一、限(xian)流(liu)孔板的(de)作用(yong)與形式(shi)
限(xian)流(liu)孔板設置在管道(dao)中用于限(xian)制(zhi)流(liu)體的流(liu)量(liang)或降低流(liu)體的壓力。有的設計單位(wei)由(you)管道(dao)專業(ye)負責選用，有的設計單位(wei)由(you)儀表(biao)專業(ye)負責選用。限(xian)流(liu)孔板根據 GB/T 2624、HG/T20570、GD 2000、GD 87等(deng)標準(zhun)設計制(zhi)造。
限流孔板用于以下幾個方面：
①. 工藝物料需要(yao)降壓且精度要(yao)求不高。
②. 在管道中閥(fa)門上、下游需要有較大壓降時，為減少流體對閥門的沖蝕，當經孔板節流不會產生氣相時，可在閥門上游串聯孔板。
③. 流(liu)體需要小流(liu)量(liang)(liang)且(qie)連續流(liu)通的地方(fang)，如泵的沖洗管(guan)(guan)道(dao)、熱備(bei)用(yong)泵的旁路管(guan)(guan)道(dao)（低流(liu)量(liang)(liang)保護管(guan)(guan)道(dao)）、分析取樣(yang)管(guan)(guan)等場所。
④. 需要降壓以減少噪聲或(huo)磨損的地方(fang)，如放空系統。
限流孔(kong)(kong)板為一同(tong)心銳孔(kong)(kong)板，用于限制流體(ti)(ti)的(de)流量或降(jiang)(jiang)(jiang)低(di)流體(ti)(ti)的(de)壓(ya)(ya)力。流體(ti)(ti)通過孔(kong)(kong)板就會產(chan)生壓(ya)(ya)力降(jiang)(jiang)(jiang)，通過孔(kong)(kong)板的(de)流量則隨壓(ya)(ya)力降(jiang)(jiang)(jiang)的(de)增(zeng)大而增(zeng)大。但當壓(ya)(ya)力降(jiang)(jiang)(jiang)超過一定(ding)數值(zhi)，即超過臨界壓(ya)(ya)力降(jiang)(jiang)(jiang)時，不論出口壓(ya)(ya)力如何降(jiang)(jiang)(jiang)低(di)，流量將維持一定(ding)的(de)數值(zhi)而不再增(zeng)加(jia)。限流孔(kong)(kong)板就是根(gen)據這個(ge)原理用來限制流體(ti)(ti)的(de)流量或降(jiang)(jiang)(jiang)低(di)流體(ti)(ti)的(de)壓(ya)(ya)力。
限流孔(kong)板(ban)作(zuo)為節流元(yuan)件，由于(yu)具有結構簡單、易加工、制(zhi)造(zao)成本低、安裝方便(bian)等優點，在(zai)滿(man)足工藝(yi)(yi)要求(qiu)的(de)前(qian)提下，使用限流孔(kong)板(ban)代(dai)替(ti)調節閥來限定流量(liang)或(huo)降低壓(ya)力，將會大大地降低投資和操作(zuo)維修費用，因此在(zai)國外(wai)已被廣泛地應用于(yu)工藝(yi)(yi)裝置，對裝置的(de)安全運(yun)行起著重要的(de)作(zuo)用。
限流(liu)孔板按孔板上開(kai)孔數(shu)(shu)分為單孔板和多孔板，按板數(shu)(shu)可分為單板和多板。公稱直(zhi)徑：10mm≤DN≤1000mm，公稱壓力：PN≤42MPa。工(gong)作溫度：50℃≤t≤550℃ ，連(lian)接(jie)方式：焊接(jie)、法蘭連(lian)接(jie)。典型限流(liu)孔板見圖6.6.4。
二、限流(liu)孔板選型的一般要求
1. 氣(qi)體、蒸汽
為了避免使用限流(liu)孔(kong)板(ban)(ban)(ban)的管路出現噎塞(sai)流(liu)，限流(liu)孔(kong)板(ban)(ban)(ban)后(hou)壓(ya)(ya)力(P2)不能(neng)(neng)小于(yu)板(ban)(ban)(ban)前壓(ya)(ya)力(p1)的55％，即P2≥0.55p1，因此當(dang)P2<0.55p1 時，不能(neng)(neng)用單板(ban)(ban)(ban)，要(yao)(yao)選擇多板(ban)(ban)(ban)。板(ban)(ban)(ban)數要(yao)(yao)保證每板(ban)(ban)(ban)的板(ban)(ban)(ban)后(hou)壓(ya)(ya)力大于(yu)板(ban)(ban)(ban)前壓(ya)(ya)力的55％。
2. 液體
當液體壓降(jiang)小(xiao)于(yu)(yu)或等于(yu)(yu)2.5MPa時(shi)，選擇單板(ban)孔板(ban)。當液體壓降(jiang)大(da)于(yu)(yu)2.5MPa時(shi)，選擇多板(ban)孔板(ban)，且使每(mei)塊孔板(ban)的壓降(jiang)小(xiao)于(yu)(yu)2.5MPa。
三、孔數的確定
管道公稱直徑(jing)≤150mm的管路，通常(chang)采用(yong)單(dan)孔(kong)(kong)(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)(kong)(kong)板(ban)(ban)(ban)；150mm時，采用(yong)多孔(kong)(kong)(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)(kong)(kong)板(ban)(ban)(ban)。多孔(kong)(kong)(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)(kong)(kong)板(ban)(ban)(ban)的孔(kong)(kong)(kong)(kong)(kong)(kong)徑(jing)（do），一(yi)般可選(xuan)(xuan)用(yong)12.5mm，20mm，25mm，40mm。在(zai)計算多孔(kong)(kong)(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)(kong)(kong)板(ban)(ban)(ban)時，首(shou)先(xian)按(an)單(dan)孔(kong)(kong)(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)(kong)(kong)板(ban)(ban)(ban)求出(chu)孔(kong)(kong)(kong)(kong)(kong)(kong)徑(jing)（d），然后按(an)式（6.6.1）求取選(xuan)(xuan)用(yong)的多孔(kong)(kong)(kong)(kong)(kong)(kong)孔(kong)(kong)(kong)(kong)(kong)(kong)板(ban)(ban)(ban)的孔(kong)(kong)(kong)(kong)(kong)(kong)數(shu)（N）。
