二位(wei)(wei)(wei)二通(tong)(tong)(tong)滑(hua)(hua)閥(fa)(fa)(fa)(fa)3導通(tong)(tong)(tong)時(shi)(shi)，液(ye)(ye)(ye)動(dong)(dong)機(ji)(ji)進給(gei)速(su)(su)(su)(su)度(du)由(you)調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)1決(jue)(jue)定(ding)。二位(wei)(wei)(wei)二通(tong)(tong)(tong)滑(hua)(hua)閥(fa)(fa)(fa)(fa)關閉(bi)后，液(ye)(ye)(ye)動(dong)(dong)機(ji)(ji)進給(gei)速(su)(su)(su)(su)度(du)由(you)調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)2決(jue)(jue)定(ding)，調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)2的(de)(de)流(liu)量(liang)(liang)應小于調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)1的(de)(de)流(liu)量(liang)(liang)。二位(wei)(wei)(wei)三通(tong)(tong)(tong)滑(hua)(hua)閥(fa)(fa)(fa)(fa)3處于圖(tu)(a)所(suo)示位(wei)(wei)(wei)置時(shi)(shi)，液(ye)(ye)(ye)動(dong)(dong)機(ji)(ji)的(de)(de)工(gong)(gong)作(zuo)進給(gei)速(su)(su)(su)(su)度(du)由(you)調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)1決(jue)(jue)定(ding)。二位(wei)(wei)(wei)三通(tong)(tong)(tong)滑(hua)(hua)閥(fa)(fa)(fa)(fa)3切換后，液(ye)(ye)(ye)動(dong)(dong)機(ji)(ji)的(de)(de)工(gong)(gong)作(zuo)進給(gei)速(su)(su)(su)(su)度(du)由(you)調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)2決(jue)(jue)定(ding)。兩個調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)的(de)(de)流(liu)量(liang)(liang)彼此不(bu)受限制(zhi)，但是由(you)于總有一(yi)個調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)的(de)(de)出油(you)口被封閉(bi)，使得調(diao)(diao)速(su)(su)(su)(su)閥(fa)(fa)(fa)(fa)中(zhong)的(de)(de)減壓(ya)(ya)閥(fa)(fa)(fa)(fa)開口最大(da)，所(suo)以滑(hua)(hua)閥(fa)(fa)(fa)(fa)3切換后，減壓(ya)(ya)閥(fa)(fa)(fa)(fa)來不(bu)及復位(wei)(wei)(wei)，在此瞬間流(liu)量(liang)(liang)過大(da)，往往會形成(cheng)液(ye)(ye)(ye)動(dong)(dong)機(ji)(ji)的(de)(de)突然前沖。采用(b)圖(tu)的(de)(de)回(hui)路可(ke)以避免瞬時(shi)(shi)前沖，但總有一(yi)部(bu)分(fen)壓(ya)(ya)力油(you)流(liu)回(hui)油(you)箱，因而造成(cheng)功率(lv)損失(shi)。液(ye)(ye)(ye)壓(ya)(ya)系(xi)統(tong)需要兩種(zhong)以上的(de)(de)速(su)(su)(su)(su)度(du)工(gong)(gong)作(zuo)時(shi)(shi)，應考慮多速(su)(su)(su)(su)回(hui)路。如(ru)圖(tu)是采用兩個節流(liu)閥(fa)(fa)(fa)(fa)的(de)(de)回(hui)路。

它(ta)(ta)可以(yi)獲(huo)得快速(su)(su)(su)、中速(su)(su)(su)、低速(su)(su)(su)三(san)種速(su)(su)(su)度(du)。回(hui)(hui)路采用(yong)回(hui)(hui)油(you)(you)(you)(you)節流(liu)，當換(huan)向(xiang)(xiang)閥(fa)(fa)1處于(yu)左(zuo)端工作位(wei)置(zhi)時(shi)，液(ye)(ye)(ye)壓(ya)缸的(de)回(hui)(hui)油(you)(you)(you)(you)經換(huan)向(xiang)(xiang)閥(fa)(fa)1直(zhi)接流(liu)回(hui)(hui)油(you)(you)(you)(you)箱(xiang)，液(ye)(ye)(ye)壓(ya)缸快速(su)(su)(su)運(yun)(yun)動。換(huan)向(xiang)(xiang)閥(fa)(fa)1處于(yu)中間(jian)位(wei)置(zhi)時(shi)，回(hui)(hui)油(you)(you)(you)(you)經3兩個(ge)節流(liu)閥(fa)(fa)節流(liu)后流(liu)入(ru)油(you)(you)(you)(you)箱(xiang)，液(ye)(ye)(ye)壓(ya)缸中速(su)(su)(su)運(yun)(yun)動。當換(huan)向(xiang)(xiang)閥(fa)(fa)處于(yu)右端位(wei)置(zhi)時(shi)，回(hui)(hui)油(you)(you)(you)(you)只經節流(liu)閥(fa)(fa)2流(liu)回(hui)(hui)油(you)(you)(you)(you)箱(xiang)，液(ye)(ye)(ye)壓(ya)缸作慢(man)(man)速(su)(su)(su)運(yun)(yun)動。當滑閥(fa)(fa)3處于(yu)中間(jian)位(wei)置(zhi)時(shi)，大流(liu)量(liang)(liang)泵(beng)(beng)(beng)1和(he)小(xiao)流(liu)量(liang)(liang)泵(beng)(beng)(beng)2同時(shi)向(xiang)(xiang)系統(tong)(tong)(tong)供油(you)(you)(you)(you)，液(ye)(ye)(ye)動機(ji)快速(su)(su)(su)運(yun)(yun)動。滑閥(fa)(fa)處于(yu)左(zuo)端工作位(wei)置(zhi)時(shi)，大流(liu)量(liang)(liang)泵(beng)(beng)(beng)1向(xiang)(xiang)系統(tong)(tong)(tong)供油(you)(you)(you)(you)，小(xiao)流(liu)量(liang)(liang)泵(beng)(beng)(beng)卸荷，此時(shi)液(ye)(ye)(ye)動機(ji)中速(su)(su)(su)運(yun)(yun)動。滑閥(fa)(fa)切換(huan)到右端工作位(wei)置(zhi)時(shi)，小(xiao)流(liu)量(liang)(liang)泵(beng)(beng)(beng)2向(xiang)(xiang)系統(tong)(tong)(tong)供油(you)(you)(you)(you)，大流(liu)量(liang)(liang)泵(beng)(beng)(beng)卸荷，液(ye)(ye)(ye)動機(ji)慢(man)(man)速(su)(su)(su)運(yun)(yun)動。根(gen)據同樣的(de)原理(li)，采用(yong)三(san)個(ge)定量(liang)(liang)泵(beng)(beng)(beng)可以(yi)獲(huo)得七種不同的(de)工作速(su)(su)(su)度(du)。多(duo)速(su)(su)(su)液(ye)(ye)(ye)壓(ya)缸如圖所示，在它(ta)(ta)的(de)主活(huo)塞中有(you)一個(ge)柱塞。

如果液(ye)壓(ya)缸內(nei)徑為(wei)D1，主活塞桿直徑為(wei)D2，柱塞直徑為(wei)D3，并(bing)且D12－D22<D32時(shi)，按(an)照圖示的回(hui)路可以得到六種不同的前進(jin)速(su)度。兩個滑(hua)閥均(jun)處(chu)(chu)于(yu)中間位(wei)置(zhi)時(shi)，液(ye)壓(ya)缸A、B、C三個腔均(jun)通(tong)入(ru)(ru)(ru)壓(ya)力油(you)(you)(you)，此時(shi)為(wei)差動聯接，液(ye)壓(ya)缸前進(jin)，速(su)度為(wei)V1。滑(hua)閥1處(chu)(chu)于(yu)左(zuo)端(duan)工作(zuo)(zuo)位(wei)置(zhi)，滑(hua)閥2處(chu)(chu)于(yu)中間位(wei)置(zhi)時(shi)，B腔和C腔通(tong)入(ru)(ru)(ru)壓(ya)力油(you)(you)(you)，A腔回(hui)油(you)(you)(you)，液(ye)壓(ya)缸前進(jin)，速(su)度為(wei)V2。滑(hua)閥1處(chu)(chu)于(yu)左(zuo)端(duan)工作(zuo)(zuo)位(wei)置(zhi)，滑(hua)閥2處(chu)(chu)于(yu)右(you)(you)端(duan)位(wei)置(zhi)時(shi)，C腔通(tong)入(ru)(ru)(ru)壓(ya)力油(you)(you)(you)，A腔回(hui)油(you)(you)(you)，液(ye)壓(ya)缸前進(jin)，速(su)度為(wei)V3，此時(shi)B腔吸油(you)(you)(you)。滑(hua)閥2均(jun)處(chu)(chu)于(yu)左(zuo)端(duan)工作(zuo)(zuo)位(wei)置(zhi)，B腔通(tong)入(ru)(ru)(ru)壓(ya)力油(you)(you)(you)，A腔回(hui)油(you)(you)(you)，液(ye)壓(ya)缸前進(jin)，速(su)度為(wei)V4，此時(shi)C腔吸油(you)(you)(you)。滑(hua)閥2均(jun)處(chu)(chu)于(yu)右(you)(you)端(duan)工作(zuo)(zuo)位(wei)置(zhi)，A、B兩腔通(tong)入(ru)(ru)(ru)壓(ya)力油(you)(you)(you)，在差壓(ya)作(zuo)(zuo)用下。

液(ye)(ye)(ye)壓(ya)(ya)缸(gang)前進，速(su)(su)(su)度(du)為V5，此時C腔(qiang)吸油。滑(hua)閥(fa)(fa)1處(chu)于右端工(gong)(gong)作(zuo)位(wei)置(zhi)(zhi)，滑(hua)閥(fa)(fa)2處(chu)于左端工(gong)(gong)作(zuo)位(wei)置(zhi)(zhi)時，A、C腔(qiang)通(tong)(tong)入(ru)壓(ya)(ya)力油，液(ye)(ye)(ye)壓(ya)(ya)缸(gang)在(zai)差壓(ya)(ya)作(zuo)用下(xia)(xia)前進，速(su)(su)(su)度(du)為V6，此時B腔(qiang)吸油。采用這(zhe)種(zhong)回路還(huan)可以(yi)得(de)到五種(zhong)不(bu)(bu)(bu)同的(de)前進速(su)(su)(su)度(du)和(he)兩種(zhong)不(bu)(bu)(bu)同的(de)后退速(su)(su)(su)度(du)。液(ye)(ye)(ye)動機若要獲(huo)得(de)穩(wen)(wen)(wen)定(ding)的(de)工(gong)(gong)作(zuo)速(su)(su)(su)度(du)，首先應該得(de)到穩(wen)(wen)(wen)定(ding)的(de)流(liu)(liu)量(liang)(liang)(liang)。采用恒流(liu)(liu)量(liang)(liang)(liang)式變(bian)量(liang)(liang)(liang)泵和(he)調(diao)速(su)(su)(su)閥(fa)(fa)調(diao)速(su)(su)(su)是最常用的(de)方法。下(xia)(xia)面介紹(shao)幾種(zhong)除(chu)此以(yi)外的(de)其(qi)它穩(wen)(wen)(wen)速(su)(su)(su)回路。節流(liu)(liu)閥(fa)(fa)通(tong)(tong)過的(de)流(liu)(liu)量(liang)(liang)(liang)是隨負(fu)載而變(bian)化的(de)，因而使液(ye)(ye)(ye)動機速(su)(su)(su)度(du)不(bu)(bu)(bu)穩(wen)(wen)(wen)定(ding)。若在(zai)節流(liu)(liu)閥(fa)(fa)與液(ye)(ye)(ye)壓(ya)(ya)缸(gang)之間設置(zhi)(zhi)一個(ge)減(jian)壓(ya)(ya)閥(fa)(fa)，這(zhe)樣使節流(liu)(liu)閥(fa)(fa)前后的(de)壓(ya)(ya)力差保持穩(wen)(wen)(wen)定(ding)，因而通(tong)(tong)過節流(liu)(liu)閥(fa)(fa)的(de)流(liu)(liu)量(liang)(liang)(liang)也(ye)比較(jiao)穩(wen)(wen)(wen)定(ding)，使液(ye)(ye)(ye)壓(ya)(ya)缸(gang)能穩(wen)(wen)(wen)定(ding)的(de)運動。調(diao)速(su)(su)(su)閥(fa)(fa)的(de)最小穩(wen)(wen)(wen)定(ding)工(gong)(gong)作(zuo)流(liu)(liu)量(liang)(liang)(liang)都有(you)一定(ding)的(de)限(xian)度(du)，超過這(zhe)個(ge)限(xian)度(du)流(liu)(liu)量(liang)(liang)(liang)就不(bu)(bu)(bu)穩(wen)(wen)(wen)定(ding)了。

當液(ye)動(dong)機(ji)(ji)要求以很低的(de)速(su)度穩(wen)定地運(yun)動(dong)，并且工(gong)作(zuo)流(liu)(liu)量(liang)(liang)小于(yu)調速(su)閥的(de)最小穩(wen)定工(gong)作(zuo)流(liu)(liu)量(liang)(liang)時(shi)(shi)，可以采(cai)用(yong)如(ru)圖所(suo)示回(hui)(hui)路(lu)。它采(cai)用(yong)兩(liang)個(ge)調速(su)閥，進(jin)(jin)入液(ye)壓(ya)(ya)缸的(de)工(gong)作(zuo)流(liu)(liu)量(liang)(liang)為兩(liang)個(ge)調速(su)閥調整(zheng)的(de)流(liu)(liu)量(liang)(liang)差，這樣兩(liang)個(ge)調速(su)閥都能在(zai)穩(wen)定流(liu)(liu)量(liang)(liang)的(de)范圍內工(gong)作(zuo)，并且使(shi)液(ye)壓(ya)(ya)缸實現穩(wen)定的(de)低速(su)運(yun)動(dong)。在(zai)液(ye)壓(ya)(ya)系統(tong)中(zhong)，液(ye)動(dong)機(ji)(ji)的(de)啟動(dong)、停(ting)止(zhi)和換向依靠(kao)控(kong)(kong)制(zhi)(zhi)(zhi)元件(jian)控(kong)(kong)制(zhi)(zhi)(zhi)油(you)液(ye)的(de)通斷及換向來實現，進(jin)(jin)行這些控(kong)(kong)制(zhi)(zhi)(zhi)的(de)回(hui)(hui)路(lu)稱為方向控(kong)(kong)制(zhi)(zhi)(zhi)回(hui)(hui)路(lu)。液(ye)壓(ya)(ya)系統(tong)可以用(yong)啟停(ting)電動(dong)機(ji)(ji)的(de)方法實現液(ye)動(dong)機(ji)(ji)的(de)啟停(ting)，但這對電機(ji)(ji)和電網供電都不利，因此(ci)可用(yong)以下幾種控(kong)(kong)制(zhi)(zhi)(zhi)油(you)路(lu)的(de)方法控(kong)(kong)制(zhi)(zhi)(zhi)液(ye)壓(ya)(ya)系統(tong)的(de)啟停(ting)。圖示為開(kai)啟位置，液(ye)壓(ya)(ya)系統(tong)正常工(gong)作(zuo)。二位二通閥切換后，切斷油(you)路(lu)，壓(ya)(ya)力油(you)自溢流(liu)(liu)閥流(liu)(liu)回(hui)(hui)油(you)箱，此(ci)時(shi)(shi)液(ye)壓(ya)(ya)系統(tong)停(ting)止(zhi)工(gong)作(zuo)。斷路(lu)啟停(ting)回(hui)(hui)路(lu)一(yi)般(ban)用(yong)于(yu)流(liu)(liu)量(liang)(liang)較小的(de)系統(tong)。

工(gong)作(zuo)系統停止工(gong)作(zuo)時，二位三通(tong)閥切(qie)換(huan)(huan)(huan)(huan)到(dao)(dao)(dao)(dao)左(zuo)(zuo)端(duan)工(gong)作(zuo)位置(zhi)，除了切(qie)斷通(tong)往(wang)工(gong)作(zuo)系統的(de)壓力(li)(li)油(you)外，還將(jiang)壓力(li)(li)油(you)引回(hui)油(you)箱(xiang)卸荷。液動(dong)機的(de)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)有(you)(you)手動(dong)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)和自動(dong)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)。自動(dong)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)回(hui)路有(you)(you)以(yi)下(xia)幾種。電(dian)(dian)(dian)(dian)(dian)磁(ci)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)閥換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)是(shi)應用(yong)較廣的(de)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)方(fang)法。圖(tu)(a)是(shi)用(yong)限位開關控制(zhi)電(dian)(dian)(dian)(dian)(dian)磁(ci)閥動(dong)作(zuo)的(de)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)回(hui)路。液壓缸(gang)啟動(dong)向(xiang)(xiang)(xiang)(xiang)右運(yun)動(dong)，當(dang)碰(peng)到(dao)(dao)(dao)(dao)限位開關2時，電(dian)(dian)(dian)(dian)(dian)磁(ci)鐵2DT吸(xi)，滑閥切(qie)換(huan)(huan)(huan)(huan)到(dao)(dao)(dao)(dao)右端(duan)工(gong)作(zuo)位置(zhi)，壓力(li)(li)油(you)進入液壓缸(gang)右腔(qiang)，活塞(sai)(sai)向(xiang)(xiang)(xiang)(xiang)左(zuo)(zuo)運(yun)動(dong)，碰(peng)到(dao)(dao)(dao)(dao)限位開關節時，電(dian)(dian)(dian)(dian)(dian)磁(ci)鐵2DT斷電(dian)(dian)(dian)(dian)(dian)，電(dian)(dian)(dian)(dian)(dian)磁(ci)鐵1DT吸(xi)，滑閥切(qie)換(huan)(huan)(huan)(huan)到(dao)(dao)(dao)(dao)左(zuo)(zuo)端(duan)的(de)工(gong)作(zuo)位置(zhi)，壓力(li)(li)油(you)進入液壓缸(gang)左(zuo)(zuo)腔(qiang)，活塞(sai)(sai)向(xiang)(xiang)(xiang)(xiang)右運(yun)動(dong)，這樣進行往(wang)復循環自動(dong)換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)。圖(tu)(b)是(shi)用(yong)壓力(li)(li)繼(ji)電(dian)(dian)(dian)(dian)(dian)器控制(zhi)的(de)電(dian)(dian)(dian)(dian)(dian)磁(ci)閥換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)回(hui)路。當(dang)活塞(sai)(sai)運(yun)動(dong)到(dao)(dao)(dao)(dao)終點(dian)時，壓力(li)(li)繼(ji)電(dian)(dian)(dian)(dian)(dian)器發出信號，控制(zhi)電(dian)(dian)(dian)(dian)(dian)磁(ci)閥換(huan)(huan)(huan)(huan)向(xiang)(xiang)(xiang)(xiang)。

轉閥(fa)作(zuo)(zuo)先導閥(fa)，它(ta)在(zai)液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)拖動(dong)(dong)(dong)的(de)撞塊的(de)帶動(dong)(dong)(dong)下(xia)往(wang)復旋轉改(gai)變(bian)(bian)控(kong)制壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)油(you)(you)的(de)流(liu)向(xiang)(xiang)(xiang)(xiang)(xiang)，使(shi)液(ye)(ye)動(dong)(dong)(dong)換(huan)(huan)向(xiang)(xiang)(xiang)(xiang)(xiang)閥(fa)左(zuo)右(you)切換(huan)(huan)，控(kong)制液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)往(wang)復運(yun)動(dong)(dong)(dong)的(de)自動(dong)(dong)(dong)換(huan)(huan)向(xiang)(xiang)(xiang)(xiang)(xiang)。但它(ta)只(zhi)適用于高速運(yun)動(dong)(dong)(dong)的(de)液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)，同時還要求轉閥(fa)換(huan)(huan)向(xiang)(xiang)(xiang)(xiang)(xiang)的(de)過(guo)渡區(qu)域很(hen)短(duan)的(de)情(qing)況下(xia)。除了(le)(le)采用換(huan)(huan)向(xiang)(xiang)(xiang)(xiang)(xiang)閥(fa)換(huan)(huan)向(xiang)(xiang)(xiang)(xiang)(xiang)外，還可以(yi)采用雙向(xiang)(xiang)(xiang)(xiang)(xiang)變(bian)(bian)量泵(beng)，通過(guo)改(gai)變(bian)(bian)輸出壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)油(you)(you)的(de)流(liu)向(xiang)(xiang)(xiang)(xiang)(xiang)來控(kong)制液(ye)(ye)動(dong)(dong)(dong)機的(de)運(yun)動(dong)(dong)(dong)方向(xiang)(xiang)(xiang)(xiang)(xiang)，它(ta)一(yi)般用于閉式回路。如下(xia)圖所示(shi)為強制退回回路。主液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)1與液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)2共同支承工(gong)作(zuo)(zuo)。液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)允(yun)許的(de)工(gong)作(zuo)(zuo)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)較低，以(yi)防頂緊力(li)過(guo)大使(shi)工(gong)件變(bian)(bian)形，所以(yi)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)油(you)(you)經減壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)閥(fa)6減壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)后進入(ru)液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)2。當主液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)1的(de)活塞向(xiang)(xiang)(xiang)(xiang)(xiang)右(you)運(yun)動(dong)(dong)(dong)時，強制液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)2的(de)活塞向(xiang)(xiang)(xiang)(xiang)(xiang)右(you)退回，為了(le)(le)防止液(ye)(ye)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)缸(gang)(gang)2右(you)腔的(de)壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)升高，設置了(le)(le)溢流(liu)閥(fa)5，使(shi)其壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)保持一(yi)定值。一(yi)般溢流(liu)閥(fa)的(de)調定壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)應略大于減壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)閥(fa)5的(de)調定壓(ya)(ya)(ya)(ya)(ya)(ya)(ya)力(li)。

采用(yong)三位(wei)(wei)(wei)四通(tong)換(huan)向(xiang)閥(fa)(fa)，用(yong)它(ta)的(de)中(zhong)間位(wei)(wei)(wei)置(zhi)就可以(yi)將通(tong)往液動(dong)機(ji)的(de)油路(lu)(lu)切斷，使(shi)它(ta)保持(chi)一定(ding)(ding)的(de)位(wei)(wei)(wei)置(zhi)，如O型(xing)、M型(xing)等三位(wei)(wei)(wei)四通(tong)閥(fa)(fa)。但(dan)(dan)是(shi)由(you)于(yu)滑閥(fa)(fa)的(de)密封(feng)較差(cha)，特別是(shi)在液壓(ya)缸垂直放(fang)置(zhi)的(de)回(hui)(hui)路(lu)(lu)中(zhong)，活塞(sai)仍難免自行下滑，所以(yi)這種鎖緊(jin)回(hui)(hui)路(lu)(lu)一般只用(yong)在要求較低的(de)場合。為(wei)了提(ti)高鎖緊(jin)能(neng)力，常(chang)常(chang)采用(yong)錐閥(fa)(fa)式液控(kong)單向(xiang)閥(fa)(fa)，組成(cheng)(cheng)下圖所示的(de)鎖緊(jin)回(hui)(hui)路(lu)(lu)。由(you)于(yu)錐閥(fa)(fa)關閉時(shi)沒有間隙，所以(yi)密封(feng)效果較好。有些液壓(ya)裝置(zhi)要求運動(dong)部(bu)件(jian)停留(liu)在某一位(wei)(wei)(wei)置(zhi)進(jin)行工作，完(wan)成(cheng)(cheng)這種機(ji)能(neng)的(de)回(hui)(hui)路(lu)(lu)稱為(wei)定(ding)(ding)位(wei)(wei)(wei)回(hui)(hui)路(lu)(lu)。當液壓(ya)缸前(qian)(qian)進(jin)碰到限位(wei)(wei)(wei)開(kai)關時(shi)，立刻(ke)發出信號使(shi)電磁閥(fa)(fa)回(hui)(hui)到中(zhong)間停止位(wei)(wei)(wei)置(zhi)，這時(shi)液壓(ya)缸停止不動(dong)。采用(yong)這種方法定(ding)(ding)位(wei)(wei)(wei)比較靈便(bian)，但(dan)(dan)是(shi)由(you)于(yu)控(kong)制環節較多，工作不太可靠。液壓(ya)缸前(qian)(qian)進(jin)，壓(ya)下行程閥(fa)(fa)時(shi)，將液壓(ya)缸右腔回(hui)(hui)油截斷。

使液(ye)壓(ya)(ya)缸停(ting)止不動。采(cai)(cai)用這種回(hui)路定(ding)位(wei)(wei)精度較(jiao)(jiao)高，但(dan)它(ta)受液(ye)壓(ya)(ya)缸運(yun)動速度的影響(xiang)較(jiao)(jiao)大，它(ta)的工作(zuo)(zuo)比(bi)(bi)限(xian)位(wei)(wei)開關定(ding)位(wei)(wei)回(hui)路可(ke)靠。由于(yu)它(ta)需(xu)增加單向(xiang)閥和行程閥，又需(xu)在(zai)(zai)(zai)外部配(pei)管，所(suo)以比(bi)(bi)較(jiao)(jiao)麻(ma)煩。當液(ye)壓(ya)(ya)缸前進碰(peng)上死擋鐵(tie)后(hou)即停(ting)止運(yun)動，這種方法(fa)定(ding)位(wei)(wei)最(zui)精確(que)，但(dan)是它(ta)只能(neng)用于(yu)終端(duan)(duan)停(ting)止定(ding)位(wei)(wei)的裝置(zhi)(zhi)。需(xu)要(yao)在(zai)(zai)(zai)三(san)個(ge)不同(tong)位(wei)(wei)置(zhi)(zhi)停(ting)留時，可(ke)采(cai)(cai)用三(san)位(wei)(wei)液(ye)壓(ya)(ya)缸。當換(huan)(huan)向(xiang)閥處(chu)于(yu)中間位(wei)(wei)置(zhi)(zhi)時，C腔(qiang)通入壓(ya)(ya)力油(you)(you)，A、B腔(qiang)回(hui)油(you)(you)，兩個(ge)活(huo)塞均在(zai)(zai)(zai)最(zui)左邊(bian)。當換(huan)(huan)向(xiang)閥處(chu)于(yu)右(you)端(duan)(duan)工作(zuo)(zuo)位(wei)(wei)置(zhi)(zhi)時，A腔(qiang)、C腔(qiang)通入壓(ya)(ya)力油(you)(you)，B腔(qiang)油(you)(you)液(ye)，在(zai)(zai)(zai)差壓(ya)(ya)作(zuo)(zuo)用下活(huo)塞1處(chu)于(yu)右(you)端(duan)(duan)位(wei)(wei)置(zhi)(zhi)，活(huo)塞2在(zai)(zai)(zai)中間位(wei)(wei)置(zhi)(zhi)。當換(huan)(huan)向(xiang)閥處(chu)于(yu)左端(duan)(duan)工作(zuo)(zuo)位(wei)(wei)置(zhi)(zhi)時，B、C兩腔(qiang)通入壓(ya)(ya)力油(you)(you)，A腔(qiang)能(neng)油(you)(you)箱，此(ci)時在(zai)(zai)(zai)差壓(ya)(ya)作(zuo)(zuo)用下，活(huo)塞2移到(dao)最(zui)右(you)端(duan)(duan)。如此(ci)完成(cheng)三(san)位(wei)(wei)停(ting)留動作(zuo)(zuo)。

當油口5被截(jie)(jie)止(zhi)(zhi)閥(fa)(fa)(fa)(fa)關(guan)閉時(shi)(shi)，該液(ye)壓(ya)(ya)(ya)(ya)(ya)缸(gang)相當于一只普通(tong)(tong)的液(ye)壓(ya)(ya)(ya)(ya)(ya)缸(gang)，可以往復(fu)運(yun)(yun)動(dong)。當需要液(ye)壓(ya)(ya)(ya)(ya)(ya)缸(gang)在(zai)某一位(wei)(wei)(wei)(wei)置(zhi)停(ting)(ting)留(liu)時(shi)(shi)，將(jiang)那個位(wei)(wei)(wei)(wei)置(zhi)的截(jie)(jie)止(zhi)(zhi)閥(fa)(fa)(fa)(fa)打開(kai)，并(bing)(bing)將(jiang)二位(wei)(wei)(wei)(wei)三(san)通(tong)(tong)閥(fa)(fa)(fa)(fa)移到左端工件位(wei)(wei)(wei)(wei)置(zhi)，使打開(kai)的截(jie)(jie)止(zhi)(zhi)閥(fa)(fa)(fa)(fa)經(jing)換(huan)(huan)向(xiang)閥(fa)(fa)(fa)(fa)B與換(huan)(huan)向(xiang)閥(fa)(fa)(fa)(fa)A相通(tong)(tong)。當液(ye)壓(ya)(ya)(ya)(ya)(ya)缸(gang)向(xiang)右運(yun)(yun)動(dong)，達到預定位(wei)(wei)(wei)(wei)置(zhi)后(hou)，將(jiang)該油口封(feng)閉，切斷回油路，使活塞(sai)停(ting)(ting)止(zhi)(zhi)運(yun)(yun)動(dong)。需液(ye)壓(ya)(ya)(ya)(ya)(ya)缸(gang)回程時(shi)(shi)，將(jiang)兩個換(huan)(huan)向(xiang)閥(fa)(fa)(fa)(fa)切換(huan)(huan)到圖(tu)示位(wei)(wei)(wei)(wei)置(zhi)，壓(ya)(ya)(ya)(ya)(ya)力油經(jing)換(huan)(huan)向(xiang)閥(fa)(fa)(fa)(fa)A、B、油口岸(an)，進入液(ye)壓(ya)(ya)(ya)(ya)(ya)缸(gang)右腔，活塞(sai)向(xiang)左運(yun)(yun)動(dong)到終端。采(cai)用特殊(shu)結構的點位(wei)(wei)(wei)(wei)液(ye)壓(ya)(ya)(ya)(ya)(ya)缸(gang)在(zai)一定范圍內可以獲得一定步距的任意位(wei)(wei)(wei)(wei)置(zhi)。它(ta)用兩位(wei)(wei)(wei)(wei)三(san)通(tong)(tong)電磁閥(fa)(fa)(fa)(fa)控制各活塞(sai)的動(dong)作。為了(le)便于各活塞(sai)復(fu)位(wei)(wei)(wei)(wei)，并(bing)(bing)防止(zhi)(zhi)它(ta)們產(chan)生誤動(dong)作，在(zai)主活塞(sai)右端通(tong)(tong)入低壓(ya)(ya)(ya)(ya)(ya)油。當活塞(sai)向(xiang)右運(yun)(yun)動(dong)時(shi)(shi)，為了(le)防止(zhi)(zhi)右腔壓(ya)(ya)(ya)(ya)(ya)力升(sheng)高，設置(zhi)了(le)溢流閥(fa)(fa)(fa)(fa)Y2。