft.

Generally, it is difficult to obtain fully satisfactory sealing for the driving shaft of the pump during use. In practice, one must always reckon that sooner or later one or more large leakages will occur as a result of overheating, wear, sealing failure and the like, so that it is difficult to guarantee a leakfree seal.

in the case of such pumps, it has been found either desirable or necessary to maintain quite separate (a) the fluid cargo to be pumped from the bearings of the driving shaft, and (b) the driving medium for the prime mover means and the lubricating medium for the bearings from the fluid cargo.

One prominent pump assembly which has been employed has several pump rooms equipped with conventional suction pumps from which a network of suction conduits extends to the various tanks. For example, a tanker for freighting solvents might have 30 to 40 tanks. The disadvantages of transferring all the cargoes to one or more pump rooms are many. There is the danger of mixing the cargoes by faulty operation of the pumps and valves, so that in the course of a few seconds whole portions of the highly expensive cargo can be destroyed or contaminated. When poisonous fluids are involved, it is important to avoid leakage of gas, a danger which is especially great when a few pumps are used in a centralized room, or when the driving medium for a pump submerged in a tank communicates with, for example, a steam system in the machine room, or has the possibility of mixing with the cargo. The fact that the fresh water tank often connects with the water installation for the steam system, clearly presents an extra hazard for the crew. Fluid or vapor leakage through the valve spindles and packings results in the collection of fluid or vapor in the pump room thus creating a perilous area. Furthermore, there are problems with long suction pipes on pumping viscous fluids which do not flow to the pump unless the pipes and valves are overdimensioned, sealed and have the least possible bends. This makes for an expensive and spacedemanding installation. Finally, the dead space" which the one or more pump rooms occupy adds to the cost of tank capacity, in addition to the increase in construction costs.

Another pump assembly which finds some application today is based on using a submerged pump in each tank and a mechanical transmission from the driving source on deck via a -20 metre long shaft down to the pump in the bottom of the tank. This system provides an effective feeding of the cargo to the pump and the omission of separate pump rooms thereby avoiding mixing of the cargo. However, this assembly has not been preferred to the first-mentioned assembly of the last-preceding paragraph. In using the long shaft having many separate bearing locations, the risk of overheating and consequent explosion is present. Owing to the fact that the long shaft is supported by bearings in or against one or more bulkheads, distortion is produced due to the fact that the ship lives." Outward and inward bulges on the bulkheads are produced as a consequence of an adjacent tank being full, half-full or empty. As a result, the bearings and/or shaft can be ruined with consequent overheating, unintended leakage of the pump and mixing of the cargo and lubricating means.

It has also been proposed to use bearings which are lubricated by means of the cargo. The cargo is transported through a pipe which surrounds the shaft and bearings. Even in the few instances where such a solution is possible since only a few types of cargo are suitable for this purpose, it is far from satisfactory because of the continued risk of explosion especially when the tank is empty and the pumps are not stopped immediately thus causing the bearings to become dry in a few minutes. The same risk of explosion exists when the intake opening to the pump becomes blocked by a foreign body, e.g. a rag, on emptying the tank.

None of the above three pump assemblies is really satisfactory in practice since they involve a significant risk to the crew's as well as to the ship's security, not to mention the risk of damage to the cargo and the pump assembly.

According to the present invention a pump assembly for submersion in and the transfer of fluid ships cargoes comprising a hydraulic motor connected by a relatively short driving shaft to a rotor means, the driving medium for the motor and the fluid medium to be pumped being separated by a zone in which the pressure is lower than that of either of the two mediums and which receives as a result of said pressure differences substantially any leakage of said mediums which may occur, and means for controlling the removal of said leakage from said zone.

Preferably, the leakage removal means is remotely controlled.

Conveniently, the zone surrounds a substantial portions of the .driving shaft and the whole of the hydraulic motor. The main effect of this arrangement is to isolate and insulate the driving medium for the motor from the fluid medium to be pumped, and vice versa. Thus it is a first object of this arrangement to prevent any contamination of the pump medium by the driving medium. Likewise, it is an object to prevent contamination of the driving medium by the pump medium. A further object of this arrangement is to prevent or control the thermal transmission between the driving medium and the pump medium.

Said zone can comprise a drainage chamber and a pressure discharge passage the one end of which communicates with the atmosphere and the opposite end of which communicates with said drainage chamber, the latter being located between first and second packing means arranged on the driving shaft between the rotor and the prime mover means, the first packing means forming a sealagainst the fluid pump medium and the second packing means forming a seal against the driving medium.

It is a main object of said pressure discharge passage to reduce to the absolute minimum the risk of the driving medium and the pump medium contaminating each other. This is achieved by communication with the atmosphere at one end of the passage and with the drainage chamber at the other endof the passage. lt is a further object of said pressure discharge passage to form a venting system for the driving means and especially for the driving medium, i.e. a system by means of which it is possible to circulate a temperature regulating medium (e.g. air or gases) in said zone containing said pressure discharge passage and said drainage chamber in order to regulate or maintain the temperature of the driving medium as-deemed appropriate and independently of the temperature of the pump medium. In one case the pump medium may be liquid gases (low-pressure gases) having a temperature substantially below the temperature of the driving medium, and in another case the pump medium may be heated heavy oil or heated molasses having a temperature above the temperature of the driving medium. In each case it is an object to observe and regulate the temperatures of the driving medium enclosed by said zone and the pump medium surrounding said zone.

By means of the drainage chamber, pressure drainage passage and the associated leakage removal means or drawing-off arrangement, it is possible to collect and to drain possible leakage beyond the first set of packings before it forces past the remaining set of packings.

It is preferred that the driving shaft at its mounting extends from the hydraulic motor in discharge oil and in that the drainage chamber communicates via a first conduit connection with atmospheric pressure and via another conduit connection, which is coupled to an ejector mechanism, with a suitable drawing-off location.

As a consequence of the pressure of the pump medium on the one side of the drainage chamber and the pressure of the discharge oil on the opposite side of the drainage chamber and the connection of the drainage chamber with atmospheric pressure, a fall in pressure into the drainage chamber can be obtained beyond the first and second sets of packings respectively, so that leakage can if necessary be permitted inwardly into the drainage chamber, but on the other hand not the opposite way.

As a consequence of the drainage chambers connection with atmospheric pressure drawing off of the drainage fluid via the conduit connection which is coupled to the ejector mechanism can be effected, during controlled pressure conditions in the drainage chamber, so that the said drawingoff does not need to affect the leakage to the drainage chamber.

Conveniently, the zone between the driving medium and the pump medium communicates with an additional supply of a temperature regulating medium of the group consisting of low thermal conducting gases, cooling air, heating air, steam and other appropriate medium to maintain a desired temperature level in said zone. Said ejector mechanism may also be used in a venting system to transport said temperature regulating medium in said zone.

In order that the invention can be more readily understood, a convenient embodiment thereof will now be described by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a view of a pump assembly, in which the pump according to the invention appears.

FIG. 2 is the same as FIG. I viewed from the side.

FIG. 3 is a section along the line III-III of FIG. 2.

FIG. 4 is a vertical section through the lower part of the pump assembly according to FIG. I illustrated on a larger scale.

FIG. 5 is a detail of FIG. 4.

The pump assembly as illustrated in FIGS. 1 and 2 is specially designed for use on board tankers of the parcel tanker type, that is to say, tankers which are constructed for the storage of the various cargoes in the different holds and in which it can be desirable to utilize a pump in each tank. The illustrated pump can, however, also be utilized in conventional tankers or in other ships where there is a need for such pumps, since the pump installation is designed to pump arbitrary fluids such as cargo oils, solvents and molasses. Special regard is paid to avoiding every leakage or possibility of leakage in the pump and pump installation to and from the driving mechanism of the pump, so as to avoid thereby, first, contamination of the pump medium with foreign materials from the driving mechanism of the pump and, second, to prevent access of active pump medium into the pumps driving mechanism.

In FIGS. 1 and 2, a pump is shown in a pump housing which is arranged in a recess 11 at the bottom 12 of a ship's tank 13, so that the pump can be submerged in the pump medium in the tank 13 and during use a certain static feeding pressure prevails dependent on the height of the fluid in the tank. The pump is thus correctly positioned also when viscous pump media and readily volatile pump media are concerned. The driving shaft 14 of the pump is disposed vertically and the inlet 15 of the pump is disposed at the lower end of the pump and is directed downwards towards and disposed just above the bottom of the recess 11. The outlet 16 of the pump extends first laterally outwards from the pump and thereafter upwards to communicate with a vertically extending pressure conduit 17. The pressure conduit 17 passes through a removable hatch cover 19 secured to a hatch in the top 20 of the ship's tank and is connected above the hatch cover by a transport conduit 21 to a discharge position (not shown). The pump housing 10 is supported by a first housing portion 22, a second housing portion 23 and a pipe 24. The pipe 23 runs concentrically with the pump shaft 14 and vertically upwards through the hatch cover 19 via a union 25.

The pump and the pump installation as illustrated in FIG. 1 and 2 can be delivered as a ready-assembled unit from the factory. The unit of the pump housing 10, pressure conduit 17,

housing portions

22, 23 and the pipe 24 thus form a connected assembly unit. The conduit 17 and the pipe 24 are secured in the direction of height with a suitable intermediate space by means of guide shoes 26. 27 vertically displaceable on rails 28,

29 which are secured to a tank wall 30. After having removed 5 the hatch cover 19 the unit l0, 17, 22, 23, 24 can be raised out through and lowered downwards into position in the tank through the associated hatch opening by means of a mobile crane or lifting horse on board ship or by means of a crane on land. The whole pump unit can thus, if so desired, still be raised out while it is submerged in the cargo without special difficulty for repair, checking or replacement of certain parts, so as thereafter to be lowered in place again in the tank in the position ready for operation.

The rotor 32 (FIG. 4) of the pump is connected by means of a relatively short driving shaft 14 to a high-pressure hydraulic motor 33, so that a relatively strongly compacted unit of pump rotor 32 and driving motor 33 is obtained. This arrangement offers several operational technical advantages, but at the same time there is the problem of protecting the driving motor 33 and the bearings 34-36 of the driving shaft 14 together with the driving motors hydraulic cyclic circuit 37-38 above the pump medium in the tank 13.

The hydraulic cyclic circuit of the driving motor is ensured in such manner that the feed pipe 37, which brings the pressure oil to the motor 33 at a pressure of, for example, 150 kg./cm. is received inside the return pipe 38, in which the pressure oil can have a pressure of, for example, l.5-2 kg./cm. If pressure oil should leak for one or another reason from the pipe 37 out into the pipe 38, the pressure oil will not cause any damage for this reason. The pipe 38 is in turn received in the pipe 24 which forms a shield pipe for the pipe 38 (and 37) and additional pipes which are to be described below, so that a possible leakage from the pipe 38 can be collected in the pipe 24. These safety provisions are of significance in such cases where contamination of the cargo with pressure oil must be avoided. Not only will leakage outwards to the cargo be prevented, but also in addition the various conduits will be protected against shocks and jolts, against attack by aggressive cargo fluids, intrusion of such fluids in the pressure oil, etc. At the top of the hatch cover 19 (FIG. I) there is shown a coupling to a hydraulic cyclic circuit 41-42 via a valve arrangement 43 having a bypass valve 44 for shutting off the

cyclic circuit

37, 38.

With reference to FIG. 4 there are shown the details in the pump installation illustrated in FIG. 1 and 2.

The pump is a conventional centrifugal pump including a pump rotor 32 received in a pump chamber 45 which is produced between three

housing portions

17a, 17b, 17c and the rotor is sealed against the pump housing 10 by means of the packings 46-48. Just above the pump housing 10 there is formed in the housing portion 22 a chamber 49 which communicates with the pump medium in the tank 13 via a port opening 50 (FIG. 1), so that a static fluid pressure prevails in the chamber 49 which encloses the shaft 14 in front of a first set of

packings

51, 52 which seal off the driving shaft above a base pedestal 53a. Between the

packings

51, 52 and a higher disposed set of

packings

53, 54 there is located a metal support ring 55a having a radial opening 55b and between the ring 55a and the shaft 14 together with

packings

52 and 53 there is formed a drainage chamber 55 which will be described further below after other parts are described.

Between the inwardly projecting collar portion 56 of the housing portion 22 and the pedestal portion 53a there is secured a pipe-shaped support member 57 which carries the bearings 34-36 of the driving shaft 14. The collar portion 56 carries the driving motor 33 and between the bottom side of the driving motor and the upper side of the pedestal portion 530 there is formed in the support member 57 a support chamber 58 which contains hydraulic oil from the hydraulic cyclic circuit of the driving motor 33. At 590 there is shown a freely and outwardly opening main outlet for return oil from the driving motor 33 and at 59 a drainage conduit from the driving motor.

The conduit 59 communicates via a channel 60 in the collar portion 56, a channel 61 in the support member 57 and a pipe stump 62 with the lower portion of the chamber 58. At the upper portion of the chamber 58 a channel 63 communicates with an oil discharge chamber 64. The chamber 64 is formed in a housing portion 65 which freely surrounds the driving motor 33 and which communicates above with the return pipe 38 of the hydraulic cyclic circuit. The main outlet 59a from the driving motor opens freely outwards into the chamber 64 and oil is led away therefrom via the pipe 38. In the event of the leakage occurring in the said driving motor or its

conduit connections

37, 59 this leakage is caught in the chamber 64 without causing damage and is led away via the pipe 38 together with the remaining return oil. At 66 there is shown a slide valve which is regulatable from the chamber 49 in the housing portion 22 via the port opening 50 (FIG. 1). The valve 66 can as required regulate the amount of the oil discharged from the conduit 59 in direct connection with the chamber 64 in the housing portion 65 via a channel 67 and can thereby cause a certain amount of the oil to bypass the passage 60 to 63 and pass directly to the chamber 64. It is also possible to close the whole passage 60 to 63 when repairs or inspection of pump rotor, shaft, bearings, packings and the like is to be effected. The passage 60 to 63 however is supplied during operation with such a large amount of oil from the driving motor that a lively circulation of the oil is ensured in the chamber 58 so as to obtain thereby satisfactory lubrication of the bearings 34 to 36.

The housing portion 23 which communicates above via the shield pipe 24 with atmospheric pressure, surrounds the freelying housing portion 65, so that a protective chamber 68' is formed between the housing portion 23 and the housing portion 65 and its coupling to the collar portion 56. The housing portion 23, which is secured to the housing portion 22, communicates below via a downwardly extending pipe connection 69 and a horizontal channel 70 with the drainage chamber 55 between the two sets of

packings

51, 52 and 53, 54 on the shaft l4, so that the drainage chamber 55 also communicates with atmospheric pressure. ln this way a certain drop in pressure towards the drainage chamber is ensured via each of the two sets of packings, and on the opposite side of the set of packings 51, 52 a certain static pressure prevails dependent on the height of fluid in the tank 13, while on the opposite side of the set of

packings

53, 54 there prevails a pressure corresponding to the pressure of the oil. These fluid pressures each form a barrier, so that any leakage from the chamber 55 and past the respective set of packings is avoided. lf leakage takes place past the set of

packings

51, 52 or 53, 54 to the chamber 55 the pressure in the chamber 55 can be maintained so low the whole time that any leakage from the chamber 55 through the adjacent set of packings can be avoided. In order to be able to keep the leakage to the chamber 55 under observation and in order to be able to remove fluid which has collected in the chamber 55 and

adjacent conduit connections

70, 69, 68, regardless of whether this comes from the sets of packings S1, 52 or 53, 54 or the remaining leakage of pump medium or pressure oil which are introduced into the chamber 68, the pump is equipped with a drawing-off arrangement for draining the fluid. At 71 there is shown an approximately vertical suction pipe the lower end edge of which is obliquely cut off and communicates with the bottom of the channel 70 at the lower end of the pipe 69. The suction pipe 71 is connected up in the chamber 68 to an end of an ejector pipe 72 which also receives a feed pipe 73 for pressure air or steam at a pressure of 7l0 kg./cm. while its opposite end is connected to'a discharge pipe 74. It is the intention thatflthe drawing-off arrangement can be actuated intermittently. by suitable remote control. For example, prior to starting up the pump, the ejector mechanism can be set in motion so as to expel possible collections of fluid. By means of suitable apparatus (not shown) the extent of leakage can be estimated by collecting up the drained-off fluid from the ejector mechanism. Moreover, by inspecting the liquid which has leaked into the draining chamber 55 or adjacent connections the nature and location of the leak can be ascertained, enabling a prompt decision to be taken as to whether immediate repair is necessary.

As shown in FIG. 3 the feed pipe and discharge pipe of the ejector mechanism are also received screened within the shield pipe 24, so that even a leakage in the

pipes

73, 74 will not cause any damage to the cargo or driving mechanism of the pump.

With the illustrated arrangement there is ensured an effective enclosing of the driving motor and associated pressure oil conduits and the ejector mechanism. Furthermore by means of the special sealing off of the driving shaft of the pump and the associated drawing-off arrangement, a reliable sealing system is provided which can be controlled and drained off of draining fluid at any time. ln this way a pump installation is-obtained which can be submerged into, so to speak, arbitrary pump media without showing the effects of damage.

As shown in FIG. 1 in dotted lines, there is an additional supply pipe 76 leading into the upper open end of the pipe 24 from a source (not shown) of a temperature-regulating medium. All according to the need in each case the temperature-regulating medium may consist of a low thermal conducting gas, cooling air (or gas), heating air (or gas), steam, etc. in the illustrated embodiment the drawing-off arrangementfor draining fluid is used to obtain a venting effect in the pipe 24, the chamber 68, the passage 69 and the conduit 70 in order to transport the temperature-regulating medium from the supply pipe 76 through said

passages

24, 68, 69, 70 and discharge said medium through the drawing-off arrangement by means of the ejector pipe 72 therein. By means of this venting system it is possible to control and regulate the temperature in the zone which is separating the pump medium from the driving medium. it is further possible by means of this venting system to combine the temperatureregulating effect and the draining effect in order to secure continuous and complete remote control of said zone in respect of leakage as well as temperature level at discharge end of the drawing-off arrangement.

lclaim:

1. ln a pump assembly for submersion in and transfer of fluid ship's cargoes comprising a hydraulic motor, a rotor means, a relatively short driving shaft connecting said motor to said rotor means and a conduit for transferring up to the ship's deck the fluid cargo to bepumped on actuation of said rotor means, the improvement comprising a zone for ensuring separation of a driving medium for said motor from the fluid cargo, said zone having a pressure lower than the pressure of both said driving medium and said fluid cargo, said low pressure zone receiving substantially all leakage from the fluid cargo and from the driving medium which may occur to prevent-leakage of driving medium to said fluid cargo and leakage of fluid cargo to said driving medium, and means for controlling the removal of said leakage from said zone.

2. A pump assembly according to claim 1, wherein the leakage removal means is remotely controlled.

3. A pump means according to claim 1, wherein the zone surrounds substantial portions of the driving shaft and the whole of the hydraulic motor.

4. A pump means according to claim 1, wherein the zone comprises drainage chamber and a pressure relief passage the one end of which communicates with the atmosphere and the opposite end of which communicates with said drainage chamber, the latter being located between first and'second packing means arranged on the driving shaft between the rotor and the prime mover means, the first packing means forming a seal against the fluid pump medium and the second packing means forming a seal against the driving medium.

5. A pump assembly according to claim 4, wherein supply and discharge conduits forming part of the hydraulic prime mover means together with said means for controlling the removal of said leakage are received in the zone.

6. A pump assembly according to claim 5, wherein said means for controlling the removal of said leakage comprises a pressure driven ejector mechanism including an ejector pipe having feed and discharge branches at opposite ends thereof, the end connected to the feed branch being also connected to a suction pipe the intake of which is positioned at the level of the drainage chamber.

7. A pump assembly according to claim 5, wherein the motor supply conduit is received within the motor discharge conduit, the latter conduit communicating with a housing chamber for the hydraulic motor and forming an additional protection against thermal transmission and pressure around the supply conduit.

8. A pump assembly'according to claim 7, wherein the driving shaft passes in a region between the motor and the second packing means, in which region the shaft bearings are mounted through oil received from the motor, said oil being forcibly fed through this region through a passage between the motor and the discharge conduit and thereby lubricating said bearings.

9. A pump assembly according to claim 1, wherein the zone between the driving medium and the pump medium communicates with a supply of a temperature-regulating medium of the group consisting of low thermal conducting gases, cooling air, heating air, steam and other appropriate medium to maintain a desired temperature level in said zone.

10. A pump assembly according to claim 1, wherein the leakage removal means is remotely controlled.

11. A pump assembly according to claim I, mounted for vertical displacement towards and away from the fluid medium to be pumped.

12. A pump assembly for submersion in and transfer of fluid ship cargoes, comprising a hydraulic motor, a rotor means, a relatively short driving shaft connecting said motor to said rotor means and a conduit for transferring up to the ships deck the fluid cargo to be pumped on actuation of said rotor means, the improvements which comprise constructing said pump assembly with a zone for ensuring separation of the driving medium for said motor from the fluid cargo, said zone comprising a drainage chamber located around the driving shaft between said rotor means and said motor and a pressure discharge passage, one end of which communicates with the atmosphere and the opposite end of which communicates with said drainage chamber, the latter being located between first and second packing means arranged on the driving shaft between the rotor and the motor, the first packing means forming a seal against the fluid pump medium and the second packing means forming a seal against the fluid cargo, said zone having a pressure lower than those of said driving medium and said fluid cargo and being able, as a result of said pressure differences, to receive substantially any leakage thereof which may occur, and means for controlling the removal of said leakage from said zone.

Claims

1. In a pump assembly for submersion in and transfer of fluid ship''s cargoes comprising a hydraulic motor, a rotor means, a relatively short driving shaft connecting said motor to said rotor means and a conduit for transferring up to the ship''s deck the fluid cargo to be pumped on actuation of said rotor means, the improvement comprising a zone for ensuring separation of a driving medium for said motor from the fluid cargo, said zone having a pressure lower than the pressure of both said driving medium and said fluid cargo, said low pressure zone receiving substantially all leakage from the fluid cargo and from the driving medium which may occur to prevent leakage of driving medium to said fluid cargo and leakage of fluid cargo to said driving medium, and means for controlling the removal of said leakage from said zone.

4. A pump means according to claim 1, wherein the zone comprises drainage chamber and a pressure relief passage the one end of which communicates with the atmosphere and the opposite end of which communicates with said drainage chamber, the latter being located between first and second packing means arranged on the driving shaft between the rotor and the prime mover means, the first packing means forming a seal against the fluid pump medium and the second packing means forming a seal against the driving medium.

8. A pump assembly according to claim 7, wherein the driving shaft passes in a region between the motor and the second packing means, in which region the shaft bearings are mounted through oil received from the motor, said oil being forcibly fed through this region through a passage between the motor and the discharge conduit and thereby lubricating said bearings.

11. A pump assembly according to claim 1, mounted for vertical displacement towards and away from the fluid medium to be pumped.

12. A pump assembly for submersion in and transfer of fluid ship cargoes, comprising a hydraulic motor, a rotor means, a relatively short driving shaft connecting said motor to said rotor means and a conduit for transFerring up to the ship''s deck the fluid cargo to be pumped on actuation of said rotor means, the improvements which comprise constructing said pump assembly with a zone for ensuring separation of the driving medium for said motor from the fluid cargo, said zone comprising a drainage chamber located around the driving shaft between said rotor means and said motor and a pressure discharge passage, one end of which communicates with the atmosphere and the opposite end of which communicates with said drainage chamber, the latter being located between first and second packing means arranged on the driving shaft between the rotor and the motor, the first packing means forming a seal against the fluid pump medium and the second packing means forming a seal against the fluid cargo, said zone having a pressure lower than those of said driving medium and said fluid cargo and being able, as a result of said pressure differences, to receive substantially any leakage thereof which may occur, and means for controlling the removal of said leakage from said zone.