THE STORAGE OF GAS
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(«) The provision of an internal trussing to the crown, on the lines of the framing
of an umbrella.
(6) The erection of a crown rest in the tank.
In the former method the framing is affixed to a series of rafters radiating from the centre and attached to the crown curb. A strong centre column is also provided, and when the holder is grounded this rests on a bed-plate or pier in. the centre of the tank. For smaller holders the crown. trussing is
Telescopic Holder.
generally employed, and Cripps says 7 that it would be unwise to abolish the system in the case of the smaller
w crowns, for, owing to its lightness, it would be impossible to put any-
• thing cheaper into the tank in the form of separate frames. The
• ämount of metal, and consequently the cost, increases rapidly as the holder
• * becomes larger, so that it maybe said that the trussed crown must be
' » limited to holders not having a greater diameter than about 170 feet.
The weight of the trussing in large holders would tend to distort the j spherical shape of the crown, which the upward gas pressure is assisting. ’ The internal framing should be as independent of the crown sheet-
ing as possible in order to prevent the possibility of straming the seams.