- Settore: Industrial valves
- Number of terms: 3113
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The location where cross-sectional area of the flow stream is at its minimum size, where fluid velocity is at its highest level, and where fluid pressure is at its lowest level. The vena contracta normally occurs just downstream of the actual physical restriction in a control valve.
Industry:Industrial valves
The high and low values of pressure applied to the diaphragm to produce rated travel with stated conditions in the valve body. The “stated conditions” referred to here mean the actual pressure drops at operating conditions. Example: A control valve may have an inherent diaphragm pressure or bench set of 8 to 15 psig. But when subjected to a 600 psig. Inlet pressure, it may start to open at 3 psig. And be full open at 15 psig. It is because of the forces acting on the valve plug and the direction of flow through the valve (flow-to-open or flow-to-close) that the installed diaphragm pressure will differ from the inherent diaphragm pressure.
Industry:Industrial valves
The movable part of the valve which is positioned in the flow path to modify the rate of flow through the valve. Some of the different types of closure members are the Ball, Disk, Gate, and Plug.
Industry:Industrial valves
The flow control orifice and seat that is an integral part of the valve body or cage. The seat is machined directly out of the valve body and is normally not replaceable without replacing the body itself – although some can be repaired by welding and remachining.
Industry:Industrial valves
The flow characteristic when the pressure drop across the valve varies with flow and related conditions in the system in which the valve is installed. The purpose of characterizing a control valve is to help compensate for nonlinearities in the control loop.
Industry:Industrial valves
The contact force between the seat and the valve plug. When an actuator is selected for a given control valve, it must be able to generate enough force to overcome static, stem, and dynamic unbalance with an allowance made for seat load.
Industry:Industrial valves
The body of the valve is the main pressure boundary. It provides the pipe connecting ends and the fluid flow passageway. It can also support the seating surface and the valve closure member.
Industry:Industrial valves
The distance the plug or stem moves in order to go from a full-closed to a full-open position. Also called stroke.
Industry:Industrial valves
The difference between up-scale and down-scale results in instrument response when subjected to the same input approached from the opposite direction. Example: A control valve has a stroke of 1. 0 inch and we give the valve a 9 psig signal. The valve travels 0. 500 of an inch. We then give the valve a 12 psig signal, and the valve travels to 0. 750 of an inch. When the valve is then given a 9 psig signal, the stroke is measured at 0. 501. That represents hysteresis. Hysteresis can be caused by a multitude of variables, packing friction, loose linkage, pressure drop, etc. If someone asks you what the hysteresis of your control valve is, it is a bum question because hysteresis is more aptly applied to an instrument than to a control valve. There are simply too many variables in the valve and the system to answer the question properly. The control valve only responds to the controller signal and will move to a position to satisfy the controller – thus negating the effects of hysteresis.
Industry:Industrial valves
The configuration provided to make a pressure-tight joint to the pipe carrying the fluid to be controlled. The most common of these connections are threaded, flanged, or welded.
Industry:Industrial valves
