Principles of naval engineering - Historic Naval Ships Association

Chapter 14. -PIPING,FITTINGS, AND VALVESdisks across each other in such a way as to removeany particles that have collected on themetal surfaces. Some metal- edge type filtershave magnets to aid in removing fine particlesof magnetic materials.VALVES147.104XFigure 14-8.— Bimetallic steam trap.STRAINERS AND FILTERSStrainers are fitted in practically all pipinglines to prevent the passage of grit, scale, dirt,and other foreign matter which could obstructpump suction valves, throttle valves, or othermachinery parts.Figure 14-9 illustrates three common typesof strainers. Part A shows a bilge suctionstrainer located in the bilge pump suction linebetween the suction manifold and the pump.Any debris which enters the piping is collectedin the strainer basket. The basket can be removedfor cleaning by loosening the strongbackscrews, removing the cover, and lifting thebasket out by its handle. Part B of figure 14-9shows a duplex oil strainer of the type commonlyused in fuel oil and lubricating oil lines,where it is essential to maintain an uninterruptedflow of oil. The flow may be diverted from onebasket to the other, while one is being cleaned.Part C of figure 14-9 shows a manifold steamstrainer. This type of strainer is desirablewhere space is limited, since it eliminatesthe use of separate strainers and their fittings.The cover is located so that the strainer basketcan be removed for cleaning.Metal-edge filters are used in the lubricationsystems of many auxiliary units. A metaledgefilter consists of a series of metal platesor disks. Turning a handle moves the plates orEvery piping system must have some meansof controlling the amount and direction of theflow of the contained fluid through the lines.The control of fluid flow is accomplished by theinstallation of valves.Valves are usually made of bronze, brass,iron, or steel. Steel valves are either cast orforged, and are made of either plain steel oralloy steel. Alloy steel valves are used in highpressure, high temperature systems; the disksand seats of these valves are usually surfacedwith Stellite, an extremely hard chromium-cobaltalloy.Bronze and brass valves are not used inhigh temperature systems. Also, they are notused in systems in which they would be exposedto severe conditions of pressure, vibration, orshock. Bronze valves are widely used in saltwater systems. The seats and disks of bronzevalves used for sea water service are oftenmade of Monel, a metal that is highly resistantto corrosion and erosion.Many different types of valves are used tocontrol the flow of liquids and gases. The basicvalve types can be divided into two groups,stop valves and check valves. Stop valves arethose which are used to shut off— or partiallyshut off— the flow of fluid. Stop valves are controlledby the movement of the valve stem.Check valves are those which are used to permitthe flow of fluid in only one direction. Checkvalves are designed to be controlled by themovement of the fluid itself.Stop valves include globe valves, gate valves,plug valves, piston valves, needle valves, andbutterfly valves. Check valves include ball-checkvalves, swing-check valves, and lift-checkvalves.Combination stop-check valves are valveswhich function either as stop valves or as checkvalves, depending upon the position of the valvestem.In addition to the basic types of valves, agood many special valves which cannot reallybe classified either as stop valves or as checkvalves are found in the engineering spaces.Many of these special valves serve to control371