Patent GB-737099-A (GB)
Title: Improvement in pneumatic control system
IPC: G01G17/04
Filed: 1952-10-24
Abstract: 737,099. Fluid-pressure servomotor-control apparatus. FOXBORO CO. Oct. 24, 1952 [Oct. 27, 1951], No. 26805/52. Class 135. The weight of a quantity of liquid is measured by repeatedly filling a tank to a pre-determined level and then delivering the successive charges of liquid through a discharge pipe, the automatic filling and emptying of the tank being controlled by a valve-mechanism which is operated by a pneumatic relay under the control of means responsive to a series of pneumatic input signals consisting of pressure variations determined by the head of liquid in the tank. In an embodiment, liquid is fed into tanks 10, 11, Fig. 1, alternately past stop valves 13, 15, and the tanks are emptied alternately past valves 18, 20. Each tank is provided with a depending pipe 22, 23 through which airÀ is supplied and allowed to bubble through the liquid in the tank. Assuming the valves have been actuated so that tank 10 is being filled and tank 11 is being emptied, then a valve 31 will also have been actuated so that air is supplied only to pipe 22. As the level in tank 10 rises, the back pressure of the air in pipe 11 will increase and cause a bellows 38 to expand, and the bellows will push over a spring-loaded hinged baffle plate 42 until, when'the required level in the tank is reached, the baffle plate will be closing off the outlet from a nozzle 44. Pressure air is supplied to the nozzle from a pipe 46 and through a restriction, and, when the back pressure upstream of the nozzle is a maximum due to the nozzle being closed by the baffle plate, a diaphragm with associated inlet and exhaust values 49 in a relay 45 will be actuated to supply pressure air from the pipe 46 to a bellows 54. The expansion of the bellows actuates a lever 58 carrying a pusher arm 65 to cause the latter to rotate a toothed wheel 63 through one step, this movement being recorded on a counter 62 and also rotating a pentagonal cam 66 through a tenth of a revolution. A spring-pressed baffle plate 69 resting on the cam will thus be lowered to obturate a nozzle 68, and the ensuing back pressure behind the nozzle will actuate a relay 52, similar to relay 45, to supply pressure air to the valves 13, 15, 18, 20, 31. This will reverse the operation of the apparatus, i.e. tank 10 will now empty, tank 11 will commence to fill, and the supply of air for bubbling through the liquid will be transferred from pipe 22 to pipe 23. In a modification, the signal from relay 45 is fed in parallel through restrictions 82, 83, Fig. 2, to interconnected bellows 80, 81 and to nozzles 87, 89, respectively. Nozzles 87, 89 are obturated alternately by a single baffle plate 90. With the apparatus in the position shown, a pressure pulse coming from relay 45 will be able to flow unimpeded through nozzle 87 giving no pressure in bellows 80 but it will build up a back pressure upstream of nozzle 89. This back pressure will be applied to bellows 81 causing the latter to expand and swing over a lever 94. The latter has a toothed connection with a a rack 98 which will thus be moved to the right and, through a snap-acting spring 102, a lever 100, and a link 103, will swing over baffle plate 90 so that it will free nozzle 89, will close off nozzle 87, and will free a nozzle 92 corresponding to nozzle 68.