限流孔(kong)板(ban)（Restriction Orifice）是(shi)在(zai)板(ban)面上開一個(ge)小錐孔(kong)（該(gai)小錐孔(kong)的尺寸由工藝專業(ye)提出），如圖4-19所示。它(ta)也應有(you)兩個(ge)和匹配法蘭同(tong)樣的密封(feng)面。限流孔(kong)板(ban)可(ke)以(yi)作為流量測(ce)量(liang)元(yuan)件用來測量(liang)流(liu)(liu)量(liang)，也可以作為(wei)節流(liu)(liu)元(yuan)件用來限定(ding)(ding)流(liu)(liu)量(liang)和(he)(he)降低壓(ya)(ya)(ya)(ya)力。當孔(kong)(kong)(kong)(kong)(kong)板(ban)前后存(cun)在(zai)一(yi)定(ding)(ding)壓(ya)(ya)(ya)(ya)差(cha)(cha)，流(liu)(liu)體(ti)流(liu)(liu)經(jing)孔(kong)(kong)(kong)(kong)(kong)板(ban)，對于一(yi)定(ding)(ding)的(de)孔(kong)(kong)(kong)(kong)(kong)徑(jing)，流(liu)(liu)經(jing)孔(kong)(kong)(kong)(kong)(kong)板(ban)的(de)流(liu)(liu)量(liang)隨(sui)著壓(ya)(ya)(ya)(ya)差(cha)(cha)增(zeng)(zeng)大(da)而(er)增(zeng)(zeng)大(da)。但(dan)當壓(ya)(ya)(ya)(ya)差(cha)(cha)超過某一(yi)數(shu)值（稱(cheng)為(wei)臨界壓(ya)(ya)(ya)(ya)差(cha)(cha)）時(shi)，流(liu)(liu)體(ti)通(tong)過孔(kong)(kong)(kong)(kong)(kong)板(ban)縮孔(kong)(kong)(kong)(kong)(kong)處的(de)流(liu)(liu)速(su)達到音(yin)速(su)，這時(shi)，無論(lun)壓(ya)(ya)(ya)(ya)差(cha)(cha)如(ru)何增(zeng)(zeng)加(jia)，流(liu)(liu)經(jing)孔(kong)(kong)(kong)(kong)(kong)板(ban)的(de)流(liu)(liu)量(liang)將(jiang)維持在(zai)一(yi)定(ding)(ding)數(shu)值而(er)不再增(zeng)(zeng)加(jia)。限流(liu)(liu)孔(kong)(kong)(kong)(kong)(kong)板(ban)就(jiu)是根據這一(yi)原理來限定(ding)(ding)流(liu)(liu)體(ti)的(de)流(liu)(liu)量(liang)和(he)(he)降低壓(ya)(ya)(ya)(ya)力的(de)。限流(liu)(liu)孔(kong)(kong)(kong)(kong)(kong)板(ban)按(an)孔(kong)(kong)(kong)(kong)(kong)板(ban)上(shang)開孔(kong)(kong)(kong)(kong)(kong)數(shu)量(liang)分(fen)為(wei)單孔(kong)(kong)(kong)(kong)(kong)板(ban)和(he)(he)多孔(kong)(kong)(kong)(kong)(kong)板(ban)；按(an)孔(kong)(kong)(kong)(kong)(kong)板(ban)數(shu)量(liang)可分(fen)為(wei)單級和(he)(he)多級。

 限流孔(kong)板主要使用在(zai)下(xia)列場(chang)合：

   ①. 工藝物料需要(yao)降壓的場合。

   ②. 在(zai)管道中閥(fa)門(men)上(shang)、下游需要有較(jiao)大壓降(jiang)時(shi)(shi)，為減(jian)少流體對閥(fa)門(men)的(de)沖蝕，當(dang)經孔(kong)板(ban)節流不(bu)會產生氣相(xiang)時(shi)(shi)，可在(zai)閥(fa)門(men)上(shang)游串聯(lian)孔(kong)板(ban)。

   ③. 流(liu)體需要小流(liu)量且連續流(liu)通的地方(fang)，如泵的沖(chong)洗管道(dao)、熱(re)備用泵的旁(pang)路管道(dao)（低流(liu)量保護管道(dao)）、分析取樣管等場所(suo)。

   ④. 需要(yao)降壓以(yi)減少噪聲或磨損的(de)地方，如放空系統。

  限流孔(kong)板有關(guan)的標準有：HG/T 20570.15、ISO 5167和GB/T 2624。

 混(hun)合(he)孔板（Mixing Orifice）是在板面(mian)上開設一個或若干個小孔，以便于兩(liang)(liang)種介質在經(jing)過(guo)混(hun)合(he)孔板時(shi)能充分混(hun)合(he)而達(da)到工(gong)藝操作的(de)目(mu)的(de)。它也應有兩(liang)(liang)個和匹(pi)配法蘭同(tong)樣的(de)密(mi)封面(mian)。