DE1550361A1 - Pressure control device - Google Patents

Description

Frederick A. Krause Associates, Inc., of Prenchtown, N.J., USA

Pressure control device

The present invention relates to hydraulic systems, and more particularly to a novel water pressure system which is useful used in conjunction with multiple punch presses.

In modern presses that pull or deform sheet metal into different, complicated shapes, different Parts assembled, hydraulically operated multiple dies are used. These dies consist of a large number of die elements, each of which is associated with actuating pistons of different sizes. The actuating pistons are

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hand supplied with press oil at common pressure, so that the Water pressure when opening or moving apart the die jaws of the press the pistons and those connected to them Holds die elements in the fully extended position. When closing the die jaws between which the workpiece sheet metal, the die elements are withdrawn in a predetermined order - a process that is at least partially dependent on the cross-sections of the die elements actuating the die elements Piston depends. When the die jaws are subsequently opened, the die elements begin again in reverse Order to advance. Through this retraction and advancement of the various die elements in particular Controlled sequence, the production of different, complicated shapes in a single operation of the press is possible.

The die arrangement described above places certain demands on the hydraulic system, the liquid under . Directs pressure to the actuating piston. This system must e.g. B. be suitable for supplying a sufficient amount of hydraulic fluid and, when the die jaws are opened, if there is sufficient pressure, all actuating pistons and the die elements connected to them can be fully extended. However, this pressure must not be too high, otherwise the die elements will move with such rapidity when the press is opened move into their extended position so that the drawn workpiece is forcibly thrown out of the dies and either destroyed

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or is severely damaged. On the other hand, the hydraulic system has to do the whole thing during the closing of the die jaws can absorb displaced liquid; moreover, it must be fluid pressure choosing this operation on a very high level hold high so that the workpiece is deformed accordingly by the stretched die elements.

In addition, the fact that the rapid activity of the press results in very large changes in the Enter the flow rate and speed of the hydraulic fluid in the system, another difficulty. Such sudden changes in flow rate or speed have very serious hydrodynamic effects, which the valve action detrimental and of course the action of the dies have a particularly negative impact. To these disadvantageous, hydrodynamic effects include foaming of the liquid, bubble formation, pressure reflections, pressure increases, Slow valve response times and uneven valve | task.

The present invention provides a novel hydraulic system System suitable for use in combination with multiple punch presses of the type described above. In this system, hydraulic fluid is first supplied under low pressure in order to activate the pistons of a multiple

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advance punch press while opening the same; afterward the fluid displaced by the retraction of the pistons when the dies are closed is controlled by a absorbs higher pressure. This system also allows adaptation to sudden and very large changes the flow rate or flow rate, without corresponding changes to the prevailing system in the system Pressure or the adverse hydrodynamic effects customary under such conditions occur.

The present invention creates a novel printing system, which consists of a housing with a container, .ein with this communicating container chamber, an inlet-outlet chamber and a novel valve arrangement, which the connects both chambers. The inlet-outlet chamber is through a hydraulic line with a die assembly or another evaluation device.

The two chambers are connected by two channels, one of which is equipped with a regulating valve which liquid flows into the inlet-outlet chamber, while the other feast with a coil-like control valve is. The control valve is shaped and arranged so that it does not respond to a pressure increase in the inlet outlet chamber. However, there is a pressure channel between the inlet / outlet chamber and a chamber in the control valve arranged so that increases in actual pressure

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on the end of the spool-like control valve for the purpose of Actuation of the same are transmitted.

The control valve itself is shaped so that it can derive a pressure increase; it is _(further t with specially shaped recesses, through which controlled the rate of change of the valve opening in accordance with the displacement of the valve and the liquid flow is directed uniformly without foaming.

Above for a better understanding of the following detailed description of the invention and for a better appreciation of its contribution to the state of the art, the important inventive features have been outlined in broad outline claims bilden.Für professionals is clear ersieht- (borrowed that idea on which this disclosure is based, can be easily evaluated for the designing of other structures with which the invention aims are also achieved. It is therefore important to point out that all such similar constructions, which do not depart from the spirit and scope of the invention, are to be regarded as covered by the claims.

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Further details of the invention emerge from the description of the illustrated in the accompanying drawing Embodiment.

In the drawing is:

1 shows a detail, seen from the side, which shows the external features of a printing system according to the invention;

Fig. 2 is a section on the line H-II of Fig. 1 with part of a die assembly which is hydraulically connected to the printing system of Figure 1;

FIG. 3 is a view similar to that of FIG. 2, showing a section and the system in a different operating phase shows;

FIG. K shows a partial section on the line IV-IV of FIG. 1;

Fig. 5 is a perspective view of one in the embodiment valve spool used by FIG. 1; and

6 is a perspective view of a modified embodiment of a valve spool similar to that of FIG is similar.

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1 shows a printing system 10 according to the invention. This printing system consists of a main part 12 on which a cylindrical container Ik is placed. To read the pressure of the hydraulic fluid flowing into and out of the system, a pressure gauge 16 is connected to the main part 10 via a valve.

The internal structure of the printing system 10 and its integration with the recycling system can best be seen from the cross-sections of FIGS. 1 and 2. These show the cylindrical container Ik placed on the main part 12 with a sealing ring 20 lying there in the form of a seal, which prevents the ingress of liquid. The container is covered with a lid 22. The whole assembly is mounted on the main part 12 by an axially extending support bar Zk, which is screwed at one end to the main part 12, viäh rend to its second end extending through the lid 22nd A nut 26 I is screwed onto this second end of the rod 2k.

A liquid level glass 28 is attached to the outside of the container Ik , which optically indicates the liquid level in the container. Hydraulic fluid is fed into the container via a fluid inlet nozzle 30 screwed into the cover 22. In normal operation, the container is filled to about two thirds, ie

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the liquid level is close to that indicated in the drawing Line 32. During normal operation, the liquid in the container is under an overpressure of about 7 to 9 kg / cm; For this purpose, an air nozzle 34 connected to an air pressure line (not shown) is also located in the lid 22 of the container used.

"In the main part 12 is a container chamber 36 and a

Entry and exit chamber 38 formed. These chambers lie next to one another and are separated by an inner wall 40. The container chamber 36 opens into the container 14, while the inlet and outlet chamber 38 is connected to a hydraulic line 42, which in turn is connected to a recycling plant to be described in more detail below. Upper and lower communication channels 44 and 46, respectively, extend through inner wall 40 between chambers 36 and JQ. A regulating valve 48 is provided for setting the opening width of the upper channel 44, while the setting of the opening width of the lower channel 46 is carried out by a control valve 50.

The regulating valve 48 is arranged so that liquid from the container chamber 36 into the inlet-outlet chamber 38, but not in the opposite direction can flow. The valve has one in the first outer wall

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of the main body screwed plug 52 carrying a valve element $ 6 which reciprocates towards and away from a valve seat ring 58. The valve seat ring is inserted into the upper connecting channel with a press fit. Between the plug 53 ^{un (i} äeni valve element 56 is disposed a spring 6O for biasing the regulator valve, which presses the valve element against the valve seat ring 58 in g a position in which the channel is sealed. The spring 60 for biasing the regulator valve, however, is not very strong, so that in the event of a pressure drop in the inlet «outlet chamber 38 below the pressure in the container chamber 36, the resulting pressure difference overcomes the spring force and presses the valve element 56 back, so that liquid, as indicated by the arrow A, flows out of the container 14 through the upper connection channel 44 and the inlet-outlet chamber to the hydraulic line 42. Excess pressure in the inlet outlet chamber 38, on the other hand, presses the gating valve element 56 only more firmly onto the valve seat ring, so that no liquid can flow back through the upper connecting channel into the container 14 .

The control valve 50 consists essentially of a coil 62, which is shown in perspective in Fig. $. This coil is cylindrical and has two end sections 64, 66 with a larger diameter than that of a section 68 located in between. The end sections 64,

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are, as shown in FIGS. 2 and 3, hollowed out, whereby a pressure chamber 70 and a spring seat chamber 72 are formed. Between the two chambers there is a liquid connection in the form of a central channel 7 ^ _t which extends axially to the coil 62nd The speed at which the liquid flows through the central channel is limited to a predetermined value by a measuring nozzle 76 inserted into the channel with a press fit.

It should be noted that the pressure chamber 70 in the coil 62 tapers gradually towards the central channel 7 ^. This gradual taper is a novel feature of the invention and works in concert with the valve assembly the mitigation of the effects of transition pressure values or pressure drops, ("knocks"), so that at all times a fully effective and uniform control of the valve activity is guaranteed.

The valve spool 62 also has a plurality of recesses 78 which are distributed on the circumference of the right end section 66 , specifically where it adjoins the intermediate section 68. These recesses are semicylindrical and their axes extend radially outward from the coil neck. As can be seen from the following description of the work

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Beitsweise the device can be seen, make this possible Recesses a lighter and more balanced control of the liquid flow, without the high pressure values, large Flow rates and rapid switching operations in the system, a surge or foaming of the liquid occurs.

The first enlarged diameter end portion 64 extends through an opening 80 formed in the first outer wall 54 of the main body 12. Similarly, the second end portion 66 of the spool extends through both the lower connecting passage 46 in the inner wall 40 and another .Opening 82 in the second outer wall 84 of the main part. The two openings 80, 82 in the outer walls 54 _S 8 ^ f- of the main part have the same orientation and the same Durohmesser as the lower, through the inner © Viand 40 connecting channel 46 _e

The control valve spool 62 is thus between the position shown in FIG. 2, in which it closes the connecting kssial 4-6. _{the position s} shown in Fig. 3, in which oil can flow in on the path indicated by arrow B, can be pushed back and forth. In the closed position, the second end section 66 completely fills the lower connecting channel 46, while in the open position oil from the inlet and outlet chamber 38 via the Zviisohen section 68 of the coil 62

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can flow through the recesses 78 into the container chamber 36. A spring 86 is fitted into the spring seat chamber 72 of the valve spool 62 for biasing the valve spool pushes to the left into the valve closed position shown in FIG.

W is a pressure cap 88 and an adjustment cap 90 screwed to the two outer walls 5 ^ 8 ^ of the main part 12 which serve in these outer walls for covering the valve spool openings 80, 82nd As shown in the partial section of Fig. ^, An inner pressure channel 92 is formed in the pressure cap 88, which, as shown, establishes a connection between the inlet / outlet chamber 38 and the pressure chamber 70 of the control valve spool 62. Changes in pressure occurring in the inlet / outlet chamber 38 are transmitted via the channel 92 and act on the left end of the coil against the force of the spring 86, so that the coil, as shown in FIG. 3, is displaced to the right and the lower end Connecting channel ^ 6 between the inlet and outlet chamber 38 and the container chamber 36 is opened «,

The adjusting cap 90 is provided with an adjusting valve 9 ^, which has its opening 96 with the spring seat chamber of the valve spool 62 _ : n! Via the measuring nozzle 6 and the central channel 4 of the coil with its pressure chamber 70 is in communication .

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The adjustment valve 94 has a tubular valve seat 98 into which a conical, adjustable valve element 100 extends. The valve element 100 is pretensioned against the seat 98 by a spring 102, the tension of which can be adjusted by an adjusting screw 104 screwed into the adjusting cap 90. A locking nut I06 is provided on the adjusting screw, with which any setting of the screw can be fixed. As shown in partial section in FIG. 4, the area behind the adjusting valve 94 is connected to the container chamber 36 via a return duct 108.

Furthermore, a safety valve 110 is provided which connects the inlet and outlet chamber 38 to the container 14. In this safety valve there is an opening 112 which extends from the inlet and outlet chamber to the container. On the container side, the opening of a valve housing 114 is surrounded%. A valve seat 116, in which a valve ball 118 rests, is arranged in the housing 114. The ball is urged onto the valve seat by a spring clamped between the upper end of the housing 114 and a ball alignment member 120. The pressure exerted on the spring can be adjusted by means of an adjusting screw 122. Normally the spring is set so that the valve only opens and liquid can flow into the container when the pressure is applied

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in the inlet and outlet chamber rises above 350 kg / (m.

The system also includes a cooling device, which is a spiral extending inside the container Has cooling coil 12 ^. The cooling coil is connected to various internal channels 126 in the main part 12, through which a coolant is passed.

The inlet and outlet chamber 38 is connected to a recycling plant, for example a die assembly 128, via a hydraulic line kZ. In this die arrangement, upper and lower die carriers I30, I32 are provided, which are attached to a press shown in light, which moves them towards one another or away from one another with great force. Different shaped die elements 13 ^ are attached to opposite surfaces of the die carriers; When the die supports are forcibly moved together over a piece of bleed, the die elements pull the metal of the workpiece into a certain shape.

For the purpose of dividing intricately shaped metal objects in a single pressing operation, certain Die elements are movably attached to the die carriers and are operated by actuating cages I36 with different large cross-sections in a stretched or in a retracted

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.15

pulled position pressed. These actuating pistons are available Via passages I38 in the die beams I30, I32 with the hydraulic line 42 and the pressure system 10 in liquid connection. If when closing the press the die beam be pressed against each other with ever greater force, the actuating pistons and the parts connected to them are in a predetermined order defined by the piston cross-sections is set in their corresponding die beams pushed back.

The printing system 10 absorbs when the press is closed the liquid displaced by the retracting pistons, which is essential for satisfactory metalworking necessary, high resistance pressures (about 320 kg / cm) be maintained; when opening the press is through

136 the printing system 01 is supplied, the piston / push forward, the die elements are returned to their original position and the workpiece that has already been drawn is ejected.

The system operates as follows. When the press, as shown in Figure 2 öflhet, and the die supports 130, I32 _s are away from each other "moved acts on the Betätigmigskolben I36 no retracting force The pressure in the passages I385 hydraulic line k2 and. the arrival

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The outlet chamber 38 of the pressure system 10 therefore drops as it approaches atmospheric pressure. In a similar manner, the pressure in the pressure chamber 70 of the spool 62 of the control valve also falls, since this chamber is in fluid communication with the inlet and outlet chamber 38 via the inner pressure channel 92. The spring 86 for biasing the valve spool therefore moves the valve spool 62 unhindered, as shown in FIG. 2, to the left, so that the end section 66 of the spool 62 completely closes off the lower connecting channel 46. However, if this reduced pressure drops below the pressure level in the container, the valve element 56 moves away from its valve seat 58 due to the disturbance of the equilibrium of forces, causing liquid at a pressure of about 7 to 9 kg / cm from the container 14 through the upper connecting channel 44 the inlet-outlet chamber 38 and the hydraulic line 42 is pressed against the upper and lower die support I30, 132, where it urges the actuating piston into the illustrated, extended position.

When the die elements are moved against each other over the workpiece when the press is closed, they press against the actuating piston I36 and thereby loosen in the hydraulic Line 42 and the inlet outlet chamber 38 from a pressure increase. This pressure increase closes the regulating valve 48. This pressure increase is transmitted

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however, via the inner pressure channel $ 2 on the pressure chamber 70 in the spool 62 of the control valve and acts against the force of the spring 86 on this spool end. In this way, the valve cylinder is moved to the left, as a result of which a connection is established between the inlet chamber 38 and the container chamber 36 via the recesses in the coil 62. Ie when the press is displaced by the piston moving back liquid passes through the opening in the lower * ren valve channel ^ 6, which is regulated by the movement of the valve spool 62nd

For many purposes, but especially in the case of using a hydraulic press described here, It is important to take precautions to accommodate the rough changes caused by the piston retraction to meet, at the same time, however, to keep the pressure in the system at around 320 kg / cm when the press is being released at different times f begin to move back, the system must have large increases in volume and pressure can process without the control system failing or a flooding effect occurring on the valves, which is the case with known Valve systems easily occurs under such conditions.

In the present system, the diameters of the two end sections 6kj66 of the control valve are the same.

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The pressure rises occurring in the inlet outlet chamber Jd are therefore compensated for at the two end portions of the spool. The control of the coil movement is based exclusively on a pressure connection via the inner pressure channel 92 to the end of the coil. The coil is therefore not adversely affected by the hydrodynamic effects of the liquid forced through it. The various changes in direction of the fluid flow on its way from the inlet and outlet chamber 38 to the pressure chamber 70 also dampen the effects of volume and pressure increases, so that the valve only responds to actual pressure changes and not to effects of the mentioned increases. As mentioned above, this damping of increases in volume and pressure is further promoted by the gradual tapering within the pressure chamber 70.

Due to the semi-cylindrical. Recesses 78 in the Valve spool 62, the liquid pressed into the container chamber 36 is deflected in different, radial directions, in order to bring about a compensatory effect. In addition, the liquid is transported in contrast to that when it is used spray effect resulting from a continuous, peripheral opening in whole streams. This reduces the tendency to foam.

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When the pressure at the left end of the valve spool 62 increases, it is pushed to the left against the spring 86 to bias the valve spool. Characterized all the liquid is forced through the opening 96 of the spring seat chamber 72 outside and against the adjusting valve 100, which opens as soon as the pressure in constitute inlet outlet chamber 38 has a sufficiently high value that is, about 320 kg / cm, has been reached. Even if this pressure is maintained, hydraulic fluid flows through the central channel 7 ^ - and the measuring nozzle 76 into the spring seat chamber 72, where it equalizes the pressure in the pressure chamber 70. In this way it is possible for the spring 86 to move the valve flush 62 back to the left until the liquid flow flowing through the lower connecting channel k6 is reduced to such an extent that the pressure in the system rises again. The valve arrangement thus maintains a d7 / "namic equilibrium; it is also able to cope with pressure and volume fluctuations at speeds of almost% b0 periods / sec. Without impacting the pistons, foaming of the oil or trapping of air.

Fig. 6 shows a modified embodiment of a control valve spool 62 '. This modified coil is similar in general characteristics to the spool of Figure 5; however, their dimensions and of course their volumetric capacity are somewhat smaller. To get the right relationship between the valve movement and the duct opening are easier

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the recesses 78 of the coil described above are replaced by segment-shaped tapered edges 78 ¹ . These edges or corners
can be obtained simply by sanding the edge of the right one
At the end it cut with an enlarged diameter at the countersunk
Places, creating the required, tapered contour.

Based on the above description with particular reference to a preferred embodiment of the invention it is now apparent to those skilled in the art that the invention can be changed or modified in various ways without depart from the spirit and scope defined in the appended claims.

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Claims (18)

Claims 1. Hydraulic supply system, characterized in that it contains a housing (12) with two adjacent chambers (36, 38) separated by an inner wall (40), that in the wall (40) an opening connecting the chambers ( 46) is designed that ä Furthermore, a valve spool (62) with two spaced apart, widened end sections (64, 66) of equal cross-sections separated by a narrowed section (68) of smaller cross-section is provided so that one (66) of these end sections just enters the opening ( 46) fits, while the other (64) fits exactly into a corresponding opening (80) in an opposite wall (54) of one (38) of the chambers, that the valve spool between the described first position and a second position in which the one End portion (66) is completely moved away from the wall (40), and a part of the other end portion (64) remains in the opposite wall, is axially movable, that further a device (86) for elastic biasing of the valve spool (62) in the in the sindj provided first position, a supply channel (44) for supplying a chamber (38) to regulating, hydraulic fluid, and a fluid channel (92), the mi defining a chamber (38) fc dom against the opposite Wall (54) weiDQndön üacle (6k) der Vonbilspulo (62) iroiafe 9Ü98'J9 / Ü73 7 BATH O. 2. Hydraulic system according to claim 1, characterized in that the inner wall (4-0) and the chambers (36, 38) are arranged in a housing (12) with a first (54-) and a second (84) outer wall, that in each of the outer walls one with the other balanced and equal-sized opening (80, 82) is formed, into which the End sections (64 ·, 66) of the valve spool (62) are each precisely set%) ß, and that in the first position of the spool each end portion lies partially in opening 80 and 82, respectively. 3. Hydraulic system according to one of claims 1 or 2, characterized in that it contains a fluid supply container (14-) which is in fluid communication with one (38) of the chambers, that between the chambers (36, 38) a first (4 -4) and a second (46) channel are provided that a regulating valve (4-8) is arranged in the first channel (4-4), which regulates a flow of liquid from one chamber (36) into the other chamber (38 ) enables an end portion {66) of a spool valve (50) to be slidable back and forth between a first position that fully closes the second channel (4x6) and a second position that partially opens the second channel (4-6) that an opening is formed in the other chamber (38) through which the system is in fluid communication with a recycling plant, and that the spool valve (50), according to its arrangement, can only be actuated by pressure fluctuations acting on one (64) of its ends . 909839/0737 -23-BAD OBiGfNAt 4 “Hydraulic system according to one of the preceding Claims, characterized in that a movable valve element for closing and opening the first liquid channel is provided that according to the shape and arrangement of this movable valve element, the closing and opening of the first liquid channel take place essentially independently of the liquid in the second chamber that one end of the movable valve element extends through the second chamber to the other side J thereof and is arranged to be on this end acting fluid pressure responds or is movable, and that a second fluid channel is arranged away from the first channel, which a connection forms between the second chamber and one end of the movable valve element. 5. Hydraulic system according to one of the preceding Claims, characterized in that the container (14) is provided with a device (10) for maintaining it a certain fluid pressure in the container is connected that one (36) of the Kamimi in open connection with the container (14), while the other chamber (38) for connection to a recycling plant accordingly is designed that a regulating valve (48) the flow of liquid through the first channel in the direction of the one (36) in the other (38) chamber limits that the -24- 909839/0737 BATH ORIGINAL • - 24 - first end portion (66) from one chamber (36) in the second channel (46) and out of this is movable that the second end portion (6 * 0 through a similar canal in the opposite side (5 ^) of the other chamber (38) that extends the cross-sectional areas of the end portions to neutralize the effect of the Liquid pressure in the other chamber (38) are essentially the same, and that the liquid channel (92) for exerting a static fluid pressure counteracting the pretensioning effect of the device (86) on one end (64). 6. · Hydraulic system according to one of the preceding claims, characterized in that in the housing (12) a container Karamer (36) and an opening (44) leading into the latter are formed that a Valves lenient (48) is provided, which is to close the opening into this and to open the latter moved out of it that the position of the valve element due to its shape and arrangement substantially from the the liquid surrounding the opening remains unaffected that a device (60) for biasing the valve element is provided in a first, the opening closing position, and that a device (56) is provided which for proportional movement of the valve element (48) against the force of the pretensioning device (60) exclusively is responsive to the static pressure exerted on one side of the opening (44), 909839/0737 -25- 7. Hydraulic system according to one of the preceding claims, characterized in that the first chamber (38) interferes with a discharge line (42), and the second chamber (36) with the container (14) in connection that the regulating valve (48) the flow of the liquid from the second (36) into the first (38) chamber is only restricted if the pressure in the container (14) or in the chamber (36) exceeds the pressure at the dispensing end (42) or in the chamber ( 38) exceeds that the position of the movable valve element (42) due to its arrangement is essentially unaffected by the inflowing liquid in the first chamber (38), and that the regulation of the opening of the other channel (46) by the liquid pressure in the first chamber (38) responsive movement of the valve element (62) takes place. 8. Hydraulic system according to one of the preceding claims, characterized in that the effects of the liquid in the chamber (38) on the axial movement of the valve spool (62) are compensated for by the extension of an end section (64) into the opening (80). 9. Hydraulic system according to one of the preceding claims, characterized in that a device is provided which the movement of the valve spool (62) on the movement between the first and the second Position restricted. 909839/0737 -26- BATH ORIGINAL 10. Hydraulic system according to one of the preceding Claims, characterized in that the pressure of the spool valve (50) in the channel closed position by conducting the static pressure in the chamber (38) through the inner channel (92). 11. Hydraulic system according to one of the preceding claims, characterized in that the Cross-section of the opening (80) into which one end of the valve spool is located (62) extends, and the cross section of the channel (46) are the same size. 12. Hydraulic system according to one of the preceding claims, characterized in that the intermediate section (68) lying between the end sections (64, 66) has an axial length which is used for bridging the length of the first opening (46) is sufficient. 13. A hydraulic system according to one of the preceding claims, characterized in that the spool valve (50) is formed substantially tubular and has in the subsequent to the intermediate section (68) end portion (66) notches (78). 14. Hydraulic system according to one of the preceding claims, characterized in that open the sink notches in the end section (66). 909839/0737 ~ ^2? ~ 15. Hydraulic system according to one of the preceding claims, characterized in that each Notch (78) is diametrically opposed to another notch. 16. Hydraulic system according to one of the preceding claims, characterized in that the cross-section of each notch (78) increases towards the intermediate portion (68). 17. Hydraulic system according to one of the preceding claims, characterized in that the liquid channel (92) from the chamber (38) to the opening (82) aligned with the openings (80) and (46) extends beyond the other end of the valve spool (62). 18. Hydraulic system according to one of the preceding claims, characterized in that in the spool valve (50) an axially extending passage (74) of reduced cross-section is arranged, which extends from the balanced opening (80) at one end of the spool valve that a pressure reducing valve (94) with the opposite end of the axially extending Passage is in communication, and that further means (108) for connecting the outlet opening of the pressure reducing valve (94) with one chamber (36) is provided. 909839/0 73 7