Q3. In reference to waterborne diseases, what does "incubation period" mean?

Q4. What are the two major categories of impurities in water?

Q5. Eruptions of the skin and frequent bowel movements, without fever are symptoms of what waterborne disease?

Q6. Natural gravity action is the mechanism for what method of water treatment?

Q7. What is the most commonly used disinfectant in water treatment?

CHLORINATION EQUIPMENT

LEARNING OBJECTIVE: Recognize types, functions, and safety precautions associated with chlorinators.

Chlorination equipment used to feed chlorine gas or hypochlorite solution may be classified by type, depending on the methods of control. The three methods of control are manual, semiautomatic, and fully automatic.

1. The manually controlled type equipment must be started and stopped manually, and the rate of feed must be manually adjusted to the rate of water flow.

2. In the semiautomatic type, equipment starts and stops automatically as water flow starts and stops; however, it must be manually adjusted to the rate of water flow. This type is normally used with water pumped at a fairly uniform rate.

3. In the fully automatic type, the rate of feed is automatically adjusted to the rate of flow of the water being treated through pressure of a metering device.

In all three types, the ratio of feed to water treated, or dosage, is set by manual adjustment.

Chlorinators may also be classified generally by type of feed. Here you have two types of machines - DIRECT-FEED and SOLUTION-FEED. Direct-feed machines are designed to operate without a pressure water supply, feeding the chlorine gas directly into the flow to be treated. Solution-feed machines dissolve the gas in a minor flow of water and inject the resultant solution into the flow to be treated and require a pressure water supply for operation.

Another method of classifying chlorinators is by the type of diaphragm used in controlling the chlorine feed. There are two types-the water diaphragm and the mechanical diaphragm. The water diaphragm is always a vacuum type, solution -feed machine and has the advantages of being friction-free and punctureproof. The mechanical diaphragm machine may be either direct- or solution-feed pressure type or solution-feed vacuum type only.

DIRECT-FEED CHLORINATORS

Direct-feed chlorinators are used chiefly as emergency equipment and on small installations where it is not possible to obtain a water supply suitable for operating a solution-feed machine. They cannot be used where the pressure of the water being treated is more than 20 psi and are limited in the types of semiautomatic and automatic controls that may be used. Because the chlorine is under pressure as a gas at all times, direct-feed machines may easily leak gas into a confined or poorly ventilated space where the leakage could corrode adjacent equipment and structures. If you should be called upon to operate a direct-feed chlorinator, carefully follow the recommendations and instructions of the equipment manufacturer. You, as the operator, must be thoroughly familiar with the equipment to ensure its proper operation, adjustment, and minor repair.

SOLUTION-FEED CHLORINATORS

A solution-feed chlorinator introduces chlorine gas into the water supply by means of a chlorine solution. This supply is usually formed by drawing chlorine gas into a jet stream of water at the low-pressure point of the injector mechanism of the chlorinator.

The chlorinator (figs. 7-5 and 7-6) controls and indicates the rate of flow of chlorine; provides a simple means of manually setting the feed rate; mixes chlorine gas and water; and delivers the solution to the point of application. Figures 7-7 and 7-8 show a typical cylinder connection and scales.

The chlorinator operates under a vacuum, produced by a flow of water through the injector. The installation must allow a 5-inch vacuum.

Chlorine gas under pressure enters the chlorinator at the chlorine inlet connection where it is electrically heated to reduce the deposit of impurities and to prevent reliquefaction of the gas when the chlorinator is shut down with the supply turned on. Chlorine expands into a gas at a ratio of 1:460; that is, 1 cubic inch of chlorine expands into 460 cubic inches of gas. This volummetric expansion can rupture lines. For the same reason, there should be no dips or traps in any piping installation.