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Because ball valves stem can't rise. It turns 90° but it doesn't rise. Back seat test ( appicable for gate and globe valves only) can be carried out by means of the full opening of the valve. Once the valve is in full open position the stem should be in contact with the bonnet ( generally hardfaced on that area) , in a manner that a sealing between bonnet and stem allows the packing to be replaced with the pressure inside the valve. Of course this is possible only because the stem rises. In the ball valves ( standard) the stem only rotate 90° , then the back seat test can't be done.
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What is the difference between Trunnion mounted ball valves and floating ball valves?
Sealing Makes all the difference. The key difference beteween a floating ball valve and a trunnion mounted ball valve is how each achieves a line seal. Trunion mounted ball valves are uses a spring mechanism and/or line pressure assistance to drive the upstream seat against the stationary ball. The surface area exposed to the pressure through the relatively small passageway is actually just the back of the seat. The floating ball valve utilize natural line pressure to press and seal the ball against the downstream seat. The line pressure is exposed to a greater surface area - the entire upstream face of the ball, which is an area equal to the actual pipe size.
What is the difference between plug valves and globe valves with plug?
A Plug Valve is a Globe Valve. Very generally speaking there are two major catagories of Industrial Process Control Valves, Sliding Stem and Rotary. Globe Bodies valves fall into the category of Sliding Stem Valves. Butterfly and Ball valves fall into the category of Rotary valves. However there are what is referred as Rotary Plug Valves, whereby a partial sphere has a shaft eccentrically mounted, that rotates into and out of a metal or composition seat acting as a plug. Most plug valves are sliding stem.
How do you reassemble the spring and ball in a check valve?
If in a well replace it as it is worn out. If something was stuck in it set the ball on the seat and the spring on the ball to push ball to seat, then the ball retainer. Pressure should push the ball open and the spring should close the ball. (make sure all the spring is there)
What are the uses of a globe valve?
To throttle the medium being used as a globe is NOT a positive shut off A globe valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body. For example, globe valves or valves with a similar mechanism may be used as sampling valves, which are normally shut except when liquid samples are being taken. Since the baffle restricts flow, they're not recommended where full, unobstructed flow is required.
What is the difference between a globe valve and a ball valve?
The Globe valves are generally used to control the flow rate and ball valve used for open /close purpose only.A globe valve is a type of valve used for regulating flow in a pipeline, consisting of a movable disk-type element and a stationary ring seat in a generally spherical body.A ball valve is a valve with a spherical disc, the part of the valve which controls the flow through it.
