Abstract:
A filtering device, especially a suction return filter includes a filter housing having two useful connections and a tank connection, and accommodates at least one filter element. The filter housing also provided with three return valves, two of which are held in the closing position by spring loads. All of the return valves are combined as a module at one end of the filter housing. The remaining return valve is configured as an integral constituent part of one of the spring-loaded return valves, has an opposite opening direction relative to it, and is not spring loaded. This arrangement enables the return valve unit to have a compact arrangement which can be structurally easily connected to the filter housing at a central point.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a filtering device, especially a suction return filter, having a filter housing which includes two utility connections and a tank connection. The filter housing serves as a holder of at least one filter element, and is provided with three non-return valves. Two of the non-return valves are maintained in closed settings under spring bias. 
     BACKGROUND OF THE INVENTION 
     In known filtering devices that are presently commercially available, the return valves are mounted at different points on the filter housing, and consequently, take up considerable structural space thereon. Futhermore, this arrangement increases the outlay for construction of the filtering device and raises its overall cost. Known solutions provide that primary filtered fluid can be fed to the user connected by a utility connection. The known suction return filters are provided primarily for use in the tank connection for an oil container. The filter housing and the utility and tank connections are designed such that they can withstand pressure peaks without damage. Use of a return valve guarantees that when a pressure peak occurs in the tank connection, and consequently in the tank or oil container, the resulting peak can be deconstructed by discharge in the direction of at least one of the utility connections. 
     DE 195 16 657 A1 discloses a filtering device for a telescopic-hydraulic cylinder of simple operation for raising and lowering a load surface or a loading platform or the like in or on trucks. One spring-loaded return valve is arranged in a bypass line to the filter element, while another spring-loaded return valve is connected to the rear of the bypass branch and the filter element. These spring-loaded return valves, together in one modular unit, facilitate the driving of the hydraulic cylinder with unfiltered fluid passing through the bypass. With the lowering or displacement of the hydraulic cylinder, the fluid moving in the direction of a collection container is filtered by the filter element, whereby the return valve in the bypass line is closed. Another, not spring-loaded return valve between a hydraulic pump and a valve arrangement for the control of the filter element protects against overload of the hydraulic pump in the case of an undesired reversal of the flow of the fluid. In another embodiment, a comparable arrangement includes a spring-loaded return valve in the bypass and two return valves having no spring load, one of them in another bypass line and one of them in the direct feed to the filtering element. The return valves, fitted within the filtering device as independent modular parts, likewise take up considerable structural space. With disruptions of the operation, exchange of the return valve is possible only with great difficulty. 
     A filtering device disclosed in DE 195 15 962 A1 serves in supplying a hydraulic user with hydraulic liquid. The associated hydraulic connection includes a tank connection for a supply tank, a hydraulic pump for making available the hydraulic liquid and a return filter, through which the hydraulic liquid flowing back from the hydraulic user is filtered. The leading edge of the return filter is connected through a line with the tank for the hydraulic liquid. A non-parallel connection includes a pressure limiting valve and a retrofitted suction valve and ends beneath the hydraulic liquid level of the supply tank. These two valves are spring-loaded return valves, the same as another spring-loaded return valve arranged between tank and filter element. The three spring-loaded return valves, as independent structural parts, form no interdependent modular unit, hut rather produce a hydraulic emergency supply for the user. The spring-loaded return valves in this case are mounted at different points and separated from one another on a part of the filtering device. This solution also embodies a large construction. Since the return valves are to be controlled hydraulically at different points, disruptions of the operation during operation of the device cannot be totally excluded. 
     SUMMARY OF THE INVENTION 
     Objects of the present invention are to provide an improved filtering device which is of low-cost construction and remains operationally reliable during operation. 
     According to the present invention, all of the return valves are arranged together as one modular unit at one end of the filter housing. The return valve opens in a direction counter to this and is in the form of an integral component part of one of the spring-loaded return valves. A compact arrangement of the entire return valve unit is possible and can be mounted in a constructively simple manner at a central point on the filter housing. This arrangement also simplifies the exchange of the modular unit for another modular unit, when an unexpected breakdown of any one of the return valves occurs. 
     Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
     FIG. 1 is a side elevational view in section of a filtering device according to an embodiment of the present invention; 
     FIG. 1 a  is a partial side elevational view in section of the modular unit including the three return valves of the filtering device of FIG. 1; 
     FIG. 2 is an end view of the top end of the filtering device of FIG. 1; and 
     FIG. 3 is a hydraulic circuit diagram of the filtering device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The filtering device illustrated in the drawings relates to a suction return filter  10  having a filter housing  12  incorporating two utility connections A, B and one tank connection T. As shown in FIGS. 1 and 2, tank connection T is arranged at one end of filter housing  12 . Utility connections A, B are on the opposite side, with utility connection B, as opposed to utility connection A as seen in longitudinal direction, offset from connection A around a radial angle of 90 degrees. Filter housing  12  envelops at least one filter element  14 . The filtering mat  16  is laid out against a support pipe  18  arranged in the interior of filter element  14 . Filter element  14  is guided at its free ends into end caps  20 , which produce the connection of filter element  14  with filter housing  12  and create a sealed connection. 
     Suction return filter  10  also incorporates three return valves V 1 , V 2  and V 3 . Return valves V 1  and V 2  are spring-loaded or spring-biased. The third return valve V 3 , as shown particularly in FIGS. 1 and 3, is not spring-loaded or spring-biased. As shown particularly in FIG. 1, all of the aforementioned return valves V 1 , V 2  and V 3  are combined in one modular unit  22  and are arranged on the free end opposite the top part of filtering housing  12 . Return valve V 3 , free of spring load, is embodied as an integral component part of the spring-loaded return valve V 1 , with a direction of opening counter to that of valve V 1 . 
     Return valves V 1 , V 2  and V 3  are connected together all carrying fluid to tank connection T. Spring-loaded return valves V 1  and V 2  can be displaced in the direction of tank connection T to their open settings, as is shown in FIG.  3 . Also shown in FIG. 3, return valves V 1 , V 2  and V 3  are connected in parallel relative to one another between tank connection T and utility connections A, B. In a first connection line  24  between the two spring-loaded return valves V 1 , V 2 , filter element  14  is connected. In another connection line  26  opening into the first connection line  24  between the two spring-loaded return valves V 1 , V 2  and leading to utility connection B, another filter element  28  is arranged. Filter element  28  is preferably a mechanical filter in the form of a protecting screen or mesh. With normal operation of the filtering device, utility connection A represents the fluid-guiding input to filter element  14  where fluid flows from the exterior inward for the main filtration of the fluid. Downstream of filter element  14 , the resulting uncontaminated fluid from the interior to the exterior flows to the other filter element  28  configured in the form of a protecting screen or the like. The fluid is then discharged through utility connection B. The utility connections A, B can be embodied in a plurality of different designs. Particularly, discharge B can be configured of two utility connections, as shown in FIG.  2 . 
     As shown particularly in FIG. 1, modular unit  22  embodies a housing part  30  including return valves V 1 , V 2  and V 3  therein. Housing part  30  can be connected through a jointed flange connection  32  with filter housing  12 . The resulting enclosure formed by the jointed flange connection over corresponding sealing devices, such as sealing rings, is to be fluid-tight. The spring force of spring-loaded return valve V 1 , combined with return valve V 3  having no spring load, is lower than the spring force of the other spring-loaded return valve V 2 , so that return valve V 1  is pressure-controlled and includes cyclically filtering filter elements  24 ,  28 . In any case, spring-loaded return valve V 1  opens before the spring-loaded return valve V 2 . Return valve V 3  with no spring bias is located in closing part  34  of the associated spring-loaded return valve V 1 , is guided by means of a longitudinal guide  36 , and can be controlled by means of the corresponding fluid pressure applied in the direction of its opening. 
     A screw bolt is provided as longitudinal guide  36 , which is securely connected with the closing plate  38  of return valve V 3 . In longitudinal displacement, guide  36  engages through a middle opening in closing part  34  of return valve V 1 . Closing part  34  of return valve V 1  is likewise configured as a plate and is supported in its closed setting as indicated on corresponding interior walls of housing part  30 . In this case, the associated compression spring of return valve V 1  presses closing part  34 , in the direction of the drawing away from tank connection T and into the left end setting. Closing plate  38  of return valve V 3  having no spring bias is supported in its closed setting, as shown in the drawings, both on closing part  34  and on the associated housing walls of housing part  30 . 
     If the pressure in tank connection T rises, for example as a result of a pressure peak or the like in the tank, valve V 3  opens counter to the fluid pressure in the interior of filter element  14 . Valve V 3  thereby frees the passage between tank connection T and utility connection B. If the pressure in the interior of filter element  14  is higher than the pressure in tank connection T, which is the general rule, valve V 3  remains in its closed position. A predeterminable threshold value for valve V 3  is dependent upon the closing force of spring-loaded return valve V 1 . The valve combination V 1  and V 3  opens, when the interior pressure in filtering element  14  is greater than the spring force of valve V 1  in connection with the natural residual pressure in tank connection T, which pressure customarily corresponds to normal environmental or ambient conditions. Closing part  34  and closing plate  38  are then both displaced to the right in the direction of viewing of FIGS. 1 and 1 a , insofar as closing plate  38  is not to be supported on the stationary wall parts of housing part  30 . If however such a support is provided, as shown in the drawings, closing plate  38  remains in its closed contact position with housing part  30 . Also, a fluid connection is then provided between closing part  34  and the interior chamber of filter element  14 . Under that interior pressure, only closing part  34  can be moved to the right in the direction of the drawings into an open setting. 
     Housing part  30  engages with a fluid-permeable flange  40  in one end of filter element  14 . This engagement forms a position-fixing arrangement for one end of filter element  14 . 
     For better understanding of the present invention, the filtering device is explained in greater detail hereinafter relative to its principle function, as shown in FIG.  3 . The contaminated fluid entering through input connection A is very finely filtered through filtering element  14 , and is conducted thereafter through the coarse protecting screen  28  to utility connection B. The resulting arrangement can be used for the drive of building machinery, hydrostatic power drives or the like. A contamination level indicator VA monitors the level of contamination in filter element  14 . If filter element  14 , for example, becomes obstructed by an excessive degree of contamination, the rising pressure in utility connection A can be carried away into the tank without harm. Such pressure is eliminated or relieved through return valve V 2  designed to be reinforced in the manner of a spring arrangement. Return valves V 1 , V 3  in such a case remain in their closed position. 
     If pressure peaks occur in utility connection B in a direction counter thereto, in other words in the direction of utility connection A, spring-loaded return valve V 1  can open in the direction of the tank. If pressure peaks arise in tank connection T, return valves V 1  and V 2  remain in their closed position, whereupon valve V 3  opens in the direction of utility connection B. Thus, flowing but contaminated fluid is displaced from tank connection T into the device, but is at least coarsely cleaned by filtering through the alternate filter element  28 . The flowthrough direction from A to B can be reversed, in other words from B to A, insofar as filter element  14  is of a construction suitable for this purpose, for example of a constructive design wherein the filtering device would be provided with an exterior support pipe. 
     The modular unit including return valves V 1 , V 2  and V 3  according to FIG. 3 provides a compact, versatile, multi-use operational unit. Upon breakdown, it can be easily exchanged for a replacement modular unit. The compact unit is of simple construction and can be produced at low cost and by simple manufacturing technology. 
     While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.