In the semiautomatic type, equipment starts and stops automatically as water flow starts and stops but must be manually adjusted to rate of water flow; this type is normally used with a water pump having a fairly uniform delivery.

In the fully automatic type, rate of feed is automatically adjusted to rate of flow of water being treated by the differential pressure of a metering device. In all types, the ratio of feed to water treated, or dosage, is set manually.

Figure 8-1 shows a typical gas chlorination equipment piping diagram.

Hypochlorinators, or solution feeders, (fig. 8-2) introduce chlorine into the water supply in the form of hypochlorite solution. They are usually modified positive displacement piston or diaphragm mechanical pumps. However, hydraulic displacement hypochlorinators are used. Figure 8-3 shows a typical hypochlorination hookup.

Fully automatic types of hypochlorinators are actuated by pressure differentials produced by orifices, venturis, valves, meters, or similar devices. Care is necessary in their installation in mains to avoid restricted flows, which may limit the required amount of water for fighting a fire. Hypochlorinators are sometimes used as standby equipment for gas chlorinators.

Portable hypochlorination equipment is also available which may be used for primary disinfect- ion or during emergencies. They can also be used to feed chemicals for scale and corrosion control. A common type of portable Hypochlorinator used is the Proportioneers Chlor-O-Feeder. The Proportioneers Chlor-O-Feeder is a positive displacement diaphragm- type pump with an electric drive or a hydraulic operating head. The maximum capacity of the most popular type, the heavy-duty Midget Chlor-O-Feeder, is 95 gallons of solution in 24 hours. This unit can be operated in a semiautomatic or automatic application as follows:

Semiautomatic control. The motor-driven type may be cross connected with a pump motor for semiautomatic control. The hydraulic type can be synchronized with pump operation by means of a solenoid valve.

Fully automatic control. Motor-driven types are made fully automatic by the use of a secondary electrical control circuit actuated by a switch inserted in a disk or compound meter gearbox. This switch closes momentarily each time a definite volume of water passes through the meter, thus starting the feeder. A

Figure 8-1. - Typical gas chlorination equipment piping diagram.