Thursday, August 30, 2012

Valve Basics

Definition of Valve

  • In mechanical engineering, a Valve is a mechanical device that controls the flow of fluid and pressure within a system or process. 
  • Valve is any device for closing or modifying  the passage through a pipe, outlet, inlet, or the like, in order to stop, allow, or control the flow of a  fluid media.
  • Valve is mechanical or electromechanical device by which the flow of a gas, liquid, slurry, or loose dry material can be started stopped, diverted, and/or regulated or throttled.
Use of Valve or Applications of valves

Valve is found everywhere. Applications of valves have great variety and breath. Where there is flow of fluid, there would be valve to control the flow. 

Can you think of pipe having fluid (liquid or gas) running through it and no valve to stop, start or regulate the flow? 
Valves are found in power plants, process plants, hydal applications, hvac application and domestic applications. Valve is used in steam lines and gas lines also for control purposes. Air control valve is also use for control purposes .Failures of valves may be catastrophic for the whole system depending upon the type of application. 

Leaky, rusty and noisy valves indicate the lack of right Maintenance Programs for valves. Sometimes valve leaks may have health hazards .Obviously no one wants to waste chemistry controlled fluid through these valves. Your leaky valve would make it impossible to isolate any equipment or system at the time of maintenance so all valves need attention before they become headache for you.
Function of valve

A valve controls system or process fluid flow and pressure. These aforesaid objectives of valves are achieved by performing any of the following functions:
  • Stopping and starting flow of fluid
  • Varying (throttling) the amount of flow of fluid
  • Regulating downstream system or process pressure
  • Controlling the direction of flow of fluid
  • Relieving component or piping over pressure
Flow control Valve  ------- 4 Methods By which it works

As a student of mechanical engineering, plant engineers, plant technician, maintenance technician or plant operator you might be interested in knowing how flow is controlled in these valves. In general, there are four methods of controlling flow through a valve.

  1. Move a disc, or plug into or against an orifice (for example, globe or needle type valve).
  2. Slide a flat, cylindrical, or spherical surface across an orifice (for example, gate and plug valves).
  3. Rotate a disc or ellipse about a shaft extending across the diameter of an orifice (for example, a butterfly or ball valve).
  4. Move a flexible material into the flow passage (for example, diaphragm and pinch valves).
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