Patent Publication Number: US-2009217983-A1

Title: Hydraulic valve assembly

Description:
The invention relates to a hydraulic valve assembly, which is used in particular for controlling hydraulic consumers of mobile work machines and which has the characteristics of the preamble to claim  1 . 
     One such valve assembly is known for instance from German Patent Disclosure DE 199 48 232 A1 or DE 103 25 294 A1, European Patent Disclosure EP 1 092 095 B1, or from the Data Sheet RD 64 295/07.02 or RD 64 282/05.00 of the present Applicant and can be embodied as a single valve disk, which can be combined with other valve disks into a control block, or as a valve disk of a so-called monoblock. The valve disks in these references are embodied as so-called load-sensing valves, and in a valve bore of a valve housing they contain a valve slide, with which the opening cross section of a metering aperture and the flow direction of the pressure fluid in the existing consumer conduits can be controlled. 
     In the valve housings, in a further bore, a pressure balance is also accommodated in a further bore; in the case of the valve disk in Data Sheet RD 64 282/05.00, it is located upstream of the metering aperture, and its regulating piston is urged in the closing direction by the pressure upstream of the metering aperture and in the opening direction by the pressure downstream of the metering aperture and by a spring. In the case of the valve disks of the other references, the pressure balance is located downstream of the metering aperture and is urged in the closing direction by the maximum load pressure of all the simultaneously actuated hydraulic consumers and in the opening direction by the pressure downstream of the metering aperture. Such valve disks make a flow distribution that is independent of load pressure possible, if at the same time a plurality of hydraulic consumers are to be supplied with pressure fluid, and the quantity of pressure fluid pumped by a pump is less than the required quantity of pressure fluid. 
     Moreover, the known valve disks in the valve housing have two pressure-limiting and feed valves, each of which is associated with one of the two consumer conduits. A pressure-limiting and feed valve of this kind responds regardless of the position of the valve slide when the pressure in the corresponding consumer conduit reaches a defined value, and it limits the pressure to that value by causing pressure fluid to flow out of the consumer conduit in throttled fashion to the outflow conduit (pressure limiting function). This can happen for instance if the valve slide, in the neutral position blocks off the consumer conduit, and pressure fluid located in the consumer conduit, in a consumer line connected to it, and in the hydraulic consumer itself heats up, and if the hydraulic consumer is located at a stop. 
     The pressure-limiting and feed valve also responds when the load is acting in the desired direction of motion, and the pressure in the consumer conduit, by way of which pressure fluid flows to the hydraulic consumer, drops below the pressure in the outflow conduit (feed function). The pressure in the outflow conduit can be raised to above atmospheric pressure with the aid of a backup valve. 
     A pressure-limiting and feed valve is not always connected to a consumer conduit. For certain applications, it suffices for a pressure-limiting and feed valve to be associated with only one of the two consumer conduits of a valve disk. Sometimes, a valve disk has no pressure-limiting and feed valve whatever. For the various different uses, different valve housings must therefore be manufactured and upon assembly combined with the correct valve slides. This involves considerable handling costs. Since having to cast different blanks is undesirable, the cast valve housings are always made with installation spaces for two pressure-limiting and feed valves. 
     The object of the invention is to develop a hydraulic valve assembly, having the characteristics of the preamble to claim  1 , further in such a way that lower production costs and smaller size are possible. 
     The stated goal is attained, in a hydraulic valve assembly having the characteristics of the preamble to claim  1 , according to the invention in that according to the body of claim  1 , the pressure-limiting and feed valve is accommodated in a hollow chamber of the valve disk. In such an embodiment, the valve housing can be a standard element, whose rough form and further design no longer need to depend on whether the valve disk is intended to hold one, or two, or no pressure-limiting and feed valves. Installation space for the pressure-limiting and feed valves no longer has to be reserved in the valve housing, and thus the valve housing can be smaller than in known valve disks. The various variants of valve disks are not formed until near the end of the manufacturing process, using a suitable valve slide that is already adapted in other respects to the particular application. As needed, the valve slide can receive one or two pressure-limiting and feed valves. 
     Advantageous features of a hydraulic valve assembly according to the invention can be found in the dependent claims. 
     An especially expedient embodiment is found in claim  3 , according to which the valve slide is movable from the neutral position into work positions in both directions, and according to which the hollow chamber in the valve slide can be made to communicate with the outflow conduit via a radial bore, which is located so close to one end of the valve slide that, upon a displacement of the valve slide from the neutral position, it is closed toward the outflow conduit in the sense of a communication of the second consumer conduit with an inflow conduit. This embodiment is based on the concept that, in a work position of the valve slide in which the consumer conduit communicates with the outflow conduit, the hollow chamber in the valve slide need not be open toward the outflow conduit. Accordingly, the radial bore can be located far outward, to the end of the valve slide. A long stroke of the valve disk can be preserved. The control chamber, which forms the outflow conduit at the valve bore, need not be enlarged axially. 
     Various versions of pressure-limiting and feed valves exist that can be built into the valve slide; the various versions can differ in their structural length or in the feed flow cross section. If according to claim  4 , toward the consumer conduit, two radial bores discharge into the hollow chamber and are spaced apart from one another in the axial direction of the valve slide, and of them, in one work position of the valve slide, one radial bore is open toward the consumer conduit and the other radial bore is open toward the inflow conduit or the outflow conduit, then it is possible to use a certain version of a pressure-limiting and feed valve for which the hollow chamber, with a large diameter, must reach into a region of the valve slide in which the valve slide in the known valve assemblies has an annular groove in order to establish the various fluidic communications. In the embodiment, the hollow chamber is also located in the fluidic communication of the consumer conduit with the inflow conduit or the outflow conduit. An annular groove is unnecessary. 
     If another version of a pressure-limiting and feed valve is used that does not necessitate having the hollow chamber with a large diameter extend far into the valve slide, and if the valve slide according to claim  5 , in the region of the consumer conduit, has an annular groove by way of which the consumer conduit can be made to communicate with an inflow conduit or with the outflow conduit, then, as recited in claim  6 , a radial bore advantageously extends into the hollow chamber from the annular groove. Via this radial bore, pressure fluid then flows only whenever the pressure-limiting and feed valve responds. 
     Claim  7  is directed to a hydraulic valve assembly having a pressure-limiting and feed valve that can be constructed with an especially small diameter, so that the wall of the valve slide surrounding the hollow chamber can be thick enough that it readily meets all the demands made of it with regard to dimensional stability and security against breakage. The pressure-limiting and feed valve of claim  7  can be refined advantageously in accordance with claims  8  through  11 . 
     A plurality of exemplary embodiments, embodied as LIFD valves, of a hydraulic valve assembly according to the invention are shown in the drawings. 
    
    
     
       The invention will now be described in further detail in conjunction with these drawings. 
         FIG. 1  shows a longitudinal section through a valve disk having two consumer conduits and one valve slide, in which the valve slide accommodates two pressure-limiting and feed valves of different design; 
         FIG. 2  shows a longitudinal section through a valve disk having two consumer conduits and one valve slide, in which only one pressure-limiting and feed valve, in a third version, is accommodated in the valve slide; 
         FIG. 3  is an enlarged view of the valve disk of  FIG. 2  in the region of the pressure-limiting and feed valve; and 
         FIG. 4  is a longitudinal section through one of the two pressure-limiting and feed valves in  FIG. 1 . 
     
    
    
     The valve slides in  FIGS. 1 and 2  have a disklike valve housing  10 , through which a valve bore  11 , located in a central disk plane, passes. A valve slide  12  is axially movable in this bore. In the exemplary embodiment of  FIG. 1 , the valve slide is mechanically actuatable and to that end, on an end protruding from the valve housing  10 , it has a pivot with cheeks  13 , on which a hand lever can be secured. On the other end of the valve slide  12 , which likewise protrudes from the valve housing  10 , but which is covered by a cap  14  screwed onto the valve housing, a helical compression spring  17  is tethered with two spring cups  15  and  16  inside the cap, and this spring centers the valve slide in a neutral position, and upon each motion of the valve slide out of the neutral position, regardless of the direction of the motion, is compressed more markedly, beginning at a basic initial tension. 
     In the exemplary embodiment of  FIG. 2 , the valve slide is hydraulically actuatable. For that purpose, both ends of the valve slide  12  that protrude from the valve housing  10  are covered with solid caps  18 , which are screwed onto the valve housing  10  and have a connection opening  19  for a control line. With the aid of a hydraulic pilot control unit, a control pressure can be fed into one or the other cap via the control lines, and this pressure generates a force on the cross-sectional area of the valve slide  12  that displaces the valve slide far enough toward the helical compression spring  17 , which as in the first exemplary embodiment is tethered between two spring cups  15  and  16 , that an equilibrium prevails between the compression force and the spring force. 
     The valve bore  11 , in both exemplary embodiments, is surrounded by eight control chambers axially spaced apart from one another, which serve to control the inflow of hydraulic fluid from a hydraulic pump to a hydraulic consumer, such as a hydraulic cylinder, and from the hydraulic consumer to a tank. Between each three control chambers on both sides are two control chambers  25  and  26 , which in the neutral position of the valve slide  12  as shown in  FIGS. 1 and 2  are fluidically separated from one another by a slide collar  27 , which is adjoined on both sides by a slide neck with a respective annular groove  28  and  29  and which has two rows of fine-control grooves  30  and  31 , are offset from one another in the circumferential direction, of which the fine-control grooves  30  are open toward the annular groove  28 , and the fine-control grooves  31  are open toward the annular groove  29 . The control chamber  25  is intended for connection to a pump line and can therefore also be called a pump chamber. Let it be assumed that the control chamber  26  is an intermediate chamber. Depending on the direction in which the valve slide  12  moves from the neutral position, a flow cross section from the pump chamber  25  to the intermediate chamber  26 , which forms the metering aperture of the valve assembly, is opened by either the fine-control grooves  30  or the fine-control grooves  31 . 
     One inflow chamber  32  is located on one side of the two control chambers  25  and  26 , and another inflow chamber  33  is located on the other side. These two inflow chambers are part of a bridgelike inflow conduit  34 , which the hydraulic fluid reaches from the intermediate chamber  26  via a pressure balance  35 . All that needs to be said here about this pressure balance is that its one-piece ( FIG. 1 ) or two-piece ( FIG. 2 ) regulating piston is urged in the closing direction by the highest load pressure of all the hydraulic consumers that are simultaneously actuated, and optionally by a weak spring, and in the opening direction by the pressure in the intermediate chamber  26 . The pressure balance is accordingly located downstream of the metering aperture and in the intermediate chamber backs up a pressure that results from the applicable highest load pressure. The valve assemblies shown in  FIGS. 1 and 2  are accordingly LIFD valves. 
     The inflow chamber  32  is followed by a consumer chamber  36 , and the inflow chamber  33  is followed by a consumer chamber  37 . Each consumer chamber is part of a respective consumer conduit  38  and  39 , which ends in a consumer connection of the valve housing  10 . Each consumer chamber  36  and  37  is followed by a respective outflow chamber  40  and  41 . The two outflow chambers are joined together in a completed valve block and are part of an outflow conduit  42 , which leads to a tank connection, optionally via a backup valve. 
     In the neutral position of the valve slide  12 , all the control chambers  25 ,  26 ,  32 ,  33 ,  36 ,  37 ,  40  and  41  are blocked off from one another. If the valve slide  12  is moved out of the neutral position, then the metering aperture is opened by the fine-control grooves  30  or  31 . Moreover, one consumer chamber is opened toward an inflow chamber, and the other consumer chamber is opened toward an outflow chamber. 
     In addition to the components described thus far, the valve disk of  FIG. 1  also has two pressure-limiting and feed valves  45  and  46 , and the valve disk of  FIG. 2  also has one pressure-limiting and feed valve  47 . According to the invention, each of the pressure-limiting and feed valves are accommodated in a respective hollow chamber  48 ,  49  ( FIG. 1) and 50  ( FIG. 2 ) of the valve slide  12 . In  FIG. 1 , the valve slide is equipped with two different pressure-limiting and feed valves. 
     The hollow chambers  48 ,  49  and  50  are each introduced into the main part from a face end of a main part of the valve slide  12 , and are closed by a respective end piece  51 ,  52  or  53  that is screwed into the main part. In the closed position, the pressure-limiting and feed valves separate a first region of a hollow chamber, on the side toward the outflow chamber, from a second region of a hollow chamber, toward a consumer chamber. The first region is open to the outside of the valve slide  12 , via a radial bore  55  in the valve slide. The radial bore  55  in turn, in the neutral position and upon an adjustment of the valve slide in a direction in which the corresponding consumer chamber  36  or  37  communicates with the associated inflow chamber, is open toward the applicable outflow chamber  40  or  41 . Upon an adjustment of the valve slide  12  in the other direction, the radial bore  55  is closed after a short distance. This has no effects in terms of the function whatever, since the corresponding consumer chamber already communicates with the outflow chamber via the valve slide anyway. 
     The second region of the two hollow chambers  48  and  49  of  FIG. 1  is open toward the outside of the valve slide, via two axially spaced-apart rows of radial bores  56  and  57 , respectively. In the neutral position, shown in  FIG. 1 , of the valve slide  12 , the bores  56  and  57  are open on the outside toward the respective consumer chamber  36  and  37 . If the valve slide  12  is moved out of the neutral position, to the right in the view in  FIG. 1 , then the radial bores  57  of the hollow chamber  48  remain open toward the consumer chamber  36 , while the radial bores  56  are closed toward the consumer chamber  36  and are opened toward the outflow chamber  40 . Moreover, the radial bores  56  of the hollow chamber  49  remain open toward the consumer chamber  37 , and the radial bores  57  of the hollow chamber  49  are closed toward the consumer chamber  37  and opened toward the inflow chamber  33 . Hydraulic fluid arriving from the metering aperture and the pressure balance can accordingly now flow from the inflow chamber  33 , the radial bores  57 , the second region, and the radial bores  56  of the hollow chamber  49  of the consumer chamber  37 , and from there to a hydraulic consumer. Hydraulic fluid flowing back from this hydraulic consumer reaches the outflow chamber  40 , via the consumer chamber  36 , the radial bores  57 , the second region, and the radial bores  56  of the hollow chamber  48 . Thus in the exemplary embodiment of  FIG. 1 , the two regions of the hollow chambers  48  and  49  are located in the fluid path of the operating fluid and each replace one annular groove on the valve slide. An advantageous aspect of this is that the hollow chambers can have a large diameter far into the valve slide. This is favorable for accommodating pressure-limiting and feed valves that are embodied in a specific way. 
     Each of the pressure-limiting and feed valves  45 ,  46  and  47  has a valve body  70 , which is urged in the opening direction by the pressure in the corresponding consumer chamber and in the closing direction by the pressure in the adjacent outflow chamber and by a strong helical compression spring  71 , whose pressure equivalent may for example be 300 bar, and for limiting the pressure in a consumer chamber, each pressure-limiting and feed valve opens a flow cross section from that consumer chamber to the adjacent outflow chamber. Moreover, each pressure-limiting and feed valve has a valve body  72 , which is urged in the closing direction by the pressure in the corresponding consumer chamber and in the opening direction by the pressure in the adjacent outflow chamber and by a weak helical compression spring  73 , whose pressure equivalent may for example be 0.5 bar. If the pressure in the consumer chamber drops below the pressure in the outflow chamber by more than the pressure equivalent of the helical compression spring  73 , the valve body  72  opens a flow cross section, so that hydraulic fluid is fed from the outflow chamber into the consumer chamber. 
     In the case of the pressure-limiting and feed valve  46  in  FIGS. 1 and 4 , the valve body  70  has a guide rod  74 , and downstream of a plunge cut  75 , extending all the way around, the guide rod has a closing cone  76 , which has a conical seat face  77  toward the plunge cut. The valve body  72  is thrust onto the guide rod  74 ; around the plunge cut  75 , it has an annular groove and a plurality of radial bores  78 , beginning at the annular groove, and protrudes radially past the closing cone  76 , and outside the closing cone, it has a conical seat face  77  oriented counter to the seat face  77  of the closing cone. After the valve body  72 , the helical compression spring  71  is thrust onto the guide rod  74 . Behind it, a spring cup  78  is screwed onto the guide rod  74 , so that the helical compression spring  71  is fastened between the valve body  72  and the spring cup  78  and presses the closing cone  76 , with its conical seat face  77  against an inner seat edge of the valve body  72 . The seat diameter is equal to the diameter of the guide rod  74 . The parts of the pressure-limiting and feed valve  46  mentioned such thus far are accordingly combined in captive fashion into one unit. The valve also includes the helical compression spring  73 , which after assembly is located between the spring cup  78  and the bottom of the hollow chamber  46 . The seat edge for the seat face  79  of the valve body  72  is embodied on the end piece  51  of the valve slide  12 . For that purpose, the end piece reaches with a hollow portion to beyond the radial bores  55  of the valve slide  12 , into the hollow chamber  46 . The valve body  72 , in the position of repose, is seated on an inner edge of the face end of the end piece. The first region of the hollow chamber  46  is thus embodied entirely inside the end piece  51 . For fluidic communication outward to the radial bores  55  in the main part of the valve slide  12 , the end piece has an annular groove  80  on the outside, at the level of the radial bores  55 , and also radial bores  81  extending inward from the annular groove. Between the annular groove  80  and the face end of the end piece  51 , between the end piece and the inner wall of the valve slide  12  is a sealing ring  82  that rests in an annular groove of the end piece. 
     In operation, the pressure prevailing in the consumer chamber  36  acts on the valve body  70  in the direction of opening, on an area that is defined by the diameter of the guide rod  74 . The helical compression spring  71 , which is braced on the end piece  51  via the valve body  72 , keeps the closing cone  76  of the valve body  70 , with its face  77  in contact with the valve body  72 , as long as the pressure in the consumer chamber, taking into account the pressure prevailing in the outflow chamber  40 , does not exceed the pressure equivalent of the spring. As soon as that pressure is exceeded, the valve body  70 , or in other words the guide rod  74  together with the closing cone  76 , is displaced to the right—in the views in FIGS.  1  and  4 —so that a flow cross section between the closing cone  76  and the valve body  72  opens, and hydraulic fluid flows in throttled fashion out of the consumer chamber  36  into the outflow chamber  40 . The pressure in the consumer chamber  36  is thus limited to the pressure at which the valve body  70  opens. 
     In the above-described configuration, the valve body  72  remains in repose. Conversely, if the pressure in the consumer chamber  36  drops below the pressure in the outflow chamber  40  by more than the pressure equivalent of the helical compression spring  70 , then the valve body  70 , the valve body  72 , and the helical compression spring  71  are displaced as a unit counter to the helical compression spring  73 , until the guide rod  74  meets the bottom of the hollow chamber  46 . Between the valve body  72  and the face end of the end piece  51 , a flow cross section opens up, by way of which hydraulic fluid can flow virtually unthrottled from the outflow chamber  40  to the consumer chamber  36 . Thus in the consumer chamber  36  and in the lines and consumer chambers communicating with it, the creation of an underpressure is reliably avoided. 
     The pressure-limiting and feed valve  45  of  FIG. 1  also has one valve body  70 , which serves the purpose of pressure limitation, and one valve body  72 , which serves the purpose of feeding. The valve body  72  is embodied as a ring with a central opening and is located axially between the radial bores  55  and  56  of the valve slide  12 . On an inner shoulder, it is urged in a direction out of the hollow chamber by the weak helical compression spring  73 , which is also braced on a shoulder of the hollow chamber  49 . A sealing ring  83  is located in an outer annular groove of the valve body  72 . From a position of repose, which is shown in  FIG. 1 , the valve body  72  can be moved counter to the force of the helical compression spring  73  until it is against a further shoulder of the hollow chamber  49 , and in the position that the valve body  72  then assumes, the radial bores  56  remain open to the hollow chamber  49 . 
     The valve body  70  of the pressure-limiting and feed valve  45  includes a closing cone  85 , which is located in the region of the hollow chamber  49  toward the outflow chamber and which can be seated, with a conical face, on an edge of the central opening in the valve body  72 ; a stop finger  82 , which points toward the end piece  52 ; the strong helical spring  71 , which is fastened, surrounding the stop finger  86 , between the closing cone  85  and the end piece  52 ; and a bracing rod  87 , which passes through the valve body  72 , extends into the interior of the helical compression spring  73 , and on the far side of the radial bores  57  dips into an end portion of the hollow chamber  49  and braces the closing cone  85 , in its position of repose, on the valve slide  12  counter to the action of the helical compression spring  71 . It is advantageous here that given a suitable choice of the sealing of the hollow chamber by the end piece  52 , the initial tension of the helical compression spring  71  can be varied, even after the installation of the pressure-limiting and feed valve  45 , by rotating the end piece  52  that is screwed into the main part of the valve slide  12 . 
     In the position of repose of the two valve bodies  70  and  72  and without pressures in the chambers  37  and  41 , the valve body  72  rests, under the influence of the helical compression spring  73 , on the closing cone  85  of the valve body  70  that is braced on the valve slide  12  via the bracing rod  87 . The valve body  72  then has a slight spacing from a stop ring  88 , which is inserted into the valve slide and which limits the travel of the valve body  72  toward the radial bores  55  upstream of them. 
     In operation, when the valve slide is in the neutral position or in a work position, in which the consumer chamber  37  communicates fluidically with the inflow chamber  33 , the pressure prevailing in the consumer chamber  37  acts on the valve bodies  70  and  72  counter to the helical compression spring  71  and counter to a backup pressure that may prevail in the outflow chamber. The first effective area for the consumer chamber pressure is initially determined by the diameter of the valve body  72 . If the consumer chamber pressure rises to such a value that the compression force generated at the first effective area reaches the force of the helical compression spring  71 , then the valve bodies are moved so far that the valve body  72  reaches the stop ring  88 . From that point on, the consumer chamber pressure can now generate a compression force on the valve body  70 , directed counter to the force of the helical compression spring  71 , only at a surface area determined by the diameter of the central opening in the valve body  72 . If the consumer chamber pressure now reaches the value predetermined by the initial tension of the helical compression spring  71 , the valve body  70  lifts from the valve body  72 , so that a flow cross section opens between the closing cone  85  of the valve body  70  and the valve body  72 , and hydraulic fluid flows, throttled, out of the consumer chamber  37  into the outflow chamber  41 . The pressure in the consumer chamber  37  is thus limited to the pressure at which the valve body  70  lifts from the valve body  72 . 
     Conversely, if the pressure in the consumer chamber  37  drops below the pressure in the outflow chamber  41  by more than the pressure equivalent of the helical compression spring  73 , then the valve body  72  is lifted, counter to the helical compression spring  73 , from the closing cone  85 , braced via the rod  87 , of the valve body  70  and is pressed against the aforementioned shoulder of the valve slide. Between the valve body  72  and the closing cone  85 , a flow cross section opens by way of which hydraulic fluid can flow virtually unthrottled from the outflow chamber  41  to the consumer chamber  37 . The helical compression spring  73  is still far away from being compressed into a block, and thus the hydraulic fluid can flow freely to the radial bores  56 . 
     The pressure-limiting and feed valve  47  in  FIGS. 2 and 3 , in its fundamental construction, is equivalent to the valve  45  in  FIG. 1 . In particular, the valve body  72  with the seal  83  is the same as in  FIG. 1 . A helical compression spring  73  and a stop ring  88  for the valve body  72  are located in the same way as the valve  45  in  FIG. 1 . 
     What is designed differently is the valve body  70 . This valve body now has a collar  90 , pointing in the direction of the end piece  53  and offset radially outward from a closing cone  89 ; with this collar, it can rest in the direction of the effective force of the helical compression spring  71  on a shoulder  91 , located upstream of the radial bores  55 , of the valve slide  12 , on the one hand, and on the other, it can rest, counter to the effective force of the helical compression spring  71 , on the end piece  53 . The possible travel of the valve body  70  results, in the illustration in  FIGS. 2 and 3 , from the inside spacing of the collar  90  from the end piece  53 . 
     The pressure-limiting and feed valve  47  in  FIGS. 2 and 3  is distinguished over the valves  45  and  46  in that its components are not located as deep in the valve slide  12  and therefore the dimensions of the hollow chamber  50  for accommodating the valve  47  can be smaller than those of the hollow chambers  48  and  49  in  FIG. 1 . The valve slide  12  of the exemplary embodiment of  FIGS. 2 and 3  is provided, not only in the region of the consumer chamber  36  but also in the region of the consumer chamber  37 , with an annular groove  94 , which serves the purpose of fluidic communication of the consumer chamber  37  with the inflow chamber  33  and with the outflow chamber  41 . The communication with the inflow chamber  33  is established via an encompassing edge, and the communication with the outflow chamber  41  is established via outflow grooves  95 . 
     The hollow chamber  50 , as a bore of relatively small diameter, extends into the region of the annular groove  94  and is open there toward the annular groove via the radial bores  57  that discharge into the annular groove. In a distinction from the exemplary embodiment of  FIG. 1 , the radial bores  57  are now not located in the normal fluid path of the hydraulic fluid flowing from the inflow chamber  33  to the consumer chamber  37 , or the hydraulic fluid flowing away from the consumer chamber  37  to the outflow chamber  41 . Radial bores that correspond to the radial bores  56  of the exemplary embodiment of  FIG. 1  are not present in the exemplary embodiment of  FIGS. 2 and 3 . 
     The pressure-limiting and feed valve  47  functions precisely like the pressure-limiting and feed valve  45  in  FIG. 1 . In the pressure limiting function, hydraulic fluid flows out of the consumer chamber  37  to the outflow chamber  41 , via the radial bores  57 , the second region of the hollow chamber  50 , a throttle cross section between the valve bodies  70  and  72 , the first region of the hollow chamber, and the radial bores  55 . In the feed function, the hydraulic fluid takes the reverse course, but the flow cross section between the two valve bodies  70  and  72  is then wide open, and the pressure drop between the outflow chamber  41  and the consumer chamber  37  is only slight.