限流(liu)孔(kong)(kong)板(ban)(ban)(ban)（Restriction Orifice）是在板(ban)(ban)(ban)面上開(kai)一個小(xiao)錐孔(kong)(kong)（該小(xiao)錐孔(kong)(kong)的尺寸由工(gong)藝專業提出），如(ru)圖4-19所示。它(ta)也應有(you)兩個和匹配法蘭同樣的密封面。限流(liu)孔(kong)(kong)板(ban)(ban)(ban)可(ke)以作為流(liu)量測量(liang)元(yuan)件用(yong)來(lai)(lai)測量(liang)流量(liang)，也可以作(zuo)為節流元(yuan)件用(yong)來(lai)(lai)限(xian)定(ding)(ding)(ding)流量(liang)和(he)降(jiang)低壓力(li)。當(dang)孔(kong)(kong)(kong)(kong)板(ban)前后(hou)存在(zai)一(yi)(yi)定(ding)(ding)(ding)壓差(cha)，流體流經孔(kong)(kong)(kong)(kong)板(ban)，對于一(yi)(yi)定(ding)(ding)(ding)的(de)孔(kong)(kong)(kong)(kong)徑，流經孔(kong)(kong)(kong)(kong)板(ban)的(de)流量(liang)隨著壓差(cha)增(zeng)大(da)而增(zeng)大(da)。但當(dang)壓差(cha)超過某一(yi)(yi)數(shu)值（稱(cheng)為臨(lin)界壓差(cha)）時，流體通過孔(kong)(kong)(kong)(kong)板(ban)縮孔(kong)(kong)(kong)(kong)處的(de)流速(su)達到音(yin)速(su)，這(zhe)時，無論壓差(cha)如何增(zeng)加，流經孔(kong)(kong)(kong)(kong)板(ban)的(de)流量(liang)將(jiang)維持在(zai)一(yi)(yi)定(ding)(ding)(ding)數(shu)值而不(bu)再(zai)增(zeng)加。限(xian)流孔(kong)(kong)(kong)(kong)板(ban)就是根據這(zhe)一(yi)(yi)原理來(lai)(lai)限(xian)定(ding)(ding)(ding)流體的(de)流量(liang)和(he)降(jiang)低壓力(li)的(de)。限(xian)流孔(kong)(kong)(kong)(kong)板(ban)按孔(kong)(kong)(kong)(kong)板(ban)上開(kai)孔(kong)(kong)(kong)(kong)數(shu)量(liang)分(fen)為單孔(kong)(kong)(kong)(kong)板(ban)和(he)多孔(kong)(kong)(kong)(kong)板(ban)；按孔(kong)(kong)(kong)(kong)板(ban)數(shu)量(liang)可分(fen)為單級(ji)和(he)多級(ji)。

 限流(liu)孔板主要(yao)使(shi)用(yong)在下列場(chang)合：

   ①. 工(gong)藝物料需要(yao)降壓的(de)場合。

   ②. 在(zai)管道中(zhong)閥(fa)門上(shang)(shang)、下(xia)游需要有較大(da)壓降(jiang)時，為減少(shao)流體對(dui)閥(fa)門的沖蝕，當經孔板節(jie)流不會(hui)產生氣相時，可在(zai)閥(fa)門上(shang)(shang)游串聯(lian)孔板。

   ③. 流體需要小(xiao)流量且連續流通的地(di)方，如泵的沖洗管(guan)道(dao)(dao)、熱備用泵的旁路管(guan)道(dao)(dao)（低流量保護管(guan)道(dao)(dao)）、分(fen)析取樣(yang)管(guan)等(deng)場(chang)所。

   ④. 需要降壓以減少噪聲或磨損的地方，如放空(kong)系統。

  限流孔板有關的標準有：HG/T 20570.15、ISO 5167和GB/T 2624。

 混(hun)合(he)孔(kong)板（Mixing Orifice）是在板面(mian)上開設一個(ge)或(huo)若干個(ge)小孔(kong)，以便于兩種介質(zhi)在經過(guo)混(hun)合(he)孔(kong)板時能充分混(hun)合(he)而(er)達到(dao)工(gong)藝操(cao)作(zuo)的目(mu)的。它也應有兩個(ge)和(he)匹配法蘭(lan)同樣的密封面(mian)。