Patent GB-428514-A (GB)
Title: Improvements in mercury switch relays
IPC: H01H29/18
Filed: 1934-08-03
Abstract: 428,514. Mercury switches; electromagnetic relays. TRIGGS, W. W., 57, Lincoln's Inn Fields, London.-(Adlake Co. ; 319, West Ontario Street, Chicago, U.S.A.) Aug. 3, 1934, No. 22713. [Class 38 (v)] In a mercury relay of the kind in which the controlled circuit is opened or closed by changes in the level of the mercury in a sealed container 40, as occasioned by movement of a displacer 45 under the control of a winding 30, the movement of the mercury to or from a fixed electrode 42 of the relay is retarded by the provision over the electrode of a pocket adapted to contain a quantity of gas which, by movement of the displacer, is subjected to an increased or decreased pressure which is only slowly equalized with the pressure outside the pocket. In the arrangement shown in Fig. 1, the pocket is formed by the upper end of the displacer 45, and the equalization of pressure takes place through a restricted aperture 50 at the top of the displacer. A light packing 51 of asbestos fibre, felt or steel wool is mounted in the upper portion of the displacer. The coil 30 is mounted on a core 33 with polepieces 35, 36 and the container 40 is held in any desired position by frictional engagement with a spring 49. Springs 47, 48 of non-magnetic material are provided above and below the displacer to protect the relay during shipment, and to guard against damage if excessive voltages are applied to the coil 30. The electrode 42 is surrounded by an insulating tube 43, and the circuit between the electrodes 41 and 42 is broken when the level of the mercury falls below the top of the tube 43. In the arrangement of Fig. 1, the main circuit is broken when the coil 30 is energized, and is remade when the coil is de-energized, the delay action occurring both at the make and break, but the arrangement may be modified so that the main circuit is closed when the coil is energized. In the arrangement shown in Fig. 7, the relay is made independent of the voltage applied to the coil 30 by providing the gas pocket in a non- magnetic member 64 which rests loosely on a sleeve 63 of magnetic material. When the latter is displaced by energization of the coil, it separates from the member 64, which slowly gravitates to its new position as the pressure of the gas is equalized through the aperture 50, the speed at which the member 63 responds to the energization of the coil having no effect on the time taken to close the main circuit at the electrodes 41, 42. The size of the opening 50 may be made adjustable by fitting a tapered plug in the opening. The time delay in the downward stroke of the displacer may be eliminated by providing a one-way check valve in the form of a globule of mercury 70, Fig. 11, in a seating 71 at the top of the displacer, a backing 73 of asbestos or the like being packed tightly against the bottom of the seating to prevent the mercury from being drawn into the displacer. The mercury globule permits the free escape of gas on downward movement of the displacer ; on the upward movement, gas enters slowly through a restricted opening 74. In another construction, Fig. 13, instead of forming an aperture at the top of the displacer 45, a thimble 77 of porous ceramic material is provided. In this construction the main circuit is broken on energization of the coil 30, and the arrangement is such that the displacer is drawn completely out of the mercury in order to give a quick break at the electrodes 41, 42. The same effect may be obtained by providing a slot in the lower part of the displacer. In Fig. 16 the displacer 45 is slotted at 84 at its upper end, and carries an adjustable sleeve 83 closed by a porous thimble 77. The slot 84 extends below the bottom of the sleeve 83, leaving an opening 85 to the interior of the displacer. When the coil 30 is energized, the opening is closed by the mercury, and a slow make of the main circuit is obtained, but on de-energization of the coil, the opening 85 rises above the mercury, either immediately or after an interval, and a quick break is obtained. In another construction, Fig. 21, an additional electrode 94 is provided outside the displacer 45 and is connected to the electrode 42. On energizing the coil, the circuit is immediately closed at the electrode 94 to give a quick make of the main circuit, but when the coil is de-energized, the circuit remains closed at the electrode 42 until the mercury has returned to its normal level by equalization of the pressures through the porous thimble 77. The gas-containing pocket may be carried by a fixed part of the switch, instead of being formed by the displacer, and in Fig. 25 the pocket is shown in the form of a porous thimble 106 fixed to the electrode 42. In this construction, the switch container is secured to a cap having a threaded stem 115 adjustably mounted in a fixed support 114, and the time delay on making or breaking the main circuit is adjusted by moving the container relatively to the coil 30 and associated magnetic circuit by means of a nut 116.