tube stage the air breathers 94 96 98 100 and 102 each respectively communicate with an air space 12a 14a 16a 18a and 20a so that as each tube stage extends and the stroke limiters 54 56 58 60 or 62 approach the adjacent gland nut bearings 64 66 68 70 or 72 the volume of the air space decreases and air in the air space is forced out of the spiral groove along the interior surface of the gland nut bearing shown in phantom in fig1 and through the respective air breather 94 96 98 100 or 102 similarly as each hydraulic stage 12 14 16 18 20 or 22 is retracted the volume of the air space increases and air is drawn through the air breathers 94 96 98 100 or 102 and into the air spaces 12a 14a 16a 18a or 20a through the spiral channel this prevents air from being drawn through the wiper 74 76 78 80 or 82 which would tend to suck particulate material into the bearing and scratch or mar the outer surface of the adjacent tube stage the air breathers 94 96 98 100 and 102 are preferably provided with filters to clean air as it is drawn into the air spaces 12a 14a 16a 18a and 20a with the hydraulic device 10 positioned between the bed of a dump truck and the frame thereof not shown the introduction of hydraulic fluid into the hydraulic device 10 through fluid inlet 28 the various hydraulic stages 12 14 16 18 and 20 extend.