液壓(ya)機(ji)以液體(ti)(ti)為工(gong)(gong)(gong)作(zuo)介質，根據帕(pa)斯(si)卡原理制成的(de)用于傳遞能量以實現各種(zhong)工(gong)(gong)(gong)藝的(de)機器。工(gong)(gong)(gong)作(zuo)原理都是通過液壓(ya)傳動(dong)，即利用液體(ti)(ti)壓(ya)力來傳遞動(dong)力和進行控制的(de)一種(zhong)傳動(dong)方式。一般(ban)由主機、動(dong)力系(xi)統(tong)及液壓(ya)控制系(xi)統(tong)三部(bu)分組(zu)成。液壓(ya)機可以概(gai)括油壓(ya)機，但不一定以液壓(ya)油工(gong)(gong)(gong)作(zuo)介質。

油壓(ya)機也(ye)是(shi)液(ye)(ye)壓機(ji)的(de)一(yi)種，是(shi)通(tong)過(guo)專(zhuan)用液(ye)(ye)壓油(you)(you)(you)(you)做為(wei)(wei)(wei)工作(zuo)(zuo)(zuo)介(jie)質，通(tong)過(guo)液(ye)(ye)壓泵作(zuo)(zuo)(zuo)為(wei)(wei)(wei)動(dong)力(li)源，也(ye)可(ke)以(yi)使(shi)用水(shui)(shui)(shui)來驅(qu)動(dong),因為(wei)(wei)(wei)水(shui)(shui)(shui)是(shi)液(ye)(ye)體,另一(yi)個(ge)是(shi)石(shi)(shi)油(you)(you)(you)(you)和(he)(he)天(tian)然氣的(de)混(hun)合(he)物稱為(wei)(wei)(wei)空(kong)(kong)液(ye)(ye)壓機(ji)或液(ye)(ye)壓機(ji)壓床靠泵的(de)作(zuo)(zuo)(zuo)用力(li)使(shi)液(ye)(ye)壓油(you)(you)(you)(you)通(tong)過(guo)液(ye)(ye)壓管路進入油(you)(you)(you)(you)缸(gang)和(he)(he)活塞，然后油(you)(you)(you)(you)缸(gang)和(he)(he)活塞里(li)有幾(ji)組互相配合(he)的(de)密封(feng)件，不同位置的(de)密封(feng)都是(shi)不同的(de)，但都起到密封(feng)的(de)作(zuo)(zuo)(zuo)用，使(shi)液(ye)(ye)壓油(you)(you)(you)(you)不能(neng)泄露。通(tong)過(guo)單(dan)向閥使(shi)液(ye)(ye)壓油(you)(you)(you)(you)在油(you)(you)(you)(you)箱循環使(shi)油(you)(you)(you)(you)缸(gang)活塞循環做功從而完成(cheng)機(ji)械(xie)動(dong)作(zuo)(zuo)(zuo)達到生產(chan)效(xiao)果。也(ye)可(ke)以(yi)使(shi)用水(shui)(shui)(shui)來驅(qu)動(dong),因為(wei)(wei)(wei)水(shui)(shui)(shui)是(shi)液(ye)(ye)體,另一(yi)個(ge)是(shi)石(shi)(shi)油(you)(you)(you)(you)和(he)(he)天(tian)然氣的(de)混(hun)合(he)物稱為(wei)(wei)(wei)空(kong)(kong)液(ye)(ye)壓機(ji)或液(ye)(ye)壓機(ji)壓床。