Refrigerant piping in modern naval installa-tions is made of seamless copper tubing, which is good for this purpose because (1) it does not become corroded by refrigerants, (2) the internal surface of the tubing is smooth enough to minimize friction, and (3) copper tubing is easily shaped to meet installation requirements. The piping of refrigeration systems is covered with insulation after all joints have been checked for leaks. The insulation prevents condensation from forming on and dripping off the cold piping on the low-pressure side of the system. On the high-pressure side, insulation reduces heat stress conditions and protects personnel from being burned by hot piping.

PACKLESS VALVES

Nearly all hand-operated valves in large refrigeration systems are packless valves of the type shown in figure 16-19. In this type of valve, the upper part is sealed off from the lower part by a diaphragm. An upward-seating ball check

Figure 16-19.-Packless valve for a refrigeration system.

in the lower valve stem makes it possible for the spring to lift the lower stem regardless of pressure differences developed while the valve was closed. Thus, the valve will operate properly regardless of direction of flow. By backseating the valve, you can change the diaphragm without placing the system or unit out of operation.