VALVE A valve is a mechanical device that controls the flow of fluid and pressure within a system or process. A valve controls system or process fluid flow and pressure by performing any of the following functions:1. Stopping and starting fluid flow2. Varying (throttling) the amount of fluid flow3. Controlling the direction of fluid flow
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PARTS OF VALVE1. Body2. Bonnet3. Stem4. Actuator5. Packing6. Seat7. Disk
VALVE BODYThe body, sometimes called the shell, itis the principal element of a valveassemblybecause it is the frameworkthatholds everything it resists fluid pressureloads from connecting piping. It receivesinlet and outlet piping through threaded,bolted, or welded joints.
Valve bodies are cast or forged into avariety of shapes. Although a sphereor a cylinder would theoretically bethe most economical shape to resistfluid pressure when a valve is open
BonnetA bonnet acts as a cover on the valve body. It is commonly semi-permanently screwed semi- into the valve body. During manufacture of the valve, the internal parts are put into the body and then the bonnet is attached to hold everything together inside.
STEMThe stem, which connects the actuator and stem, disk, is responsible for positioning the disk.Stems are typically forged and connected to the disk by threaded or welded joints.
TYPES OF STEMSTwo types of valve stems are rising stemsand nonrising stems. these two types ofstems are easily distinguished byobservation. For a rising stem valve, thestem will rise above the actuator as thevalve is opened. There is no upward stemmovement from outside the valve for anonrising stem design.
VALVE TRIMThe internal elements of a valve arecollectively referred to as a valves trimThe trim typically includes a disk, seat andstem. A valves performance is determinedby the disk and seat interface and therelation of the disk position to the seat.
ACTUATORThe actuator operates the stem and diskassembly. An actuator may be a manuallyoperated handwheel, manual lever, motoroperator, solenoid operator, pneumaticoperator, or hydraulicram. In somedesigns, the actuator is supported by thebonnet. In other designs, a yoke mountedto the bonnet supports the actuator.
PACKINGMost valves use some form of packing toprevent leakage from the space betweenthe stem and the bonnet. Packing iscommonly a fibrous material (such as flax)or another compound (such as teflon) thatforms a seal between the internal parts ofa valve and the outside where the stem
Valve packing must be properly compressed to prevent fluid loss and damage to the valves stem. If a valves packing is too loose, the valve will leak, which is a safety hazard. If the packing is too tight, it will impair the movement and possibly damage the stem.
TYPES OF VALVESGATE VALVEBALL VALVEPLUG VALVEBUTTERFLY VALVENEEDLE VALVEDIAPHRAM VALVE
GATE VALVEA gate valve is a linear motion valve used to start or stop fluid flow; however, it does notregulate or throttle flow. The name gate is derived from the appearance of the disk in the flowstream..The disk of a gate valve is completely removed from the flow stream when the valve is fullyopen.
This characteristic offers virtually no resistance to flow when the valve is open. Hence,there is little pressure drop across an open gate valve.When the valve is fully closed, a disk-to-seal ring contact surface exists for 360°, and goodsealing is provided. With the proper of a disk to the seal ring, very little or no leakageoccurs across the disk when the gate valve is closed.
When the valve is fully closed,. With the proper mating of a disk to the seal ring, very little or no leakageoccurs across the disk when the gate valve is closed.
BALL VALVEA ball valve is a rotational motion valve thatuses a ball-shaped disk to stop or start fluidflow.The ball performs the same function as the diskin the globe valve. When the valve handle isturned to open the valve, the ball rotates to apoint where the hole through the ball is in linewith the valve body inlet and outlet. When thevalve is shut, the ball is rotatedso that the holeis perpendicular to the flow openings of thevalve body and the flow is stopped
PLUG VALVEA plug valve is a rotational motion valve used to stop or start fluid flow. The name is derivedfrom the shape of the disk, which resembles a plug. A plug valve is shown in Figure. Thesimplest form of a plug valve is the petcock. The body of a plug valve is machined to receivethe tapered or cylindrical plug.
The disk is a solid plug with a bored passage at a right angle tothe longitudinal axis of the plug.In the open position, the passage in the plug lines up with the inlet and outlet ports of the valveWhen the plug is turned 90° from the open position, the solid part of the plug blocks theports and stops fluid flow
BUTTERFLY VALVEA butterfly valve is a rotary motion valve that is used to stop, regulate, and start fluid flow.Butterfly valves are easily and quickly operated because a 90 degree rotation of the handle moves the disk from a fully closed to fully opened position..
Larger butterfly valves are actuated by hand wheels connected to the stem through gears that provide mechanical advantage at the expense of speed
NEEDLE VALVEA needle valve Is used to make relativelyfine adjustments in the amount of fluid flow. The distinguishing characteristic of aneedle valve is the long, tapered, needlelikepoint on the end of the valve stem.This "needle" acts as a disk.
The longer part of the needle is smaller than the orifice in the valve seat and passes through the orifice before the needle seats. This arrangement permits a very gradual increase or decrease in the size of the opening.
DIAPHRAM VALVESWhen the diaphragm, which is connectedto the stem of the valve by a compressor,is pulled away from the bottom of the valvebody or weir, the path of the fluid has asmooth, streamlined flow. Slurries at lowpressure that would normally clog mostother valve designs easily pass through adiaphragm
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