| 摘要 |
<p>A manhole (2) in a bricked (4) pit (3) having a small cover (7). The latter has a central ring (8) through which a cylindrical sleeve (9) supporting two vertical tubes (10, 11) is inserted. The tubes are spaced by clips (12) with adjustment screws. The upper part of the sleeve contains a rotating drum (15) over which a belt (16) passes to a hollow float (19) in one tube (10) and to a counterweight (20) in the other tube (11). The belt is sufficiently wide to carry graduation marks and numbers and it is viewed through a glass screen (23) which supports a wiper (24) operated by a know (24a).</p> |
