TEMPERATURE-REGULATING VALVES

The duplex pressure gage monitors the differential pressure between the inlet and outlet ports of the duplex strainer. The duplex gage provides a visual in- dication of a clogged strainer basket. To correctly use the gage, you should mark it when the basket is clean. When the basket is clogged, the pressure reading is usually 5 to 10 psi above the clean-basket reading. If the pressure drop is less than the clean-basket reading, you should check for a damaged or missing basket. The basket handle (spring handle) acts as a spring- load to seat and hold the basket in the housing. A damaged spring handle will permit debris to bypass the strainer basket and clog the heat exchanger tubes. In some cases, the basket may spin inside the duplex strainer and physically wear away the basket seat and/ or the side of the duplex strainer. The duplex strainer would then have to be removed for extensive repairs, possibly off the ship. New or replacement baskets should always be checked for proper spring-handle pressure against the top of the basket cover. You should use only the correct gasket material for the basket covers, as specified in the Coordinated Shipboard Allowance List (COSAL). Inferior material can stretch and can be forced out from under the cover, permitting seawater to spray out and possibly flood the space. TEMPERATURE-REGULATING VALVES The temperature-regulating valves regulate the amount of cooling water flowing through or by- passing a heat exchanger to maintain a desired tem- perature of distilled water going to the electronic equipment. Temperature regulating is usually pro- vided by a three-way or two-way temperature-regu- lating valve or a combination of both valves. The three-way valve is used where seawater is the primary cooling medium in the heat exchanger, whereas the two-way valve is used where chilled water is the pri- mary cooling medium. Three-Way Temperature-Regulating Valves Three-way temperature-regulating valves are in- stalled in liquid-cooling systems so that the incoming distilled water to the valve can be directed to the heat exchanger or caused to bypass the heat exchanger. More accurately, the distilled water is proportioned between these two paths. The valve senses the temperature of the distilled water downstream of the junction between the heat exchanger outlet and the bypass and then proportions the two flows to obtain the desired temperature. The operating range of the three-way temperature-regu- lating valve is within ±5° of the setting on the valve. The bulb contains a volatile liquid that vaporizes and expands when heated. The pressure generated in the bulb is a function of the temperature around it and is transmitted through the capillary tubing to the flexible bellows, which are loaded by the spring. Both the bellows and the 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. Movement of the bellows is opposed by the spring, which can adjust the operating temperature by the spring-tension adjustment wheel. A drop in the temperature at the thermostatic bulb reduces the pressure in the thermostatic assembly, causing it to exert less force and resulting in an up- ward 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 re- versed effect. Figure 2-10 shows a three-way temperature-regu- lating valve. 2 - 1 2