VALVE AND ITS TYPE

A valve is a mechanical device that blocks a pipe either partially or completely to change the amount of fluid that passes through it. When you turn on a faucet (tap) to brush your teeth, you're opening a valve that allows pressurized water to escape from a pipe. Similarly, when you flush the toilet, you open two valves: one that allows water to escape to empty the pan and another (called a ball valve or ballcock) that admits more water into the tank ready for the next flush.

Valves regulate gases as well as liquids. If you have a gas cooktop (hob) on your stove, the controls that turn the gas up or down are valves. When you turn up the heat, you're opening a valve that allows more gas to flow in through the pipe. More gas burns with a bigger flame so you get more heat.

Valves are usually made of metal or plastic and they have several different parts. The outer part is called the seat and it often has a solid metal outer casing and a soft inner rubber or plastic seal so the valve makes a closure that's absolutely tight. The inner part of the valve, which opens and closes, is called the body and fits into the seat when the valve is closed. There's also some form of mechanism for opening and closing the valve—either a manual lever or wheel (as in a faucet or a stop cock) or an automated mechanism (as in a car engine or steam engine).

TYPES OF VALVE :-

There are  different types of valves, all have different names. The most common ones are the butterfly, cock or plug, gate, globe, needle, poppet, and spool:

• Ball: In a ball valve, a hollowed-out sphere (the ball) sits tightly inside a pipe, completely blocking the fluid flow. When you turn the handle, it makes the ball swivel through ninety degrees, allowing the fluid to flow through the middle of it.
• Butterfly: A butterfly valve is a disk that sits in the middle of a pipe and swivels sideways (to admit fluid) or upright (to block the flow completely).
• Cock or plug: In a cock or plug valve, the flow is blocked by a cone-shaped plug that moves aside when you turn a wheel or handle.
• Gate or sluice: Gate valves open and close pipes by lowering metal gates across them. Most valves of this kind are designed to be either fully open or fully closed and may not function properly when they are only part-way open. Water supply pipes use valves like this.
• Globe: Water faucets (taps) are examples of globe valves. When you turn the handle, you screw a valve upward and this allows pressurized water to flow up through a pipe and out through the spout below. Unlike a gate or sluice, a valve like this can be set to allow more or less fluid through it.
• Needle: A needle valve uses a long, sliding needle to regulate fluid flow precisely in machines like car engine carburetors and central-heating systems.
• Poppet: The valves in car engine cylinders are poppets. This type of valve is like a lid sitting on top of a pipe. Every so often, the lid lifts up to release or admit liquid or gas.
• Spool: Spool valves regulate the flow of fluid in hydraulic systems. Valves like this slide back and forward to make fluid flow in either one direction or another around a circuit of pipes.