Abstract:
A blow valve of a blow-molding machine for containers, having a valve seat which is arranged in a valve chamber between an inflow channel mouth and an outflow channel mouth and has assigned thereto a valve piston which is shiftable linearly between a shut-off position and a lifted open position and which with a piston extension carrying a closing surface passes sealingly shiftably through a bore of a wall defining the valve chamber, wherein a flow path which extends through the valve chamber between the mouths is shut off in the shut-off position and released in the open position, at least one guide surface which is generally inclined relative to the shifting direction of the valve piston is provided for the lateral forced deflection of the flow on the wall and/or on the piston extension.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority of German Application No. 102009041253.0, filed Sep. 11, 2009. The entire text of the priority application is incorporated herein by reference in its entirety. 
     FIELD OF THE DISCLOSURE 
     The present disclosure relates to a blow valve of the type used in blow molding machines for forming blow molded containers. 
     BACKGROUND 
     In such a blow valve known in practice, the upper side of the wall, which is opposite to and spaced from the mouths, is flat and perpendicular to the shifting direction of the valve piston. The piston extension has a flat surface which is perpendicular to the shifting direction and on which the closing surface is formed. For an easier handling of the circular closing surface the surface may comprise a central, flat and shallow recess at the end of the piston extension. The flow developing in the open position of the valve piston in the valve chamber must be deflected twice. When the blow valve is opened, the flow expands into the large-volume cylindrical valve chamber, the depth of which corresponds approximately to the opening lift and the diameter of which corresponds several times to the diameter of each mouth. The turbulent and delayed medium must squeeze out of the valve chamber into at least one mouth of the outflow channel and must be accelerated again. Dead spaces as well as considerable pressure losses caused by turbulences ensue from the geometric concept in the valve chamber, i.e. the flat surfaces oriented perpendicular to the shifting direction of the piston. It is difficult to clean the blow valve in the dead spaces. The unavoidable pressure losses result in undesired long switching differences between the opening pulse and the pressurization of the preform. 
     In the blow valve known from EP 1 328 396, the flow developing in the open position is deflected at least three times, each time by 90°, and expands in the large valve chamber. Strong turbulences resulting in inexpediently great pressure losses and long switching differences are created in the valve chamber. 
     It is one aspect of the present disclosure to indicate a blow valve of the aforementioned type which in the open opposition operates with a minimum pressure loss and thus with an optimally short switching difference. It is also part of the aspect to avoid inexpedient dead spaces that increase the compressed air consumption and deteriorate the cleanability, e.g. by way of rinsing the blow valve with a cleaning medium. 
     The at least one, generally inclined, guide surface effects a lateral forced deflection of the flow in the valve chamber, whereby strong turbulences caused by great pressure loss are minimized. The decrease in pressure loss is accompanied by an optimally short switching difference. Expediently, at least one guide surface is provided both in the wall and on the piston extension to create a low-turbulence, swift and, above all, guided flow from the inflow channel into the outflow channel in the open position. An improvement is however achieved with at least one guide surface on the piston extension or in the wall. Unharmonious or sharp and turbulence-promoting surface transitions are minimized. Only minimal dead spaces are created, if at all. The formation of swirls is thus minimal and the blow valve can be cleaned easily, e.g. in a rinsing process. 
     In an expedient embodiment, the respective guide surface, facing the flow, is concavely rounded at least in portions. A concave rounding considerably improves the flow pattern in the flow and thus reduces the pressure loss caused during deflection. 
     It is advantageous when the valve seat which is substantially oriented perpendicular to the shifting direction of the valve piston and/or the closing surface on the valve piston, is/are made flat, spherical or conical. Especially spherical or conical configurations that may be similar or alternate or may be combined with a flat design result in high tightness in the shut-off position, and also help to make the flow uniform, thereby further reducing the pressure loss. 
     In an expedient embodiment, the guide surfaces on the wall and on the piston extension harmoniously pass into one another in the open position so as to put up as little flow resistance as possible to the exterior faster boundary layer of the flow. 
     In an expedient embodiment the guide surface even extends on the wall directly up to the mouth, so that the flow is directly guided up and into the mouth without any significant separation. 
     In a constructionally simple embodiment the wall is formed by a ring stationarily inserted into the valve chamber. It may be the function of the ring to define with the bottom side a pilot chamber in which the valve piston is actuated by a closing force-generating pilot pressure on an actuation surface larger than the piston extension. Preferably, because of the larger actuation surface a relatively moderate pilot pressure suffices for holding the shut-off position and after reduction of the pilot pressure the valve piston is brought by the inflow pressure very rapidly into the open position. 
     In a particularly expedient embodiment, apart from a central mouth, two exterior mouths that are diametrically arranged relative to the axis of the central mouth are provided that have each assigned thereto an outwardly ascending guide surface on the wall. By contrast, the piston extension that is oriented relative to the central mouth and immerses at least in the shut-off position into the central mouth in portions comprises two descending guide surfaces that are connected via an elevated flow division zone and oriented relative to the exterior mouths. The mouths may be circular, oval or kidney-shaped, or they may have any desired shape. It would also be possible to provide just one exterior mouth. In this configuration, an especially neat flow guiding operation with a low pressure loss is achieved. Independently of the question which mouth pertains to the inflow channel and which one to the outflow channel, either the flow from the inflow channel mouth is divided with low loss into two substantially identical partial flows that are guided to the exterior mouths, or two partial flows from the exterior mouths pertaining to the inflow channel are harmoniously combined in a flow extending into the mouth to the outflow channel. 
     To keep dead spaces as small as possible, and to enforce a neat flow-guiding process, it may be advantageous when the guide surfaces are formed in trough-like recesses in the piston extension and in the wall. The width of each recess can here correspond to the diameter of the exterior mouth or the central mouth. 
     In an expedient embodiment, these recesses have at least about the same depth in the shifting direction of the valve piston, resulting in a harmonious flow path of a large cross-section in the open position. 
     Particularly expediently, the guide surfaces are defined by displacement bodies provided on the wall and the valve piston. The displacement bodies minimize the dead volume in the valve chamber, so that the guided flow is without any expansion generating significant pressure losses and without any swirl. 
     In another expedient embodiment, the recesses in the flow direction can even gradually narrow down and preferably form a nozzle cross-section similar to a venturi nozzle that is constricted towards the outflow channel, so that the flow is made uniform and accelerated, whereby the pressure loss can even be reduced further. 
     The flow direction in the blow valve can be chosen according to requirements. The central mouth is preferably assigned to the inflow channel and the exterior mouth or both exterior mouths are assigned to the outflow channel. 
     The ring arranged in the valve chamber may be split into a lower ring providing the necessary sealing and into an upper ring serving to guide the flow. The ring serving to guide the flow could also be used for retrofitting already used blow valves, and it could even consist of plastic. 
     To improve the flow conditions also in or from the respective mouth, at least one of the mouths may comprise a counter-guide surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the subject matter of the disclosure are explained with reference to the drawing, in which: 
         FIG. 1  shows an axial section of a blow valve in shut-off position; 
         FIG. 2  shows an axial section of the blow valve in open position; 
         FIG. 3  shows a schematic axial section of another embodiment of the blow valve; 
         FIG. 4  shows a schematic axial section of a further embodiment of the blow valve; 
         FIG. 5  shows a schematic axial section of two detail variants of the switch valve; 
         FIG. 6  shows an axial section of part of a blow valve of a further embodiment; and 
         FIG. 7  is a perspective view showing a detail of a further embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The embodiment of a blow valve V as shown in  FIG. 1  (shut-off position) and in  FIG. 2  (open position) is e.g. switched by a control pressure from a pilot valve (no shown) into the shut-off position and is brought into the open position by the prevailing inflow pressure after reduction of the control pressure. Alternatively, the blow valve V could be operated mechanically or by a magnet (not shown). 
     A housing (not shown) of the blow valve V has installed therein a plate  1  which has arranged therein a central inflow channel  3 , which is designed as an axial bore, and two exterior outflow channels  2  which are diametrically positioned relative to the inflow channel  3  and are each configured as circular bores. The channels  2 ,  3  form e.g. circular mouths  4 ,  5  on the underside of the plate  1 . The respective mouth could also be made oval, kidney-shaped or formed in any desired way. A valve chamber  7  which is defined by a wall  8 , for instance in the form of a ring  9 , is located underneath the plate  1 . A valve piston  11  (differential piston) which has a lower large-diameter piston member  12  and a central piston extension  14  of a smaller diameter is sealingly displaceably guided in the valve chamber  7 . A control chamber  13  with a control pressure connection  17  leading to said chamber is provided on the underside of the valve piston  11 . On the piston extension  14 , a closing surface  15  (here for instance a circular surface arranged substantially perpendicular to the shifting direction of the valve piston  11 ) is provided on the upper end. The piston extension  14  is formed by at least one seal  18  in the bore of the ring  9 . An intermediate ring chamber  10  between the large-diameter piston member  13  and the ring  9  can be vented for instance via a connection  16 . In the shut-off position at least part of the piston extension  14  can immerse into the mouth  5  of the inflow channel  3 . 
     According to  FIG. 2  guide surfaces L 1 , L 2  that are oriented towards the channels  2 ,  3  are formed in the piston extension  14  and in the wall  8 . The guide surfaces L 1 , L 2  extend in general in oblique fashion relative to the shifting direction of the valve piston  11  and are preferably concavely rounded at least in portions for the flow developing in the open position (outlined by arrows). In the wall  8 , a surface section  20  which is ascending in obliquely curved fashion and concavely rounded in transverse direction passes into a surface section  22  which extends approximately perpendicular to the shifting direction of the valve body  11  and is also concavely rounded in transverse direction. In the piston extension  14 , and starting from an elevated flow division zone  23 , an oblique surface section  21  is provided that is curved and concavely rounded in transverse direction. The surface sections  22 ,  21  are e.g. approximately semi-round. Trough-like recesses  19 ,  19 ′ are thereby formed both in the piston extension  14  and in the wall, with the recesses passing harmoniously into each other in the open position shown in  FIG. 2 . 
     The recesses  19 ,  19 ′ are so to speak positioned between displacement bodies K of the wall  8  and of the piston extension  14 ; these bodies are provided at both sides and reduce the dead volume in the valve chamber  7  to a degree providing optimum flow guidance conditions in the valve chamber  7 . The displacement bodies K of the wall  8  may abut on the plate  1 . The displacement bodies K on the piston extension  14  end in the open position at, on or slightly in the mouth  5 . The depths of the recesses  19 ,  19 ′ as viewed in the shifting direction of the valve piston  11  are approximately identical. The width of the recesses corresponds at least to the inner width of the smaller mouths  4 . In an alternative embodiment the recesses  19 ,  19 ′ might slightly narrow down in flow direction towards the mouths  4  to form a nozzle cross-section similar to a venturi nozzle. In the open position in  FIG. 2 , the remaining surface portion of the piston extension  14  may be positioned outside the recesses  19 ′ approximately at the level of the valve seat  6 , which is here flat and circular. 
     The guide surfaces L 1 , L 2  effect a forced deflection of the flow; in  FIGS. 1 and 2  out of the channel  3  laterally outwards and then upwards into the channels  2 . The switch valve in  FIGS. 1 and 2  could alternatively operate with reversed flow directions. In an alternative embodiment (not shown) of the blow valve V, the guide surfaces L 1  or L 2  could also be arranged only on the piston extension  14  or only in the wall  8 . Furthermore, the wall  8  could be part of the housing of the blow valve V. 
     It is outlined in  FIG. 1  in broken line at  30  that the ring  9  could be subdivided into a lower ring  29 ′ and an upper ring  27 . The upper ring  27  (see  FIG. 7 ) comprises the at least one guide surface L 2  and the recesses  19 ′, respectively, with the surface portions  20 ,  22  outside of a passage  28  for the piston extension  14 , and could be a retrofit part. 
     In the embodiment of the blow valve V in  FIG. 3 , an inflow channel  3  and an outflow channel  2  are provided side by side. The valve seat  6  is flat, just like the closing surfaces  15  on the piston extension  14 . Two approximately symmetrical oblique guide surfaces L 1  are provided on the piston extension  14 ; in the open position (not shown), these guide surfaces L 1  guide the flow from the channel  3  laterally by forced deflection into the channel  2 . The guide surfaces L 1  are depicted as inclined ramps, but could also be formed in trough-like recesses and rounded, by analogy with  FIG. 2 . 
     In the embodiment of the blow valve V in  FIG. 4 , the piston extension  14  is formed with a conical peak that forms the guide surfaces L 1 , separated by the flow division zone  23 . Alternatively, the guide surfaces L 1  could be straight roof surfaces  24 , separated by a crest forming the flow division zone  23 . The closing surface  15 ′ of the piston extension  14  is here e.g. conical while the valve seat  6 ′ is rounded, resulting here in the sealing effect in the shut-off position with the pair conical surface/rounded circular ring. Either conical or ramp-like guide surfaces L 2  are formed with respect to the channels  2  in the wall  8  through which the piston extension  14  passes. The guide surfaces L 1 , L 2  can also be arranged in recesses  19 ,  19 ′, which are then expediently concavely rounded, by analogy with  FIG. 2 . In  FIG. 4 , more than only two exterior channels  2  could be distributed around the central channel  3  in the case of conical guide surfaces L 1 , L 2 . 
     In the embodiment in  FIG. 5 , the left half depicts the cooperation between a conical closing surface  15 ′ on the piston extension  14  and a valve seat  6 ″ configured as a circularly extending rectangular edge. The guide surfaces L 1  on the piston extension  14  and L 2  in the wall  8  could e.g. be made conical, by analogy with  FIG. 4 . 
     By contrast, the right half of  FIG. 5  outlines the cooperation between a spherical closing surface  15 ″ on the piston extension  14  and the edge of the valve seat  6 ″, which is here rectangular. The guide surface L 1  on the piston extension  14  is either a surrounding spherical surface or a convexly curved surface. In the wall  8 , a concavely rounded surface which is first descending from the inside to the outside and then gradually ascending up and into the channel  2  and which could be formed in a similar recess as the recess  19  in  FIG. 2  is shown in the right half as the guide surface L 2 . 
     Finally,  FIG. 6  illustrates an embodiment in which in at least one of the mouths  4 ,  5  of the channels  2 ,  3  a counter-guide surface L 3  is provided for further improving the flow guidance. The valve seat  6 ′″ is here e.g. an annular conical surface  26  and can cooperate with a conical or spherically rounded closing surface on the piston extension, which is not shown in  FIG. 6 , e.g. to carry out a shutting off without any leakage in the shut-off position. The counter-guide surfaces L 3  are e.g. conical countersunk portions in the mouths  4 ,  5 .