限流孔板(ban)（Restriction Orifice）是(shi)在(zai)板(ban)面(mian)上(shang)開一個(ge)(ge)小錐孔（該小錐孔的(de)尺寸(cun)由(you)工藝專業(ye)提出），如圖4-19所示(shi)。它也(ye)應有(you)兩(liang)個(ge)(ge)和匹配法蘭同樣的(de)密封面(mian)。限流孔板(ban)可以作為流量測(ce)量(liang)(liang)元件(jian)用(yong)來測量(liang)(liang)流(liu)(liu)(liu)量(liang)(liang)，也(ye)可以作為節流(liu)(liu)(liu)元件(jian)用(yong)來限定(ding)流(liu)(liu)(liu)量(liang)(liang)和(he)降低(di)壓(ya)(ya)力。當孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)前后(hou)存在(zai)一(yi)(yi)定(ding)壓(ya)(ya)差，流(liu)(liu)(liu)體流(liu)(liu)(liu)經孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)，對于一(yi)(yi)定(ding)的(de)孔(kong)(kong)(kong)(kong)(kong)徑，流(liu)(liu)(liu)經孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)的(de)流(liu)(liu)(liu)量(liang)(liang)隨著壓(ya)(ya)差增大而(er)(er)增大。但當壓(ya)(ya)差超過某一(yi)(yi)數(shu)值（稱為臨界壓(ya)(ya)差）時，流(liu)(liu)(liu)體通過孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)縮孔(kong)(kong)(kong)(kong)(kong)處(chu)的(de)流(liu)(liu)(liu)速達到(dao)音速，這(zhe)時，無(wu)論壓(ya)(ya)差如何(he)增加(jia)，流(liu)(liu)(liu)經孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)的(de)流(liu)(liu)(liu)量(liang)(liang)將維持在(zai)一(yi)(yi)定(ding)數(shu)值而(er)(er)不再增加(jia)。限流(liu)(liu)(liu)孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)就是(shi)根據(ju)這(zhe)一(yi)(yi)原理來限定(ding)流(liu)(liu)(liu)體的(de)流(liu)(liu)(liu)量(liang)(liang)和(he)降低(di)壓(ya)(ya)力的(de)。限流(liu)(liu)(liu)孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)按(an)孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)上(shang)開(kai)孔(kong)(kong)(kong)(kong)(kong)數(shu)量(liang)(liang)分(fen)為單(dan)孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)和(he)多孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)；按(an)孔(kong)(kong)(kong)(kong)(kong)板(ban)(ban)數(shu)量(liang)(liang)可分(fen)為單(dan)級(ji)和(he)多級(ji)。

 限流孔板主要使(shi)用在下列場合：

   ①. 工藝物料需要降(jiang)壓的(de)場合。

   ②. 在(zai)管道中閥門(men)上、下游(you)需要有較大壓降時(shi)，為減少(shao)流體(ti)對閥門(men)的沖蝕，當(dang)經孔板節流不會產生氣(qi)相時(shi)，可在(zai)閥門(men)上游(you)串聯孔板。

   ③. 流體(ti)需要(yao)小流量且(qie)連續(xu)流通(tong)的(de)地方，如泵的(de)沖洗管(guan)(guan)道、熱(re)備(bei)用泵的(de)旁路管(guan)(guan)道（低流量保(bao)護管(guan)(guan)道）、分(fen)析取樣管(guan)(guan)等場所。

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

  限流(liu)孔板有(you)關的標準有(you)：HG/T 20570.15、ISO 5167和GB/T 2624。

 混(hun)合孔板（Mixing Orifice）是在(zai)板面(mian)上開設一個(ge)或若干個(ge)小孔，以便于(yu)兩種介質在(zai)經過混(hun)合孔板時能充分混(hun)合而達到工藝操作的(de)目的(de)。它(ta)也應有兩個(ge)和匹配法蘭同樣的(de)密封面(mian)。