An apparatus for softening water consists of a mixing chamber for the chemical reagents, a settling basin for the treated water after the reagent is added and a filter to remove from the softened water the base acted upon by the chemical.

There are two general arrangements of apparatus for softening water. One arrangement is known as the closed or pressure system, and the other arrangement, as the gravity system.

Fig. 114

The general arrangement of the Scaife pressure system as used for softening feed water for boilers is shown in Fig. 114.

Feed water enters the open heater, a, where some of the temporary hardness is removed by raising the temperature to 200 or 210 degrees Fahr., thus driving off some of the free carbonic acid gas and precipitating carbonates of lime and magnesia on removable pans inside of the heater. From the heater the water is forced by the boiler feed pump, b, into a large precipitating tank, c, where the chemical reagents are introduced by means of two small pumps, d, d. In the precipitating tank most of the remaining carbonates and sulphates of lime and magnesia are precipitated; some of the lighter particles, however, are carried in suspension to the filters, e, e, where along with other impurities they are removed.

When this system is used for industrial or for domestic purposes, the heater and feed water pumps may be omitted and the hard water discharged directly into the precipitating tank. When the heater is omitted, however, a large quantity of reagent is required.

A gravity apparatus for water softening is shown in Fig. 115. In this system of treatment, lime is slacked in the trough, a, after which it is emptied into the saturator, b, where it can be diluted to the required consistency and be kept agitated by revolving paddles. In a tank, c, a solution of soda ash is prepared, which, like the lime solution, is agitated by revolving paddles operated by the water motor, d. Lime solution is fed to the raw water through pipe e, and soda solution is fed to the raw water through pipe f. By means of an automatic pro-portional water motor, a measured quantity of water and proportional amounts of either lime, soda, or both lime and soda, are introduced into the standpipe, g, the water flowing in through pipe, h. Baffle plates in the standpipe thoroughly mix and agitate the treated water, thus aiding precipitation. The lime deposited in standpipe, g, is washed out through the valved pipe, i. The treated water overflows the top of the standpipe, passes under the baffle plate, j, up through the filters and overflows through trough, k, and pipe, l, to a collecting or storage reservoir. Sludge from precipitation in the tank settles to the cone-shaped bottom and is washed out through pipe, m. A float, n, controls the supply valve, o, thus making the apparatus automatic in operation.

Fig. 115

When the water to be treated is obtained from a stream or other surface source where the conditions of the water are not uniform, it is better to use an intermittent type of apparatus. By this system a large quantity of water is put in a tank and treated; while that tank is being emptied, a second tank is filled, the water tested and the right proportion of reagent mixed to treat it. In this manner each tank of water is separately tested and the correct proportion of chemicals added.