Hydraulic piston and cylinder arrangement in which the outer wall of the piston rod is free from fluid

A hydraulic piston and cylinder arrangement comprising a cylinder having an outer wall defining a bore therein, an end plug fixed to said outer wall at one end thereof, a stem fixed relative to said end plug and extending along the bore centrally thereto and providing a bearing surface externally of the stem and coaxial to said bore, a piston comprising a sleeve having an inner and outer surface such that the inner surface coaxially surrounds said bearing surface and is spaced therefrom by a first gap so as to define therewith a first annular chamber and such that the outer surface lies coaxially inwardly of said bore and is spaced thereform by a second gap so as to define therewith a second annular chamber, an end closing member on said sleeve and a bearing member including a seal carried by and extending from said sleeve to cooperate with said bearing surface whereby to bridge said first gap and support the sleeve in axial sliding movement relative to said bearing surface, head means on an end of the stem remote from the end plug having a seal there around for cooperating with said inner surface to close said first chamber and to define with said end closing member a third chamber, closure means on an end of said outer wall remote from said end plug defining a seal there around for cooperating with said outer surface, said stem comprising a first tube having one end mounted in said end plug and carrying said head means on an opposed end thereof, a second tube mounted inside the first tube, the second tube extending from an outer surface of the end plug so as to define first channel means in said stem for communicating fluid to and from the end thereof remote from the end plug so as to communicate fluid only to said third chamber and second channel means defined in an annular space between said first tube and said second tube including an annular cavity in said end plug surrounding said second tube and closed by an end plate on said end plug, and including at least one radial hole in said first tube at said opposed end for communicating fluid only to and from said first chamber at a position therein adjacent said head means whereby the application of fluid under pressure to said first channel means causes an expansion stroke of said piston relative to said cylinder and the application of fluid under pressure to said second channel means causes a retraction stroke of said piston relative to said cylinder, said bearing member having an inner cylindrical surface surrounding and closely adjacent the bearing surface of the stem and an annular recess surrounding the stem in an end surface of the bearing member closing said first annular chamber, said annular recess defining a recess cylindrical surface at a position of increased radial spacing from said stem than said inner cylindrical surface and a base surface spaced axially of said end surface of the bearing member, said first and second channel means, said end plug, said bearing member and said stem being arranged such that said second annular chamber is free from fliud whereby said outer surface of said piston sleeve remains free from said fluid.