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What is a ball valve?
In this article, we will introduce the design and operation of the ball valve.
Ball valves are one of the most popular valves on the market, and all ball valves operate in the same way: the ball opens and closes, allowing flow through the valve.
We will study four key points of the ball valve:
**Design and testing
One of the most important factors in designing a ball valve is dimensional control of all metal parts, surface finish and tolerances between each other. The ball must be perfectly round and preset to fit soft Teflon materials, or harder seats such as reinforced PTFE, peep or metal.
The secret of any seal design is local deformation (ie the yield of the seat produced at the point of contact) and filling the gap between the metal ball and the soft seat. Without such local yielding, bubble or vacuum properties cannot be obtained.
Design and testing
Most floating design ball valves are hydraulic housing tested at 1.5 times the ANSI rated pressure. The valve seat is tested at 80 or 100 psi in the closed position.
(Note: It is important not to test the ball valve above the working pressure in the closed position. For system pressure tests above the expected working pressure, it is important to keep the ball valve in the open position.)
The rated pressure at the weld or threaded end of most smaller (1/4" - 3") float valves is WOG (water, oil or gas) or MAWP (maximum allowable working pressure). At normal ambient temperatures, the MAWP or WOG pressure rating is considered to be no more than pressure.
In most soft seat valves, there is a pressure-temperature curve, the maximum pressure at ambient temperature and the maximum pressure at the seat's maximum temperature rating. This depends on the stress level of the seat and its thermal cycling capability within these limits. The seat must be strong enough and thick enough to achieve a hydrodynamic effect without folding or deforming.
The design of each seat varies with the application, material strength and manufacturing of the physical compound. Pressure - The temperature profile and torque curve vary with the material of the seat and the design of each valve.
Floating principle of ball valve
Historically, engineered ball valves have soft seats made of plastic material to create a tight seal against the float. The ball valve floating principle means that three things happen inside the valve:
The ball floats freely and does not stick to the pole.
Under pressure, the ball should move into the downstream seat and form a preset suitable for sealing the soft seat material.
The seat will perform an optimal seal at the highest working pressure.
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