Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGINLET FLANGESTRONGBACKCOVERBASKETHANDLEBASKETSTRAINER4 WAV PLUG COCK B OUTLET FLANGETO PUMPSUCTIONFigure 14-9.— A. Bilge suction strainer. B. Duplex oil strainer.C. Manifold steam strainer.11.329Xthe pressure of fluids and are therefore generallycalled pressure-control valves. Others areidentified by names which indicate their generalfunction— as, for example, thermostatic recir -culating valves . The following sections deal firstwith the basic types of stop valves and checkvalves and then with some of the more complexspecial kinds of valves.Globe ValvesGlobe valves are one of the commonest typesof stop valves. Globe valves get their namefrom the globular shape of their bodies. It isimportant to note, however, that other types ofvalves may also have globe-shaped bodies;hence it is not always possible to identify a globevalve merely by external appearance. The internalstructure of the valve, rather than the externalshape, is what distinguishes one type ofvalve from another.The disk of a globe valve is attached to thevalve stem. The disk seats against a seatingring or a seating surface and thus shuts off theflow of fluid. When the disk is moved off theseating surface, fluid can pass through the valve.Globe valves may be used partially open aswell as fully open or fully closed.Globe valve inlet and outlet openings arearranged in several ways, to suit varying requirementsof flow. Figure 14-10 shows threecommon types of globe valve bodies. In thestraight type, the fluid inlet and outlet openingsare in line with each other. In the angle type,the inlet and outlet openings are at an angleto each other. An angle-type globe valve isused where a stop valve is needed at a 90° turnin a line. The cross type of globe valve hasthree openings rather than two; it is often usedin connection with bypass piping.A globe-type stop valve is shown in crosssectionalview in figure 14-11. Figure 14-12shows a cutaway view of a similar (but notidentical) globe valve.Globe valves are commonly used in steam,air, oil, and water lines. On many ships, thesurface blow valves, the bottom blow valves,372