THE STORAGE OF GAS
671
a leak develop in one it can be repaired without interfering with the working of the holder. There has been no trouble with excess of tar passing through the seal: but the quantity passing in summer is larger than in winter. Gauges are provided for showing the level of the tar in the seal and in the bottom of the holder.
The weight of this new gasholder is considerably less than that of the old design, in view of the absence of the large quantity of water. This is a consideration parti-cularly important in Holland, where the ground is generally not capable of carrying heavy weights, as it involves a large saving in foundations. । |; i..
NOTABLE GASIIOLDERS
The largest gasholder in the world is that at New York, having a capacity of 14 million cubic feet. The next largest is that which was recently erected for the Australian Gas Company at Sydney, the capacity being 12f million cubic feet. The largest holder in this country, the beil of which was almost completely destroyed by th.e Silvertown explosion in 1916, is that at the East Greenwich works of the South Metropolitan Gas Company. It has a capacity of 12 million cubic feet.
THE LIVESEY MAN-LID
The man-lid introduced by the late Sir George Livesey is a convenient device commonly fitted to holders for facilitating inspection of the gas inlet and outlet pipes.
In the ordinary way, if a simple manhole water-level and the crown would be lost. The man-lid, however, prevents this. It consists (Fig. 416) of a circular hood bolted to the underside of the gasholder crown. To the side of the hood is afrtached a seal tank with a feather plate projecting halfway down ' into it. There is an aperture in the hood, near the crown, to allow the gas in the hood to escape when the holder is coming down on to the rest stenes. When the beil is at rest the seal tank is filled with water nntil the seal on the hanging plate is greater than the pres-sure in the holder. The man-lid may then be removed.
cover was employed the gas between the
Fig. 416.—The Livesey Man-lid.
THE CARE OF GASHOLDERS
It may be said without fear of contradiction that the gasholder receives in general less attention tlian any other portion of gasworks apparatus. Once the holder has been erected and put into commission it is more often than not permitted to look after its own welfare, with the result that imperfections develop which might readily be avoided. The following points in particular should be watchcd. periodical in-