In many engines, freshwater temperature is regulated by an automatic regulating valve which maintains the freshwater temperature at any desired value by bypassing a portion of the water around the freshwater cooler. An automatic temperature regulator of the type commonly used in the cooling systems of marine engines is shown in figure 3-7. Even though these regulators are automatic (self-operated), provisions are included in most installations for manual operation in the event that the automatic feature fails.

Figure 3-7.Automatic temperature regulator.

The temperature regulator consists of a valve and a thermostatic control unit mounted on the valve. The thermostatic control unit consists of a temperature-control element and a control assembly.

The temperature-control element is essentially two sealed chambers consisting of a bellows connected by a flexible armored capillary tube to a bulb mounted in the engine cooling-water discharge line. One chamber is formed by the bellows and cap, which are sealed together at the bottom; the other chamber is in the bulb. The entire system (except for a small space at the top of the bulb) is filled with a mixture of ether and alcohol which vaporizes at a low temperature. When the bulb is heated, the liquid vaporizes and the pressure within the bulb increases. This forces the liquid out of the bulb and through the capillary tube to the bellows. As the bellows is moved down, it operates the valve.

The control assembly consists of a spring-loaded

mechanical linkage which connects the temperature-control element to the valve stem. The coil spring in the control assembly provides the force necessary to balance the force of the vapor pressure in the temperature-control element.

Thus, the downward force of the temperature-control element is balanced, at any point, by the upward force of the spring. This permits the valve to be set to hold the temperature of the engine cooling water within the allowed limits.

The regulator operates only within the temperature range marked on the nameplate; it may be adjusted for any temperature within this range. 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 which is attached to the regulator frame. The scale is graduated from 0 to 9, representing the total operating range of the regulator.

The location of a temperature regulator in one type of installation is shown in figure 3-8. Note that this particular regulator is located in the seawater circuit. In most engines, however, the regulator is located in the freshwater circuit.

When located in the seawater circuit, the regulator controls the amount of seawater flow-ing through the coolers. As the temperature of the freshwater 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. On the other hand, when the freshwater temperature is below the temperature for which the regulator is set, the regulator actuates the valve and decreases the flow of seawater through the coolers.

In installations where the regulator is in the freshwater circuit, water is directed to the cooler when the temperature of the water is above the maximum setting of the regulator. After passing through the cooler where the temperature of the water is lowered, the water returns to the suction side of the freshwater pump to be recirculated.

When the temperature of the water is below the maximum setting of the regulator, the water bypasses the cooler and flows directly to the suction side of the pump. Bypassing the cooler permits the water to be recirculated through the engine; in this way, the temperature of the water is raised to the proper operating level. Regardless of whether the regulator is in the fresh or seawater circuit, the bulb which causes the regulator to operate is located in the freshwater discharge line of the engine.

Temperature regulators not only control the temperature of the freshwater but also control indirectly the temperature of the oil discharged from the lubricating oil cooler. Control of the lubricating oil temperature is possible because the water (freshwater or saltwater) that is passed through the regulator and the freshwater cooler is also the cooling agent for the lubricating oil cooler. When the lubricating oil is cooled by seawater, two temperature regulators are installed in the seawater circuit. The temperature regulator bulb of the regulator that controls the temperature of the freshwater is installed in the freshwater cir-cuit; the bulb of the regulator that controls the temperature of the lubricating oil is installed in the lubricating oil system.