| 摘要 |
A cylindrical casing 12 of glass reinforced plastic having an end cap 42.2 at each end thereof, the end caps each having at least one opening 52 therein through which water can flow and each end cap 42.2 being held in place by a mounting ring 34 embedded in the wall of the casing 12 and encircling the casing 12 internally, an internal groove extending circumferentially of the mounting ring 34, a first locking ring having a peripherally extending external rib, the rib being in the groove, a second locking ring which fits into the first locking ring to expand it outwardly and press the rib into the groove, there being stud holes in the end cap 42.2 and in the second locking ring, and studs securing the second locking ring to the end cap 42.2.
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