GB802199A - A movable piston structure for a fluid storage tank - Google Patents

Abstract

802,199. Gas-holders; tanks. WIGGINS, J. H. Jan. 11, 1957, No. 1189/57. Classes 54 and 69 (1). The weighted piston of a storage tank for gas or a volatile liquid consists of a relatively flexible diaphragm 17 reinforced by an annulus 18 which is braced to the diaphragm in such a manner that the torsional moments applied to the annulus from the inner and outer portions 19 and 20 of the diaphragm are in opposite directions and tend to minimize the torsional stresses in the annulus. As applied to the gasholder 10 of Fig. 1, the annulus is formed by concrete cast in situ between permanent or removable forms 21, 22. Upstanding struts 33, 34 and 35 on the central portion 19 of the diaphragm are braced to the bottom of the annulus by tension rods or cables 36, 36a and the outer portion 20 and an upright fender 28 are braced to the annulus by struts 25, 29 and 32; the bracing is anchored to the annulus by means of plates 30 or 38 connected to rods 31 or 38a extending radially through the concrete. Circular re-inforcing members may be embedded in the upper portion of the annulus. For supporting the piston on the base of the holder in a position accessible from underneath, flanged pipes 50 with gas-tight caps 54 are welded to the diaphragm and embedded in the concrete and support legs may be fitted to these pipes. A curtain seal 24 or other type of seal is provided between the fender 28 and the side of the holder. The piston is balanced to maintain a horizontal position by a pair of weights 39 arranged at 90 degrees spacing and each connected by a pair of double cables to opposite sides of the piston. In the tank shown in Fig. 6, the vapour above a volatile liquid is maintained at a pressure either greater or less than atmospheric pressure by a piston sliding in the upper portion 75 of the tank and comprising a relatively flexible diaphragm 79 reinforced by an annulus 81 of channel-section steel, the annulus being braced to the diaphragm by struts 84, 85. The piston is balanced by a pair of counterweights 91 and double cables at 90 degrees to each other. Where the weight of the counterweights is greater than that of the piston assembly, in order to maintain the vapour at a pressure less than atmospheric pressure, circular backing bands 102 are provided to support a curtain seal 86, when the piston is in its lower position.