Abstract:
A hydraulic cylinder comprises a piston reciprocally mounted in a housing thereof. A pair of annular sealing means, slidably receiving a rod of the piston, are disposed on either side of an annular chamber which has pressurized fluid pumped therethrough for flushing purposes.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part Application of U.S. Pat. Application Ser. No. 431,328, filed on Jan. 7, 1974, now abandoned, by Lawrence F. Schexnayder, entitled HYDRAULIC CYLINDER ROD SEALING AND FLUSHING ARRANGEMENT, of common assignment herewith. 
    
    
     BACKGROUND OF THE INVENTION 
     Conventional hydraulic cylinders of the type used for actuating earthworking implements normally seal the rod end of the cylinder by means of a plurality of static seals. The seals perform a dual function; namely, to prevent egress of hydraulic fluid from the cylinder&#39;s working chamber and to prevent ingress of contaminants into the cylinder. U.S Pat. Nos. 3,540,741 and 3,578,341, for example, exemplify such prior art sealing structures. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide an economical and compact flushing arrangement for a hydraulic cylinder to prevent the leakage of hydraulic fluid therefrom and to prevent contamination of such fluid. The cylinder comprises inboard and outboard annular sealing means mounted on a housing of the cylinder to slidably receive the rod of a piston, reciprocally mounted in the housing. The flushing arrangement comprises an annular chamber formed in the housing and disposed axially between the inboard and outboard sealing means. A pressurized fluid source, including a pump, continuously circulates fluid through the chamber, by suitably arranged conduits, to continuously flush-out working fluid which may leak past the inboard sealing means and to further flush-out contaminants which may pass by the outboard sealing means and into the chamber. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing schematically illustrates a hydraulic circuit including a hydraulic cylinder, in cross section, and a flushing arrangement therefor. 
    
    
     DETAILED DESCRIPTION 
     Referring to the drawing, the illustrated hydraulic circuit comprises a double-acting cylinder 10 having a housing 11 and a piston 12 reciprocally mounted therein. A rod 13 of the piston is slidably received in sealing contact by inboard and outboard annular sealing means 14 and 15, respectively. The rod may be operatively connected to a work implement, such as one of those employed on a heavy-duty earthworking machine. 
     The inboard sealing means comprises a buffer seal 16, having a rectangular cross section, and a first radial lip seal 17. The buffer seal functions to protect seal 17 against high fluid pressures. The outboard sealing means comprises a second radial lip seal 18, similar to seal 17 and also facing axially towards seal 16, and a third radial lip seal 19 having its outer case attached to the housing and facing axially away from seal 18. The radial lip seals 17, 18, 19 may be constructed in accordance with U.S. Pat. No. 3,167,323 to Appleton et al, assigned to Disogrin Industries. The seals must be capable of lateral flexure while maintaining efficient sealing characteristics because they are utilized in cooperation with the rod 13 of the reciprocating piston 12 which rod tends to urge the seal elements from side to side during reciprocation. Seals intended for use in sealing rotary elements would not be effective in the present environment. 
     The hydraulic circuit further comprises a pressurized fluid source, including an engine driven first pump 20 adapted to selectively pump highly pressurized hydraulic fluid from a reservoir 21 to the cylinder. In particular, working chambers 22 and 23, located at the head and rod ends of the cylinder, respectively, may be alternately pressurized and exhausted via conduits 24 and 25 under the control of a three-positioned directional control valve 26. A conventional pilot operated relief valve 27 is also incorporated into the circuit to maintain circuit pressures at the desired level. 
     The hereinafter described flushing arrangement for the cylinder is adapted to return any fluid which may leak past inboard sealing means 14 to reservoir 21 and to also flush-out contaminants which may pass by outboard sealing means 15. Such arrangement comprises a second engine driven pump 28 which is adapted to continuously pump low pressure fluid through a conduit 29 and into an annular chamber 30, formed in housing 11. The chamber is disposed axially between the inboard and outboard sealing means and has its outlet connected to a conduit 31 which returns the circulating low pressure fluid through a filter 32 and back to reservoir 21. If so desired, one or more additional cylinders 10&#39;, identical to cylinder 10, may be integrated into the fluid circuit to take advantage of the flushing arrangement above described. Also, a cylinder 10&#34; could be added to the circuit in parallel as indicated by phantom lines in the drawing.