The background of the safety balve

As soon as mankind was able to boil water to create steam, the necessity of the safety device became evident. As long as 2000 years ago, the Chinese were using cauldrons with hinged lids to allow (relatively) safer production of steam. At the beginning of the 14th century, chemists used conical plugs and later, compressed springs to act as safety devices on pressurised vessels.

Early in the 19th century, boiler explosions on ships and locomotives frequently resulted from faulty safety devices, which led to the development of the first safety relief valves.
The first safety valve was invented by Denis Papin for his steam digester, an early pressure cooker rather than an engine. A weight acting through a lever held down a circular plug valve in the steam vessel. By using a "steelyard" lever a smaller weight was required, also the pressure could easily be regulated by sliding the same weight back and forth along the lever arm. Papin retained the same design for his 1707 steam pump.
A safety valve is a valve mechanism which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits.
Safety Valve is a one type of valve that automatically actuates when the pressure of inlet side of the valve increases to a predetermined pressure, to open the valve disc and discharge the fluid ( steam or gas ) ; and when the pressure decreases to the prescribed value, to close the valve disc again. Safety valve is so-called a final safety device which controls the pressure and discharges certain amount of fluid by itself without any electric power support.
Safety Valve is mainly installed in a chemical plant, electric power boiler, gas storage tank, preventing the pressure vessels from exploding or damaging.
Pressure safety valves are automatic or manual release devices designed to expel gas or liquid from a mechanical system if the pressure rises above a set limit. Also known as pressure relief valves, they are mechanical devices that function by way of weights or springs, or electronic that has sophisticated sensors to engage operation. There are three main types of pressure safety valves used in both industry and commercial machines are thermal, flow and shut-off valves.
Flow valves are different from thermal valves in that they are very often considerably larger. Flow valves are sized for situations when larger quantities of gas or liquids may need to be quickly released to relive growing pressure. Flow valves are often used for larger storage tanks or pipelines when a significant rupture could cause much damage.
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