Automatic shuttle valve
BACKGROUND OF THE INVENTION 
     The invention concerns an automatic shuttle valve with a piston that slides back and forth in a bore that extends through a housing, distributing hydraulic fluid from a driving mechanism among at least two driven mechanisms in accordance with how much power each is demanding. 
     Manually activated shuttle valves for distributing hydraulic fluid are known. Published German Application 1 903 792 discloses an automatic shuttle valve for regulating liquid levels in motor vehicles. Two spring loaded seats are connected by a rocker and respond to different demands for power. The seat that does not demand power keeps the hydraulic circulation system from the driving mechanism to the driven mechanism closed until the same power consumption ratio is again attained in both driven mechanisms. The valve has several precision parts, two pistons, an adjustable rocker, and springs, that must be produced separately, making it expensive to manufacture the valve and necessary to keep a wide range of parts in stock. 
     The applicant is presently distributing metal, or the like material, plate and strip tearing and prying type rescue equipment under the trademark &#34;Lukas&#34;. This rescue equipment may be employed to extract passengers from a wrecked vehicle with jammed doors. One driven mechanism makes an incision in the plate material of the body of the wrecked vehicle. If the incision is not wide enough to remove the victims from the vehicle, another driven mechanism expands the opening. There is often not enough time in an emergency situation to uncouple the incision cutter from the driving mechanism and to attach the expander. It would accordingly be desirable to have both tools mounted and ready at the same time. To operate both mechanisms alternately or simultaneously off the same driving mechanism, however, has always required manual switching from the driving mechanism. 
     OBJECT OF THE INVENTION 
     The object of the present invention is accordingly to simplify an automatic shuttle valve to the extent that it will be less expensive to manufacture and that fewer parts will need to be kept in stock. 
     This object is attained with the invention wherein a rounded cross section conically shaped block at each end of the shiftable piston can engage a correspondingly profiled seat in a high pressure fitting and seal off the respective end of the bore. The piston also has a central position at which both fittings are not sealed. Because the driving mechanism communicates with the driven mechanisms through hydraulic fluid-conveyance branches, this ensures that any driven mechanism that is being operated will be supplied with power and that any driven mechanism that is not being operated will be deprived of power due to one or more of the seats respectively opening or closing. 
     With the automatic shuttle valve of the invention, whatever driven mechanism is in operation will be activated and the requisite hydraulic power will be accordingly supplied. The driven mechanism that is not being employed will be automatically deprived of hydraulic power by the piston. 
     The branches may accommodate throttles of a known design that regulate the flow and eliminate surges. 
     Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The two drawings are sections through an automatic shuttle valve in accordance with the invention. FIG. 1 shows the valve at rest, while FIG. 2 shows the valve with one driven mechanism in operation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A driving mechanism 9 supplies power to two driven mechanisms 7 and 8 in accordance with how much each driven mechanism demands in a way that will now be described. 
     Each driven mechanism 7 and 8 is activated by a respective manual diversion valve 7a and 8a. Driving mechanism 9 obtains hydraulic fluid from a reservoir 13 and supplies it under pressure to one or both of the hydraulic fluid delivery branch conduits 10a and 10b, which deliver the fluid to the opposite ends of an automatic shuttle valve that distributes the fluid through respective manually operable valves 7a and 8a, to either of the driven mechanisms 7 and 8 or directly back to reservoir 13, depending upon the state of the manual valves. 
     The automatic shuttle valve has a housing 1 and a piston 3 that slides back and forth in a bore 2 extending through the housing 1. A circular cross section, conical end part block 4a and 4b at each end of the piston 3 can engage a respective seat 5c and 6c in a respective fitting 5 and 6 and block off communication between that fitting and the associated hydraulic fluid conduit 10a and 10b leading from the common driving mechanism 9. The conduits 10a and 10b meet the bore 3 inward of the respective seats 5c and 6c. The fittings 5 and 6 are inserted in respective ends of the otherwise open ended bore. Each fitting 5 and 6 opens into a respective hydraulic fluid line that leads to one of the driven mechanisms. Specifically, block 4a can engage seat 5c in fitting 5. The seat 5c is shaped, sized and inclined to the cone angle of the block 4a. Their engagement blocks off communication of the fitting 5 with the branch conduit 10a and with the driven mechanism fluid conduit to the respective driven mechanism 7 or 8. Similarly, block 4b can engage seat 6c in fitting 6, blocking off communication of the fitting 6 with the branch conduit 10b and with the driven mechanism fluid conduit to the respective driven mechanism 7 or 8. 
     When neither driven mechanism 7 and 8 is in operation, the manual valves 7a and 8a that activate the mechanisms are in direct communication with the fluid reservoir 13, and fluid flows from the driving mechanism to the automatic shuttle valve, which distributes fluid equally through each manual valve to the reservoir 13. 
     When only one driven mechanism, mechanism 7 for example, is to be operated, its manual valve 7a is thrown to an operating position, and this diverts fluid into the mechanism 7. The fluid forces the piston 3 to the left and into the position illustrated in FIG. 2, with block 4b depriving the driven mechanism 8 of fluid and hence of power, but ensuring a full supply of both the fluid and the power to the driven mechanism 7 from the hydraulic power generator 9. 
     When both mechanisms 7 and 8 are to be employed, both manual valves are thrown to an operating position, and the piston 3 remains at the neutral mid position illustrated in FIG. 1, with fluid distributed equally to both of the driven mechanisms 7 and 8. 
     To stabilize the switching function and to suppress any surge occasioned in the hydraulic fluid by driving mechanism 9, known throttles 11 and 12 can be accommodated in the branches 10a and 10b, respectively. 
     Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.