Gravity tank is used in ships to, among other things, pressurize the propeller unit's propeller shaft seal case or other propeller unit space. Lower part of the propeller unit, or an independent propeller shaft seal space must be pressurized compared to the seawater pressure corresponding to the draft of the unit. The oil sump leaks slowly oil outwards and the leaking must be compensated intermittently, therefore filling the tank has been arranged according to an alarm. The pressure is created by the height of the oil column in the pipe between the freely breathing tank and the space to be pressurized. The required pressure determines the height where the gravity tank is located in the ship's constructions, that is the static elevation creat- ing the overpressure.

In some cases, installing the gravity tank to an adequate height is difficult, labori- ous and sometimes even impossible, because the ship's constructions are not high enough for achieving the required elevation, nor can the tank be located too far from the propeller unit cabin. These kinds of problems are common with tugboats.

In current solutions, a common arrangement is also to create a suitable overpres- sure in the gravity tank, which is sealed and partially filled with oil, or in the seal space, with separate valves, as is known from the US patent 5683278. The ship's compressed air network, or tank, or a separate air compressor is used for the pneumatic pressurizing. In some cases there is no compressed air available in a ship.

A known solution for pressurizing the pressure lubricating oil is also to pressurize the oil tank by using an oil-filled piston/cylinder device, with e. g. motor-moving screw mechanism or liquid hydraulics being used as an actuator.

This invention is designed to replace the additional pressure caused in the gravity tank, which has according to the prior art primarily been created by the static ele- vation of the gravity tank or generated by the compressed air. The arrangement according to the invention for pressurizing the gravity tank without compressed air can also be used in ships that are not high enough to mount the gravity tank in a height sufficient to create a required lubricant column, or in vessels, where there is no compressed air available. Pressurization executed according to this arrange- ment is reliable and demands only little maintenance.

Characteristic to the arrangement according to the invention for pressurizing the gravity tank without compressed air is what is referred to in the claims.

The required additional pressure in the gravity tank is according to the invention, preferably created by using a mass. Material with density greater than the density of the lubricant used in the system is used as a mass. The mass causing the addi- tional pressure can be mass composed of solid or liquid material. Changing the mass that causes the pressure can modify the pressure. In practice, suitable weights can be used as the mass, and the number of weights is adapted according to the requirements for achieving the desired additional pressure. The invention can be put into practice in many different ways. In the gravity tank, there can be a lid sealed into the walls and moving with the lubricant level, or a membrane at- tached to the walls and elastically stretching with the lubricant level, or the gravity tank can contain a bladder. The pressurizing part can also be a separate compo- nent external to the gravity tank connected to the gravity tank via a pipe or some other manner. Leaking of the system from e. g. the propeller shaft seal to be sealed, is compensated by the drop in the tank liquid volume caused by the lower- ing of the lid that functions as a piston, or by the contracting of the elastic mem-

brane/bladder. The filling of the tank from a store tank that contains lubricant can be arranged to be manual or remote by using valves.

In each solution, the tanks can be disposed above or in the immediate vicinity of the propeller unit.

The gravity tank and the pressurizing component that is conceivably operationally connected to it via a pipe or some other means are, according to the invention, disposed as close as possible to the object to be pressurized. To avoid loss of pres- sure and costs, short pipelines are preferred. The pipelines should have the least number of bends and connections. The pipes are arranged to be continuously in- clining, so that no air pockets would be created. The necessary venting means are arranged for the venting.

In the first embodiment of the invention, a second tank has been connected adja- cent to the gravity tank, to operate as a pressurizing component. The gravity tank includes the necessary pipe connections for the lubricant to be filled and for the lubricant leading to the space to be pressurized, and an operational connecting pipe connection coming from the second tank operating as a pressurizing compo- nent external to the tank. Preferably, the connection unit of the filler pipe that is located at the bottom surface of the gravity tank and that is coming from the store tank containing the lubricant via the relevant pipes and valves, has, if required, a closing valve and by using it, it is possible to empty the tank, unless a separate discharge valve has been installed. The gravity tank, from which the pressurized lubricant is lead to the space to be pressurized, is in this embodiment, pressure- sealed. If required, it is provided with a level sensor for controlling the lubricant volume and for the visual inspection of the level, with gauges and oil level mini- mum and maximum lines. The pipe connections that are arranged into the tank are disposed preferably below the lubricant minimum level. The air volume in the tank is adjusted preferably so, that the lubricant level keeps, despite of the varia- tion in pressure, between the minimum and maximum lines, when operated in

pressure range that is within the planned boundaries. To pre-adjust the air volume and to vent the air that comes with the filled lubricant, there are the necessary venting means in the gravity tank. The aim is to keep the lubricant level in the gravity tank constant, and to compensate the leaking of the lubricant a tank, oper- ating as an actual pressurizing component with a sliding lid arranged to be moving downward with the leaking lubricant, is arranged adjacent to the gravity tank and connected to the close vicinity of it. A block with a suitable mass has been ar- ranged as a weight on top of the lid in order to maintain the planned overpressure level corresponding to the draft of the space to be pressurized. The block is made of material whose density is greater than the density of the lubricant to be pressur- ized. In this embodiment, the tank operating as a pressurizing component is, above the sliding lid, that is on the side of the mass, in the pressure of the sur- rounding air. When the amount of the leaking lubricant reaches the filling alarm level, that is when the lubricant level in the pressurizing tank drops below the minimum line, the level sensor, arranged, when necessary, in the pressurizing tank, sends a signal to the control system, or warns in some other manner, or the user can visually detect from the lubricant gauge in the pressurizing tank that the level has dropped. At this point, lubricant is added manually to the gravity tank, for example by using the filler pipe's closing valve at the lower end of the gravity tank, to the extent that the user visually detects, for example from the lubricant gauge in the pressurizing tank, that there is enough lubricant, or the lubricant is preferably added with the aid of the control system remotely with the valves, to the extent that the control system receives information from the level sensor that the lubricant level maximum line has been reached. When necessary, lubricant level minimum and maximum level sensors are arranged in the adjacently con- nected tank. For example, a mechanical indicator attached to the lid, can be used as a measuring device.

In the second embodiment of the invention in an arrangement for pressurizing the gravity tank to create additional pressure, there is no adjacently connected second tank, unlike in the first embodiment, but operating as a gravity tank, is a freely

breathing pressurizing tank structure, similar to the external pressurizing compo- nent of the first embodiment of the invention, comprising of a tank, with a lid constructed to be sliding and arranged to be moving downward with the leaking lubricant, and pipe connections for the lubricant to be filled and for the lubricant leaving to the pressurized space. A block, with a mass that can be controlled cor- responding to the pressure conditions in the space to be pressurized, is arranged on top of the lid, which is sealed to be sliding. The block creating the pressure is made of material with the density greater than the density of the lubricant to be pressurized. The tank is also provided with the lubricant level measuring means mentioned above. In this embodiment, the gravity tank is on that side of the slid- ing lid, which is opposite to the oil space, that is, on the mass side, in the pressure of the surrounding air, and it is pressure-sealed on the side of the lid's lubricant space. In this second embodiment of the invention, the pipe connections arranged to the tank are disposed to the tank sides and pressure-sealed, and below the lid that is arranged to be sliding. To discharge the air that comes with the filled lubri- cant from the tank, the necessary venting means are arranged on the lid of the gravity tank. When the amount of the leaking lubricant reaches the filling alarm level, the lubricant will be fed into the tank, in a manner known per se described above. The lubricant filler pipe feed pressure must be higher than the combined pressure that is caused by the pressurizing mass and pressure of the oil column above the filling connection.

In the third embodiment of the invention in an arrangement for pressurizing the gravity tank to create additional pressure, there is an independent pressurizing tank structure similar to the second embodiment. In this case, an elastically con- tracting bladder compensating the leaking of the lubricant is arranged in the grav- ity tank. The bladder is disposed in a fixed elevation in the tank, so that the above mass, which is contracting the bladder can be controlled corresponding to the overpressure conditions in the space to be pressurized, is in the air pressure of outside of the tank structure, in the freely breathing top part of the tank. Addition- ally, the bladder is located, at its one extremity, against the mass, and at its other

extremity against the pressure-sealed dividing wall that supports the bladder, pressed between them. The bladder is filled with lubricant and connected and pressure-sealed to the bottom part of the lubricant filled gravity tank, with a con- nection piece in the dividing wall. In this third embodiment of the invention, the pipe connections for the lubricant to be filled and for the lubricant leaving for the space to be pressurized, are preferably on the bottom part of the tank located be- low the dividing wall of the tank that supports the bladder. The tank is also pro- vided, if necessary, with the above mentioned lubricant level measuring means, for example a mechanical indicator connected to the weight that is causing the pressure. To discharge the air that comes with the filled lubricant from the tank, the dividing wall supporting the bladder in the gravity tank is shaped so that with the venting means, arranged, when necessary, in connection to the bladder, the gravity tank can be vented. When the amount of the leaking lubricant reaches the filling alarm level, the lubricant will be fed into the tank in a manner known per se described above. The lubricant filler pipe feed pressure must be higher than the combined pressure that is caused by the pressurizing mass and pressure of the oil column above the filling connection.

In the fourth embodiment of the invention, and similar to the first embodiment, a second tank has been connected as a pressurizing external component adjacent to the gravity tank. This external tank is, in this case, similar to the gravity tank de- scribed above in the third embodiment, operating as an independent pressurizing component, being provided with an elastically contracting bladder that compen- sates the leaking of the lubricant. In other words, the pressurizing component ex- ternal to the gravity tank, described above in the first embodiment of the inven- tion, comprising of the lid movingly sealed to the tank walls, with a changeable mass arranged on top of it to cause additional pressure, has in this embodiment been replaced by a tank according to the third embodiment of the invention, with a contracting elastic lubricant filled bladder, on top of which a changeable mass has been arranged to cause additional pressure, and the system leakage is compen- sated by the drop in the liquid volume in the tank caused by the contraction of the

bladder. This differs from the third embodiment of the invention so, that the tank does not have the lubricant filling connection or filler piping. The system is filled with oil through the filler piping leading to the gravity tank.

In the fifth embodiment of the invention and similar to the first embodiment, a second tank has been connected as a pressurizing external component adjacent to the gravity tank. This external tank has, in this case, been provided with an elastic pressure-sealed membrane compensating the leaking of the lubricant and attached and pressure-sealed to the inside of the tank walls, with a changeable mass ar- ranged on top of it to create additional pressure. To measure the oil volume in the pressurizing tank, for example the weight is provided with a mechanical indicator for indicating the level.

In the sixth embodiment of the invention for pressurizing the gravity tank to cre- ate additional pressure there is, similar to the second embodiment, an independent pressurizing tank structure, where in the external pressurizing tank, there is an elastic pressure-sealed membrane compensating the leaking of the lubricant at- tached and pressure-sealed to the inside of the tank walls.

The advantages of the present invention compared to the existing gravity systems are further explained in the following. The short distance between the gravity tank and the space to be pressurized, according to the invention, brings along shorter pipes and more inexpensive laying of pipes. Also there is less pressure loss in the piping and the pipes can have smaller inner diameter. The space required by the gravity tank in the structures above the ship deck can be used for other purposes, and in case of the tank structure below the deck, the deck space can be used for work purposes. By not using the compressed air to create additional pressure the solution becomes inexpensive, especially if compressed air is not needed else- where in the ship and the air compressor can be left out completely. Liquid piping and static pressure vessels according to the invention are more reliable and require less maintenance compared to the compressed air. Also, when replacing the old

pressure lubricating systems based on the static elevation, an inexpensive way to improve the pressure arrangement is to add the external pressure component creat- ing the pressure adjacent to the old gravity tank.

In the following, the invention is described with reference to the accompanying drawings of certain embodiments of the invention, to which, however, the inven- tion should not be exclusively limited.

Figure 1 shows the gravity tank location in relation to the ship's propeller unit.

Figure 2 shows the gravity tank operation without pressurization.

Figure 3 shows the gravity tank operation when pressurized with compressed air.

Figure 4 shows an example of the first embodiment of the invention where the gravity tank operation is pressurized without compressed air. Adjacent to the gravity tank is connected a tank operating as a pressurizing component with a floating lid. Changing the mass on the lid can modify the pressure inside the ves- sels.

Figure 5 shows an example of the second embodiment of the arrangement accord- ing to the invention, where the lid of the gravity tank operating as a pressurizing component is floating.

Figure 6 shows an example of the third embodiment of the arrangement according to the invention, where an elastic bladder is used for pressurizing the gravity tank operating as a pressurizing component.

Figure 7 shows an example of the fourth embodiment of the invention for pressur- izing the gravity tank, where an elastic bladder is used for pressurizing the gravity tank adjacently connected and operating as a pressurizing component.

Figure 8 shows an example of the fifth embodiment of the invention for pressuriz- ing the gravity tank, where in a tank operating as a pressurizing component con- nected adjacent to the gravity tank, an elastic membrane is used for pressurizing the tank.

Figure 9 shows an example of the sixth embodiment of the invention, where in the gravity tank operating as an independent pressurizing component there is an elas- tic membrane.

Figure 1 is a skeleton diagram of the location of the gravity tank 10 in relation to the ship's propeller unit 100. Lower part of the propeller unit 100 or an independ- ent propeller shaft seal space 21 must be pressurized in comparison to the sea- water pressure corresponding to the draft of the unit. Oil 20 leaks slowly out of the oil sump 21, and the leak must be compensated from the tank 10 through a pipe 16. The gravity tank 10 is filled intermittently in order to compensate the leaking. The pressure is created by the height of the oil column in the pipe 16 be- tween the freely breathing tank 10 and the space 21 to be pressurized.

Figure 2 shows a partial sectional drawing of an example of a state of the art grav- ity tank 10 without pressurization. Gravity tank 10 containing lubricating oil 20 and air 28 has a pipe connection 11 for the oil 20 to be filled and a pipe connec- tion 12 for the oil 20 leading to the space 21 to be pressurized through the pipe 16.

A filler pipe 15 extending through the filler piping and through the valves, not shown, from a store tank filled with lubricating oil 20, is connected to the connec- tion unit 11 located on the bottom surface of the gravity tank 10. Additionally, the connection unit 11 has a closing valve 14, which is used for filling the tank 10.

Pipe connection 13a can be used as a discharge valve. In Figure 2, the gravity tank 10 mounted on a supporting bracket 31, from where the oil 20, which is in a static elevation in relation to the space 21 to be pressurized, is lead to the space 21 to be pressurized, is freely breathing. The tank, as shown in the sectional view, is pro-

vided with a level sensor 22 with a float 22a monitoring the oil level 27 for con- trolling the lubricant volume i. e. the oil level 27, and an oil gauge 23 and a meas- uring tube 24 and an oil level 27 minimum 25 and maximum 26 mark for visual inspection of the oil 20 level. The pipe connections 11 and 12 arranged to the tank 10 are disposed below the oil minimum level. Air 28 flows freely through the open air valve 29a to the tank 10 so, that the oil 20 level 27 drops with the oil 20 leaking from the space 21 to be pressurized, while the air 28 maintains the pres- sure of the air outside the tank 10. Thus, the oil 20 level 27 is effected by the amount of leaking, and to compensate this, the gravity tank 10 must intermittently be filled with oil 20. The gravity tank 10 is disposed in a suitable static elevation Lo in relation to the space 21 to be pressurized to maintain an overpressure level corresponding the planned draft of the space 21 to be pressurized. When the amount of the oil 20 leaked reaches the filling alarm level, that is when the oil 20 level 27 in the gravity tank 10 is below the minimum level 25, the level sensor 22 connected to the connecting box signals electrically to the control system, not shown, or warns in some other manner and the user can visually detect also from the oil gauge 23 and from the measuring tube 24 that the level 27 has dropped. At this point, oil 20 is added manually to the gravity tank 10, for example by using the filler pipe's 15 closing valve 14 at the bottom surface of the gravity tank 10, so much that the user visually detects for example from the oil gauge 23 that there is enough oil 20, or preferably remotely with the aid of the control system and valves, not shown, until the control system receives information from the level sensor 22 telling that the oil level 27 maximum level 26 has been reached. When the gravity tank 10 is filled, the volume of air 28 escaping through the air valve 29a corresponds to the amount of the filled oil 20.

Figure 3 shows a partial sectional drawing of an example of the operation of the gravity tank 10 pressurized with compressed air according to the prior art. A grav- ity tank 10 containing lubricating oil 20 and air 28 has a pipe connection 11 for the oil 20 to be filled, and a pipe connection 12 for the oil 20 leading to the space 21 to be pressurized through the pipe 16. A filler pipe 15, coming from the store

tank containing the lubricating oil 20 via the filler pipes and valves, not shown, is connected to the connection unit 11 located on the bottom surface of the gravity tank 10. Additionally, the connection unit 11 has a closing valve 14 which can be used for filling the tank 10. The closing valve has not been installed. In Figure 3, the gravity tank 10 mounted by a supporting bracket 31 and from which the oil 20 is lead to the space 21 to be pressurized, is pressure-sealed. It has been provided, as shown in the cross sectional view in the Figure, with a level sensor 22 for con- trolling the amount of lubricant i. e. the oil level 27, and an oil gauge 23 and a measuring tube 24 and an oil level 27 minimum 25 and maximum 26 mark for visual inspection of the oil 20 level. The pipe connections 11 and 12 arranged to the tank 10 are disposed below the oil minimum level. Air 28 is fed from the source of compressed air 32 through the open air valve 29a to the tank 10 so, that the oil 20 level 27 drops with the oil 20 leaking from the space 21 to be pressur- ized. Thus, the oil 20 level 27 is effected by the amount of leaking, and to com- pensate this, the gravity tank 10 must intermittently be filled with oil 20. When the amount of the leaking oil 20 reaches the filling alarm level, that is when the oil 20 level 27 in the gravity tank 10 is below the minimum level 25, the level sensor 22 connected to the connecting box signals electrically to the control system, not shown, or warns in some other manner and the user can visually detect also from the oil gauge 23 and from the measuring tube 24 that the level 27 has dropped. At this point, oil 20 is added manually to the gravity tank 10, for example by using the filler pipe's 15 closing valve 14 at the bottom surface of the gravity tank 10, so much that the user visually detects, for example from the oil gauge 23 that there is enough oil 20, or preferably remotely with the aid of the control system and valves, not shown, until the control system receives information from the level sensor 22 telling that the oil level 27 maximum level 26 has been reached.

Figure 4 shows a partial sectional drawing of an example of the operation of the gravity tank 10 according to the first embodiment of the invention pressurized without compressed air. A tank 101 filled with oil acting as a pressurizing compo- nent and with a floating lid 110, is connected adjacent to the gravity tank 10 con-

taining lubricating oil 20. By changing the mass m, which preferably lies on top of the lid 110 and affects the lid and is in connection with it, the pressure p inside the containers 10 and 101 can be modified. In practice, suitable weights, not specially shown in the figures, are used as the mass m, and the number of weights is adapted according to the requirements for achieving the desired additional pres- sure.

Gravity tank 10 has a pipe connection 11 for the oil 20 to be filled, and a pipe connection 12 for the oil 20 leaving to the space 21 to be pressurized through the pipe 16, and a connection 13 of the operational connection pipe between the tanks, coming from the pipe connection 18 at the bottom of the tank 101 that op- erates as a pressurizing component external to the tank 10. A filler pipe 15 coming via the filler piping and through the valves, not shown, from a store tank filled with lubricating oil 20, is connected to the connection unit 11 located at the bot- tom surface of the gravity tank 10. Additionally, the connection unit 11 has a clos- ing valve 14 which can be used for emptying the tank 10, if a separate discharge valve has not been installed. In Figure 4, the gravity tank 10 from which the pres- surized oil 20 is lead to the space 21 to be pressurized, is, in this embodiment, pressure-sealed. It has been provided, as shown in the cross sectional view in the Figure 4, with a level sensor 22 for controlling the amount of lubricant i. e. the oil level 27, and an oil gauge 23 and a measuring tube 24 and an oil level 27 mini- mum 25 and maximum 26 mark for visual inspection of the oil 20 level. The pipe connections 11,12 and 13 arranged to the tank 10 are disposed below the oil minimum level. The air volume in the tank 10 has been preferably adjusted so, that the oil 20 level 27 keeps, despite of the variation in pressure caused by the dropping of the oil level in the tank 101, between the minimum 25 and maximum 26 lines, when operated in pressure range that is within the planned boundaries. In order to pre-adjust the air volume 28 and vent the air coming with the oil 20, there is an opening and closing venting valve 29 on top of the gravity tank 10. The leak- ing of oil 20 is compensated by a tank 101 connected close to, and adjacent to the gravity tank 10, operating as an effective pressurizing component, arranged with a

lid 110 that slides down with the leaking oil 20. A block 102, with the mass m, has been arranged as a weight on top of the lid 110 to maintain the overpressure level corresponding to the planned draft of the space 21 to be pressurized. The block 102 is made of material with density greater than the density of the oil 20 to be pressurized. In this embodiment, the tank 101 operating as a pressurizing com- ponent is in the pressure of the surrounding air above the sliding lid 110 i. e. on the side of the mass m. When the amount of the leaking oil 20 reaches the filling alarm level, that is when the lid 110 reaches the lower point of its movement range L, in the tank 101, the level sensor, not shown, arranged in the tank 101 to be pressurized, signals electrically to the control system, not shown, or warns in some other manner, and the user can also visually detect from the mechanical in- dicator, not shown, connected to the lid 110 that there is less oil 20. At this point, oil 20 is added manually to the gravity tank 10, for example by using the filler pipe's 15 closing valve 14 at the bottom surface of the gravity tank 10, so much that the user can visually detect, for example from the position of the lid 110 in the movement range Li that there is enough oil 20, or preferably remotely with the aid of the control system and valves, not shown.

Figure 5 shows a partial sectional drawing of an example of the second embodi- ment of the arrangement according to the invention, where the lid 110 of the grav- ity tank 101 operating as an independent pressurizing component is floating. In the arrangement for pressurizing the gravity tank to create additional pressure, there is no adjacently connected second tank, unlike in the embodiment in the Figure 4, but operating as a gravity tank, is a freely breathing pressurizing tank structure 101 similar to the external pressurizing component of the first embodi- ment of the invention, comprising a tank 101 with a lid 110 arranged to be sliding and moving downward with the leaking oil 20, and a pipe connection 11 provided with a closing valve 14 for the oil 20 to be filled, and a pipe connection 12 for the oil 20 leaving to the space 21 to be pressurized. The oil 20 to be filled is led through the pipeline 15 into the tank 101, and the oil 20 leaves the tank 101 through the pipeline 16. A block 102, with a mass m that can be controlled corre-

sponding to the pressure conditions in the space 21 to be pressurized, is arranged on top of the lid 110, which is sealed to be sliding. The block 102 creating the pressure is made of material with the density greater than the density of the oil 20 to be pressurized, preferably of iron or lead. The tank 101 is also provided with, at least one of the oil 20 level measuring means shown in the Figure 4, and not shown in the Figure 5. In this example of an embodiment, the gravity tank 101 is open on the side of the sliding lid 110 that is opposite to the oil space, that is, it is in the pressure of the surrounding air on the side of the mass m, and it is pressure- sealed on the side of the lid's 110 oil space. The pipe connections 11, 12 arranged to the tank 101 are disposed to the tank 101 sides and pressure-sealed, and addi- tionally they are disposed below the movement range of the lid 110 arranged to be sliding. To discharge the air that comes with the filled oil 20 from the tank 101, the lid 110 is arranged to have the required venting means. When the amount of the leaking oil 20 reaches the filling alarm level, the oil will be fed into the tank 101 in a manner known per se described above. The oil 20 filler pipe 15 feed pressure must be higher than the combined pressure of the one caused by the pres- surizing mass m and pressure of the oil column L3 above the filling connection 11.

Figure 6 shows also a sectional drawing of an example of the third embodiment of the arrangement according to the invention, where, in the gravity tank 101 operat- ing as an independent pressurizing component, an elastic bladder 120 is used in pressurizing, with an m mass block 102 on top of it, and if necessary consisting of several partial blocks. An elastically contracting bladder 120 compensates the leaking of oil 20. The bladder 120 is disposed in a fixed elevation in the tank 101, so that the above mass m that contracts the bladder, and that can be controlled corresponding to the overpressure conditions in the space 21 to be pressurized is, in the freely breathing top part 122 of the tank, in the pressure of the air outside the tank structure 101. Additionally, the bladder 120 is located, at its top extremity 121, against the mass m, and at its bottom extremity 123 against the pressure- sealed dividing wall 124 that supports the bladder 120, pressed between the mass m and the dividing wall 124. The bladder 120 is filled with oil 20 and connected

and pressure-sealed to the oil-filled 20 bottom part 125 of the gravity tank 101, with a connection piece 126 in the side wall 124. In this third embodiment of the invention, according to the Figure 6, the pipe connection 11 for the oil 20 to be filled, and the pipe connection 12 for the oil 20 leaving to the space 21 to be pres- surized, are at the bottom part 125 of the tank located below the dividing wall 124 of the tank 101 that supports the bladder 120. The tank 101 is provided with, at least one of the oil 20 level measuring means, referred to in the description of the Figure 4, and not shown here, for example a mechanical indicator connected to the pressure causing block 102, and indicating the contracting of the oil 20 filled bladder 120. To discharge the air that comes with the filled oil 20 from the tank 101, the dividing wall 124 that supports the bladder 120 is shaped so, that with the venting means, not shown, arranged in connection to the bladder, the gravity tank 101 can be vented. When the amount of the leaking oil 20 reaches the filling alarm level, the oil will be fed into the bottom part 125 of the tank 101 through the pipeline 15, in a manner known per se described above.

Figure 7 shows an example of the fourth embodiment for pressurizing the gravity tank, where, in the tank 101 connected adjacent to the gravity tank 10 and operat- ing as a pressurizing component, an elastic bladder 120 is used in pressurization.

This external tank 101 is, in the case of Figure 7, similar to the gravity tank 101 operating as an independent pressurizing component and described above in the third embodiment of the invention according to the Figure 6, being provided with an elastically contracting bladder 120 that compensates the leaking of oil 20. In other words, the pressurizing component 101 external to the gravity tank 10, de- scribed above in the first embodiment of the invention according to the Figure 4, and comprising the lid 110 movingly sealed to the tank 101 walls, with a change- able mass m arranged on top of it to cause additional pressure, has in this em- bodiment been replaced by a tank according to the third embodiment of the inven- tion similar to the one in Figure 6, with a contracting elastic oil filled bladder 120, on top of which a block 102, that has a mass m has been arranged to cause addi- tional pressure, and the system leakage is compensated by the drop of the liquid

volume in the tank 101 caused by the contraction of the bladder 120. This differs from the third embodiment of the invention shown in the Figure 6 so, that the tank 101 does not have oil filling connection or filler piping. The system is filled with oil 20 through the filler pipe 15 leading to the gravity tank 10. In the Figure 7, the oil-filled bladder 120 in an open tank 101 rests with its bottom extremity 123 on the bottom inside surface of the one-part tank 101, and the bladder 120 connection piece 126 is sealed through the tank supporting bottom surface 127 to the pipe connection 18, to which a pressure p passing connecting pipe 17 is connected be- tween the tanks 10 and 101. To measure the oil volume in the pressurizing tank 101 the block 102 is, for example provided with a mechanical indicator, not shown, for indicating the block elevation, that is, the amount of oil 20 that has leaked out of the bladder 120.

Figure 8 shows the fifth embodiment of the invention for pressurizing the gravity tank 10, where an elastic membrane 130 is used for pressurization in the tank 101 connected outside and adjacent to the gravity tank 10, and where a block 102, i. e. a changeable mass m made up, when necessary, of separate pieces of blocks, is arranged on top of the elastic membrane 130 attached and pressure-sealed inside the tank 101 walls, compensating the leaking of lubricant 20, to create additional pressure. The gravity tank 10 in Figure 8 operates similarly and is provided with the same reference numbers as in the Figures 4 and 7. The mass m above the membrane 130 that can be controlled to correspond the overpressure conditions in the space 21 to be pressurized is in the air pressure of outside of the tank structure 101, in the freely breathing top part 122 of the tank. Below the pressure-sealed membrane 130 in the bottom part 125 of the tank 101, there is oil 20 in the pres- sure p. In this fifth embodiment of the invention, the pipe connection 11 a and the closing valve 14a for the oil 20 to be filled are in the part of the tank 125, which is below the membrane 130, and an operational connecting pipe 17 between the tanks starts from the pipe connection 18 at the bottom surface of the tank 101, and connects at the other end to the tank 10 connection 13. To discharge the air com- ing in with the filled oil 20 from the tank 101, venting means, not shown, are ar-

ranged below the membrane 130 in the top part of oil space 125 in the tank 101, with which the air can be substantially discharged from the tank 101. When the amount of the leaking oil 20 reaches the filling alarm level, the oil 20 will be fed into the tank 10, 101 in a manner known per se described above, through the pipe- line 15 leading to the tank 10 and/or through the pipeline 15a leading to the tank 101. To measure the oil volume in the pressurizing tank 101, the block 102 is, for example provided with a mechanical indicator, not shown, for indicating the block elevation, that is the amount of oil 20 that has leaked out of the tank 101.

Figure 9 shows an example of the sixth embodiment of the arrangement according to the invention, where there is an elastic membrane 130 in the gravity tank 101 operating as an independent pressurizing component. The pressurizing tank 101 of the example is in its operation identical to the external pressurizing tank 101 shown in the Figure 8. A pipeline 16 for the pressurized oil 20 leads from the pipe connection 12 at the bottom surface of the tank to the space 21 to be pressurized.

Within the limits of the invention, solutions different from the ones described above can be feasible. Thus, the lid or membrane or bladder of a tank or of an external gravity component connected to a tank can be arranged vertically or in some other position other than horizontal, and/or the mass causing the pressure can be disposed so that it affects other parts of the lid or membrane or bladder, than the top, and the force component of the above mentioned mass causing pres- sure on system is used when the tank height cannot be increased, and for example the tank can be expanded only vertically.