不同的真空系統需要不同的真空度。因此,通常需要用一套真空裝置來完成,即在不同壓力范圍內工作的真空泵串聯起來。
高真(zhen)(zhen)空(kong)(kong)(kong)(kong)側的真(zhen)(zhen)空(kong)(kong)(kong)(kong)泵(beng)可以達(da)到系統所需的真(zhen)(zhen)空(kong)(kong)(kong)(kong)度,而低真(zhen)(zhen)空(kong)(kong)(kong)(kong)側的真(zhen)(zhen)空(kong)(kong)(kong)(kong)泵(beng)直接(jie)與大氣相通。顯然,最簡單的真(zhen)(zhen)空(kong)(kong)(kong)(kong)裝置是直接(jie)排(pai)放(fang)空(kong)(kong)(kong)(kong)氣的真(zhen)(zhen)空(kong)(kong)(kong)(kong)泵(beng)。然而,高真(zhen)(zhen)空(kong)(kong)(kong)(kong)系統通常需要三級(ji)單元(yuan),而中等(deng)真(zhen)(zhen)空(kong)(kong)(kong)(kong)系統通常需要兩級(ji)單元(yuan)。
高(gao)(gao)真空(kong)(kong)泵(beng)(beng)(beng)(beng)(beng)和低(di)(di)真空(kong)(kong)泵(beng)(beng)(beng)(beng)(beng)難(nan)以(yi)(yi)形成有(you)(you)(you)效的(de)(de)(de)高(gao)(gao)真空(kong)(kong)單元。這(zhe)(zhe)(zhe)有(you)(you)(you)幾(ji)個原因(yin)。連(lian)(lian)續性是(shi)(shi)其(qi)中之(zhi)一。高(gao)(gao)真空(kong)(kong)泵(beng)(beng)(beng)(beng)(beng)都有(you)(you)(you)前(qian)(qian)級(ji)(ji)耐(nai)壓(ya)的(de)(de)(de)限制,即(ji)如果前(qian)(qian)級(ji)(ji)高(gao)(gao)于一定(ding)壓(ya)力,泵(beng)(beng)(beng)(beng)(beng)就不能正常(chang)(chang)工作(zuo)(zuo)。然而,當(dang)當(dang)前(qian)(qian)級(ji)(ji)泵(beng)(beng)(beng)(beng)(beng)達(da)到該臨(lin)界壓(ya)力時(shi)(shi),泵(beng)(beng)(beng)(beng)(beng)送速度(du)通常(chang)(chang)會降(jiang)低(di)(di),因(yin)此(ci)前(qian)(qian)一級(ji)(ji)泵(beng)(beng)(beng)(beng)(beng)的(de)(de)(de)廢氣(qi)專(zhuan)利復審3)可(ke)能小(xiao)于主泵(beng)(beng)(beng)(beng)(beng)的(de)(de)(de)廢氣(qi)流(liu)(liu)(liu)量(liang)。這(zhe)(zhe)(zhe)種不一致性流(liu)(liu)(liu)量(liang)破(po)壞了連(lian)(lian)續性流(liu)(liu)(liu)量(liang)的(de)(de)(de)要求(qiu),并將不可(ke)避免地導致真空(kong)(kong)裝置不能正常(chang)(chang)工作(zuo)(zuo)。然而,如果另一個真空(kong)(kong)泵(beng)(beng)(beng)(beng)(beng)連(lian)(lian)接(jie)在(zai)高(gao)(gao)真空(kong)(kong)泵(beng)(beng)(beng)(beng)(beng)和低(di)(di)真空(kong)(kong)泵(beng)(beng)(beng)(beng)(beng)之(zhi)間,它(ta)可(ke)以(yi)(yi)作(zuo)(zuo)為上下之(zhi)間的(de)(de)(de)連(lian)(lian)接(jie),流(liu)(liu)(liu)量(liang)是(shi)(shi)連(lian)(lian)續的(de)(de)(de),并且(qie)每個泵(beng)(beng)(beng)(beng)(beng)可(ke)以(yi)(yi)在(zai)最佳狀態(tai)下工作(zuo)(zuo)。羅(luo)茨泵(beng)(beng)(beng)(beng)(beng)可(ke)以(yi)(yi)在(zai)中等真空(kong)(kong)范圍(wei)內(nei)工作(zuo)(zuo),這(zhe)(zhe)(zhe)是(shi)(shi)最合適的(de)(de)(de),所以(yi)(yi)它(ta)也被(bei)稱為羅(luo)茨增(zeng)壓(ya)泵(beng)(beng)(beng)(beng)(beng)。因(yin)為它(ta)的(de)(de)(de)壓(ya)縮比不高(gao)(gao),它(ta)可(ke)以(yi)(yi)連(lian)(lian)接(jie)在(zai)幾(ji)帕(pa)到幾(ji)百帕(pa)的(de)(de)(de)范圍(wei)內(nei)。當(dang)三級(ji)(ji)高(gao)(gao)真空(kong)(kong)機組進入的(de)(de)(de)真空(kong)(kong)度(du)相對較高(gao)(gao)時(shi)(shi),由(you)于主泵(beng)(beng)(beng)(beng)(beng)的(de)(de)(de)廢氣(qi)流(liu)(liu)(liu)量(liang)明顯減少,此(ci)時(shi)(shi)只有(you)(you)(you)較小(xiao)的(de)(de)(de)前(qian)(qian)級(ji)(ji)泵(beng)(beng)(beng)(beng)(beng)能保持(chi)抽氣(qi)的(de)(de)(de)連(lian)(lian)續性,這(zhe)(zhe)(zhe)是(shi)(shi)實際應(ying)用中經常(chang)(chang)采用的(de)(de)(de)方法,從而降(jiang)低(di)(di)了機組的(de)(de)(de)能耗。
高真空(kong)機組通常(chang)需(xu)要(yao)三(san)級(ji)機組的(de)(de)另一個原(yuan)因(yin)是(shi)高真空(kong)泵(beng)(beng)(beng)的(de)(de)吸入壓力(li)(li)的(de)(de)限(xian)制(zhi)。泵(beng)(beng)(beng)具有初始(shi)工(gong)作壓力(li)(li),傳統(tong)的(de)(de)高真空(kong)泵(beng)(beng)(beng)在(zai)幾帕的(de)(de)范(fan)圍(wei)內。因(yin)此(ci),在(zai)主泵(beng)(beng)(beng)開(kai)始(shi)工(gong)作之前(qian)(qian)(qian),前(qian)(qian)(qian)級(ji)泵(beng)(beng)(beng)必須預泵(beng)(beng)(beng)至(zhi)該(gai)(gai)壓力(li)(li)。然(ran)而(er),直接排(pai)放(fang)大氣的(de)(de)前(qian)(qian)(qian)級(ji)泵(beng)(beng)(beng)通常(chang)需(xu)要(yao)很長(chang)時(shi)(shi)間(jian)來泵(beng)(beng)(beng)送至(zhi)該(gai)(gai)壓力(li)(li),因(yin)為隨著壓力(li)(li)降低,泵(beng)(beng)(beng)的(de)(de)泵(beng)(beng)(beng)送速度(du)降低,特(te)別(bie)是(shi)對于周期性泵(beng)(beng)(beng)送空(kong)氣的(de)(de)真空(kong)單元,需(xu)要(yao)時(shi)(shi)間(jian)來達到工(gong)作真空(kong)度(du)。預抽時(shi)(shi)間(jian)越長(chang),進(jin)入工(gong)作真空(kong)度(du)越長(chang),增加一臺真空(kong)泵(beng)(beng)(beng)與前(qian)(qian)(qian)級(ji)低真空(kong)泵(beng)(beng)(beng)配合,可以在(zai)短時(shi)(shi)間(jian)內達到主泵(beng)(beng)(beng)的(de)(de)工(gong)作壓力(li)(li),使系統(tong)盡快(kuai)工(gong)作進(jin)入,保證設備(bei)的(de)(de)使用效率。
羅茨泵(beng)(beng)(beng)和油增(zeng)壓(ya)(ya)(ya)泵(beng)(beng)(beng)都可(ke)以(yi)用(yong)作中(zhong)型真(zhen)(zhen)空(kong)(kong)泵(beng)(beng)(beng)。分子(zi)(zi)增(zeng)壓(ya)(ya)(ya)泵(beng)(beng)(beng)具(ju)(ju)有(you)非常(chang)(chang)(chang)高(gao)(gao)的(de)(de)壓(ya)(ya)(ya)縮(suo)比(bi),這不僅使(shi)其能夠獲得(de)清(qing)潔(jie)的(de)(de)真(zhen)(zhen)空(kong)(kong),而且具(ju)(ju)有(you)優異的(de)(de)高(gao)(gao)真(zhen)(zhen)空(kong)(kong)性能。同時,它在(zai)中(zhong)等真(zhen)(zhen)空(kong)(kong)范圍內也(ye)有(you)很強(qiang)(qiang)的(de)(de)抽吸能力。這使(shi)得(de)分子(zi)(zi)增(zeng)壓(ya)(ya)(ya)泵(beng)(beng)(beng)成為(wei)目前(qian)(qian)(qian)唯一具(ju)(ju)有(you)中(zhong)高(gao)(gao)真(zhen)(zhen)空(kong)(kong)性能的(de)(de)真(zhen)(zhen)空(kong)(kong)泵(beng)(beng)(beng),因此只有(you)與低真(zhen)(zhen)空(kong)(kong)泵(beng)(beng)(beng)相匹配,才能形成與三級(ji)(ji)(ji)機組(zu)性能相當的(de)(de)高(gao)(gao)真(zhen)(zhen)空(kong)(kong)機組(zu)。具(ju)(ju)體地,因為(wei)分子(zi)(zi)增(zeng)壓(ya)(ya)(ya)泵(beng)(beng)(beng)的(de)(de)耐壓(ya)(ya)(ya)性高(gao)(gao),所以(yi)前(qian)(qian)(qian)級(ji)(ji)(ji)泵(beng)(beng)(beng)可(ke)以(yi)容易地處(chu)于(yu)高(gao)(gao)流量狀態(tai);然(ran)而,分子(zi)(zi)增(zeng)壓(ya)(ya)(ya)泵(beng)(beng)(beng)的(de)(de)高(gao)(gao)吸入壓(ya)(ya)(ya)力減緩(huan)了(le)前(qian)(qian)(qian)級(ji)(ji)(ji)泵(beng)(beng)(beng)的(de)(de)預(yu)泵(beng)(beng)(beng)送(song)(song)負載(zai)。分子(zi)(zi)增(zeng)壓(ya)(ya)(ya)泵(beng)(beng)(beng)可(ke)以(yi)在(zai)100-50Pa下工作。前(qian)(qian)(qian)級(ji)(ji)(ji)泵(beng)(beng)(beng)從大(da)氣到(dao)該(gai)壓(ya)(ya)(ya)力的(de)(de)壓(ya)(ya)(ya)力基本上遵循每經過一段時間(jian)壓(ya)(ya)(ya)力降低一個數量級(ji)(ji)(ji)的(de)(de)規(gui)律。因此,該(gai)單元可(ke)以(yi)具(ju)(ju)有(you)非常(chang)(chang)(chang)高(gao)(gao)的(de)(de)泵(beng)(beng)(beng)送(song)(song)效(xiao)率。簡化(hua)高(gao)(gao)真(zhen)(zhen)空(kong)(kong)裝置(zhi)和取消羅茨泵(beng)(beng)(beng)是分子(zi)(zi)增(zeng)壓(ya)(ya)(ya)泵(beng)(beng)(beng)的(de)(de)另(ling)一個優點。對于(yu)較大(da)的(de)(de)高(gao)(gao)真(zhen)(zhen)空(kong)(kong)應用(yong)設(she)(she)備,前(qian)(qian)(qian)級(ji)(ji)(ji)泵(beng)(beng)(beng)的(de)(de)預(yu)抽能力也(ye)可(ke)適(shi)當加強(qiang)(qiang),以(yi)進一步縮(suo)短泵(beng)(beng)(beng)送(song)(song)時間(jian)。由(you)于(yu)預(yu)抽時間(jian)與整個排(pai)氣過程相比(bi)非常(chang)(chang)(chang)短,所以(yi)前(qian)(qian)(qian)級(ji)(ji)(ji)泵(beng)(beng)(beng)的(de)(de)使(shi)用(yong)時間(jian)也(ye)非常(chang)(chang)(chang)短,所以(yi)它也(ye)可(ke)以(yi)作為(wei)多(duo)臺(tai)設(she)(she)備的(de)(de)預(yu)抽功能,這通常(chang)(chang)(chang)是非常(chang)(chang)(chang)現實(shi)的(de)(de)。這大(da)大(da)簡化(hua)了(le)大(da)規(gui)模(mo)應用(yong)的(de)(de)真(zhen)(zhen)空(kong)(kong)裝置(zhi)。
在一些中等真空應用中,需要進入10-1Pa的范圍,這對于羅茨泵的次級單元來說通常是難以實現的。然而,使用與兩級羅茨泵串聯的三級單元可以將真空度增加一個數量級,并且進入10-1Pa。因此,三級裝置也常用于中等真空應用。由于分子增壓泵能以10-1Pa的全速泵送,它也能代替三級介質真空裝置中的兩級羅茨泵。一般來說,分子增壓泵可以完全取代在中真空低壓范圍內長期工作的羅茨泵泵。但是,在介質真空的高端壓力范圍內長時間工作的羅茨泵應該比較少,因為在這個壓力范圍內的前置泵往往具有很強的泵送速度。