Abstract:
A releasable check valve for use with very high system pressures. The check valve is formed such that the poppet piston is relatively smooth-running and that good action and a long service life of the seals are obtained, wherein the receiving bore has essentially the same diameter in the region of the inserts and between the inserts. A spacer bushing is arranged axially between the inserts, in which bushing the piston collar can move separating the two annular spaces on both sides of it fluidically from each other. The bore can be machined from one side, so that the inserts are centered precisely with respect to one another and the poppet piston is guided precisely. This reduces the risk of jamming and the risk of an uneven load on the seals.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The invention proceeds from a releasable check valve which is intended to be useable for very high system pressures. 
     Check valves readily permit pressure medium to flow from a first orifice to a second orifice with the closing element being raised from a seat counter to the force exerted by the pressure prevailing in the second orifice and counter to the force of the closing spring by means of a force produced by the pressure in the first orifice. Since the closing element is conventionally acted upon by the pressures on surfaces of identical size, a pressure arises in the first orifice which is higher than the pressure in the second orifice by a pressure difference which is equivalent to the force of the closing spring. The closing spring is only weak so as to keep the losses via the valve small unless the intention is to deliberately build up the pressure medium in the first orifice. The flow through a check valve in the direction from the second orifice to the first orifice is possible only by additional measures through which a releasable check valve is provided. A poppet part is then provided which can act on the closing element in the opening direction and can raise it from the seat counter to the force of the closing spring and counter to the pressure difference between the first and second orifice. 
     DE 197 14 505 Al has disclosed a releasable check valve. The internal high-pressure forming of tubular semi-finished products is mentioned in the abovementioned document as an example of use of a check valve of this type. The check valve which is shown has a valve housing having a continuous receiving bore which is stepped and is composed essentially of three sections. The diameter of the receiving bore is larger in the two outer sections than in a central section into which the two outer sections merge in steps lying in radial planes. High-strength inserts which are exposed to the system pressure and inserts serving to guide a poppet piston are placed into the two outer sections. The central section of the receiving bore is divided by a piston collar of the poppet piston into two annular spaces of which the one can be acted upon by control pressure via a pilot valve in order to control the check valve or can be relieved from pressure to a tank, and the other is permanently connected to a pressure-medium reservoir and contains a restoring spring for the poppet piston. 
     It has been found that in the known check valve the poppet piston is not always smooth-running to the desired extent. In addition, the sealing action and the service life of various sealing arrangements between the poppet piston and the inserts were not always unproblematical. 
     SUMMARY OF THE INVENTION 
     The invention is therefore based on the object of developing a releasable check valve in such a manner that the poppet piston is not stiff beyond the extent to be expected because of the frictional forces at the seals and a high sealing action and service life of the seals is possible. 
     According to the invention, this object is achieved in a releasable check valve. The invention is first of all based on the finding that stiffness of the poppet piston, deficient action and limited service life of the seals in the known valve are caused by alignment errors. These in turn are attributed to the fact that those sections of the receiving bore which receive the inserts are machined from different sides of the valve housing. According to the invention, the receiving bore now has essentially the same diameter in the region of the inserts and between the latter, apart from short turned grooves in the axial direction which may be present, so that said receiving bore can be machined from just one side of the valve housing, i.e. without changing the position of the valve housing or of the tool. Arranged axially between two inserts is a spacer bushing which ensures a fixed spacing between two inserts on different sides of the piston collar even when the diameter of the receiving bore is constant. At the same time, by means of the spacer bushing and the piston collar, the two annular spaces on the two sides of the piston collar are separated fluidically from each other, preferably with an additional seal being used. 
     It is preferred for the two inserts bearing directly against the two end sides of the spacer bushing to be identical to each other, so that the number of different components is small. 
     In a releasable check valve according to the invention, two inserts may be situated on one side of the spacer bushing, which is advantageous, for example the installation of seals. If a releasable check valve according to the invention is used at very high system pressures, which may amount to 4000 or 6000 bar in internal high-pressure forming, for example, then it is important that the separating gaps between the two inserts are relieved from pressure so that the high system pressure cannot build up there. This is because this pressure would produce such a force at the mutually facing end sides of the radially relatively large inserts that there would be the risk of the valve ripping apart. An annular channel also lies between the inserts and the valve housing in the fluid path for the pressure relief. It is then important for the separating gap between the two inserts to be situated in the region of the annular channel. A check is then possible in a simple manner by the fact that the outermost of the inserts on the one side of the spacer bushing has an edge or surface which, in the designated position of the inserts with respect to the annular channel, lies flush with an end surface of the valve housing. 
     The effect achieved by the refinement is that the annular spaces on the two sides of the piston collar cannot be acted upon by maximum pressure from the two end sides of the end sections of the poppet piston. To this end, two axially spaced-apart seals are provided between which the gap between the end sections of the poppet piston and an insert is relieved from pressure via a leakage oil connection. The particular refinement of this pressure relief ensures that part of the sealing arrangement in the open turn-out of the second insert can bear axially against a smooth surface of the first insert, which surface does not have any discontinuities. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of a releasable check valve according to the invention and the principle of a hydraulic circuit for the internal high-pressure forming, within which circuit a check valve according to the invention can be used, are illustrated in the drawing. The invention is now explained in greater detail with reference to the figures of this drawing, in which 
     FIG. 1 shows the hydraulic circuit diagram, and 
     FIG. 2 shows a longitudinal section through the exemplary embodiment of a check valve according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The circuit diagram of FIG. 1 only shows an excerpt from the hydraulic part of an internal high-pressure forming system. The most important part of the hydraulics of a system of this type is a pressure intensifier  10  which contains, in a multi-part housing  11 , a differential piston  12  whose surface ratio determines the ratio of pressure intensification. The diameter of the differential piston  12  is substantially smaller at a secondary piston section  13  than at a primary piston section  14 . The latter divides an interior space of the housing  11  into an annular space  15  and a cylindrical space  16 . The two spaces are connected via working lines  17  and  18  to a proportionally adjustable directional control valve  19  which, in its central rest position, connects the two working lines, and therefore the annular space  15  and the cylindrical space  16 , to a tank via a tank connection T. In a first working position of the directional control valve  19 , the annular space  15  is connected to a hydraulic pump  20  via a pump connection P, while the cylindrical space  16  remains connected to the tank. In the other working position of the directional control valve  19 , the cylindrical space  16  is connected to the hydraulic pump and the annular space  15  is connected to the tank. 
     A displacement sensor  23  senses the position of the differential piston  12  with respect to the housing  11 . 
     The space  24  upstream of the end side of the secondary piston section  13  is connected, on the one hand, via a simple check valve  25  which opens toward it, to a storage container  26  which contains a hydraulic fluid based on water. On the other hand, a releasable check valve  30  according to the invention is connected to the pressure space  24  and through said check valve  30  pressure medium can readily flow out of the pressure space  24  to a line  31  which can be connected to the semi-finished product to be formed. The line  31  is also connected to the storage container  26  via a check valve  32  which opens toward it. During operation, the semi-finished product is filled with hydraulic fluid from the storage container  26  via the line  31  and the check valve  32 , it also being possible to arrange a pump between the storage container  26  and the check valve  32 , which pump brings about filling up to a certain pressure. The directional control valve  19  is then brought into its second working position in which hydraulic oil is supplied by the pump  20  to the cylindrical space  16  of the pressure intensifier  10 . The differential piston  12  moves upwards, as viewed in FIG. 1, and displaces hydraulic fluid from the pressure space  24  via the releasable check valve  30  into the line  31 , so that the pressure in the semi-finished product to be deformed increases. Depending in each case on how large the volume of the semi-finished product, the increase in the volume by the deformation and the level of the final pressure are, one or more strokes of the differential piston  12  are necessary. For a second stroke, the directional control valve  19  is brought into its first working position, so that the differential piston  12  travels downward and hydraulic fluid is sucked into the pressure space  24  from the storage container  26  via the check valve  25 . After the directional control valve  19  is again switched over, hydraulic fluid is pressed in turn out of the pressure space  24  into the line  31  via the check valve  30 . 
     After deformation and calibration of the workpiece is finished, the check valve  30  is released, by applying a control pressure to a control channel  33 , so that the space within the workpiece and the line  31  can be decompressed by the differential piston  12  moving back. 
     The construction and the manner of operation of the check valve  30  emerge in greater detail from FIG.  2 . The exemplary embodiment shown there has, according to the invention, a valve housing  35  through which a receiving bore  36  passes whose axis may be referred to as the valve axis  37 . The receiving bore  36  has the same diameter throughout, apart from two sections  38  at its two ends, which sections are provided with an internal thread, and apart from flat turned grooves  39 ,  40 ,  41  and  42  further to the inside, and in the region of this constant diameter can only be machined from one side of the valve housing  35 . A total of six parts are inserted clamped axially against one another into the receiving bore  36 . First of all, high-strength inserts  43  and  44  are screwed into the sections  38  of the receiving bore  36  and each of said inserts has, on the valve axis  37 , a respective threaded bore  45  or  46 , which bores serve as the first or second orifice of the valve and to which a respective pressure line can be connected. The inserts  43  and  44  dip via the sections  38  into the region of constant diameter of the receiving bore  36  and are centered therein. The insert  44  has an inwardly open blind bore  47  which is connected via a relatively narrow channel  48  to the threaded bore  46  and which receives and guides a closing element  50 , which is loaded in the direction out of the blind bore  47  by a weak closing spring  51 . The insert  44  is followed axially by a likewise high-strength insert  55  which is in the form of a washer and has a central passage  56  with two steps. Around the narrowest section of the central passage the insert  55  serves as a seat for the closing element  50 . The insert  55  is followed by a washer  60  having a central passage  61 , then by a spacer bushing  62  whose inside diameter is substantially larger than the diameter of the central passage  61  in the washer  60 , then by a further washer  60  having a central passage  61 , which washer is fitted in the opposite direction to the first washer  60 , and then by the insert  43 . Like the insert  44 , said insert  43  has an inwardly open blind bore  63  which, however, is less deep than the blind bore  47  and also has a smaller diameter. This diameter corresponds with the diameter of the central passages  61  in the washers  60  and with the diameter of the central section of the central passage in the insert  55 . The blind bore  63  is also connected to the threaded bore  55  via a channel  64  which is narrower in diameter. 
     All of the inserts  43 ,  44 ,  55 ,  60  and  62  are centered by the receiving bore  36 . 
     A poppet piston  70  is accommodated in the interior of the inserts  55 ,  60  and  43  and in the interior of the spacer bushing  62  and with the aid of the poppet piston the closing element  50  can be raised from its seat counter to the force of the closing spring  51  and counter to a force produced by the pressure in the second orifice  46  of the valve. 
     The poppet piston has a piston collar  71  which is situated within the spacer bushing  62  and divides the space surrounded by the washers  60  and the spacer bushing  62  into two annular spaces  72  and  73 . The two annular spaces are sealed off from each other by a sealing arrangement  74  in the piston collar  71 . The annular space  72  can be acted upon by a control pressure or relieved from pressure via an external connection  75  and with the aid of a pilot valve (not shown in greater detail). The turn-out  40  of the valve housing  35  and an oblique bore  76  in the spacer bushing  62  lie in the flow path between the external connection  75  and the annular space  72 . The other annular space  73  is connected via a second external connection  77  to an oil container for the purpose of equalizing the volume and for conducting away leakage oil, and also accommodates a restoring spring  78  for the poppet piston  70 . On both sides of the piston collar  71  the poppet piston has shaft-journal-like end sections  79  and  80  with which it dips through the central passages  61  of the washers  60  and into the blind bore  63  of the insert  43  and into the central passage  56  of the insert  55 . Toward the closing element  50  the one end section  80  is extended by a finger  81  which can act upon the closing element  50  through the narrowest section of the central passage  56  of the insert  55 . In the rest position shown of the poppet piston  70 , there is a small spacing between the finger  81  and the closing element  50 . The flow path between the orifices  45  and  46  of the valve leads axially through the poppet piston  70  which, for this purpose, has a long axial bore  82 , which opens into the blind bore  63  of the insert  43 , and a plurality of small oblique bores  83  at the base of the finger  81 . 
     A maximum pressure seal  86  is accommodated in that section of the central passage  56  of the insert  55  which is the widest and open axially toward the one washer  60 , said seal being pressed by the maximum pressure axially against a smooth, uninterrupted encircling surface of the washer  60 , but, of course, also acting radially with respect to the poppet piston  70 . A seal  87 , which is accommodated approximately centrally in an annular groove of the washer  60 , which groove is open toward the end section  80 , also acts radially. Identical seals  86  and  87  are located in the insert  43  and in the other washer  60 . Other seals  88  are located on the outside of the washers  60  between the connection  75  and the turn-out  39  of the valve housing and between the connection  77  and the turn-out  42  of the valve housing and on the outside of the spacer bushing  62  between the two turn-outs  40  and  41 . 
     In the valve which is shown, the separating gaps between the one washer  60  and the insert  43  and between the other washer  60  and the insert  55  and also between the insert  55  and the insert  44  are relieved from pressure. For the pressure relief between the two inserts  55  and  44 , that end side of the insert  55  which faces the insert  44  is formed such that it is slightly conical toward the outside at a distance from the valve axis  37 , with the result that, on the one hand, for radial sealing, the inserts  44  and  45  can bear tightly against each other far inwards and, on the other hand, an annular space  89  is provided which increases in its axial extent radially toward the outside and from which leakage oil is conducted away via a housing bore  90 . For the pressure relief between the washers  60  and the inserts  43  and  55 , the washers  60  have in the central passage  61  between the seal  87  and their end side which faces the insert  43  or the insert  55  an axially short and flat annular groove  91  from which an oblique bore  92  originates which, at a radially small distance from the seal  86 , appears at that end side of a washer  60  which faces the insert  43  or the insert  55  and is open there to an annular groove  93  formed in the insert  43  or the insert  55 . One or more radial channels  94  of small diameter lead from the annular groove  93  outwards to the turn-out  39  or  42  of the valve housing  35  from which in turn leakage oil can be conducted away through housing bores  90 . The washers  60  are therefore never exposed to the maximum pressure which is possible in the orifices  45  and  46  of the valve and as regards the selection of material can be matched entirely to their function as guides for the poppet piston  70 . They are primarily produced from a copper beryllium alloy. In contrast, the inserts  43 ,  44  and  55  are loaded by the maximum pressure during operation and are therefore produced from a high-strength material. The fit between the end sections  79  and  80  of the poppet piston and the inserts  43  and  55  is selected in such a manner that the guiding of the poppet piston  70  takes place in the washers  60 . Tilting and wedging of the poppet piston  70  is as good as eliminated in the process, since the washers  60  are centered in a region of the receiving bore  36 , which region has been machined in a single operation at the same setting of the valve housing and while maintaining the position of the tool. 
     The seals  87  and  88  in the washer  60  between the spacer bushing  62  and the insert  55  seal off spaces from each other in which essentially the same pressure prevails. Their function essentially involves separating different hydraulic fluids from one another. This is because the annular space  73  is conventionally filled with oil, while the pressure medium used for the high-pressure forming is water. 
     The insert  44  has a surface  95  which is brought during installation of the valve into alignment with an end surface  96  of the valve housing. This ensures that the separating gaps between the inserts are open toward the turned grooves  39  and  42  and toward a bore  90  and are relieved from pressure. The insert  43  may also be formed in such a manner that a surface on it is aligned, at the correct, axial position of the inserts in the valve housing  35 , with the other end surface of the valve housing. 
     When the releasable check valve which is shown in FIG. 2 is used in the hydraulic circuit according to FIG. 1, the first orifice  45  is connected to the pressure space  24  of the pressure intensifier  10  and the second orifice  46  is connected to the line  31 . If the pressure intensifier displaces water out of the pressure space  24 , said water flows to the second orifice  46  via the channels  64 ,  82 ,  83 ,  56 , via the closing element  50  which is raised from its seat and via the channel  48  in the insert  44 . For the decompression which has already been mentioned of the liquid forming means, the annular space  72  is acted upon via the external connection  75  with control pressure, so that the poppet piston moves toward the closing element  50  and raises the latter from its seat. The raising takes place counter to the force of the restoring spring  78  and counter to a compressive force which is caused by a possible pressure difference between the orifices  45  and  46  and by different engagement surfaces on the closing element  50  for the pressures in the orifices  45  and  46 , and counter to the virtually negligibly small force of the closing spring  51 . The compressive force can indeed be brought virtually to zero at the beginning by a pressure-controlled movement of the differential piston  12 . However, during the compression which then follows, a quantity of hydraulic fluid, the amount of which depends on the desired speed at which said compression takes place, has to flow out of the line  31  via the valve  30  into the pressure space  24 , as a result of which a pressure difference occurs via the closing element  50 . The closing element has to be held open by the poppet piston  70  counter to this pressure difference. Because of the large diameter of the piston collar  71 , this is achieved by control pressures which are conventionally built up today by hydraulic pumps.