Valves

This chapter discusses the characteristics and uses of the various types of valves and examines their flow characteristics. Valves used for on–off purposes have full or slightly reduced ports and are of symmetrical, straightway design such as ball valves and most gate valves. The closure members of some types of valves are traditionally called gates, discs, wedges, and plungers. These valves are referred to as multiturn or linear motion valves. Diaphragm valves have three simple elements: the valve body, the diaphragm, and the bonnet. A quarter turn opens or closes these valves. The closure members are in the form of a sphere, cylinder, or tapered plug that can be rotated to direct flow. The relief or safety valve is a self-actuated, fast opening valve used for quick relief of excessive pressure. The opening or closing of control valves is done by means of control mechanisms powered electrically, pneumatically, electro-hydraulically.