Sealing hydropneumatic suspension units

In a mono-tube suspension strut a tubular extension 9 depending from a closure plug 6 for one end of a cylinder 2 carries at its lower end a seal 17 through which a piston-rod 15 projecting through the plug 6 works. The extension 9 is separate from the plug 6 and is provided at its upper end with an outwardly directed radial flange 10 of an external diameter substantially less than the internal diameter of the cylinder 2, and a seal 11 of cup-shaped cross-section, including a pair of radially spaced inner and outer annular lips 31, 32 depending from an annular web 30, is disposed in the annular space between the extension 9 and the cylinder 2. The web 30 is provided with an outwardly directed annular recess 33 in which the flange is sealingly received, the outer lip 32 seals against the cylinder 2 and the inner lip 31 seals against the extension 9. The extension 9 is retained in position by the pressure within the cylinder 2 which acts on the seal 11, in turn to clamp the flange 10 against the plug 6 and separate the lips 31, 32 to enhance the sealing effect against the cylinder 2 and the extension 9. The annular space 22 contains gas above liquid, the liquid level being above the seal 17. <IMAGE>