Abstract:
A pressure indicator comprising a piston which is displaceably mounted in a housing counter to the pressure of a spring on an axis and which can be impinged upon with pressure which is to be measured; also comprising optical display means actively cooperating with the piston. According to the invention, the structure of the indicator is simplified, compact and robust. This is achieved in that the optical display means comprise a front glass arranged perpendicular to the axis and one or several display elements which can be moved by the piston relative to said front glass and which respectively alternate at various pressures between a first position wherein they are optically visible from outside through the front glass and a second position wherein they are not optically visible from outside through the front glass.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the field of the indication of pressures which prevail in a volume filled with a medium, in particular, a gas. 
   DESCRIPTION OF THE RELATED ART 
   Conventional pressure indicator devices (manometers) indicate the current pressure in a volume filled with a medium, in particular gas, usually on a dial by means of a pointer rotatable about an axis of rotation. The pressure is converted into a small rotational movement by means of a tube spring, capsule spring, plate spring or the like. However, manometers are also known. (JP-A2-04145335), in which, by means of the pressure, a piston arranged in a cylinder is displaced counter to the force of a spring and the displacement travel is converted into a pointer rotation about the axis of displacement. Other manometers such as are used, for example, for indicating tire pressures on a tire valve, indicate the displacement travel of the piston directly on a scale extending in the direction of displacement (see, for example, U.S. Pat. No. 3,592,218). 
   In most manometers, a small movement caused by the pressure is stepped up mechanically, in order to obtain a clearly visible pointer deflection. Pressure surges, mechanical vibrations or even knocks may damage such instruments. If they are seriously damaged or even broken away, a hole appears which results in the emergence of the fluid or gas. The construction size does not allow such instruments to be used at all in instances where only a little space is available. On the other hand, comparatively high read-off accuracy is possible as a result of the large dial. In the direct indicators according to U.S. Pat. No. 3,592,218, there is no step-up. 
   SUMMARY OF THE INVENTION 
   The object of the invention is to provide a pressure indicator device which allows an easily read-off optical indication of the pressure by the simplest possible mechanical means, is extremely robust in mechanical terms, has a highly compact construction and can easily be mounted on a vessel which is under pressure. 
   The essence of the invention is that the optical indicator means comprise a front glass arranged transversely to the axis and indicator elements which are movable in relation to the front glass by means of the piston and which in each case change in the event of different pressures between a first position, in which they are optically visible from outside through the front glass, and a second position, in which they are optically not visible from outside through the front glass. 
   A first preferred embodiment of the pressure indicator device according to the invention is characterized in that the optical indicator means comprise a plunger displaceable toward the underside, acting as a contact face, of a front glass by means of the piston, the front glass and plunger being designed in such a way that they are at a different distance from one another at different locations in a plane perpendicular to the axis. As a result, when the piston is displaced, an optically active contact between plunger and front glass is made at different locations, depending on the piston position, and causes the contact points to become visible through the, for example, matt front glass. If the contact points are in the form of characters, in particular digits or numerals, then, depending on the pressure on the piston, different characters (for example, bars or the like arranged in a radiating manner on a circular ring) thus become visible in succession. 
   A preferred development of this embodiment is distinguished in that the front glass has a plane contact face, and that raised characters of different height are formed on that surface of the plunger which is located opposite the contact face. The advantage of this is that a simple plane glass pane can be used as the front glass. Preferably, in this case, the plunger consists of an elastomeric material, in particular rubber. 
   It is also conceivable, however, that the plunger consists of a hard inelastic material, in particular of a plastic or a metal, and in that the interspace between the plunger and the front glass is filled with a displaceable contrast medium. 
   Another preferred development is distinguished in that that surface of the plunger which is located opposite the contact face is plain, and that raised characters of different heights are formed in the contact face of the front glass. 
   A second preferred embodiment of the pressure indicator device according to the invention is characterized in that the optical indicator means comprise a pointer spring engaged with the piston and having a plurality of pointers, in that the pointer spring is designed in such a way that, during the pressure-induced displacement of the piston in the axial direction and during the associated bending of the pointer spring, the pointers move transversely to the axis, in particular in the radial direction, and in that, on the front glass, optical masking means are provided, through which the pointers are visible or not visible through the front glass from outside, depending on the pressure. 
   In particular, the pointer spring is of disk-shaped design, the pointer spring being supported with its outer margin on a stop spring arranged above it and fastened to the housing and being acted upon in the central region by the piston, and the pointers extending upward in the axial direction, being bent transversely to the axial direction at the upper end and having pointer heads of different lengths in the bent region, and the masking means comprising a circular printed face which is arranged on the underside of the front glass and which optically masks the pointer heads when the pressure indicator device is in the pressureless state. 
   The pressure indicator device according to the invention can be used in a particularly versatile and simple way when it has the external configuration of a screw with a head part and with a threaded part, and when the optical indicator means are arranged in the head part and the piston is arranged in the threaded part. 
   In such a compact pressure indicator device, safety and capability during use under rough conditions can be further increased when a predetermined breaking point is provided between the head part and the threaded part in the housing, when the piston is sealed off below the predetermined breaking point by means of a seal, and when a pressure plate for distributing the piston pressure is arranged between the upper end of the piston and the plunger or the pointer spring. 
   Further embodiments may be gathered from the dependent claims. 

   
     DESCRIPTION OF THE DRAWINGS 
     The invention will be explained in more detail below with reference to exemplary embodiments, in conjunction with the drawing in which: 
       FIG. 1  shows a longitudinal section through a first preferred exemplary embodiment of a pressure indicator device according to the invention with an elastomeric plunger; 
       FIG. 2 . shows a longitudinal section through a second preferred exemplary embodiment of a pressure indicators device according to the invention: with a pointer spring; and 
       FIG. 3  shows a top plan view of the exemplary embodiment from  FIG. 2  in the case of low or absent pressure ( FIG. 3   a ; pointer heads are masked) and in the case of high pressure ( FIG. 3   b ; pointer heads emerge from behind the mask). 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The first exemplary embodiment, illustrated in  FIG. 1 , shows a pressure indicator device (pressure indicator)  10  which comprises a one-piece housing (monobloc)  18 . 
   The housing  18  has the external form of a screw with a screw axis  26  and with a head part (screw head)  28  and a threaded part  29 . The housing  18  has in the head part  28  corresponding key faces  15  on the outer circumference. In the low region of the housing  18 , the threaded part  29 , a screw-in thread  22  is arranged coaxially to the axis  26 , by means of which screw-in thread the pressure indicator device  10  can be screwed preferably into a cock attached to a compressed gas bottle. A piston  21  with a head plate  25  is guided in the direction of the axis  26  within the housing portion provided with the screw-in thread  22 . The head plate  25  faces the pressure side. A spring  20 , which is supported at the lower end on the head plate  25  and at the upper end on the housing  18 , acts counter to the piston  21 , which is under pressure, and determines the axial travel of the latter. 
   In order to prevent an emergence of gas between the piston  21  and housing  18 , an annular seal  19 , preferably in the form of an O-ring, is installed. The end of the screw-in part of the housing  18  receives a solid cover  23  with a small damping bore  24  which limits the gas throughflow. This form of construction prevents the situation where gas may emerge if the upper part of the pressure indicator  10 , which corresponds to the screw head, is damaged or even broken away. A predetermined breaking point  11  in the middle region of the housing  18  between the head part  28  and the threaded part  29  is intended, if the bottle falls down or the like, to make it easier for a break to occur at the correct point, without the threaded part having the screw-in thread  22  being torn out of the corresponding threaded bore of the cock. The piston  21  terminates level with the predetermined breaking point  11  and is therefore not put at risk in the event that the housing  18  breaks away at the predetermined breaking point  11 . 
   Located in the upper portion of the pressure indicator  10  is a pressure plate  16  which is acted upon by the piston  21  and which presses a plunger  14 , arranged above it, toward the underside, acting as a contact face  13 , of a matt front glass  12  which closes off the housing  18  upwardly. The plunger  14  consisting of an elastically deformable material, for example rubber, is fixed at a margin between the front glass  12  and the housing  18  and in the inner region carries arranged so as to be distributed on the top side, characters  27  formed with different heights. The matt front glass  12  prevents the characters (digits, letters or the like) of unequal height from being directly visible from above when the pressure indicator  10  is viewed on top. If, then, the piston  21  is pressed upward (outward) by the gas pressure, the pressure plate  16  is pushed, together with the plunger  14 , toward the matt side of the front glass  12 . Due to the contact of the preferably dark-colored rubber or rubber-like plunger with the bright matt surface of the front glass  12 , the highest of the characters  27  is the first to become visible from outside. The height gradations of the characters  27  on the plunger  14  correspond to the stroke which the piston  21  executes in the event of increasing pressure. When the compressed gas bottle is full, all the characters  27  are pressed against the matt front glass  12 . The characters are “extinguished” in series in the event of falling pressure, in a similar way to an LCD (Liquid Crystal Display) indicator. 
   For practical reasons, the indicator, that is to say the arrangement of the characters  27  on the top side of the plunger  14 , is configured in such a way that it does not appear in any position after being tightened firmly when being mounted on the head. In another embodiment (not illustrated in  FIG. 1 ), instead of the plunger  14  with the raised characters  27 , a flat plunger is installed. In the pressureless state, the plunger, remains back from the front glass and does not make any contact. In this embodiment, the front glass, injection-molded from plastic, carries the characters projecting inward. There is the possibility, here, of lettering on the inside of the front glass. The remaining functioning is identical to that of the first embodiment. 
   A further embodiment is distinguished in that the space between the smooth front glass  12  and the plunger  14  is filled with a contrast medium. The plunger  14  or a comparable indicator means therefore no longer has to be soft and elastic. They can be manufactured from harder plastic or from metal. In the pressureless state, the plunger  14  is not visible on account of the contrast medium. When it is pressed against the front glass  12  by the pressure in the bottle, the interposed contrast medium is displaced, and the contour of the character  27  on the plunger  14  becomes visible. 
   In this respect, however, even an indication which is as it were continuous is possible: If, for example, an elastomeric plunger  14  is used, which does not carry any special characters  27 , but is designed upwardly in conical form or in the form of a spherical cap, the plunger is pressed to a greater or lesser extent onto the matt front glass  12 , depending on the pressure, and is thus compressed. The indication which appears is a filled-out circle with a greater or lesser diameter, the diameter changing continuously with the pressure. It goes without saying that, in this refinement, scale circles corresponding to a specific pressure value may be formed on the front glass  12 . 
     FIG. 2  illustrates in longitudinal section a second preferred exemplary embodiment of the invention. The pressure indicator device  10 ′ of.  FIG. 2  is identical in most parts to the example of  FIG. 1 , and therefore the same reference symbols are used for these parts. Instead of the plunger  14  from  FIG. 1 , a special pointer spring  32  is installed here. The (disk-shaped) pointer spring  32  sits on a pressure plate  16   b  and engages with its outer margin behind a stop ring  30  fastened to the housing  18 . Said pointer spring carries, on its circumference, a number of pointers  34  which extend upward and are bent at the upper end and which have pointer heads  33  of unequal length which have a high contrast with respect to an (opaque) printed face  31  on the underside of the front glass  12 . In a state free of pressure, the pointer spring  32  is in the position of rest. All the pointer heads  33  are located behind the round printed face  31  on the front glass, that is to say are masked by this face and are therefore not visible ( FIG. 3   a ). 
   When the bottle is full, the pressure plate  16   b  is pressed forward (upward) to the greatest possible extent. As a result, the pointer spring  32  bends in the region between the pressure plate  16   b  and the stop ring  30 . The result of this is that all the pointers  34  and consequently all the pointer heads  33  move outward and, according to their length, emerge successively behind the printed face  31  and thereby become visible ( FIG. 3   b ). If the pressure in the bottle falls, the pressure plate  16   b  moves away from the front glass  12 . The bent region between the pressure plate  16   b  and the stop ring  30  can thereby bend back a little. The result of this is that the pointer  34  with the shortest pointer head  33  is the first to disappear under the printed face  31  of the front glass  12 . The number of remaining pointer heads gives information as to the filling state of the bottle. In the printing of the front glass  12 , a labeling can be inserted in a simple way, which can give further information as to the gas in the bottle. 
   Manufacturer&#39;s imprints may also be made. In a pressure indicator of this construction type, it is possible to ensure an even finer subdivision of the indicator. Moreover, maximum indication contrast is possible. The example according to  FIG. 2  is therefore distinguished by the following features:
         The correct design of the pointer spring  32  achieves a step-up which results in a large deflection of the pointer head  33 , without further parts being necessary.   A change in the step-up, is achieved in a simple way by the diameter of the pressure plate  16   b  being varied.       

   Overall, in instances where no particular accuracy is demanded, the invention affords a novel and particularly advantageous possibility for pressure indication: the pressure indicator according to the invention is in the manner of a screw. It consequently becomes possible to indicate the pressure of a gas bottle constantly. The pressure indicator is screwed directly into an additional bore laterally on the cock. The hard-wearing capacity of the indicator far exceeds all manometers known hitherto, even that of the cock into which it is screwed. Even the failure or breaking away of the above mentioned part does not cause any accident or any leak. At the same time, the size is dimensioned (with a length of, for example, 20 mm and with a maximum diameter of, for example, 19.5 mm, this corresponding to a screw head with the key width of 17 mm) such that a protective cap, which, according to regulations, protects the cock, can continue to be used. In bottles with valves which do not have to be protected by protective caps for transport purposes, an even greater advantage is afforded in that the pressure in the bottle is visible at a glance without manipulations. Logistical problems are consequently solved. The construction is very simple, so that, while the high degree of safety remains unchanged, costs can be saved. 
   Since no step-up or other awkward parts are required, the pressure indicator  10  according to the invention is very hard-wearing. The installation of the piston  21  with a head plate  25  prevents a damaged or broken-away upper part from causing leaks and accidents. The use of a plunger  14  with “lettering” of unequal height or of a pointer spring  32  with pointer heads  33  of different lengths leads to a very simple monobloc housing ( 18 ) which at both ends receives a “cover” (cover  23  and front glass  12 ) which is rolled in or crimped in. For protection in the event of a leak of the seal  19 , the pressure indicator is provided with a pressure equalizing or safety bore  17 . The front glass  12  is thus protected from excess pressure. 
   LIST OF REFERENCE SYMBOLS 
   
       
         10 ,  10 ′ Pressure indicator device (pressure indicator) 
         11  Predetermined breaking point 
         12  Front glass 
         13  Contact face 
         14  Plunger 
         15  Key face 
         16 ,  16   b  Pressure plate 
         17  Pressure equalizing bore 
         18  Housing (one-piece) 
         19  Seal 
         20  Spring 
         21  Piston 
         22  Screw-in thread 
         23  Cover 
         24  Damping bore 
         25  Head plate 
         26  Axis 
         27  Character (digits, letters, etc.) 
         28  Head part 
         29  Threaded part 
         30  Stop ring 
         31  Printed face 
         32  Pointer spring 
         33  Pointer head 
         34  Pointer