電(dian)動(dong)(dong)執(zhi)(zhi)行(xing)器的選(xuan)購(gou)全部(bu)是(shi)看你需要(yao)什(shen)么，看你買這個執(zhi)(zhi)行(xing)器是(shi)干什(shen)么。電(dian)動(dong)(dong)執(zhi)(zhi)行(xing)器是(shi)實現電(dian)動(dong)(dong)調(diao)節閥程控、自控和遙(yao)控優良的設備，其(qi)運動(dong)(dong)過程可由行(xing)程、轉矩或軸向推(tui)力的大小(xiao)來控制。因此，正確選(xuan)擇電(dian)動(dong)(dong)執(zhi)(zhi)行(xing)器，對防(fang)止出現超負荷現象至關重要(yao)。那么，電(dian)動(dong)(dong)執(zhi)(zhi)行(xing)器的選(xuan)購(gou)應依據哪些方面呢(ni)？

首先，操(cao)作力(li)矩是選擇電(dian)(dian)動(dong)(dong)(dong)執行(xing)(xing)器的(de)主(zhu)要參(can)數(shu)。電(dian)(dian)動(dong)(dong)(dong)執行(xing)(xing)器輸(shu)出力(li)矩應為(wei)閥門操(cao)作大力(li)矩的(de)1．2～1．5倍。操(cao)作推力(li)：電(dian)(dian)動(dong)(dong)(dong)執行(xing)(xing)器的(de)主(zhu)機(ji)結構(gou)有兩種(zhong)：一種(zhong)是不配置推力(li)盤(pan)，直接(jie)輸(shu)出力(li)矩；另一種(zhong)是配置推力(li)盤(pan)，輸(shu)出力(li)矩通過推力(li)盤(pan)中的(de)閥桿螺(luo)(luo)母轉(zhuan)換為(wei)輸(shu)出推力(li)。輸(shu)出軸(zhou)轉(zhuan)動(dong)(dong)(dong)圈(quan)數(shu)：電(dian)(dian)動(dong)(dong)(dong)執行(xing)(xing)器輸(shu)出軸(zhou)轉(zhuan)動(dong)(dong)(dong)圈(quan)數(shu)的(de)多(duo)少與閥門的(de)公(gong)稱通徑、閥桿螺(luo)(luo)距、螺(luo)(luo)紋(wen)頭數(shu)有關。

其次，是(shi)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)桿(gan)(gan)(gan)(gan)直徑(jing)。對(dui)多(duo)回轉(zhuan)(zhuan)類明(ming)桿(gan)(gan)(gan)(gan)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)門，如(ru)果電動(dong)執行器允許通過的(de)(de)(de)(de)大閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)桿(gan)(gan)(gan)(gan)直徑(jing)不(bu)(bu)(bu)能(neng)通過所配閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)門的(de)(de)(de)(de)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)桿(gan)(gan)(gan)(gan)，便不(bu)(bu)(bu)能(neng)組裝(zhuang)成電動(dong)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)門。因此，電動(dong)執行器空(kong)心輸(shu)出軸的(de)(de)(de)(de)內(nei)徑(jing)需要(yao)大于(yu)明(ming)桿(gan)(gan)(gan)(gan)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)門的(de)(de)(de)(de)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)桿(gan)(gan)(gan)(gan)外徑(jing)。對(dui)部分(fen)回轉(zhuan)(zhuan)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)門以及多(duo)回轉(zhuan)(zhuan)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)門中的(de)(de)(de)(de)暗(an)桿(gan)(gan)(gan)(gan)閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)門，雖不(bu)(bu)(bu)用考慮閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)桿(gan)(gan)(gan)(gan)直徑(jing)的(de)(de)(de)(de)通過問(wen)題，但在選配時亦應充分(fen)考慮閥(fa)(fa)(fa)(fa)(fa)(fa)(fa)桿(gan)(gan)(gan)(gan)直徑(jing)與(yu)鍵槽(cao)的(de)(de)(de)(de)尺寸，使組裝(zhuang)后能(neng)正常工作。

閥門的(de)啟閉速(su)度若過(guo)快(kuai)，易(yi)產(chan)生(sheng)水擊現(xian)象。因(yin)(yin)此(ci)，應根據不同的(de)使(shi)(shi)用(yong)(yong)條件選(xuan)擇恰當的(de)啟閉速(su)度。電(dian)(dian)動(dong)執(zhi)行(xing)器有其特別要(yao)求，即(ji)需(xu)(xu)要(yao)能夠(gou)限(xian)定(ding)(ding)轉矩(ju)(ju)(ju)(ju)或軸向力。通常電(dian)(dian)動(dong)執(zhi)行(xing)器采(cai)用(yong)(yong)限(xian)制(zhi)轉矩(ju)(ju)(ju)(ju)的(de)連(lian)軸器。當電(dian)(dian)動(dong)執(zhi)行(xing)器規(gui)格確定(ding)(ding)之后，其控制(zhi)轉矩(ju)(ju)(ju)(ju)也就確定(ding)(ding)了。一般在預先確定(ding)(ding)的(de)時間(jian)內運行(xing)，電(dian)(dian)機(ji)(ji)(ji)不會超負荷。但如出現(xian)下(xia)列情況便可能導致超負荷：一是電(dian)(dian)源電(dian)(dian)壓低(di)，得(de)不到所需(xu)(xu)的(de)轉矩(ju)(ju)(ju)(ju)，使(shi)(shi)電(dian)(dian)機(ji)(ji)(ji)停止轉動(dong)；二是錯誤地調定(ding)(ding)轉矩(ju)(ju)(ju)(ju)限(xian)制(zhi)機(ji)(ji)(ji)構(gou)，使(shi)(shi)其大于停止的(de)轉矩(ju)(ju)(ju)(ju)，造成(cheng)連(lian)續(xu)產(chan)生(sheng)過(guo)大轉矩(ju)(ju)(ju)(ju)，使(shi)(shi)電(dian)(dian)機(ji)(ji)(ji)停止轉動(dong)；三是斷續(xu)使(shi)(shi)用(yong)(yong)，產(chan)生(sheng)的(de)熱量積蓄，超過(guo)了電(dian)(dian)機(ji)(ji)(ji)的(de)允許溫(wen)(wen)升(sheng)值；四是因(yin)(yin)某種原因(yin)(yin)轉矩(ju)(ju)(ju)(ju)限(xian)制(zhi)機(ji)(ji)(ji)構(gou)電(dian)(dian)路(lu)發生(sheng)故障，使(shi)(shi)轉矩(ju)(ju)(ju)(ju)過(guo)大；五(wu)是使(shi)(shi)用(yong)(yong)環境溫(wen)(wen)度過(guo)高，相對使(shi)(shi)電(dian)(dian)機(ji)(ji)(ji)熱容量下(xia)降。因(yin)(yin)此(ci)，從以(yi)上可知，過(guo)負荷的(de)基本保(bao)(bao)護方法是：對電(dian)(dian)機(ji)(ji)(ji)連(lian)續(xu)運轉或點動(dong)操作的(de)過(guo)負荷保(bao)(bao)護，采(cai)用(yong)(yong)恒溫(wen)(wen)器；對電(dian)(dian)機(ji)(ji)(ji)堵轉的(de)保(bao)(bao)護，采(cai)用(yong)(yong)熱繼電(dian)(dian)器；對短路(lu)事故，采(cai)用(yong)(yong)熔斷器或過(guo)流繼電(dian)(dian)器。