Abstract:
Exemplary embodiments are direct to a valve system for actuating the piston of a piston cylinder arrangement for a hydraulic or fluid device, and for actuating the piston cylinder arrangement for actuating the movable contact piece of a high-voltage circuit breaker. The system including a main control valve arrangement, having two 2/2-way valves used as main valves and which can be controlled by a pilot control valve arrangement. The main control valve arrangement directs a path for the high pressure fluid to the chamber above the piston and connects the chamber to a low-pressure tank for discharging the chamber above the piston. Two 2/2-way valves which form the pilot control valve arrangement are associated with the main control valve arrangement such that the 2/2-way valves direct or supply either a high-pressure control pressure or a low-pressure control pressure to the main control valve arrangement.

Description:
RELATED APPLICATIONS 
     This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/EP2010/066043, which was filed as an International Application on Oct. 25, 2010 designating the U.S., and which claims priority to German Application 102009053901.8 filed in Germany on Nov. 20, 2009. The entire contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     FIELD 
     The present disclosure relates to a valve, such as a valve arrangement or valve system for actuating a piston of a piston/cylinder arrangement for a hydraulic or fluidic device. 
     BACKGROUND INFORMATION 
     A generic valve arrangement is known from DE 201 16 920 U1. Valve arrangements of this type are used to activate piston/cylinder arrangements in which, within a cylinder space, a piston is located, to one side face of which is connected one end of a piston rod which is extendable out of the cylinder space and is retractable into this. The space beneath the piston is located on that side of the piston which the piston rod adjoins, whereas the space above the piston is arranged on the other side of the piston. As a result, the cross-sectional area of the space above the piston is greater than the cross-sectional area below the piston, because, in the case of the latter, the cross-sectional area of the piston rod is subtracted. When high-pressure fluid is supplied to the spaces above and below the piston, the piston moves in the direction of the extension of the piston rod; when the space above the piston is relieved in that this space and the fluid located in it are connected to a reservoir which is at low pressure, also called a low-pressure tank, the piston moves in the opposite direction on account of the high pressure in the space below the piston, so that the piston rod is retracted. 
     By means of this piston/cylinder arrangement, for example, the movable contact pieces of a high-voltage circuit breaker can be actuated. 
     Of course, by means of such a piston/cylinder arrangement, other components can also be moved, such as, for example, crane arms, buckets or bucket excavators, and the like. 
     In many applications, for example, a changeover is to take place without reversal losses, that is to say when a volume flow from the pressure connection via the two control edges to the low-pressure tank is to be avoided during the switching operation, so that a different flow resistance or volume flow, depending on the switching position, a short switching time or actuation by means of a low pilot control volume can be achieved. 
     However, when a 3/2-way valve is used, these specifications often can be fulfilled only inadequately or at a high outlay in production terms and with high production costs. If two 2/2-way valves are used as main control valves, in the event of a changeover the open valve first has to be closed before the closed valve is opened, if a reversal loss is to be avoided and if no further measures are taken. However, for this purpose, in the case of pilot-controlled valves, at least two pilot control valves with suitable activation electrics, for example with time-delayed or sensor-controlled triggering of the second valve, should be used. This entails further high costs and an unnecessarily long delay in the opening of the second 2/2-way valve after the closing of the first. 
     SUMMARY 
     An exemplary valve arrangement for actuating a piston of a piston/cylinder arrangement for a hydraulic or fluidic device, and for actuating the piston/cylinder arrangement for actuating of a movable contact piece of a high-voltage circuit breaker is disclosed. The valve arrangement comprising: a main control valve arrangement including two 2/2-way valves which are activatable by a pilot control valve arrangement and provides a way for the fluid, which is under high pressure, to flow into a space above the piston and connects the space to a low-pressure tank for relieving pressure in the space, wherein the 2/2-way valves are connected to a pilot control valve arrangement, such that the 2/2-way valves feed or deliver fluid to the main control valve arrangement at either a high pressure or a low pressure, wherein when the fluid, which is under high pressure, is supplied to the space above the piston, a first pilot control valve of the pilot control valve arrangement opens a path for the fluid which is under high pressure to flow into a main control face of a first main control valve of the main control valve arrangement, so that the first main control valve feeds the fluid which is at high pressure to the space above the piston and a second pilot control valve of the pilot control valve arrangement is closed, and wherein when pressure is relieved in the space above the piston, the second pilot control valve opens a path from a main control face of a second main control valve of the main control valve arrangement to the low-pressure tank and the second main control valve opens a path from the space above the piston to the low-pressure tank. 
     A valve arrangement for actuating a piston of a piston/cylinder arrangement for a hydraulic or fluidic device is disclosed, comprising: a main control valve arrangement including two 2/2-way valves which are activatable by a pilot control valve arrangement and provides a way for the fluid, which is under high pressure, to flow into a space above the piston and connects the space to a low-pressure tank for relieving pressure in the space; and a pilot control valve arrangement having first and second pilot control valves that are connected to the two 2/2 way valves, respectively, of the main control valve arrangement, wherein when high pressure fluid is supplied to the space above the piston, the first pilot control valve opens a path for the high pressure fluid to flow into a first main control valve of the main control valve arrangement, so that the first main control valve feeds the high pressure fluid to the space above the piston, and wherein when pressure is relieved in the space above the piston, the second pilot control valve opens a path from a second main control valve of the main control valve arrangement to the low-pressure tank and the second main control valve opens a path from the space above the piston to the low-pressure tank. 
     A valve arrangement for actuating the piston/cylinder arrangement for actuating of a movable contact piece of a high-voltage circuit breaker is disclosed, comprising: a main control valve arrangement including two 2/2-way valves which are activatable by a pilot control valve arrangement and provides a way for the fluid, which is under high pressure, to flow into a space above the piston and connects the space to a low-pressure tank for relieving pressure in the space; and a pilot control valve arrangement having first and second pilot control valves that are connected to the two 2/2 way valves, respectively, of the main control valve arrangement, wherein when high pressure fluid is supplied to the space above the piston, the first pilot control valve opens a path for the high pressure fluid to flow into a first main control valve of the main control valve arrangement, so that the first main control valve feeds the high pressure fluid to the space above the piston, and wherein when pressure is relieved in the space above the piston, the second pilot control valve opens a path from a second main control valve of the main control valve arrangement to the low-pressure tank and the second main control valve opens a path from the space above the piston to the low-pressure tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure and also further advantageous refinements and improvements and further advantages will be explained in more detail and described by means of the drawing which illustrates two exemplary embodiments of the disclosure and in which: 
         FIG. 1  shows a circuit arrangement of a valve system in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 2  shows a diagrammatic illustration of the second main valve in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 3  shows a diagrammatic illustration of a first arrangement of the first main valve in accordance with an exemplary embodiment of the present disclosure; 
         FIG. 4  shows a second arrangement of the first main valve in accordance with an exemplary embodiment of the present disclosure; and 
         FIG. 5  shows a force/path graph of the second arrangement of the main valve according to  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present disclosure improve further and to simplify a valve arrangement of the type initially mentioned. 
     The advantages can be achieved by the exemplary embodiments disclosed herein, in particular, that, by means of a valve arrangement composed of two commercially available pilot control valves and of two correspondingly designed 2/2-way valves as main valves or main control valves, the specifications stated above, such as, for example, changeover without reversal losses, a different flow resistance or volume flow depending on the switching position, a very short switching time and actuation by means of a low pilot control volume, can be fulfilled in spite of a comparatively low outlay in production terms. 
     In this case, according to an exemplary embodiment, the valve arrangement is characterized in that, to supply the high-pressure fluid into the space above the piston, the first pilot control valve opens the way for the fluid which is at high pressure to the main control face of the first main valve, so that the latter feeds the fluid which is at high pressure to the space above the piston, the second pilot control valve being closed, and in that, to relieve the space above the piston, the second pilot control valve opens the way from the main control face of the second main control valve to the low-pressure tank and consequently the second main control valve opens the way from the space above the piston to the low-pressure tank. 
     A further advantageous embodiment of an exemplary valve arrangement may be that a orifice having a small cross section is provided between the main control faces of the main control valves and the space above the piston of the piston/cylinder arrangement. 
     This orifice is important inasmuch as, in the event of leakage of, for example, the pilot control valves, it can maintain the high pressure or even the low pressure upstream of the piston/cylinder arrangement, so that faulty movement of the piston in the event of an undesirable lowering of the high pressure or an undesirable rise in the low pressure due to leakage is prevented. 
     According to the exemplary embodiments disclosed herein the piston of the first main control valve, designed as a bistable valve, is retained in its end positions. In a first embodiment, this is achieved in that the piston is retained mechanically by means of a spring-assisted ball latching. In a further refinement, the piston can be retained in its end positions mechanically and magnetically. In this case, the piston can move in a cylinder, a permanent magnet being provided at one end of the cylinder and a spring being provided between this end and the piston, and the force acting upon the piston having a zero crossing. 
       FIG. 1  shows a circuit arrangement of a valve system in accordance with an exemplary embodiment of the present disclosure.  FIG. 1  illustrate a valve arrangement  10  serving for activating a piston/cylinder arrangement  11 , by means of which an electrical high-voltage circuit breaker  12  can be actuated. The piston/cylinder arrangement  11  includes a cylinder  13  in which is movable a piston  14 , to one side of which is connected a piston rod  15  which is connected to a movable contact piece  16  of the high-voltage circuit breaker  12 . The piston  14  subdivides the cylinder inner space into a space  17  above and a space  18  below the piston  14 , the latter space receiving the piston rod  15 . Since the piston rod  15  adjoins the piston face which delimits the space  18  below the piston  14  and consequently reduces the piston face by the amount of the cross section of the piston rod  15 , the piston face which delimits the space  17  above the piston  14  is greater than the piston face confronting the space  18  below the piston  14 . 
     To drive the piston  14  so that the latter is extended, hydraulic fluid is supplied by means of a pump or in another way from a high-pressure reservoir  19 , depending on the position of the valve arrangement, to the space  17  above the piston  14  and to the space  18  below the piston  14 , as follows, this being an operation to switch on the circuit breaker. 
     The high-pressure reservoir  19  has adjoining it a first line section or line length  20  which connects the high-pressure reservoir  19  to the space  18  below the piston  14 . The first line section  20  has adjoining it a second line section  21  which is connected to a first pilot control valve  22 . The pilot control valve  22  is connected to a third line section  23  which issues into the space  17  above the piston  14  and connects the first pilot control valve  22  to the space  17  above the piston  14 . The first line section  20  and there, in particular, the junction point between the first and the second line section  20 ,  21  have adjoining them a fourth line section  24  which is connected to the first port, also called below the inlet port  25  of a first main control valve  26 . The second port, also called below the outlet port  27  of the first main control valve  26 , has adjoining it a fifth line section  28  which is connected to the third line section  23  at a junction point  29 . On the first main control valve  26 , a first return  30  is provided, which adjoins the inlet port  25  and which is connected to a second control face F 2 / 26 . Furthermore, a third control face F 3 / 26  is provided, which is connected to the outlet port  27  via a second return  31 . 
     The first main control valve  26  includes a first control face F 1 / 26  which is dimensioned such that the following relation applies:
 
 F   1 /26 =F   2 /26 +F   3 /26.
 
     The first control face F 1 / 26  is connected to the third line section  23  via a second junction point  32 . Between the first junction point  29  and the second junction point  23  is located a orifice  33  having a small cross section, see also further below. 
     Connected to the third line section  23  is a sixth line section  34  in which a second pilot control valve  35  is located. 
     The sixth line section  34  is connected to a seventh line section  36  which issues, on the one hand, into a low-pressure tank  37  and, on the other hand, into a first port, also called below the inlet port  38  of a second main control valve  39 . The second port, also called below the outlet port  40  of the second main control valve  39 , is connected to the first junction point  29  via an eighth line section  36   a.    
     A first control face F 1 / 39  of the second main valve  39  is connected to the second junction point  32 ; the second main control valve  29  includes in each case a second and a third control face F 2 / 39  and F 3 / 39  corresponding to the control faces F 2 / 26  and F 3 / 26 , here, too, the rule: F 1 / 39 =F 2 / 39 +F 3 / 39  applying, the pressures acting upon the control faces F 1 / 39  and F 2 / 39 +F 3 / 39  acting in the opposite direction upon the piston (see further below) of the main control valve  39 . As in the case of the first main control valve  26 , the inlet port  38  of the second main control valve  39  is connected to a first return  42  and to the second control face F 2 / 39 , and the outlet port  40  of the second main control valve  39  is connected to the third control face F 3 / 39  via a return  43 . 
     The pilot control valves  22 ,  35  are driven electromagnetically and are brought out of the blocking position shown in  FIG. 1  into the passage position by means of an electromagnetic system  44  or  45 ; in each case a restoring spring  46  and  47  replaces the pilot control valves  22  and  35  in the blocking position. 
     The valve arrangement  10 , then, operates as follows: 
       FIG. 1  shows the circuit breaker  12  in the switch-off position. When the circuit breaker  12  is to be switched on, the first pilot control valve  22  is briefly brought into the opening position. High pressure thereby arrives via the line length  23  at the first control face F 1 / 26 , with the result that the first main valve  26  is opened and the line length  24  is connected to the line length  28 , so that the high-pressure fluid is conveyed into the space  17  above the piston  14 . On account of the different piston faces, a force is generated which moves the piston  14  and consequently the piston rod  15  in the direction of the arrow P 1 , with the result that the movable contact piece  16  is brought into the switch-on position. Since the first main control valve  26  is a bistable 2/2-way valve, as will be explained in more detail further below, the first main control valve  26  remains in the passage position. The hydraulic forces upon the piston  14  are in this case zero on account of the above formula. The control face F 1 / 39  of the second main control valve  39  is also acted upon with high pressure via the junction point  32 , so that the second main control valve  39  remains in the closing position. 
     The pilot control valve  22  then returns to the blocking position on account of the restoring spring  46 . The region between the first main control valve  26  and, via the line length  41 , also between the second main control valve  39  and the piston/cylinder arrangement  11  is consequently at high pressure. 
     In a switch-off action, the valve arrangement  10  operates as follows: 
     When the movable contact piece  16  is to assume the opening position, the space  17  above the piston  14  must be relieved. This takes place in that the second pilot control valve  35  is reversed to passage, with the result that low pressure prevails in the line length  23  between the second pilot control valve  35  and the orifice  33 , so that low pressure likewise prevails at the first control face F 1 / 26  of the first main valve  26 . As a result, the first main control valve  26  (it may be added here that “main control valve” and “main valve” are the same) is reversed back to the blocking position again on account of the force generated on the piston of the first main valve  26  by the control forces F 2 / 26  and F 3 / 26 . Furthermore, low pressure prevails at the first control face F 1 / 39 , so that the second main valve  39  is reversed to passage, because, although low pressure prevails at the second control face F 2 / 39 , high pressure nevertheless acts at the third control face F 3 / 39  on account of the return  43 . As a result, the piston (see further below) of the second main control valve  39  moves into the passage position, so that the space  17  above the piston  14  is relieved via the second main control valve  39 . As a consequence of this, owing to the high pressure located in the space  18  below the piston, the piston  14  and consequently the piston rod  15  move in an arrow direction which is opposite to the direction of the arrow P 1 . A switch-off of the circuit breaker  12  is thereby brought about. 
       FIG. 2  shows a diagrammatic illustration of the second main valve in accordance with an exemplary embodiment of the present disclosure. The second main valve  39 , as illustrated diagrammatically in  FIG. 2 , includes a cylinder body  50 , also called in brief a cylinder  50 , in which a piston  51  is movable back and forth, the piston  51  having a free face  52  which is connected to the low-pressure tank  37  and is consequently not acted upon by the high pressure. An inner duct  55  issues into the inner face  54  lying opposite the free face  52  and engaging into a depression  53  of the cylinder  50 , the other end of said inner duct issuing into the free face  52 , so that the low pressure which prevails at the free face  52  acts upon the inner face  54 , also called briefly the inside face  54 , so that the inner face  54  is connected to the tank  37 . The free face  52  merges via a sealing edge  56  into a first piston section  57  which has adjoining it a step  58 , via which the first piston section  57  is connected to a second piston section  59 , the outside diameter of which is larger than the outside diameter of the first piston section  57 . The second piston section  59  merges via a further step  60  into a third piston section  61  which engages into the depression  53 , the outside diameter of which is smaller than the outside diameter of the piston section  57 , the inner face  54  adjoining said third piston section. 
     In the region of the free face  52 , the cylinder body  50  includes a first cylinder section  62 , the inside diameter of which is smaller than the outside diameter of the first piston section  57 , the inner end of the first cylinder section  62  having a chamfer  63  which opens at an angle of about 45 degrees into the interior of the cylinder  50 , so that this chamfer  63  serves as a sealing seat for the sealing edge  56 . Provided on the cylinder body  50  is a second cylinder section  50   a , the inside diameter of which corresponds to the outside diameter of the second piston section  59 , so that the second piston section  59  is movable slidably in the second cylinder section  50   a . This second cylinder section  50   a  has adjoining it a step  50   b  which runs radially and via which the second cylinder section  50   a  merges into the depression  53 . 
     The two faces  52  and  54  form as a whole the second control face F 2 / 39 , whereas the step  58  forms the control face F 3 / 39 . The step  60  then corresponds to the first control face F 1 / 39 . 
     The piston  51  is under the pressure of a spiral compression spring  64  which is located in the depression  53  between the inner face  54  and the bottom of the depression  53 . 
     Located in the cylinder body  50  are two holes  65  and  66 , of which the hole  65  corresponds to the outlet port  40 , whereas the free face  52  is assigned to the inlet port  38 . The depicted position of the second main control valve  39  corresponds to the position in which the relief to the tank  37  is concluded. 
     The hole  66  issues with a generatrix into the step  50   b.    
       FIG. 3  shows a diagrammatic illustration of a first arrangement of the first main valve in accordance with an exemplary embodiment of the present disclosure 
     The first main control valve  26  according to  FIG. 3  includes a cylinder body  70  in which a piston  71  is arranged movably. The piston  71  includes a free face  72  which has adjoining it a first piston section  73  which merges via a first radial step  74  into a second piston section  75  and which has a reduced diameter with respect to the first piston section  73 . This second piston section  75  has adjoining it a third piston section  76 , a second radial step  77  being provided between the second and the third piston section  75  and  76 . The edge between the second step  77  and the third piston section  76  forms a sealing edge  78 . The third piston section  76  has adjoining it a fourth piston section  79  which engages into a depression  80  in the cylinder body  70 . 
     The outside diameter of the first piston section  73  is larger than the outside diameter of the second piston section  75 . The third piston section  76  includes an outside diameter which is larger than the outside diameter of the first piston section  73 , and the inside diameter of the depression  80  and in consequence the inside diameter of the fourth piston section  79  are smaller than the outside diameter of the first piston section  73 . Inside the depression  80 , the piston  71  is delimited by an inner end face  91 . 
     The cylinder body  70  includes a first cylinder section  81 , the inside diameter of which corresponds to the outside diameter of the first piston section  73  and which merges via a step  82  into a second cylinder section  83 , there being formed at the transition point between the first cylinder section  81  and the step  82  a chamfer  84  which corresponds to the chamfer  63  and which together with the sealing edge  78  forms a seal. 
     Located on the outer face of the fourth piston section  79  is a radially projecting projection  85  which has two oblique faces  86  and  87  assigned to one another in the form of a roof. The depression  80  has issuing into it radially a blind hole bore  88  in which is guided a ball  89  which is pressed permanently against the oblique faces  86  or  87  by a spiral spring  90 . 
     In the position which is shown in  FIG. 3 , the ball  89  presses against the oblique face  86  and thus prevents the piston  71  from being capable of moving into the depression  80  in the direction of the arrow P 1  when no special forces are acting upon the piston  71 . When the first main valve  26  is reversed by the pilot control valve  22 , high pressure acts upon the first control face F 1 / 26  which corresponds to the free face  72 , so that the piston  71  is displaced in the direction of the arrow P 1 , with the result that the ball  89  runs up on the oblique face  86  and is pressed into the interior of the blind hole bore  88 . As soon as the ball  89  reaches the oblique face  87 , with no further forces otherwise acting upon the piston  71 , the ball  89  will retain the piston  71 , the ball  89  being located between the oblique face  87  and the third piston section  76 . 
     A duct  92  issues into the second piston section  75  and into the inner end face  91  and connects the space outside the second piston section  75  to the inner space of the depression  80 . The same pressure consequently prevails at the step  77  and at the inner face  91 . 
     The cylinder body  70  includes a first radial hole  93  and a second radial hole  94 , the first hole  93  issuing into the region of the second piston section  75  and the hole  94  issuing into the second cylinder section  83 . The position according to  FIG. 3  is that position which the piston  71  assumes when low pressure prevails at the first control face F 1 / 26 =free face  72 . As soon as the first pilot control valve  22  is controlled in the passage direction and the second pilot control valve  35  is in the blocking position, the piston  71  is moved to the right on account of the high pressure prevailing at the face  72 , with the result that the sealing point  78 / 84  is opened, so that high-pressure fluid can flow via the hole  94 . The hole  94  then corresponds to the inlet port  25  and the hole  93  to the outlet port  27 . 
     When the first pilot control valve  22  is reversed, high pressure prevails both on the face F 1 / 26  of the first main control valve  26  and on the face F 1 / 39  of the second main control valve  39 . Since the pilot control valve  22  is opened only briefly, high pressure prevails at both first control faces F 1 / 26  and F 1 / 39 . The second pilot control valve  35  is closed. If leakage then occurs at the second pilot control valve  35 , the pressure between the two control faces F 1 / 26  and F 1 / 39  may then fall, so that undesirable switching actions of the two main control valves  26  and  39  may be caused. The orifice  33 , which is located between the two control faces F 1 / 26  and F 1 / 39  and the space  17  above the piston, is intended to deliver pressure fluid to these two control faces F 1 / 26  and F 1 / 39 , so that compensation can thereby take place. 
     In the case when the second pilot control valve  35  is opened briefly, low pressure prevails at the two first control faces F 1 / 26  and F 1 / 39 . On account of leakage in the first pilot control valve  22 , high pressure could pass into the line  23  and consequently arrive at the two first control faces F 1 / 26  and F 1 / 39 , so that undesirable switching actions would be caused even as a result of this, if the orifice  33  were not to ensure compensation. 
     In other words: 
     the two steps, to be precise the pilot control valve step and the main control valve step, are connected to one another via the orifice  33 , so that compensation leading to unwanted switching actions is achieved via the orifice  33 . 
       FIG. 4  shows a second arrangement of the first main valve in accordance with an exemplary embodiment of the present disclosure. In the exemplary embodiment shown in  FIG. 4 , the first main control valve is constructed in a similar way to the embodiment shown in  FIG. 3 , and it therefore receives the reference numeral  26   a  here. It includes a cylinder body  100  in which is guided a piston  101  which engages by means of an inner face  102  in a depression  103 . Arranged on the bottom of the depression  103  is a permanent magnet  104  which is embedded into a non-magnetizable material part  105 ; arranged between the inner face  102  and the free face of the non-magnetizable material part  105  is a spiral spring  106  which seeks to press the piston  101  permanently in the direction of the arrow P 2 . Integrally formed on the inner face  102  is an axial extension  107  which, when the piston  101  is pressed into the interior of the depression  103  opposite to the direction of the arrow P 2  and the free face of the axial extension  107  comes to bear against the free face of the non-magnetizable material part  105 , is permanently attracted by the permanent magnets  104  counter to the pressure of the spring  106 . As soon as the piston  101  is pressed in the direction of the arrow P 2  on account of the hydraulic pressure forces, the force of the compression spring  106  predominates in the direction of the arrow P 2 , as a result of which, overall, a stable valve is brought about. The main valve  26   a  is otherwise constructed identically to the main valve  26 , but without the latching. 
       FIG. 5  shows a force/path graph of the second arrangement of the main valve according to  FIG. 4 .  FIG. 5  shows force conditions corresponding to the exemplary embodiment of  FIG. 4 . The force is plotted against the path S which the piston covers, the spring force decreasing linearly from its maximum value F springmax  during the movement of the piston to the left in the direction P 2 , whereas the magnetic force F magnet  approaches zero non-linearly from a maximum value, when the piston  101  is in the position in which the spring force is at a maximum, when the piston  101  moves away from the permanent magnet  104 . The resultant force F total  includes a zero crossing N. On the left of the zero crossing, that is to say when the distance between the piston and the permanent magnet is small, the force of attraction of the permanent magnet predominates, and on the right of the zero crossing, when the magnetic force decreases, the force of the spring predominates, so that the resultant curve F total  is formed. 
     It should be understood that both the cylinder body  100  and the movable piston  101  can be produced from ferromagnetic material, whereas the embedding mass  105  should be formed as a non-magnetizable material part. 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein. 
     LIST OF REFERENCE SYMBOLS 
     
         
           10  Valve arrangement 
           11  Piston/cylinder arrangement 
           12  High-voltage circuit breaker 
           13  Cylinder 
           14  Piston 
           15  Piston rod 
           16  Movable contact piece 
           17  Space above the piston 
           18  Space below the piston 
           19  High-pressure reservoir 
           20  First line section, line length 
           21  Second line section, line length 
           22  First pilot control valve 
           23  Third line section 
           24  Fourth line section 
           25  Inlet port 
           26  First main control valve 
           26   a  First main control valve 
           27  Outlet port 
           28  Fifth line section 
           29  Junction point 
           30  First return 
           31  Second return 
           32  Second junction point 
           33  Orifice 
           34  Sixth line section 
           35  Second pilot control valve 
           36  Seventh line section 
           37  Low-pressure tank 
           38  Inlet port 
           39  Second main control valve 
           40  Outlet port 
           41  Eighth line section 
           42  First return 
           43  Second return 
           44  Electromagnetic system 
           45  Electromagnetic system 
           46  Restoring spring 
           47  Restoring spring 
           50  Cylinder body 
           51  Piston 
           52  Free face 
           53  Depression 
           54  Inner face 
           55  Inner duct 
           56  Sealing edge 
           57  First piston section 
           58  Step 
           59  Second piston section 
           60  Further step 
           61  Third piston section 
           62  First cylinder section 
           63  Chamfer 
           64  Spiral compression spring 
           70  Cylinder body 
           71  Piston 
           72  Free face 
           73  First piston section 
           74  First step 
           75  Second piston section 
           76  Third piston section 
           77  Second step 
           78  Sealing edge 
           79  Fourth piston section 
           80  Depression 
           81  First cylinder section 
           82  Step 
           83  Second cylinder section 
           84  Chamfer 
           85  Projection 
           87  Oblique face 
           88  Blind hole bore 
           89  Ball 
           90  Spiral spring 
           91  Inner face 
           92  Duct 
           93  First hole 
           94  Second hole 
           100  Cylinder body 
           101  Piston 
           102  Inner face 
           104  Permanent magnet 
           105  Material part 
           106  Spiral spring 
           107  Projection