Thursday, 10 May 2012

Valves and blowout preventers

Valves control the flow of liquids like gas. Either it opens, closes or partially obstructs the passage through which the fluid flows. In an open valve, fluids flow from high pressure level to low pressure. Gate valves restrict or allow the flow of liquid.
They are suitable where full flow is needed or where the flow needs to be restricted completely. The gate valve has to be operated fully closed or fully open. Gate valves have an ability to cut through liquids thus they are used in petroleum industry.
Discs are part of gate valves. Rising stem and non rising stem are types of discs. Expanding gate valve can have either of these discs. Rising stem gate valve has a handle that rotates around a thread shaft. The shaft or the stem rises as the valve opens and descends as the valve is closed. Non rising stem is used where there are space constraints. When the handle is rotated to the left the valves are fully open and when rotated to the right they are fully closed.
Annular Blowout Preventers
Blowout preventers are a type of valve used to protect the oil and gas wells. During drilling there can be extreme pressures from the fluid flowing from the reservoir. There are two types of blowout preventers, Ram and Annular blowout preventers.  Annular preventers use wedge to shut the well bore. Annular Blowout preventer was invented by Granville Sloan Knox. It seals around pipes of various sizes. It is commonly known as the “Hydril” at the rigs.
Annular blowout preventer proves effective in sealing around the drill pipe as it rotates around during drilling. Ram preventers are more effective in providing a seal around the wellbore than annular blowout preventers.
Blowout preventers and valves typically control the flow of the fluid and prevent a blowout.


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