sealing ring is disposed in a groove in the tube 26 the groove may be produced for example in a hardened tube simply by grinding referring to fig4 like reference characters indicate like parts as above in the embodiment of fig4 support shoe 20 is used which is essentially like the support shoe of the preceding embodiments a tube 26 carried sealingly in a bore 12 engages in the support shoe 20 in contrast to the preceding embodiments the bore 12 is in this case somewhat shorter bore 12 however is extended coaxially by a bore 60 which in the example illustrated crosses the axial bore 11 projecting element 61 is rigidly fixed in the tube 26 through element 61 a rod 63 is passed which is fixed by a pin 62 at the end of the rod 63 remote from the supporting shoe 20 a guide member 64 is fixed which is carried slidingly in the bore 60 for balancing the pressures at both sides of the guide member at least one slot 65 is provided at the end of the rod 63 found inside the supporting shoe 20 a bushing 66 with spherical outer surface is fixed the bushing is supported slidingly in a spherical bearing bushing which is held in a central bore 68 of the support shoe 20 by a threaded bushing 70 the mode of operation of the support element of fig4 is the same as that of the elements of fig2 and 3 the hydraulic pressure fluid supplied through the bore 11 acts.