Principles of naval engineering - Historic Naval Ships Association

^iChapter 14. -PIPING.FITTINGS, AND VALVESLIST OF PARTS11.320Figure 14- 1 7. — Cutaway view of lift- checkvalve.Pressure-Control ValvesPressure- control valves are used to relieveor prevent excessive pressure, to reducepressure, and to control or regulate pressure.Several common types of pressure-controlvalves are described in the following paragraphs.RELIEF VALVES .-Relief valves are designedto open automaticially when the pressurein the line or in the machinery unit becomestoo high. There are several different types ofrelief valves, but most of them have a disk ora ball which acts against a coil spring. The springpushes downward against the disk or ball andso tends to keep the valve closed. When thepressure in the line or in the unit is greatenough to overcome the resistance of the spring,the disk or ball is forced upward and the valveis thereby opened. After the pressure has beenrelieved by the escape of fluid through the relief