Patent GB-685624-A (GB)
Title: Improvements in instruments for detecting hardness in water
IPC: G01N21/83
Filed: 1949-08-11
Abstract: 685,624. Softening water. BOBY & CO., Ltd., W., BOBY, W M. T., and SCOWEN, J. J. E. Aug, 11, 1950 [Aug. 11, 1949]. No. 20960/49. Class 46. [Also in Group XL (b)]. In control apparatus for a water-softening plant, sampling and testing means are provided wherein the supply pipe to a sampling pump is directly connected to the discharge pipe of a softening unit to receive a more or less constant supply therefrom, and is provided with a submerged connection to a vessel having an overflow to a drain whereby such supply normally passes to drain when the vessel is full, but on the suction stroke of the pump the charge is drawn from the discharge pipe and any excess or shortage of the flow in the supply pipe in relation to the quantity drawn by the pump is delivered to or from the vessel. The testing may be done by a photoelectric cell. In the arrangement shown, wherein the invention is applied to a plant having two water-softening units, discharge pipes 18, 19 from these units are connected with U-shaped pipes 20, 21 in vessels 22, 23. The pipes 20, 21 are formed with holes 24 and are connected by rubber tubes 26, 27 to a pipe junction 28, from which a pipe 29 extends to a pump cylinder head 30 through a non-return valve 31. The valve comprises a ground-glass plug co-operating with a ground-glass seating. The rubber tubes 26, 27 pass through selector valves in the form of pinch-cocks 34, 35 which are operated by spring-urged push rods 36, 37 from a cam 38 on a shaft 39. The shaft 39 is geared through a counter-shaft 40 to a crank-shaft 11 which is driven intermittently by means which include an electric motor 10, a reduction gear 12, and pinion 13 and a mutilated gear 14. The counter-shaft 40 operates a metering valve 41 in a pipe 44 extending from a supply tank 45 of standardised soap solution to the cylinder-head 30. The cylinder 47 is of glass and is located between an electric light bulb 48 and a photoelectric cell 49. The cell is connected to an amplifier 50 and the circuit is controlled by an automatic switch 51. A rotary switch 54 directs the impulses from the cell to the regeneration control of the softening unit being tested or to a delayaction relay in the event of more than one unit requiring regeneration at the same time. While the crank-shaft 11 is driven continuously for one sampling period the pump makes four complete strokes. During the first three strokes the cylinder is washed clean by samples of effluent drawn in from a softening unit and evacuated to drain 32. During the fourth stroke a sample together with a measured quantity of soap solution is drawn into the pump. The crank-shaft 11 then ceases to revolve and after an interval of time the photoelectric cell circuit is closed. If the sample of effluent indicates hardness opalescence occurs in the cylinder and an impulse is given out by the cell which sets the regeneration process in operation. During the next cycle of operations the pinch-cock formerly opened is now closed and the other pinch-cock is opened to allow the other softening unit to be tested. In a modification for use for example to avoid inaccuracies due to ageing of the electric light bulb the sampling pump is in series with a second similar pump provided with photo-electric cell-testing means but not connected to the metering valve 41, the two cells being connected in a bridge circuit to give an output which is proportional to the difference in opulescence between the contents of the two pump cylinders. In a water-softening plant comprising a number of softening units, selector switches operated by the pump motor may be provided to connect the output from the photo-electric cell or cells to each of the control units for the various softening units to initiate the regeneration either immediately or after a delay.