Valve Interview Questions and Answers - Scribd

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The document discusses different types of valves, their functions, materials, and uses. It provides definitions for 50 different types of valves including gate, globe, check, ball, butterfly, plug, diaphragm, and specialty valves. It describes the steps in selecting a valve based on its application and discusses common valve components, materials, and tests.

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I assume that you are saying that, in a specific test set up, when using three different valves of the same nominal size, the apparent opening of the valves is different depending on the type of the valve (gate/globe/ball)

If my interpretation is correct, your observation is probably a result of the different pressure drops across the seat which will be specific to the internal physical arrangement of the valve. A ball valve could be the least pressure drop just because it might have a full size port which aligns precisely with the pipe, whereas the other two valves have more complicated flow paths and protrusions to create internal turbulence (pressure drop). Actually, I would expect the ball to be the best and the globe valve to be the worst.

David Pressure drop is almost never an issue during a test, if the fluid can pass, the pressures will equilze because the rate of pressurization is much too slow for friction drops to be a factor.

A possible explaination:
- Gate valve full open (and on the back seat) to keep test pressure off the packing gland.
- Globe valve full open (and on the back seat) to keep pressure off the packing gland.
- Ball valve part open to pressurize the body cavity (full open doesn't pressurize the area between the ball and the casing).