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Unformatted text preview: Lecture notes by Prof. M.W.Barve Valve 1 Introduction Introduction Introduction Introduction Valves are integral components in piping systems they are the primary method of controlling the flow, pressure and direction of the fluid. Valves may be required to operate continuously e.g. control valves, or they may be operated intermittently e.g. isolation valves, or they may be installed to operate rarely if ever e.g. safety valves. A valve can be an extremely simple, low cost item or it may be and extremely complicated, expensive item. In piping design the valves probably require more engineering effort than any other piping component. Valve Classification alve Classification alve Classification alve Classification Isolation/Stop valve- The isolation of the downstream system from the upstream system by use of and isolation /stop valve is a critically important function..The prime requirements of this valve are tight shut off when closed and minimum restriction to flow when open. Valves used for this function include gate valves, globe valves, ball valves, plug valves, butterfly valves, diaphragm valves and pinch valves Regulation of flow Many applications require the flow of the fluid be regulated (throttled) at some fixed or variable level between fully zero and maximum flow limits. This is achieved by introducing resistance to flow, or by bypassing flow or by changing the direction of the flow. An important feature for control valves is that the output variable (flow) is related to the input variable (valve position). An ideal operating characteristic of a hand operated flow control valve is that the flow is directly proportional to the position of the handwheel Valve types for this function include globe, needle, ball, butterfly. Globe and needle valves are best suited for this duty but ball valves are also easily adapted to give reliable flow control.. Back flow prevention In some circumstances it is important to prevent reversed fluid flow. The type of valve for this duty is a non-return-valve (NRV) or check valve. The important criteria when selecting these valves are, tight shut off against reverse flow, low resistance to flow for forward flow, fast response. The valve can be operated to close by gravity, fluid flow, or spring. Two main valve types are available for this function lift check valves or swing check valves. Pressure Regulation In many applications, more generally associated with gases, there is a need to reduce the supply press to a set fixed value. It is also necessary to maintain this reduced pressure over a range of fluid flow conditions. The pressure regulator valve is engineered for this application. The valve is basically a globe valve biased open by an adjustable spring force with the feedback pressure tending to move the valve to a closed position such that at the set pressure the feedback pressure force just exceeds the spring force The pressure regulator valve operates using the downstream fluid pressure as feedback. This is mostly taken from within the valve (self acting). For more accurate control a feedback connection can be taken from the downstream piping. Lecture notes by Prof. M.W.BarveLecture notes by Prof....
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