TEMPERATURE REGULATING VALVES

The duplex strainer (fig. 1-14) consists of two removable baskets located in parallel at the seawater inlet. Seawater flows into the top of one basket and out through the perforated sides to the outlet. This arrangement allows maintenance to be performed on one basket while the system is in operation, A selector valve is arranged so that with the handle in one position, seawater flows through one of the baskets, leaving the other basket accessible for removal and cleaning. By switching the valve handle to the alternate position, flow is shifted over to the other basket. A duplex pressure gauge monitors the differential pressure between the inlet and outlet ports of the duplex strainer. The purpose of the duplex gauge is to provide a visual indication of a clogged strainer basket. To correctly use the gauge, it should be marked 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, a check should be made for a damaged basket 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 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 COSAL. Inferior material can stretch and be forced out from under the cover, and then seawater could spray out and possibly flood the space. TEMPERATURE REGULATING VALVES The temperature regulating valve regulates the amount of cooling water flowing through or bypassing a heat exchanger to maintain a desired temperature of distilled water going to the electronic equipment. Temperature regulating is usually provided by either a three-way or a two-way temperature regulating valve or a combination of both valves, as shown in figure 1-7. The three-way valve is used where seawater is the primary cooling medium in the heat exchanger, and the two-way valve is used where chilled water is the primary cooling medium. Three-Way Temperature Regulating Valve The three-way regulating valve (fig. 1-7) is installed 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 Figure 1-14.-Seawater duplex strainer. 1-12