a hydraulic telescoping ram of the type suitable to tip dump trucks and the like , which permits the use of outer aggressive seals and a bore sealing device by providing a conduit which hydraulically connects the upper end of each cylinder of the telescopic ram with an oil reservoir . this makes it possible to use seals which are not aggressive and which can run on surfaces of somewhat less than top quality , on the internal bottom faces of the rams so as to allow the passage of a small quantity of oil into a gap formed within the ram and cylinder and between the aggressive and non - aggressive seals . the oil which passes the non - aggressive seal is returned to the oil reservoir when the ram is extended .