限(xian)流(liu)(liu)孔(kong)板(ban)（Restriction Orifice）是在板(ban)面上開一個小錐孔(kong)（該小錐孔(kong)的尺寸由工藝(yi)專業提(ti)出），如圖4-19所示(shi)。它(ta)也應(ying)有(you)兩個和匹配(pei)法(fa)蘭同樣的密封面。限(xian)流(liu)(liu)孔(kong)板(ban)可以作為流(liu)(liu)量測量(liang)(liang)元(yuan)件用(yong)來(lai)(lai)測量(liang)(liang)流(liu)(liu)(liu)量(liang)(liang)，也可以作(zuo)為(wei)節流(liu)(liu)(liu)元(yuan)件用(yong)來(lai)(lai)限(xian)(xian)定流(liu)(liu)(liu)量(liang)(liang)和降低壓(ya)(ya)力。當(dang)孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)前(qian)后存在(zai)一(yi)定壓(ya)(ya)差，流(liu)(liu)(liu)體(ti)流(liu)(liu)(liu)經(jing)孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)，對于一(yi)定的(de)(de)(de)孔(kong)(kong)(kong)(kong)徑，流(liu)(liu)(liu)經(jing)孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)的(de)(de)(de)流(liu)(liu)(liu)量(liang)(liang)隨著(zhu)壓(ya)(ya)差增(zeng)(zeng)大而增(zeng)(zeng)大。但當(dang)壓(ya)(ya)差超過(guo)某一(yi)數(shu)(shu)值（稱為(wei)臨界壓(ya)(ya)差）時，流(liu)(liu)(liu)體(ti)通過(guo)孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)縮孔(kong)(kong)(kong)(kong)處的(de)(de)(de)流(liu)(liu)(liu)速達到音速，這時，無論壓(ya)(ya)差如何增(zeng)(zeng)加(jia)，流(liu)(liu)(liu)經(jing)孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)的(de)(de)(de)流(liu)(liu)(liu)量(liang)(liang)將維(wei)持在(zai)一(yi)定數(shu)(shu)值而不(bu)再增(zeng)(zeng)加(jia)。限(xian)(xian)流(liu)(liu)(liu)孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)就(jiu)是根(gen)據這一(yi)原理來(lai)(lai)限(xian)(xian)定流(liu)(liu)(liu)體(ti)的(de)(de)(de)流(liu)(liu)(liu)量(liang)(liang)和降低壓(ya)(ya)力的(de)(de)(de)。限(xian)(xian)流(liu)(liu)(liu)孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)按孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)上開孔(kong)(kong)(kong)(kong)數(shu)(shu)量(liang)(liang)分為(wei)單孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)和多孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)；按孔(kong)(kong)(kong)(kong)板(ban)(ban)(ban)(ban)(ban)數(shu)(shu)量(liang)(liang)可分為(wei)單級和多級。

 限流孔(kong)板主要使(shi)用在下(xia)列場合：

   ①. 工藝物料(liao)需要降壓的場合。

   ②. 在(zai)管道中閥門(men)上、下游(you)(you)需要(yao)有較大壓降時，為減少流(liu)體(ti)對(dui)閥門(men)的沖蝕，當經孔板(ban)節流(liu)不會產生氣(qi)相時，可在(zai)閥門(men)上游(you)(you)串聯孔板(ban)。

   ③. 流(liu)體需要小(xiao)流(liu)量且連續流(liu)通的地方，如(ru)泵的沖洗管(guan)(guan)道、熱備用泵的旁路(lu)管(guan)(guan)道（低(di)流(liu)量保護管(guan)(guan)道）、分析(xi)取樣管(guan)(guan)等場所。

   ④. 需要降壓以減少噪聲(sheng)或(huo)磨損的(de)地方，如放空(kong)系統(tong)。

  限(xian)流孔板有關的標準有：HG/T 20570.15、ISO 5167和(he)GB/T 2624。

 混合(he)孔板（Mixing Orifice）是在板面(mian)上開(kai)設一個或(huo)若(ruo)干個小孔，以便于(yu)兩種介(jie)質在經過混合(he)孔板時(shi)能充分(fen)混合(he)而(er)達到工藝操作的目的。它也(ye)應有兩個和匹配法蘭同(tong)樣的密封面(mian)。