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Views: 74 Author: Site Editor Publish Time: 2018-01-02 Origin: www.fuchun-casting.com
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).
It's often critically important for valves that are switched off to allow absolutely no escape of liquid or gas through a pipe to avoid accidents, explosions, pollution, or the loss of valuable chemicals (even a dripping faucet can be expensive if your water is metered). That's why the seal on a valve needs to be perfectly secure and a valve that's turned off must be tightly closed. Turning off a high-pressure flow of liquid or gas by obstructing it with a valve is physically hard work: in other words, you need to use a lot of force to do it. That's why some valves are operated by long levers (as in our top photo) or large wheels (as in the photo shown here). If really big valves require too much force for a human to supply, they're operated by hydraulic rams.
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.
The many 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.