Abstract:
Governor valve device for a pressure fluid operated tool having a ball valve ( 23, 24 ), the valve ball ( 24 ) of which is provided in a cavity ( 25 ), open towards the seal ring ( 23 ) of the valve, in a movable piston ( 26 ). A spring-loaded member ( 30 ) urges the valve ball against the seal ring. By movement of the piston, the ball can be moved out of and into, respectively, a sealing position against the seal ring in order to permit and to prevent, respectively, the passage of pressure fluid to a drive chamber ( 17 ) in the tool.

Description:
SUMMARY OF THE INVENTION 
     The present invention relates to a governor valve. It is known, in pressure fluid operated tools, to arrange, in different ways, a governor comprising a piston which is movable in two opposed directions to open and to close, respectively, a supply channel for pressure fluid which leads to a drive chamber and a drive mechanism arranged in the tool. 
     The present invention aims at arranging, particularly in smaller, long and narrow pressure fluid operated tools, such as a pressure fluid operated engraving pen, a governor valve having a movable piston extending transversally through the housing of the tool and having the advantages that, for one thin, it can be located easily accessible for the fingers of the operator during operation of the tool, and for another thing, that it protrudes only slightly from the tool housing through which it extends and will therefore not be unwieldy and spoil the appearance of the tool. As the piston is only required to perform small movements, it is possible to use the device in accordance with the invention also in narrow tools—such as, for example, an engraving pen—the housings of which have a small thickness of the walls through which the piston extends and therefore have little room for movements of seal rings fitted on the piston without these rings coming outside the walls. These advantages have been obtained with the device in accordance with the present invention. 
     The governor valve device in accordance with the invention is described in closer detail below, with reference to the attached drawing, which shows a pressure fluid operated engraving pen provided with said device. The device can also be used in other types of pressure fluid operated tools and devices and be varied in its design within the scope of the Claims; the illustrated embodiment of the invention constituting, therefore, only an example of one of several possible applications of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 of the drawing shows a side elevation of the engraving pen. 
     FIGS. 2 and 3 show, on an enlarged scale, a piston forming part of the governor valve device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the drawing, the numeral  1  denotes the pen body or housing as a whole,  2  is its front part,  3  a middle part screwed together with the front part, and  4  a rear part screwed together with the middle part. A hose  5  for the supply of compressed air is inserted into the rear part and is rotatably retained in same with the help of a nipple  6  and a sleeve  7 . Seal rings  8 ,  9  and  10  are provided to seal between nipple and rear part, between rear part and middle part and between middle part and front part. The seals  9  and  10  are thereby also forming a practical friction locking of the thread joints, these therefore not having to be drawn tightly but being conveniently tightened and loosened only with the fingers. 
     The front part  2  of the housing is fitted with a bushing  11 . In the bushing and the front part, holes  12 ,  13  are provided for exhaust air. Through the brushing and the front part an engraving needle  14  is passed which at its rear end is provided with a drive plate  15 . Between the drive plate and the bushing, a compression spring  16  is provided which urges the drive plate and a seal ring  35  fitted inside a flange of the drive plate towards the bottom of a drive chamber  17  provided in the middle part  3  of the housing. A portion of the peripheral walls of the chamber is provided with slots  18 . 
     A supply channel for air from the hose  5  to the drive chamber  17  is formed by a bore  19  in the nipple  6  and a bore  20  with narrowing portions  21 ,  22  in the middle part of the housing. In the channel portion  21  a seal ring  23  is provided. Against the seal ring a valve ball  24  rests which is provided in a cavity  25  in a piston  26  extending transversally through the pen housing and being sealed against the housing with the help of seal rings  27 ,  28 . The cavity  25  has, on one side of the piston, an opening which faces the seal ring  23 . In the opposite side of the piston, a slot  29  is made which communicates with the cavity. Through the slot a pin  30  is inserted which via thicker portion  31  and a spring  32  exerts pressure against the valve ball  24 . 
     The cavity  25  in the piston  26  is deep enough to make room for the whole valve ball  24  inside the piston. With the ball placed in the cavity, the piston is inserted into the middle part  3  of the housing and is turned so that the opening of the cavity faces the seal ring  23  and the slot  29  faces in the opposite direction. With the rear part  4  of the housing unscrewed from the middle part, the member  31  is inserted into the middle part so that the pin  30  passes through the slot  29 , whereupon the spring  32  is also inserted and the rear part  4  with its hose  5 , nipple  6 , sleeve  7  and seal ring  8  fitted in it is screwed to the middle part. 
     In the position shown from FIG. 1, the pin  30  keeps the valve ball  24  in a sealing position against the seal ring  23 . By engaging end surfaces  40 ,  41  of the slot  29  the pin also limits the movements of the piston  26 . According to FIG. 1, the piston is in a closing position, its lower end surface  34  in the figure being maximally pushed towards one side  37  of the middle part  3  and its opposite end surfaces  33  protruding a couple of millimetres outside the opposite side  36  of the middle part. If the piston is now pushed down, so that its upper end surface  33  is no longer protruding outside the surface of the middle part, a limiting wall  38  of the cavity  25  pushes the valve ball a short distance away from its sealing position against the seal ring  23 . The member  31  is provided with slots or the like, not shown, for the passage of pressure fluid which will now flow past the valve ball and into the drive chamber  17 . The length of the movement of the piston  26  is limited by the pin  30  acting as a stop against an upper end surface  40  of the slot  29 . 
     When pressure fluid flows into the drive chamber  17 , the drive plate  15  and the needle  14  move forward a short distance, compressing the spring  16 . The seal ring  35  keeps the drive chamber sealed until the slots  18  are reached, whereupon the pressure drops quickly and the spring  16  returns the drive plate to the sealing position. This cycle of forward movement and return movement is repeated until the supply of pressure fluid is stopped by the piston  26  being returned to the position shown from FIG.  1 . The frequency of the exemplified engraving pen is around 500-600 strokes per second. 
     As described in the foregoing, the pin  30  and the slot  29  limit the movements of the piston  26  and secure the piston against being pushed out in its entirety from the middle housing part  3 . Therefore, no space requiring heads are required at the ends of the piston to keep it in place, and the movements which are required for the opening and closing of the ball valve  23 ,  24  are small. The piston can therefore be made so that it protrudes only a couple of millimetres from the housing part  3 , which provides for an attractive appearance. The short movements mean that the wall thickness of the housing part will be sufficient for the movements of the seal rings  27 ,  28  of the piston even in the case of small and narrow tools such as, for example, the exemplified engraving pen. The pen is in FIG. 1 shown on an enlarged scale and has a diameter of only 17 mm where the piston is passed through it. 
     The pin  30  is suitably made with a thickness which is close to the width of the slot  29 . In addition to limiting the movements of the piston  26  axially, the two members therefore also cooperate to prevent turning of the piston. Therefore, the opening  25  of the piston always faces the seal ring  23 , so that the valve ball is held in the correct position against the ring. 
     The piston  26  can be located close to the drive chamber  17 , in the front portion of the tool, conveniently accessible for being operated with a finger. The cavity  25  should suitably have a diameter which is approx. 1 mm larger than the diameter of the valve ball  24 . When the piston is returned to the position which closes the ball valve, a limiting wall  39  of the cavity will move the ball to a position in which, being acted on by the pin  30  and the flowing pressure fluid, it will snap into a sealing position against the seal ring  23 , thereby moving a short distance away from contact with the limiting wall, the movement of which is stopped just before reaching the sealing position of the ball. Therefore, no extremely narrow tolerance is required for the end positions of the piston movements, but the play between the ball and the walls of the cavity ensures that there will be no interference from the walls with the correct sealing position of the ball. 
     In the embodiment of the invention shown, the piston  26  has equally large pressure absorbing surfaces at both its ends, and its two seal rings  27 ,  28  are of the same size. The pressure fluid therefore exerts the same amount of force in both axial directions of the piston  26  and is thus not striving to displace the piston axially. If the spring  32  is made relatively weak, the piston  26  will therefore remain in position when its end  33  has been pushed down, and has to be returned by the exertion of pressure against its opposite end. 
     It is also possible to use a strong spring  32  which exerts such a strong pressure against he valve ball  24 , and via the latter against the limiting wall  38  of the cavity  25 , that the piston  26  is returned as soon as an operator is no longer with his finger keeping it in its pushed-down position. Which of these alternatives is the most suitable is determined by the type of tool and application. As an alternative to arranging an automatic return of the piston  26  with the help of a strong spring  32 , it is possible to obtain the same effect by slightly reducing the sealing diameter between the piston and the housing part  3  at the end portion of the piston which is fitted with the seal ring  28 . This results in a smaller amount of pressure from the pressure medium against the seal ring  28  than against the seal ring  27 . 
     As an alternative to making the pin  30  form part of a member  31  acted on by a separate spring  32 , it would be possible to shape one end portion of the spring as a pin protruding in the same manner. The design of the mentioned members can also be varied in other ways.