close sliding fit within the casing 1 an annular lead gasket 3 is squeezed between an annular seat 4 on the bulkhead 2 and a cooperating annular seat 5 inside the casing 1 a further cylindrical portion 6 of the housing is screwed at 7 into the end of the casing 1 and provides an annular seat 8 for a clamping ring 9 as seen in the drawing the radial thickness of the ring 9 is greater than the axial thickness thereof the ring has a plurality of circumferentially spaced thrust screws 10 disposed in its inner region for urging the bulkhead 2 to the right as shown in the drawing when the screws 10 are screwed to each give a thrust of the order of 2 5 tons the gasket 3 will be prestressed sufficiently to cause the lead to flow so as to make intimate contact with the adjacent steel faces of the bulkhead and the casing the ring has more resilience than the screws 10 or bulkhead 2 in the axial direction hence the ring 9 will be slightly 34 dished 34 and thus will act as a very strong spring well within its elastic limit it provides a small amount of 34 follow up 34 without excessive loss of pressure in the event of slight subsequent extrusion of the lead gasket the bulkhead 2 has two annular grooves 11 and 12 containing elastic o rings 11 39 and 12 39 respectively the narrow annular space not clearly shown in the drawing between the external periphery of the bulkhead 2 and the facing internal periphery of the casing 1 between the two o rings 11 39 and 12 39 contains petroleum jelly which may be introduced under pressure in order to check the.