Patent GB-462978-A (GB)
Title: Improvements in or relating to conducting liquid electric switches
IPC: H01H29/28
Filed: 1935-09-13
Abstract: 462,978. Mercury and other conducting - liquid switches. HAMILTON, W. Sept. 13, 1935, No. 25476. [Class 38 (v)] A time-delay switch comprises a chamber 1 containing a conducting liquid 2, e.g. mercury, and a volume of gas, means for varying the pressure of the gas to displace liquid from one location to another, said means including a flexible or resilient bulb 8 or equivalent gas container having its open end communicating with the inside of the chamber above the level of the liquid, a gas release and inlet element permitting gas to pass from or into the chamber at an extremely slow rate to restore the pressure to its initial value and allow the liquid to return to its initial position, and electric contacts adapted to be connected through the liquid when this is in one of its locations. In the construction shown, the gas release and inlet element comprises a tube 9 of very small bore coiled round the cover 3b of the chamber 1, one end 9b of the tube being open to the atmosphere while the other end 9a projects through the cover into the chamber. The chamber is divided into two portions by a partition 3a, which supports, by means of webs 4a, an insulating block 4 carrying a contact 5 which extends through the cover 3b to one of the terminals of the switch. The other contact 6 is mounted below the level of the liquid in the bottom of the chamber. When the bulb 8 is compressed, air is forced from the upper part of the chamber through the liquid and escapes to atmosphere through a passage 1b. On releasing the bulb, it draws in air from the upper chamber, and the liquid is forced into the upper chamber above the level of the insulating block 4 to connect the contacts 5 and 6. Air then passes slowly through the tube 9, and the level of the liquid sinks until it falls below the top of the block 4, whereupon the circuit is broken. Any desired time interval may be obtained by varying the degree of collapse of the bulb. For this purpose a plunger 13 is adapted to be displaced axially by a knob 14 formed with an internal projection 15 co-operating with a single turn helical projection 12 on a plug 11 screwed into the casing 10 of the bulb. The travel of the plunger, and hence the degree of collapse of the bulb, is regulated by turning the knob 14, which may carry a pointer 16 co-operating with a scale 17. The tube 9 may be of rubber, or it may consist of a metal tube which is filled with fibrous material and then flattened. The contact 5 may be replaced by a contact 5a normally below the surface of the liquid ; in this case the circuit is normally closed but. is opened for a predetermined period on collapsing and releasing the bulb. In a modification, the chamber 1 is replaced by a tubular member dipping into mercury in a cup, said member comprising an intermediate horizontal portion with contacts projecting into it. On collapsing and releasing the bulb, mercury is drawn into the tube above the level of the contacts to close a circuit, which remains closed until the mercury has sunk below the horizontal portion of the tube. A number of contacts may be arranged at different levels, to enable several circuits to be broken at different times.