THE DRY PURIFICATION OF COAL GAS 607
Castings for the boxes, etc., cost, to-day, from £35 to £40 per ton. The covers cost from £55 to £60 per ton, or the whole set, including cormections, from £40 to £45 per ton. I
So far as the cost of buildings is concerned, this has already been touched upon in Chapters I and II. If a steel-framed, brick-panelled structure is erected the cost will amount approximately to 6d. per cubic foot capacity, including foundations. This type of building is, however, rarely employed, and the modem tendency is to erect a liglit steel-framed shed carrying a roof, but open at the sides. Such a building may be estimated at 4s. Gd. per square foot of area covered.
PURIFIER VALVES
The valves made use of on. purifiers are commonly of three distinet types :— («) Centre valves.
b) Separate slide valves (such as the well-known rack and pinion type).
c) Hydraulic valves.
ELEVATION
SECTION ON LINE G-H
SECT1ON ON LINE A-B SECTION ON LINE C"D
Fig. 369.—Dky-faced Centre Valve.
One type of centre valve is shown in T'ig. 369. This valve is constructed with dry faces, and enables any number of the four purifiers to be in action, at one time. It is claimed that with valves of this description, as the faces are always covered