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FUNDAMENTAL PRINCIPLES OF PRESSURE REGULATORS - …

PAGE 262003 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGYFUNDAMENTAL PRINCIPLES OF PRESSURE REGULATORSP resented by Kevin ShawActaris Metering Systems970 Hwy. 127 North, Owenton, KentuckyINTRODUCTIONThe following paper will concentrate on the fundamentalsand PRINCIPLES of natural gas PRESSURE REGULATORS . In thegas regulator s conception it was mainly a device usedto reduce high PRESSURE to a more usable lower , more is expected from the performance of thepressure regulator. PRESSURE reduction is no longer theonly function needed.

Jan 07, 2003 · pneumatic load. The high-pressure inlet gas creates a pneumatic force (F i) pushing on the face of the valve seat forcing open the valve. An adjustable spring force (F s) assists the high inlet pressure by pushing on the sensing device (diaphragm), opening the valve to maintain the set pressure. These forces can be calculated as follows: (Hooke ...

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Transcription of FUNDAMENTAL PRINCIPLES OF PRESSURE REGULATORS - …

1 PAGE 262003 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGYFUNDAMENTAL PRINCIPLES OF PRESSURE REGULATORSP resented by Kevin ShawActaris Metering Systems970 Hwy. 127 North, Owenton, KentuckyINTRODUCTIONThe following paper will concentrate on the fundamentalsand PRINCIPLES of natural gas PRESSURE REGULATORS . In thegas regulator s conception it was mainly a device usedto reduce high PRESSURE to a more usable lower , more is expected from the performance of thepressure regulator. PRESSURE reduction is no longer theonly function needed.

2 The regulator is considered anintegral measurement instrument that must adhere tothe stringent codes put forth by the FederalDepartment of Transportation and many state PublicUtility order to understand the PRINCIPLES of pressureregulation this paper will focus DROOP VS. IN INLET PRESSURE ADVANTAGEIV. SAFETY MECHANISMSV. KEYS TO SELECTIONVI. CONCLUSIONSREGULATOR CLASSIFICATIONSWith few exceptions, gas PRESSURE REGULATORS can beclassified into either of the following two categories: 1.

3 Self-Operated REGULATORS (also known as Spring-Loaded) 2. Pilot REGULATORS Constant-Loaded ( Pilot-Loaded) Pilot Operated ( Two-Path Regulation) Pilot Unloading ( PRESSURE Unloading)The Pilot Regulator category can further be classified intothe three sub-categories of Constant-Loaded, PilotOperated, and Pilot Unloaded. Make no mistake; thesethree design are vastly different and, thus, will exhibitsignificantly different performance characteristics. Eachof these designs is covered in more detail later in the DEFINITIONA PRESSURE regulator is a feedback control mechanismdesigned to maintain a constant downstream pressurethrough the manipulation of gas flow.

4 By definition, aregulator is composed of three essential components(see Figure 1 illustration):1. Restricting Element A restriction which allowsgas to flow through the regulator at a reducedpressure to meet downstream demand. In mostcases this consists of a resilient valve seat (plug)and a sharp edged Measuring Element A device that continuouslysenses changes in downstream PRESSURE caused bychanges in downstream demand and transmits asignal to open or close the restricting elementaccordingly.

5 This is typically an Loading Element Adjustable force which iscontinuously compared to the downstream pressureby the measuring element to determine what signal(open/close) to transmit to the restricting pilot REGULATORS the loading element is REGULATOR OPERATIONThe main function of any regulator is to provide a flow ofgas through the regulator to match the downstreamdemand while holding PRESSURE constant. In a spring-loaded regulator three devices are employed to achievethis a restricting device (usually an orifice); a sensingdevice (diaphragm); and a loading device (spring orpressure).

6 Tying these three things together is aRestricting Element sensing ElementLoading ElementFIGURE PROCEEDINGSPAGE 27 AMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY mechanical linkage (usually called the valve stem and/or lever) that acts like a see-saw. The linkage works tobalance the forces associated with the three pseudo free-body diagram gives a representation ofthis balancing act is shown in Figure 2. Regulator Force BalanceIn all REGULATORS two types of forces exist: 1) openingand 2) closing forces. These two forces act on themechanical linkage with one trying to close the valve(shutting off gas flow) while the other works to open thevalve (increasing gas flow).

7 Under steady operation thesums of the opening and closing forces are always equalbut opposite in direction giving a static equilibriumcondition. As in any static equilibrium condition, the valvewill remain in a fixed position until one of the forceschange, upsetting the equilibrium. The valve will thenreposition again until the forces are again in a spring-loaded regulator, the sum of forces on themechanical linkage can be expressed as follows:Opening Forces = Closing ForcesorFi + Fs = FoWhere:Fi = Inlet PRESSURE ForceFs = Spring ForceFo = Outlet PRESSURE ForceThis equation assumes there are no frictional effectsinside the opening forces consist of one mechanical and onepneumatic load .

8 The high- PRESSURE inlet gas creates apneumatic force (Fi) pushing on the face of the valveseat forcing open the valve. An adjustable spring force(Fs) assists the high inlet PRESSURE by pushing on thesensing device (diaphragm), opening the valve tomaintain the set PRESSURE . These forces can be calculatedas follows: (Hooke s Law)Where:K = Spring Constant ( )x = Spring Compression (in.)Where: P1 = Inlet PressureAo = Orifice AreaThe downstream PRESSURE under the diaphragm createsa closing force (Fo) pushing against the diaphragm tryingto close off the flow of gas.

9 This force is calculated as:In normal operation, the diaphragm will sense the outletpressure force change and provide a force to the linkage moves to control the flow through the valveto maintain the set outlet PRESSURE . For instance, if theoutlet PRESSURE drops from the set PRESSURE , the forceunder the diaphragm Fo decreases allowing the springforce Fs to reposition the diaphragm. This downwardtravel acts to move the valve seat away from the orifice,bringing the outlet back to approximately the desiredset PRESSURE .

10 If the outlet PRESSURE increases, the reversehappens. The linkage responds to the increased outletpressure force and tends to restrict the orifice. The flowis reduced and the outlet PRESSURE once again returnsapproximately to the set a perfect world our loading element (the spring) wouldsupply a constant force, there would be no friction withinthe regulator or material hysteresis. If this were the casethe regulator would supply a constant outlet pressureover an infinite range of gas flows. However, thisperformance is unattainable.


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