made of a plurality of elements all connected together the piston 36 forms a first pressure chamber 28 positioned between the piston 36 the sleeve 25 and the cover 30 a second ring shaped pressure chamber 38 is formed between the sleeve 25 the piston rod 34 and the piston 36 hydraulic pressure fluid under high pressure is supplied to the first pressure chamber 28 through a connecting line 40 in the cover 30 a drain line 42 permits drainage of hydraulic pressure fluid from the cylinder space 38 an overpressure valve 44 prevents the build up of excessive pressure when the piston 36 reaches a terminal position a radial bore 46 covers the second pressure space 38 with a ball valve formed by a ball 48 the ball 48 is biassed by a spring 50 so dimensioned that possible excess pressure in the second pressure space 38 can be drained through the first pressure space 28 the spring pressure at which time the safety valve formed by the ball will open can be adjusted by an adjustment screw 52 accessible through the bore 40 seals 54 56 are provided to seal the high pressure fluid in the respective cylinder spaces the seals being located in the cover and in the sleeve the connection between the control slider 23 and the ducts 40 42 is obtained through.