Figure 1-15.—Three-way temperature regulating valve

outlet and the bypass and then proportions the two flows to obtain the desired temperature. The three-way regulating valve’s range of operation is within degrees of the setting on the valve. Refer to figure 1-15 for the following description of the operation of the three-way regulating valve. The bulb contains a volatile liquid that vaporizes and expands when heated. The generated pressure in the bulb is a function of the temperature around it. This pressure is transmitted through capillary tubing to the flexible bellows, which are loaded by the spring. Both bellows and spring rest on the end of the valve stem. Expansion or contraction of the bellows causes movement of the stem and the piston in the valve body. The flow of the liquid entering the valve at port A is proportioned between ports B and C in the proper ratio to maintain the mixed flow temperature at the valve’s set point. Total flow through the valve remains constant. Movement of the bellows is opposed by the spring, which is provided with a means to adjust the operating temperature by the spring-tension adjustment wheel. A drop in temperature at the thermostatic bulb reduces the pressure in the thermostatic assembly, causing it to exert less force, resulting in an upward movement of the stem because of the force of the spring. As the stem is connected to the piston, the piston also moves upward, enabling more liquid to pass from the bottom inlet through the right outlet (bypass) side and, at the same time, restricting flow through the left outlet (heat exchanger) side. A rise in temperature at the thermostatic bulb results in a reversed effect. Figure 1-15.—Three-way temperature regulating valve. 1-13