進口調節閥如何選型
閱讀：209發布時間：2012-12-14
進口調節閥如何選型
選擇進口調節閥時，首先要收集完整的工藝流體的物理特性參數與調節閥的工作條件，主要流體的成份、溫度、密度、粘度、正常流量、zui大流量、zui小流量、zui大流量與zui小流量下的進出口壓力、zui大壓差等。而在技術方面主要掌握和確定調節閥本身的結構、流量特性、額定流量系數Kv值、口徑大小、工藝允許壓差計算及執行機構的選擇、材料和安裝等方面的內容。
選擇進口調節閥時一般應遵循的原則有如下幾點。一、首先從動力源來選擇，美國威盾VTON根據方便和反應速度的要求來選擇用什么驅動方式的調節閥，主要有進口電動調節閥，進口氣動調節閥，進口自力式調節閥。二調節閥的結構型式：應能滿足介質溫度、壓力、流動性、流向、調節范圍以及嚴密性的要求。按結構分類主要有進口單座調節閥，進口雙座調節閥，進口套筒調節閥。三、調節閥的流量特性：應能滿足系統特性進行合理的補償。調節閥的流量特性是指介質流過閥的相對流量與閥桿相對位移間的關系，數學表達式如下：Q/Qmax=f（l/L），式中Q/Qmax為相對流量，為調節閥在某一開度時流量Q與全開流量Qmax之比；l/L為相對位移，調節閥在某一開度時閥芯位移l與全開位移L之比。選擇的總體原則是調節閥的流量特性應與調節對象特性及調節器特性相反，這樣可使調節系統的綜合特性接近于線性。選擇流量特性通常在工藝系統要求下進行，但是還要考慮下述實際情況。1、直線性流量特性適用范圍：①差壓變化小，幾乎恒定；②工藝流程的主要參數的變化呈線性；③系統壓力損失大部分分配在調節閥上（改變開度，閥上差壓變化相對較小）；④外部干擾小，給定值變化小，可調范圍要求小。2、等百分比特性適用范圍：①實際可調范圍大；②開度變化，閥上差壓變化相對較大；③管道系統壓力損失大；④工藝系統負荷大幅度波動；⑤調節閥經常在小開度下運行。3、除了以上兩種常用的流量特性之外，還有拋物線特性和快開特性等其他流量特性的調節閥。四調節閥的口徑：應能滿足工藝上對流量的要求。有進口大口徑調節閥，進口小口徑調節閥。根據已知的流體條件，計算出必要的Kv值，選取合適的調節閥口徑。
ControlvalveselectionandcommonsenseSelectthecontrolvalve,thefirstcompletecollectionofthephysicalcharacteristicsoftheprocessfluidcontrolvalveparametersandoperatingconditions,themainfluidcomposition,temperature,density,viscosity,normalflow,maximumflow,minimumflow,maximumflowandminimumflowrateimportandexportpressure,maximumpressureandsoon.Inthetechnicalaspectsofthemaincontrolvalveitselfanddeterminethestructure,flowcharacteristics,theratedflowcoefficientKvvalue,aperturesize,technologyallowsthecalculationofpressureandactuatorselection,materialsandinstallationaspects.Selectthecontrolvalvewhenthegeneralprinciplestobefollowedarethefollowing.Avalvestructuretype:shouldbeabletomeetthemediumtemperature,pressure,flow,flow,adjustthescopeandrigoroftherequirements.Twovalveflowcharacteristics:thesystemshouldbeabletomeetthecharacteristicsofreasonablecompensation.Controlvalveflowcharacteristicsisthemediumflowthroughthevalvestemrelativetoflowandtherelationshipbetweentherelativedisplacement,mathematicalexpressionsareasfollows:Q/Qmax=f（l/L）,whereQ/Qmaxfortherelativeflowrate,asadjustedWhenopeningthevalveataflowrateQandtheratiooffull-flowQmax;l/Lfortherelativedisplacementofthevalvewhenthevalveopeninginadisplacementlandtheratiooffull-shiftL.Theoverallprincipleistheselectioncontrolvalveregulatingtheflowcharacteristicsshouldbetheobjectcharacteristicsandregulatorfeaturesthecontrary,itwillgiveacomprehensivecontrolsystemfeaturesclosetolinear.Selecttheflowcharacteristicsintheprocessisusuallycarriedoutunderthesystemrequirements,butalsoconsiderthefollowingfacts.1,thelinearflowcharacteristicsofthescopeofapplication:①pressurechangeissmall,almostconstant;②Themainprocessparameterchangeslinearly;③lossofmostofthedistribut*tempressurecontrolvalveonthe（changeinopeningthevalveonthepressurechangeisrelativelysmall）;④externalinterference,giventhevalueofsmallchanges,smalladjustablerangeofrequirements.2,thepercentageofpropertiessuchasthescopeofapplication:①actualadjustablerange;②openingchange,relativelylargechangesindifferentialpressurevalve;③largepipingsystempressureloss;④processsystemloadfluctuations;⑤valveofteninsmallopeningrun.3,inadditiontotheabovetwocommonflowcharacteristics,thereareparabolicfeaturesandotherfeaturesquickopeningflowcharacteristicsofcontrolvalve.Threevalvediameter:shouldbeabletomeetthetechnicalrequirementsonthetraffic.Accordingtotheknownfluidconditions,necessarytocalculatetheKvvalue,selecttheappropriatevalvediameter.
