Fig. 123.—Dosing Syphon.
A different type of dosing apparatus is the “Coleman” valve, manufactured by The Ames Crosta Sanitary Engineering Company, [Fig. 125]. This consists of a balanced valve, suspended from a hollow lever which contains mercury, and has a branch provided with a float actuated by the rise and fall of the liquid in the tank. As the sewage rises in the tank, the float overcomes the resistance of the balance weight on the lever, which is lifted, and the mercury falls to the lower end of the lever. The combined action of the float and the mercury opens the valve, and the sewage is discharged. When the tank is emptied, the apparatus resumes its former position ready for the next dose.
Fig. 124.—Dosing Syphons.
Another type of dosing apparatus is manufactured by Messrs. Mather and Platt, Ltd. This consists primarily of a flap valve, counterbalanced weights, and a balance vessel or drum, which is filled gradually with liquid, the whole being pivoted about a horizontal axle. When the measuring chamber and balance drum are both empty, the counterbalance weights raise the latter and allow the flap valve to close, the balance drum then being in its highest position. As the measuring chamber fills, a portion of the sewage is allowed to pass from it into the balance drum, which is thus gradually filled, and at a given level its weight will suffice to overcome the counterbalance weights and the pressure of the sewage on the flap valve, and will open the latter, thus allowing a measured quantity of sewage to be discharged into the troughs or pipes for spreading over the filter. The balance drum discharges its contents meanwhile, and thus, when the measuring chamber is empty, the flap valve closes again by the action of the counterweights, and the chamber is ready to receive another quantity of sewage ([Fig. 126]).
