三道鎮機械密封包括壓力控制、溫度控制、流體替換(堵塞)和雜質去除系統。在三道鎮機械密封系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)中，上述系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)并(bing)不同時包(bao)括在內。密封(feng)(feng)(feng)系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)的(de)(de)選擇主(zhu)(zhu)要取決于主(zhu)(zhu)密封(feng)(feng)(feng)件的(de)(de)應(ying)用(yong)范圍(wei)。例如(ru)，如(ru)果主(zhu)(zhu)密封(feng)(feng)(feng)用(yong)于高(gao)溫(wen)(wen)液體，密封(feng)(feng)(feng)系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)應(ying)確保降(jiang)(jiang)(jiang)低(di)(di)(di)主(zhu)(zhu)密封(feng)(feng)(feng)的(de)(de)環(huan)境(jing)溫(wen)(wen)度，即(ji)采用(yong)溫(wen)(wen)度控制(zhi)系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)。如(ru)果主(zhu)(zhu)密封(feng)(feng)(feng)用(yong)于固體雜質(zhi)(zhi)含量高(gao)的(de)(de)工作介質(zhi)(zhi)，密封(feng)(feng)(feng)系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)應(ying)確保在主(zhu)(zhu)密封(feng)(feng)(feng)前降(jiang)(jiang)(jiang)低(di)(di)(di)固體雜質(zhi)(zhi)含量，即(ji)采用(yong)除雜系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)。在腐(fu)蝕(shi)性介質(zhi)(zhi)中，密封(feng)(feng)(feng)系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)必須確保主(zhu)(zhu)密封(feng)(feng)(feng)降(jiang)(jiang)(jiang)低(di)(di)(di)腐(fu)蝕(shi)速率或消除腐(fu)蝕(shi)，即(ji)使用(yong)流體而不是堵塞(sai)流體系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)；在高(gao)壓(ya)(ya)密封(feng)(feng)(feng)裝置中，輔助系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)應(ying)確保多(duo)級降(jiang)(jiang)(jiang)壓(ya)(ya)和其他(ta)措施，即(ji)壓(ya)(ya)力控制(zhi)系(xi)(xi)統(tong)(tong)(tong)(tong)(tong)。

　　三道鎮機械密封的三個主要(yao)功能如下：

　　1、沖洗功能，沖洗是三道鎮機械密封基本的功能，它直接將液體注入單面密封或雙面密封的高壓側。一般的三道鎮機械密封應該(gai)沖洗(xi)，特別是對于(yu)輕烴泵，沖洗(xi)時達到隔離介(jie)質(zhi)、冷卻和改(gai)善(shan)潤(run)滑的目的。隔離介(jie)質(zhi)的目的可以通(tong)過將與(yu)介(jie)質(zhi)相容的液體引入密封腔(qiang)進(jin)行外(wai)部循環沖洗(xi)來實(shi)現。

　　2、除雜和過濾功能，密封流體中的微細固體粒子、污垢等雜質對三道鎮機械密封造成的(de)(de)(de)危害(hai)非常嚴(yan)重(zhong)，可能導致密封端(duan)面的(de)(de)(de)磨損，也可能堵塞寒冷密封系統(tong)的(de)(de)(de)管線。密封性系統(tong)軟件(jian)具有去(qu)除(chu)(chu)殘渣(zha)、保(bao)持液(ye)(ye)(ye)體清潔的(de)(de)(de)作用。當(dang)(dang)殘渣(zha)的(de)(de)(de)相對密度(du)(du)小于(yu)液(ye)(ye)(ye)體媒質相對密度(du)(du)時，能用過濾裝置(zhi)去(qu)除(chu)(chu)殘渣(zha)；而當(dang)(dang)殘渣(zha)的(de)(de)(de)相對密度(du)(du)超過液(ye)(ye)(ye)體媒質相對密度(du)(du)時，可選用旋液(ye)(ye)(ye)分離設備(bei)或網式過濾器(qi)去(qu)除(chu)(chu)殘渣(zha)。

　　3、流體替代功能，含有固體顆粒的氣相介質和液相介質的直接密封難度很大，它們溫、毒、貴、易蒸發、易結晶。借助三道鎮機械密封可以用雙端三道鎮機械密封代替密封(feng)介質，將難以直接密封(feng)的介質轉化為密封(feng)潤(run)滑性能(neng)好(hao)、清潔的密封(feng)液體介質。