Valvulas

7.

VALVES
AN INTRODUCTION TO VALVES (ONLY THE BASIC)

WHAT ARE VALVES

Valves are mechanical devices that controls the flow and pressure within a system or process. They are essential components of a piping system that conveys liquids, gases, vapors, slurries et cetera. Different types of valves are available: gate, globe, plug, ball, butterfly, check, diaphragm, pinch, pressure relief,and control valves. Each of these types has a number of models, each with different features and functional capabilities. Some valves are self-operated while others manually or with an actuator or pneumatic or hydraulic is operated. Functions from valves are:  Stopping and starting flow  Reduce or increase a flow  Controlling the direction of flow  Regulating a flow or process pressure Relieve a pipe system of a certain pressure There are many valve designs, types and models, with a wide range of industrial applications. All satisfy one or more of the functions identified above. Valves are expensive items, and it is important that a correct valve is specified for the function, and must be constructed of the correct material for the process liquid. CLASSIFICATION OF VALVES Thefollowing are some of the commonly used valve classifications, based on mechanical motion:  Linear Motion Valves. The valves in which the closure member, as in gate, globe, diaphragm, pinch, and lift check valves, moves in a straight line to allow, stop, or throttle the flow.  Rotary Motion Valves. When the valve-closure member travels along an angular or circular path, as in butterfly, ball, plug,eccentric- and swing check valves, the valves are called rotary motion valves.  Quarter Turn Valves. Some rotary motion valves require approximately a quarter turn, 0 through 90°, motion of the stem to go to fully open from a fully closed position or vice versa. Classification of valves based on motion Valve types Linear motion Rotary motion Gate Valve x Globe valve x Plug valve x Ball valve xButterfly valve x Swing check valve x Diaphragm valve x Pinch valve x Safety valve x Relief valve x 7-1 Quarter turn x x x

CLASS RATINGS Pressure-temperature ratings of valves are designated by class numbers. ASME B16.34, Valves-Flanged, Threaded, and Welding End is one of the most widely used valve standards. It defines three types of classes: standard, special, and limited. ASME B16.34 coversClass 150, 300, 400, 600, 900, 1500, 2500, and 4500 valves. VALVE BODY The Valve body is the first boundary of a pressure valve. He serves as the main element of a valve assembly because it is the framework that holds all the parts together. The valve-body ends are designed to connect the valve to the piping or equipment nozzle by different types of end connections, such as butt or socket welded,threaded or flanged. Valve bodies are cast or forged in a variety of forms and each component have a specific function and constructed in a material suitable for that function. VALVE BONNET The cover for the opening in the body is the valve bonnet, and is the second most important boundary of a pressure valve. Like valve bodies, bonnets are in many designs and models available. A bonnet acts as acover on the valve body, is cast or forged of the same material as the body. It is commonly connected to the body by a threaded, bolted, or welded joint. During manufacture of the valve, the internal components, such as stem, disk and actuator, are put into the body and then the bonnet is attached to hold all parts together inside. VALVE TRIM Valve's trim is a collective name for the replaceableparts, in a valve. A typically valve design includes a disk, seat, stem, and sleeves needed to guide the stem. VALVE DISK The disc is the part which allows, throttles, or stops flow, depending on its position. In the case of a plug or a ball valve, the disc is called plug or a ball. The disk is the third most important primary pressure boundary. With the valve closed, full system pressure is applied...