THE DRY PURIFICATION OF COAL GAS
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(a) Centre valves. Are simple in operation, but may give trouble owing to gas leaking from one valve chamber to another. If this occurs a portion of the crude gas may get through to the clean gas outlet and give rise to a stain.
(b) Slide valves. These may be either of the rack and pinion or worm and rack type. They should be flanged so that they may be readily re-placed if faulty. One spare valve should always be kept as a stand-by. If this is done, all the valves in use can be overhauled in turn.
(c) Water valves. These valves are probably the safest, but they are undoubtedly cumbersome, and decidedly slow in action in comparison with the other types. The latter disadvantage is, however, not of paramount importance at the present day, owing to the extended life of each purifying vessel.
A novel device in the construction of purifier valves is the “ Bearscot ” patent operating gear
(Fig. 374), which lias for its obj eet the revolving and grind-ing in of various kinds of valve discs upon their seatings. When, as often happens, valves remain either closed or open for long periods, tar, sediment, and other undesirable substances are apt to accumulate on the exposed face, tlius preventing close contact between the disc and its seat. The method under notice makes the grinding in of the disc a very simple matter. When closing a valve, when the disc is coming in contact with the face of the valve, the small lever marked “ A ” is swung, so that the tooth gears into one of the recesses on the handwheel marked “ B.” This action locks the spindle and disc to the hand-
Fig. 373.—Common Water Valve.
Fig. 374.—“ Bearscot ” Valve Operating Gear.
wheel. The operator then moves the hånd wheel, to and fro, thus revolving the disc. The lever is then raised, releasing the spindle, and the handwheel is tumed slightly, thus tightening the disc on the seat. The lever “ A ” is again gear ed with the handwheel, and the disc further re-volved. When the disc is fairly bedded down, the lever is
raised, and the valve closed home, thereby ensuring that the faces are in complete contact and the valve absolutely gas-tight.
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