it is possible to dispose an elastic accessory sealing unit 39 for example an o ring between the axial leg of the support ring 36 and the hydraulic sealing ring 38 this accessory sealing unit 39 serves for sealing the accessory sealing areas presently for example between the radial leg of the support ring 36 and the hydraulic sealing ring 38 but also for pressing the hydraulic sealing ring 38 against the sealing area of the piston rod 3 the use of an o ring as accessory sealing unit 39 is especially advantageous because an elastic non compressible o ring converts the applied sealing medium pressure into a radial press on force by which the sealing ring 38 is pressed against the piston rod 3 but it is also possible to omit this accessory sealing unit 39 in that case the hydraulic sealing ring 38 would also be in contact with the axial leg of the support ring 36 and provide sealing action for these accessory sealing areas the l shaped support ring 36 if necessary the accessory sealing unit 39 and the hydraulic sealing ring 38 are at an axial distance relative to the center radial leg of the chamber plate 22 so that the sealing medium is able to press the sealing element 8 9 for achieving sealing action against the respective radial leg of the chamber plates 21 23 if the piston rod performs a radial movement the sealing element 8 9 presently the apparatus comprised of the l shaped support ring 36 if necessary the elastic support ring 39 and the hydraulic sealing ring is moved along with the piston rod 3 while maintaining the sealing action at the cylinder side end z of the.