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)統(tong)(tong)(tong)(tong)(tong)中，上述系(xi)統(tong)(tong)(tong)(tong)(tong)并不(bu)同(tong)時(shi)包括在(zai)(zai)內(nei)。密(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)(tong)(tong)的選擇主(zhu)要取決于主(zhu)密(mi)(mi)封(feng)(feng)(feng)件的應(ying)用(yong)范圍。例如(ru)，如(ru)果主(zhu)密(mi)(mi)封(feng)(feng)(feng)用(yong)于高(gao)溫(wen)(wen)液體(ti)，密(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)(tong)(tong)應(ying)確(que)保(bao)降(jiang)低主(zhu)密(mi)(mi)封(feng)(feng)(feng)的環境溫(wen)(wen)度(du)，即(ji)(ji)采(cai)用(yong)溫(wen)(wen)度(du)控制系(xi)統(tong)(tong)(tong)(tong)(tong)。如(ru)果主(zhu)密(mi)(mi)封(feng)(feng)(feng)用(yong)于固體(ti)雜(za)質含量(liang)高(gao)的工作介質，密(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)(tong)(tong)應(ying)確(que)保(bao)在(zai)(zai)主(zhu)密(mi)(mi)封(feng)(feng)(feng)前降(jiang)低固體(ti)雜(za)質含量(liang)，即(ji)(ji)采(cai)用(yong)除雜(za)系(xi)統(tong)(tong)(tong)(tong)(tong)。在(zai)(zai)腐(fu)蝕(shi)性(xing)介質中，密(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)(tong)(tong)必須確(que)保(bao)主(zhu)密(mi)(mi)封(feng)(feng)(feng)降(jiang)低腐(fu)蝕(shi)速率或消(xiao)除腐(fu)蝕(shi)，即(ji)(ji)使(shi)用(yong)流體(ti)而不(bu)是堵塞流體(ti)系(xi)統(tong)(tong)(tong)(tong)(tong)；在(zai)(zai)高(gao)壓密(mi)(mi)封(feng)(feng)(feng)裝(zhuang)置中，輔助(zhu)系(xi)統(tong)(tong)(tong)(tong)(tong)應(ying)確(que)保(bao)多級降(jiang)壓和其他措施，即(ji)(ji)壓力控制系(xi)統(tong)(tong)(tong)(tong)(tong)。

　　三道鎮機械密封的三個(ge)主要功(gong)能(neng)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(chong)洗(xi)，特別是(shi)對于輕烴泵，沖(chong)洗(xi)時達到隔離介(jie)質(zhi)(zhi)、冷卻和改善潤(run)滑(hua)的目的。隔離介(jie)質(zhi)(zhi)的目的可以通過將與介(jie)質(zhi)(zhi)相容(rong)的液體引入(ru)密封腔(qiang)進行外部循環沖(chong)洗(xi)來實現。

　　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危害(hai)非常(chang)嚴(yan)重，可(ke)能(neng)導致(zhi)密封(feng)(feng)端面的磨損，也可(ke)能(neng)堵塞寒(han)冷(leng)密封(feng)(feng)系(xi)統的管線。密封(feng)(feng)性系(xi)統軟(ruan)件(jian)具有去除(chu)殘(can)渣(zha)、保持(chi)液體(ti)清潔的作用。當(dang)殘(can)渣(zha)的相(xiang)對(dui)(dui)(dui)密度(du)小于液體(ti)媒(mei)質(zhi)相(xiang)對(dui)(dui)(dui)密度(du)時，能(neng)用過濾(lv)裝置去除(chu)殘(can)渣(zha)；而當(dang)殘(can)渣(zha)的相(xiang)對(dui)(dui)(dui)密度(du)超過液體(ti)媒(mei)質(zhi)相(xiang)對(dui)(dui)(dui)密度(du)時，可(ke)選用旋液分離(li)設備或網式過濾(lv)器去除(chu)殘(can)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(dai)替密封(feng)(feng)介(jie)(jie)質(zhi)，將難以直接密封(feng)(feng)的(de)介(jie)(jie)質(zhi)轉化為密封(feng)(feng)潤滑性能好、清潔的(de)密封(feng)(feng)液體介(jie)(jie)質(zhi)。