GB979798A - Electric switch - Google Patents

Abstract

979,798. Mercury switches. ELECTRO CONTROLS Inc. April 18, 1961 [July 8, 1960], No. 13997/61. Heading H2B. In a tilting mercury switch the flow of mercury from one chamber to another is controlled in part by the size of an aperture in a dividing partition through which the mercury flows and in part by the flow of an insulating liquid such as oil through a second aperture in the said partition. In the embodiment of Figs. 1 and 2 mercury (not shown) flows through aperture 20 in a partition 18 when the cylindrical housing 12 is tilted by means of knob 58, oil simultaneously flowing through tapered aperture 28. A valve member 30 attached to a flexible portion 32 of the housing co-operates with the aperture 28 and controls the rate of flow of the oil, and thus of the mercury. The partition 18 has two pockets 22 and 24 into which conductors 34 extend, and when the switch is tilted anticlockwise (Fig. 1) a small quantity of mercury is left in each pocket but this is not sufficient to bridge the conductors 34. When the switch is tilted clockwise this mercury immediately flows towards the end wall 16 and bridges the conductors 34 without delay. On turning the switch back to the anticlockwise " OFF " position the mercury continues to bridge conductors 34 until most of it has flowed through aperture 20, thereby introducing a time delay. A screw 42 serves to adjust valve member 30, against the resilience of flexible portion 32, and the time delay can thus be varied. Shields 26 on each side of aperture 28 allow a larger quantity of mercury to be used without danger of it reaching aperture 28 and thus provide a greater maximum delay time. In a modification (Fig. 8) a well 70 is provided in the switch housing below the partition 18<SP>1</SP> such that the aperture 20<SP>1</SP> is always immersed in mercury 60 thereby eliminating surface tension meniscus interference with the flow through the aperture and enabling a smaller aperture to be utilized. In a second embodiment (Figs. 9 and 10) a cylindrical housing 78 is mounted on a wall 90 for rotation about its own axis by means of an end flange 84 and a face plate 86. A partition 92 is provided with a lower aperture 94 for the mercury 60 and a V-shaped notch 106 for the oil 62. A valve member 110 (which may be an oil-tight fit in a hole 108 in a relatively thick wall 104) is attached to a flexible portion 96 under control of a screw 118 so as to vary the effective aperture of notch 106. In this embodiment two electrodes 122 are bridged by mercury while the switch is as in Fig. 10 but the circuit is broken immediately the housing 78 is rotated anticlockwise (Fig. 13, not shown). Restoration of the switch after the mercury has drained through aperture 94 does not result in electrodes 122 being bridged until the mercury has returned via aperture 94 with a delay due to flow of oil 62 through notch 106 controlled by screw 118 and valve member 110. The valve control in either embodiment may be by a cam or lever in place of a screw, or the adjustable valve maybe omitted so that the switches have a fixed delay.