市中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。在市中機械密封系(xi)統(tong)(tong)(tong)中(zhong)(zhong)，上(shang)述(shu)系(xi)統(tong)(tong)(tong)并不同時包括在(zai)內。密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)的選擇主(zhu)要取決于主(zhu)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)件的應(ying)用(yong)范圍(wei)。例如，如果(guo)主(zhu)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)用(yong)于高溫(wen)(wen)液體(ti)(ti)，密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)應(ying)確(que)保(bao)(bao)降(jiang)低(di)主(zhu)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)的環(huan)境溫(wen)(wen)度(du)，即(ji)采(cai)用(yong)溫(wen)(wen)度(du)控制系(xi)統(tong)(tong)(tong)。如果(guo)主(zhu)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)用(yong)于固(gu)體(ti)(ti)雜質(zhi)含(han)量(liang)(liang)高的工作介質(zhi)，密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)應(ying)確(que)保(bao)(bao)在(zai)主(zhu)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)前降(jiang)低(di)固(gu)體(ti)(ti)雜質(zhi)含(han)量(liang)(liang)，即(ji)采(cai)用(yong)除雜系(xi)統(tong)(tong)(tong)。在(zai)腐(fu)蝕性介質(zhi)中(zhong)(zhong)，密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)系(xi)統(tong)(tong)(tong)必須確(que)保(bao)(bao)主(zhu)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)降(jiang)低(di)腐(fu)蝕速(su)率或消除腐(fu)蝕，即(ji)使用(yong)流體(ti)(ti)而不是(shi)堵塞流體(ti)(ti)系(xi)統(tong)(tong)(tong)；在(zai)高壓(ya)密(mi)(mi)(mi)(mi)封(feng)(feng)(feng)裝置中(zhong)(zhong)，輔助系(xi)統(tong)(tong)(tong)應(ying)確(que)保(bao)(bao)多級(ji)降(jiang)壓(ya)和其他措施，即(ji)壓(ya)力控制系(xi)統(tong)(tong)(tong)。

　　市中機械密封的(de)三個主要功(gong)能如下：

　　1、沖洗功能，沖洗是市中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。一般的市中機械密封應(ying)該沖(chong)(chong)(chong)洗，特別是對于輕烴泵(beng)，沖(chong)(chong)(chong)洗時(shi)達(da)到隔離介(jie)(jie)質(zhi)、冷(leng)卻和改善潤滑的目(mu)的。隔離介(jie)(jie)質(zhi)的目(mu)的可(ke)以通過(guo)將與介(jie)(jie)質(zhi)相容的液體引入(ru)密封腔(qiang)進行外部循環沖(chong)(chong)(chong)洗來(lai)實現(xian)。

　　2、除雜和過濾功能，密封流體中的微細固體粒子、污垢等雜質對市中機械密封造成(cheng)的(de)危害(hai)非(fei)常嚴重，可能導致密封(feng)端(duan)面的(de)磨損(sun)，也可能堵(du)塞(sai)寒冷(leng)密封(feng)系統(tong)的(de)管線。密封(feng)性(xing)系統(tong)軟件具有去除(chu)(chu)殘(can)渣(zha)(zha)、保持液(ye)(ye)體清(qing)潔的(de)作用(yong)。當殘(can)渣(zha)(zha)的(de)相(xiang)對(dui)密度小于(yu)液(ye)(ye)體媒(mei)質相(xiang)對(dui)密度時，能用(yong)過濾(lv)裝(zhuang)置去除(chu)(chu)殘(can)渣(zha)(zha)；而當殘(can)渣(zha)(zha)的(de)相(xiang)對(dui)密度超(chao)過液(ye)(ye)體媒(mei)質相(xiang)對(dui)密度時，可選用(yong)旋液(ye)(ye)分(fen)離設備或網式過濾(lv)器(qi)去除(chu)(chu)殘(can)渣(zha)(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。借助市中機械密封可以用雙端市中機械密封代替密(mi)(mi)(mi)封(feng)介(jie)質，將難以直(zhi)接密(mi)(mi)(mi)封(feng)的介(jie)質轉化為密(mi)(mi)(mi)封(feng)潤滑性能好、清潔(jie)的密(mi)(mi)(mi)封(feng)液(ye)體介(jie)質。