進(jìn)口調(diào)節(jié)閥如何選型
閱讀：210發(fā)布時(shí)間：2012-12-14
進(jìn)口調(diào)節(jié)閥如何選型
選擇進(jìn)口調(diào)節(jié)閥時(shí)，首先要收集完整的工藝流體的物理特性參數(shù)與調(diào)節(jié)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(jìn)出口壓力、zui大壓差等。而在技術(shù)方面主要掌握和確定調(diào)節(jié)閥本身的結(jié)構(gòu)、流量特性、額定流量系數(shù)Kv值、口徑大小、工藝允許壓差計(jì)算及執(zhí)行機(jī)構(gòu)的選擇、材料和安裝等方面的內(nèi)容。
選擇進(jìn)口調(diào)節(jié)閥時(shí)一般應(yīng)遵循的原則有如下幾點(diǎn)。一、首先從動(dòng)力源來(lái)選擇，美國(guó)威盾VTON根據(jù)方便和反應(yīng)速度的要求來(lái)選擇用什么驅(qū)動(dòng)方式的調(diào)節(jié)閥，主要有進(jìn)口電動(dòng)調(diào)節(jié)閥，進(jìn)口氣動(dòng)調(diào)節(jié)閥，進(jìn)口自力式調(diào)節(jié)閥。二調(diào)節(jié)閥的結(jié)構(gòu)型式：應(yīng)能滿足介質(zhì)溫度、壓力、流動(dòng)性、流向、調(diào)節(jié)范圍以及嚴(yán)密性的要求。按結(jié)構(gòu)分類主要有進(jìn)口單座調(diào)節(jié)閥，進(jìn)口雙座調(diào)節(jié)閥，進(jìn)口套筒調(diào)節(jié)閥。三、調(diào)節(jié)閥的流量特性：應(yīng)能滿足系統(tǒng)特性進(jìn)行合理的補(bǔ)償。調(diào)節(jié)閥的流量特性是指介質(zhì)流過(guò)閥的相對(duì)流量與閥桿相對(duì)位移間的關(guān)系，數(shù)學(xué)表達(dá)式如下：Q/Qmax=f（l/L），式中Q/Qmax為相對(duì)流量，為調(diào)節(jié)閥在某一開度時(shí)流量Q與全開流量Qmax之比；l/L為相對(duì)位移，調(diào)節(jié)閥在某一開度時(shí)閥芯位移l與全開位移L之比。選擇的總體原則是調(diào)節(jié)閥的流量特性應(yīng)與調(diào)節(jié)對(duì)象特性及調(diào)節(jié)器特性相反，這樣可使調(diào)節(jié)系統(tǒng)的綜合特性接近于線性。選擇流量特性通常在工藝系統(tǒng)要求下進(jìn)行，但是還要考慮下述實(shí)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(shù)的變化呈線性；③系統(tǒng)壓力損失大部分分配在調(diào)節(jié)閥上（改變開度，閥上差壓變化相對(duì)較小）；④外部干擾小，給定值變化小，可調(diào)范圍要求小。2、等百分比特性適用范圍：①實(shí)際可調(diào)范圍大；②開度變化，閥上差壓變化相對(duì)較大；③管道系統(tǒng)壓力損失大；④工藝系統(tǒng)負(fù)荷大幅度波動(dòng)；⑤調(diào)節(jié)閥經(jīng)常在小開度下運(yùn)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(diào)節(jié)閥。四調(diào)節(jié)閥的口徑：應(yīng)能滿足工藝上對(duì)流量的要求。有進(jìn)口大口徑調(diào)節(jié)閥，進(jìn)口小口徑調(diào)節(jié)閥。根據(jù)已知的流體條件，計(jì)算出必要的Kv值，選取合適的調(diào)節(jié)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.
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