WO2013050047A1

WO2013050047A1 - Hydraulic system

Info

Publication number: WO2013050047A1
Application number: PCT/DK2012/050380
Authority: WO
Inventors: Poul Hakon Poulsen
Original assignee: Kpf Arkitekter A/S
Priority date: 2011-10-07
Filing date: 2012-10-05
Publication date: 2013-04-11

Abstract

The present invention relates to a hydraulic system comprising at least one hydraulic pump driven by at least one electric motor. The hydraulic system further comprises at least one cylinder, which cylinder: is formed of a flexible material; is folded in a non- pressurized situation; and starts to unfold when the pressure increases therein. The hydraulic system can further comprise at least one separation device, wherein a hydraulic pump and a motor are integrated. Said separation device divides the cylinder of a flexible material into a first high pressure volume and a second low pressure volume.

Description

Hydraulic system

Field of the Invention

The present invention relates to a hydraulic system comprising at least one hydraulic pump, which hydraulic pump comprises a low pressure inlet and a high pressure outlet, which pump is driven by at least one electric motor, which hydraulic system comprises at least one cylinder, which cylinder comprises a first and a second fluid connection, which first cylinder connection is connected to the pump.

Background of the Invention

GB 2033968 discloses a hydraulic system for raising and lowering loads. Which system includes a pump which is operable, preferably by an electric motor, to deliver fluid from a reservoir to a remote jack through a conduit and a solenoid-operated check-valve of an assembly integral with jack to effect rising of a load by the jack. The pump is adapted to allow fluid to pass through in the opposite sense and the system is arranged so that upon actuation of valve fluid is returned from the jack through a flow regulator of assembly and thence through the conduit and the pump to the reservoir in order to lower the load.

Most hydraulic systems such as GB 2033968 operate with a pump outlet pressure in a range from 100-200 times the atmospheric pressure. This high pressure reduces the diameter of the piston and cylinder in relation to the load that has to be handled.

CH 660 208 A 5 concerns a hydraulic system for mechanical activation of a shaft. The system comprises an outer cylinder which is divided into sections by a flexible dia- phragm. A movable pump moves a liquid from the lower side up to an upper volume and hereby, by also increasing the pressure in the second volume, the motor pump unit is moved downwards and activating the shaft coming out from the cylinder. The pump can rotate in only one direction and in this patent application: there is no description of any return operation from the hydraulic system. Instead, there is a bleed hole from the upper volume down towards the lower volume, and at the same time, a relatively large spring will force the motor pump units upward and in this way further press the fay- draulic liquid through the bleed opening. This means that there is an automatic return which is performed by the spring. Keeping this hydraulic system in a stable position is possible by turning on and off the pump, and only a small hysteresis is achieved. The constant bleeding liquid from the pressure side to the tank side will lead to an increas- ing demand for energy, even for keeping a stable position of the driving shaft.

Object of the Invention

It is an object of the pending application to achieve a hydraulic system operating with a low pressure in a range from 2-20 times the atmospheric pressure.

It is a further object of the pending application to use a hydraulic fluid having a boiling point at the atmospheric pressure in a range from 70-150 degrees.

Description of the Invention

The object can be achieved by a system as disclosed in the preamble to claim 1 and modified where the cylinder can be formed of a flexible material, which cylinder is folded in a non-pressurized situation, which cylinder starts to unfold by increasing volume and pressure in the cylinder.

Hereby it can be achieved that the length of the cylinder depends on the amount of hydraulic fluid that is pumped into the flexible material. By folding the cylinder in non-pressurised situation it is achieved that the length of the cylinder is reduced, in fact to a size that is compared with the size of a hydraulic pump. Therefore such a hydraulic system could be used in any place where there is limited room for the hydraulic cylinder. The disadvantage of a cylinder being formed of a flexible material, such as a fire hose, is that there is limited stabilization when activated.

In a preferred embodiment for the invention, the cylinder can comprise a first and a second steel band, which steel bands arc fastened to each other along the edges for forming a foldable cylinder there between, which cylinder is folded into a roll in a non-pressurized situation, which foldable cylinder is unrolled when pressurized. Hereby can be achieved that the cylinder can be formed of two thin steel sheets placed as a double layer but connected to each other at the edges whereby it can be achieved that the double layer of, for example, steel material well-known from automatic rolling up, for example electric wires for electric equipment, such as hovers . The same kind of steel spring actuators are used for automatic belts in automobiles. By using two layers of spring steel, the unexpected result is that, as soon as pressure is formed be- tween two layers of spring steel, a rather stable cylinder is formed. This cylinder is able to carry a relatively high load which only depends on the pressure of the fluid inside the cylinder. The length o the cylinder can be adjusted by simply increasing the pressure and the volume of liquid placed inside the cylinder. Hereby it can be achieved that a flexible hydraulic cylinder can be formed. In principle, the length of the hydrau- lie cylinder depends on the length of the spring steel sheets that are combined. Of course, for a length of several metres, some degree of instability will occur, but a hydraulic cylinder is achieved that can be reduced in length by folding the cylinder around a roll, and having a very short cylinder in a low pressure and low volume of hydraulic liquid in the cylinder. The length of the cylinder is then variable depending on the amount of liquid that is pressed into the cylinder and the pressure in the same cylinder.

In a further preferred embodiment for the invention the foldable cylinder comprises a flexible tube, which flexible tube is placed between the steel bands, which flexible tube is folded between the steel bands when non-pressurized, which flexible tube by increasing volume and pressure unfolds both the flexible tube and the foldable cylinder. I lereby it can be achieved that the liquid is not in direct contact with the steel bands, because the liquid is always inside the tube placed inside the two steel bands. In a further preferred embodiment for the invention, the first and a second steel band forming the foldable cylinder, which foldable cylinder is placed inside the flexible tube. Hereby it can be achieved that the steel band will always be protected by the tube, and the liquid pressure will still be inside the steel bands, but if there should be a small leak between the two spring steel layers, only a limited pressure difference is necessary for keeping the layers of spring steel in the unfolded situation where liquid on the outside of the spring steel has no effect on its way of operation. Only if there is sufficient pressure inside the spring steel cylinder, will it operate perfectly. The cylinder can comprise at least one separation device to divide the cylinder into a first high pressure volume and a second low pressure volume, which high pressure volume receives high pressure fluid from the high pressure outlet of the pump, which low pressure volume delivers low pressure fluid to the low pressure inlet of the pump. so the pump and the electric motor is integrated in the separation device, which separation device comprises at least one sealing towards the cylinder, which first pressure volume is placed below the separation device, which second low pressure volume is placed above the separation device, which separation device carries a mechanical connection towards an item to be moved.

Hereby can be achieved, that an integrated unit comprising at least an electric motor and pump can be integrated in a separation device, which separates a high pressure volume and a low pressure volume. The integrated device could be placed inside a cylinder where the separation device or the whole cylinder is moved by moving hy- draulic fluid from the low pressure volume to the high pressure volume. Depending on the type of pump, it is possible by changing the rotation direction of the pump to move hydraulic fluid from the high pressure volume to the low pressure volume and in that way change the low pressure volume into a new high pressure volume. Hereby is achieved a hydraulic system where a pump motor unit is placed directly in connection with the two volumes and the use of any tube or pipes for hydraulic fluid is totally avoided. Especially for hydraulic devices operating with a relatively low hydraulic pressure this invention can be very important. Low pressure hydraulic systems will typically operate in a range between 2 and 10 times the atmospheric pressure. Low pressure hydraulic systems can be used where sufficient room for cylinders having a relatively big diameter can be used and where the load that has to be carried is relatively low. It is possible by this invention to use specially designed bellows as hydraulic cylinders, because these bellows can be operated by the relatively low hydraulic pressure. The low pressure hydraulic systems could be used where traditional high pressure hydraulic systems will be all too complicated to use, because tubes or wires have to carry fluid with a pressure above 100 times the atmospheric pressure. The separation device moves in a first direction by activation of the electric motor and pump. In one possible embodiment for the invention, the separation device moves in a cylinder which cylinder, for example over the separation device, contains low pressure hydraulic fluid and where the pressure, for example below the separation device, is high pressure volume. In operation the pump will move hydraulic fluid from the upper low pressure volume into the high pressure volume below and if the separation device is movable in relation to the cylinder, the separation device will be moved upwards. Hereby can be achieved a hydraulic system that is rather compact in that it only comprises a cylinder and this cylinder simply comprises the separation unit which is a combined unit of a pump and an electric motor. Switching on the motor maybe in first direction of rotation the pump, the separation device will start moving upwards. In one possible embodiment, the opposite movement of the separation device can be performed by backwards rotation of the pump and motor. In that way a very simple control of the system can be achieved.

The separation device moves in a second direction by activating a valve, which valve opens for flow from the high pressure volume to the low pressure volume. The use of a valve for the backward flow gives the possibility that a simple pump is used which is only to be operated in one direction. The valve that is used could be a pressure activated valve which valve has two different positions where the valve in one position is closing the flow of volume from the high pressure to the low pressure which valve by pressure activation changes into a second position where a flow channel opens from the high pressure volume to the low pressure volume. In that way, a load can be carried in a relatively stable manner, because the valve closes for backfiow during operation and maybe change of a load. When the valve is opened, the return flow takes place without use of electric energy. Therefore the use of the valve will reduce the energy consumption of the system.

The valve is pressure activated which valve change from a first closet position into a second open position by increasing pressure, which valve change from the second open position into the first closed position by backfiow through the valve. The use a special valve that can be activated by pressure and in that way be moved from a first to a second position is highly effective if only a primitive control is used. It is possible in that way to move into a stop-position and there the valve will lock any flow and a load is in that way fixed in that position. I f the motor is activated again and the pressure starts increasing, the valve changes its position from its first to a second position and the motor and pump can be stopped, because a reverse flow will start. The speed of the reverse flow depends mostly on the construction of the valve. Depending on the di ferent numbers o openings in a valve, the time period used for moving a load backwards can in that way by the technical construction is controlled by designing the valve. Therefore it is possible to achieve a primitive, but highly effective hydraulic system, especially used for low pressure hydraulic systems. The sealing from the separation device towards the cylinder comprises a sealing stocking, which sealing stocking is fixed to the separation device, which sealing stocking is placed inside the cylinder, which sealing stocking comprises the high pressure volume. The use of a sealing stocking, which is fixed towards the separation unit, where the sealing stocking is folded downwards, and the sealing stocking forms a closed volume inside a tube, which tube supports the sealing stocking. The volume inside the stocking forms the high pressure volume and the high pressure volume as such also concerns the volume between the folded layers of the stocking. By starting the pump, the volume inside the stocking will increase as well as the pressure, and the separation unit starts moving upwards. In that way a highly effective hydraulic system is achieved which system is specially designed for low pressure hydraulic systems.

The sealing from the separation device towards the cylinder is a fixed scaling which fixed sealing locks the separation device to the cylinder, which high pressure volume is formed inside bellows. 1 lcrcby is achieved an alternative embodiment where a fixed sealing between the separation device and the cylinder can be used, and the cylinder as such is moved by increasing the pressure and the volume inside a bellow which bellow is unfolded. Because the stability o a bellow is reduced, the bellow is in some situations placed inside a cylinder whereby the bellow is being stabilised, because the bello is in contact with the inside of the cylinder.

Preferably the pump is a submersible pump. The pump that is integrated into a separation device has to be formed in a way where the pump can operate in the hydraulic fluid. Therefore, it is possible to use a traditional submersible pump. Especially fol^¬ low hydraulic pressures, it is possible to use centrifugal pumps which are the typical types of pumps which are used as submersible pumps. The hydraulic fluid can comprise water. For primitive hydraulic systems water is a highly effective hydraulic fluid. W ater is less compressible as typical hydraulic fluids used for high pressure hydraulic systems. Especially for a low pressure hydraulic system water can be a highly effective hydraulic fluid. The water contains an antifreezing substance. Especially for outdoor applications, it is necessaiy for hydraulic systems to use an antifreezing substance in the water. In that way, water is not exactly clean water, but maybe it contains one or more chemical substances. The pending application further concern a method for operating a system as disclosed in the description and concerns at least the following steps of operation: a. switch on the electric motor

b. the motor rotates the pump,

c. increases the pressure at the pressure outlet by rotating the pump,

d. increase the pressure in the first high pressure volume by rotating the pump, e. increase the volume in the first high pressure volume by rotating the pump, f. decrease the volume in the second low pressure volume by rotating the pump, f. move the mechanical connection and an item.

Hereby is achieved a highly effective low pressure hydraulic system.

The separation device is moving towards the low pressure volume by rotating the pump. By letting the electric motor rotate the pump, it will start moving the separation device from the pressure volume towards the low pressure volume. Description of the Drawing

Figure 1 shows a motor pump unit inside a tube according to the first aspect of the invention. Figure 2 shows a possible embodiment for the invention in a first situation and figure 3 shows the same embodiment, but in another possible position where fig- ure 4 shows the same embodiment in a top position.

Figure 5 shows an alternative embodiment comprising bellows where figure 5 shows a top position and figure 6 shows the lowest position. Figure 7 shows a combination of four system as previously described working in a combined lifting operation.

Figure 8 and figure 9 show a return valve for synchronisation of the movement of the invention disclosed at figure 7.

Figure 10 disclosed an alternative embodiment for the invention shown at figure 7 where figure 10 shows the invention in its down position and where

Figure 1 1 shows the invention in the top position.

Figure 12 shows an enlarged component which in conjunction with at least one or more mechanical components can perform locking of a load in the top position.

Figure 13 shows an alternative embodiment for a rotating actuator.

Figure 14 shows an alternative preferred embodiment for the invention where the tube comprises a rigid inner tube.

Figure 15 shows an alternative embodiment where a tube is sufficiently rigid to work when pressurised.

Figure 16 shows an embodiment where a tube is formed unto metal sheets. Figure 1 7 shows a preferred embodiment where the tube formed of metal sheets is further placed inside a flexible tube.

Detailed Description of the Invention

Figure 1 shows one first possible embodiment for the invention. At figure 1 is a sectional view of a hydraulic system indicated where only central part of the system is indicated. Inside a tube 12 is indicated a pump 4, which pump has a low pressure inlet 6 and a high pressure outlet 8. The pump is driven by an electric motor 1 0, which is directly connected to the pump 4. The pump and motor unit are placed inside the tube 12 so that the pump 4 and motor unit form a separation device 14. This separation device 14 divides the volume inside the tube 12 in a high pressure volume 16 and a low pressure volume 18. O-rings 24 is indicated in order to perform a fluid tight separation between the high pressure volume 16 and the low pressure volume 1 8. A mechanical connection 26 is indicated which mechanical can be connected directly to a load.

In operation the pump 4 will move a hydraulic fluid from the inlet 6 connected into the low pressure volume 18 into the pressure outlet 8 and into the pressure volume 16 and in that way by increasing pressure move the separation unit 14 towards the low pressure volume 18.

Depending on where a system is used in some situation a pump 4 that can perform reverse pumping could be used and in that way change the function of the two volumes 1 6 and 18 and in that also perform movement in the reverse direction. In other situations gravity or spring means can perform an active pressure towards the separa- tion unit and by a valve 34 it is possible to start a flow from the high pressure volume 16 to the low pressure volume 1 8 and in that way perform movement in the opposite direction.

Figure 2 shows an alternative embodiment with a system 102. The system at figure 2 1 02 shows a motor pump unit 104 inside a tube 1 12 which tube 1 12 comprises a low pressure volume 1 18 and a high pressure volume 1 16. Inside the high pressure volume 1 1 6 is indicated a stocking 140 which stocking is folded and the stocking is tight for fluid. The stocking 140 follows the inner part of the tube 1 12 and the inside of the high pressure volume 1 16. Inside the tube 1 12 is further indicated a support tube 142. A mechanical connection 126 is connected to the motor pump unit 104. Below the pump unit 104 is indicated a valve mechanism 134.

Figure 3 shows the same embodiment with the same features which therefore are not described. The only difference is that the volume 1 16 has increased because the pump motor unit 104 is moved upwards. At the same time the volume 1 18 is being decreased.

Further to figure 4 are the same features indicated, and the pump motor unit 104 is now indicated in its top position. It can be seen that the support stocking 140 is nearly totally unfolded, because it now follows the inner contour of the high pressure volume 1 16.

In operation of the embodiment shown at figures 2, 3 and 4, the pump is driven by an electric motor and can in that way pump hydraulic fluid from the volume 1 18 to the volume 1 16. In the reverse movement, the valve 134 is activated. This valve 134 can be a two-way valve which in a first position closes for flow, but increasing pressure from the pump unit 104 can change the valve position into a second position where there is an opening for reverse flow. In that way a very primitive operation can be performed, because first activation will move the pump motor unit 104; a second activation will change the valve position and the valve will open and there will be a reverse movement.

Figure 5 shows an alternative embodiment to what is shown on previous figures. A pump motor unit 204 is indicated above a cylinder 212 which cylinder 212 comprises at first a two-way valve 234 and a bellow 242 which bellow 242 forms the pressure volume 216 around the bellow, but inside the tube 212 is formed an extra volume 21 8 which is part of the low pressure volume. At figure 5 the motor pump unit 204 is shown in its top position. Figure 6 shows the same embodiment as figure 5. but now the motor pump unit 204 is in its lower position. Therefore, the bellows 242 are now mostly empty of hydraulic fluid. Therefore, the fluid is now present in the low pressure volume 218. Figure 7 shows a possible use of a hydraulic system as previously described. In figure 7 a system 304 is disclosed which comprises four cylinder units in the way that the four cylinders can carry a relatively heavy load such as a ear. a truck or a 20^" container. A cylinder device a, b, c and d is placed in each of the corners. Motor pump units 304 are indicated as a, b, c and d, and a pressure volume is indicated as 308 a, b, c, d. From each of the motor pump units 304 a, b, c and d is connected a wire 310 a, b, c, d which is connected so that a wire is going from, for example, 304 a to the valve 334b further is a wire 3 10b going from the motor pump unit 304b to the valve 334d. Further is a wire 31 Oc starting from the motor pump unit 304c and going to the valve 334a. Further from the motor pump unit 304 is a wire 31 Od connected to the valve 334c.

In operation wi ll one of the motor pump units 304 which is lacking its velocity, maybe because of a higher load, automatically perform an adjustment of a cooperating motor cylinder unit in automatic opening the return valve 334 and in that way lower the other motor cylinder unit until the synchronisation is further achieved. In that way an automatic compensation of maybe the difference in working effectivity in the pump motor units or change in load automatically adjust the position of a platform carried by the hydraulic system. Alternatively the wires can be fixed directly to the pumps and the platform and adjust the capacity directly.

Figure 8 shows a possible embodiment for a valve as the valves indicated at figure 7 with the number 334. The valve has an inlet 412 and a conical valve piston 416. This valve piston cooperates with a valve seat 41 8. A support 420 supports the valve piston 41 6 in its movement. Furthermore, a spring is indicated for returning the valve. An outlet 414 is where fluid is delivered. A ring 422 is for connecting the wire indicated at figure 7 as 3 1 0.

Figure 9 shows the same embodiment as figure 8. but now in an open position. Figure 10 shows an alternative embodiment for a system 502 primarily for a car lift or lift of other heavy loads. The system 502 comprises four motor pump units 504 each placed mostly in the corners. A tube 5 12 comprises the pump motor unit 504 and be- low the pump motor unit 504 is indicated a low pressure volume 516. Above the motor pump unit 504 is indicated the low pressure volume 5 18. The system further comprises a sub terrain housing which has a bottom support plate 540 and an upper load support 542. These two plates are connected mechanically to each other by supports 546. Further are indicated side plates 544 which comprise a track an axle which is connecting two of the parallel units 544 placed in each side.

Figure 10 shows the invention of a system 502 in its down position, and figure 1 1 shows with the same technical features the car lift in its upper position. Figure 12 shows one of the plates 544 where a first downwards track is shown as 550 which continue upwards into the track 552. In the top position the track is changed into the track 554 which has to pass over the top 555, before a load can end in the support groove 556. Further, protrusion 567 is indicated. The track continues in a downwards track 560 and ends in the track 562 into the track 550.

In operation will, for example, an axle have its end placed in one of the grooves 550 in a downwards position. By moving upwards through the groove 552, the axle will end up and rest in the groove 556. Thereby a load will be directly supported in its top position. Further moving upwards will move the axle over the hill 558 and into the 560 downwards movement.

This track system in combination with the hydraulic actuators can be used in many different situations, because it is a very simple way of locking a load in its upper position.

Figure 13 shows a circular activator which is produced by a circular bellow which needs mechanical support to be in the correct form. In that way it is possible to per- form an actuator which can be used if the need is angular activation up to maximum one full circle.

Figure 14 shows one possible embodiment for an invention, where a hydraulic system is operating with a flexible tube which tube can carry the whole system and perform activation. The figure 14 shows a pump 604 driven by a motor 610. There is no shown liquid inlet to the pump, and the outlet from the pump 604 is directed into the flexible tube 620 which flexible tube 620 inside comprises a flexible metal tube 61 8 which metal tube is formed by at least two longi tudinal sheets of spring steel 614,61 6 where at figure 14 is indicated that 6 sheets of spring steel 614 a, b, c and 616 a, b, c are forming a hexagonal inner tube 618 placed inside the flexible tube 620. The single sections of longitudinal sheets of spring steel 614 a-c and 616 a-c arc hinged together at the corners and thereby forming the flexible inner tube. Below the tube arc indicated two rollers 630, 632. These rollers can by decreasing pressure and decreasing volume in the tube 618 and 620 perform pressing out of the last liquid and roll the whole tube 61 8 and 620 unto a roll 640.

In operation, a system, as indicated at figure 14, can by filling liquid at a sufficient pressure by the pump into the tube 61 8 and 620 perform an unrolling of the roll 640 and in that way perform a lifting of the pump 604 and the motor 610. In that way a rather heavy load can be li fted up by this hydraulic system. It is to understand that there of course is a limit maybe up to a few metres in how high the lift may be performed without any further support. But the hydraulic system when emptied from the hydraulic fluid can be reduced in its height so that only the pump and the motor arc defining the length of the hydraulic system. This can be very important where hydraulic systems have to operate where only limited space is available.

Figure 15 shows the same embodiment as figure 14, but here it is the tube 620 without any inner tube. Hereby can be achieved that the flexible tube 620 easily can be folded when passing between the rollers 630, 632 and by decreasing pressure and removing o the hydraulic fluid by means of the pump 604. the flexible tube 620 can be folded unto the roll 640. Hereby can be achieved an effective lifting of the motor pump unit and a further load that is supported by the pump motor unit. The flexible tube 620 will perform a rather stiff connection as long as the pressure inside the tube is sufficiently high. In a hydraulic system operating primarily with water as hydraulic fluid, a pressure as low as 10 times the atmospheric pressure but up to 200 times the atmospheric pressure is possible. Even a higher pressure could be used, but the pressure operating in a flexible tube as indicated in 620, the pressure is probably in the lower end., such as between 10-20 times the atmospheric pressure.

Figure 16 shows the same pump 604 and motor 610, but the flexible tube is now formed of two longitudinal sheets o spring steel 614 and 616. These longitudinal sheets of spring steel 614,616 are welded together at the edges so there is formed a volume there between. This volume is tight, because the welding along the edges is completely tight also for hydraulic fluid under high pressure. Also by this invention is achieved that the flexible tube formed of the metal sheets 614 and 616 can be folded and rolled along the roll 640. Also by this alternative embodiment, it is possible to achieve a hydraulic cylinder that is flexible in length.

Figure 17 shows one further embodiment for the invention. Once again is indicated the pump 604 driven by the motor 610, and a tube 620 is connected to the pump. The flexible tube 620 comprises an inner flexible tube formed out of two longitudinal sheets of spring steel 614 and 616 placed inside the tube 620. By placing the longitudinal spring steel tube inside the outer flexible tube, there is in fact no need for the inner tube to be completely tight for fluid, because the unfolding of the tube 620 will automatically force the inner tube to open. So even if there is a liquid pressure inside the inner tube and the outer tube at the pressure, the unfolding of the inner tube will be performed, but if the inlet of the tube from the pump 604 is directed into the inner tube and filling of liquid in the outer tube is performed through defined lead openings in the inner tube, there is performed an automatic unfolding of the inner tube. Folding the inner and outer tube is once again performed by rollers 630 and 632 unto a roll 640. Combining the relatively stiff inner tube with the fluid tight outer tube is achieved a flexible hydraulic cylinder that can be used for a lift of sufficient height simply because forming a relatively high pressure inside the tubes will lead to stability in the lifting process for several metres.

Claims

1 . A hydraulic system (2) comprising at least one hydraulic pump (4), which hydraulic pump (4) comprises a low pressure inlet (6) and a high pressure outlet (8), which pump (4) is driven by at least one electric motor (10), which hydraulic system (2) comprises at least one cylinder (12), which cylinder comprises a first and a second fluid connection, which first cylinder connection is connected to the pump (4), characterized in that the cylinder (12) is formed of a flexible material, which cylinder (12) is folded in a non-pressurized situation, which cylinder ( 12) starts to unfold by increasing volume and pressure in the cylinder (12).

2. A hydraulic system according to claim 1 , characterized in, that the cylinder (612) comprises a at least first and a second steel band (614.61 6). which steel bands are fastened to each other along the edges, for forming a foldable cylinder (61 8) therebetween, which cylinder (618 ) is folded into a roll in a non-pressurized situation, which foldable cylinder (618) is unrolled when pressurized.

3. A hydraulic system according to claim 2, characterized in, that the foldable cylinder (61 8 ) comprises a flexible tube (620), which flexible tube is placed between the steel bands (614,61 6), which flexible tube (620) is folded between the steel bands (614,616) when un-pressurized, which flexible tube (620) by increasing volume and pressure unfold both the flexible tube (620) and the foldable cylinder (618).

4. A hydraulic system according to claim 2, characterized in, that at least a first and a second steel band (614,616) forms the foldable cylinder (61 8), which foldable cylinder (61 8) is placed inside the flexible tube (620).

5. A hydraulic system according to one of the claims 1 -4, characterized in, that the system comprises a cylinder (12) and at least one separation device (14) which separation device divides the cylinder (12) into a first high pressure volume (16) and a sec- ond low pressure volume (18), which high pressure volume (16) receives high pressure fluid (20) from the high pressure outlet (8) of the pump (4), which low pressure camber ( 1 8) deliver low pressure fluid (22 ) to the low pressure inlet (6) of the pump (4), that the pump (4) and the electric motor (10) is integrated in the separation device (14), which separation device (14) comprises at least one sealing (24) towards the cylinder (12), which first pressure volume (16) is placed below the separation device (14), which second low pressure volume ( 1 8) is placed above the separation device (14), which separation device (14) carries a mechanical connection (26) towards an item (28) to be moved.

6. A hydraulic system (2) according to claim 5. characterized in, that the separation device ( 14 ) moves in a first direction (30) by activation of the electric motor (10) and pump (4).

7. A hydraulic system (2) according to claim 5or 6, characterized in, that the separation device ( 14) moves in a second direction (32) by activating a valve (34). which valve opens for flow from the high pressure volume ( 16) to the low pressure volume (18).

8. A hydraulic system (2) according to claim 6, characterized in, that the valve (34) is pressure activated, which valve (34) changes from a first closet position (36) into a second open position (38) by increasing pressure, which valve (34) changes from the second open position (38) into the first closed position (36) by back How through the valve (34).

9. A hydraulic system (2) according to claim 8. characterized in, that the sealing (24) from the separation device ( 14) towards the cylinder ( 12) comprises a sealing stocking

(40), which sealing stocking (40) is fixed to the separation device ( 14). which sealing stocking (40) is placed inside the cylinder (12), which sealing stocking (40) comprises the high pressure volume (1 18).

10. A hydraulic system (2) according to claim 8, characterized in, that the sealing (24) from the separation device towards the cylinder (12) is a fixed sealing ( 1 24) which fixed sealing ( 1 24) locks the separation device to the cylinder (12), which high pressure volume (218 ) is formed inside bel lows (42).

1 1 . A hydraulic system (2) according to claim 8, characterized in, that the pump is a submersible pump ( 1 04).

12. A hydraulic system (2) according to claim 1 1 , characterized in, that the hydraulic fluid comprise water.

13. A hydraulic system (2) according to claim 12, characterized in. that the water contains an anti freezing substance.

14. A method for operating a system as disclosed in at least one of the claims 1 -3, characterized in that the method comprises at least the following steps of operation: a. switch on the electric motor

b. the motor (10) rotates the pump (4,104),

c. increases the pressure at the pressure outlet by rotating the pump (4, 104), d. increase the pressure in the first high pressure volume (16) by rotating the pump(4.104),

e. increase the volume in the first high pressure volume ( 16) by rotating the pump

(4, 104),

f. decrease the volume in the second low pressure volume ( 1 8 ) by rotating the pump (4, 104),

f. move the mechanical connection (26) and an item (28).

15. A method according to claim 14 characterized in that the separation device ( 14) is moving towards the low pressure volume by rotating the pump.