GB536675A - Improvements in or relating to devices for indicating and/or controlling the level of liquid in a container - Google Patents

Abstract

536,675. Indicating and controlling liquid levels. SHERLOCK, J. E., and BRITISH THERMOSTAT CO., Ltd. Feb. 19, 1940, No. 3143. [Class 123 (i)] [Also in Groups XXXV and XXXVII] The apparatus comprises two phials containing volatile liquids, one of which is heated, both being connected to pressure-responsive mechanisms which act in opposition on an electric switch connected to indicating or control apparatus. The extent of immersion of the phials in the liquid determines the dissipation of heat from the heated phial, and consequently the pressure within it. The phials A, B are arranged within a container 4 connected at 5 to a boiler. Each phial consists of an annular space 3 surrounding a central tube 1, which in the phial A contains an electric heater 9. The phials are connected by tubes 6 to bellows 7, 8 carrying axially movable rods 10, 11 which act in opposition on a pivoted lever 12. When the water level is at X, the phial A is at a slightly higher pressure than B due to the action of the heater, and the lever 12 occupies the position shown. If the level sinks and the phials are partly exposed, less heat is dissipated from the phial A to the surrounding vapour and the pressure increases so that the switch lever is moved to close contacts 15, 16 in an electric circuit controlling an electrically operated feed pump or the steam valve of a feed pump, or an audible or visible signal. If heater 9 or phial A become inoperative, pressure in the bellows 7 decreases and contacts 15, 17 are closed to operate an alarm. If phial B becomes inoperative, pressure in the bellows 8 decreases and an abutment 18 closes a switch 19 to operate an alarm. If the water level falls unduly low, pressure in phial A increases still further, and an abutment 20 opens switch contacts 21 in a circuit controlling the boiler fuel supply or an alarm, the switch lever 12 being flexible to allow bending. In a constructional form, Fig. 6, the phials (of which only A is shown) are supported from a cover plate 22 of the container 4, and the pipes 6 are connected to bellows 7, 8, the rods 10, 11 of which act upon the lever 12a. The switch 27 is actuated by a push button 28 through an arm 29 in contact with two studs 29a on the lever 12a. The switch is closed by movement of the lever 12a in either direction. A further two-way switch 30 is actuated by an arm 34 in contact with a spring- pressed plunger 35 on the end of the rod 10. The bellows 7 is loaded by a spring 7a.. The switch 30 is first actuated and controls the circuit of a relay which controls the water feed, and a further fall in water level closes switch 27 which actuates an alarm. Failure of the bellows 7 or heater 9 moves the lever 12a in the opposite direction, which also closes switch 27, and switch 30 to its alternative contact, so that both alarms are operated.