In many engines, the temperature of the fresh water is regulated automatically by a three-way control valve that maintains the temperature of the fresh water at any desired value by bypassing a portion of the water around the freshwater cooler. Even though these regulators are auto-matic or self-operated, provisions are included for manual operation in the event that the automatic feature fails.

One type of three-way, temperature-sensitive valve for changing the path of water flow is shown in figure 7-17. This valve has a temperature-sensitive element that is placed in the engine jacket-water discharge line. The element contains a liquid (a mixture of ether and alcohol) that gives off a vapor when heated by the jacket water, that produces a pressure that is proportional to the temperature to which the bulb is exposed. The pressure is transmitted through liquid-filled flexible tubing (capillary tube) to a bellows in the head of the valve. The movable end of the bellows is connected to the valve stem. When the bellows expands or contracts, the valve will open or close accordingly. The action of the bellows is opposed by a spring. The compression of the spring can be adjusted so that the specified operating temperature can be readily set.

The regulator operates only within the tem-perature range marked on the nameplate; it may be adjusted for any temperature within this range. (See fig. 7-18.) The setting is controlled by the range-adjusting wheel, located under the spring seat. A pointer attached to the spring seat indicates the temperature setting on a scale that is attached to the regulator frame. The scale is graduated from 0 to 9, representing the total operating range of the regulator.

In contrast to the valve illustrated in figure 7-17, the three-way automatic regulating valve shown in figure 7-19 does not use a gas or liquid as a sensing or activating element. The

Figure 7-18.-Scale and indicator plates of an automatic temperature regulator.

Figure 7-19.-Three-way temperature regulating valve operation.

sensing or activating element in this valve is a power pellet. The power pellet contains a special wax material (similar to that in the conventional thermostatic valve) that expands with tremendous force as it changes from a solid to a liquid when heat is applied. In this valve (as in the conventional thermostatic valve), the important characteristic of the sensing element is that when the wax material is fully liquefied, expansion stops. The manufacturer uses a different formulation to establish a suitable operating range and limiting action for each three-way automatic regulating valve. The sensing element for each of these valves is set at the normal temperature rating by the manufacturer and cannot be altered once the rating has been set. If a different rating is required, a new valve must be used.

The three-way temperature regulating (con-trol) valve that is located in the freshwater circuit automatically regulates jacket-water flow to the jacket-water cooler to maintain optimum water temperature. These valves are arranged so that flow is normally through the recirculating line which bypasses the cooler and permits the jacket water to be recirculated through the engine. (See fig. 7-19, view A.) In this way, the temperature of the jacket water rises and the valve starts to open. When the jacket water in contact with the valve element starts to exceed normal operating temperature, the valve fully opens to permit full flow to the jacket-water cooler where the excessive heat is given up. (See fig. 7-19, view B.)

It should be noted that the applications of conventional thermostatic valves or automatic regulating valves we have discussed do not control the rate of water flow through the cylinder jackets but vary the flow through whatever cooling medium is used. This design provides for the control of the temperature of the jacket water without a reduction in the rate of flow in the engine that might cause localized hot spots. When located in the seawater circuit, the regulator controls the amount of seawater flowing through the coolers. When the tem-perature of the fresh water becomes greater than the temperature for which the regulator is set, the regulator actuates a valve to increase the flow of seawater through the coolers. When the temperature of the fresh water is below the temperature for which the regulator is set, the regulator actuates a valve to decrease the flow of seawater through the coolers.

Temperature regulators are used not only to control the temperature of the fresh water but also to control indirectly the temperature of the oil discharge from the lubricating oil cooler. Control of lubricating oil temperature is possible because the water that is passed through the regulator and the freshwater cooler is the cooling agent in the lubricating oil cooler.