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目前(qian)混凝(ning)土輸送(song)(song)泵已廣泛應(ying)用于砼(tong)(tong)(tong)工程施工中。所用砼(tong)(tong)(tong)泵主要為雙缸驅動砼(tong)(tong)(tong)泵，其在(zai)(zai)泵送(song)(song)換向(xiang)(xiang)瞬間(jian)普(pu)遍(bian)存在(zai)(zai)砼(tong)(tong)(tong)斷流現象。這種斷流現象具有(you)兩大危害，一(yi)是容易導致砼(tong)(tong)(tong)離析，部(bu)(bu)分砼(tong)(tong)(tong)脫水成(cheng)干硬(ying)砼(tong)(tong)(tong)造成(cheng)堵管(guan)，尤其在(zai)(zai)泵送(song)(song)低坍落(luo)度(du)(du)的砼(tong)(tong)(tong)時更是如此(ci)；二是換向(xiang)(xiang)瞬間(jian)管(guan)路及分配閥中砼(tong)(tong)(tong)壓力釋放，對砼(tong)(tong)(tong)泵液壓系統產(chan)生沖擊(ji)，造成(cheng)某些零部(bu)(bu)件(jian)損(sun)壞并增加能量損(sun)耗(hao)。斷流對垂直向(xiang)(xiang)上(shang)尤其是向(xiang)(xiang)50m以上(shang)高度(du)(du)泵送(song)(song)時危害很明顯。

1、原因分析

如下圖1為一種開式(shi)液壓(ya)系統的(de)雙缸(gang)(gang)驅動(dong)(dong)砼(tong)(tong)泵送(song)系統的(de)液壓(ya)原理圖。該泵為全液控砼(tong)(tong)泵，恒功率主油(you)(you)(you)(you)泵通(tong)(tong)過(guo)液動(dong)(dong)閥(fa)(fa)8-1、8-2向(xiang)主油(you)(you)(you)(you)缸(gang)(gang)10-1、10-2和(he)分(fen)配(pei)閥(fa)(fa)油(you)(you)(you)(you)缸(gang)(gang)9供油(you)(you)(you)(you)。主油(you)(you)(you)(you)缸(gang)(gang)插(cha)裝(zhuang)閥(fa)(fa)和(he)分(fen)配(pei)閥(fa)(fa)油(you)(you)(you)(you)缸(gang)(gang)分(fen)別發出信號控制液動(dong)(dong)閥(fa)(fa)換(huan)向(xiang)，使主油(you)(you)(you)(you)缸(gang)(gang)和(he)分(fen)配(pei)閥(fa)(fa)油(you)(you)(you)(you)缸(gang)(gang)的(de)動(dong)(dong)作順序(xu)相互協調，實現砼(tong)(tong)泵送(song)循環，其中主油(you)(you)(you)(you)缸(gang)(gang)10雙缸(gang)(gang)交替地(di)吸(xi)-排(pai)砼(tong)(tong)實現砼(tong)(tong)的(de)連(lian)續泵送(song)。每次(ci)換(huan)向(xiang)過(guo)程中砼(tong)(tong)流(liu)(liu)通(tong)(tong)常(chang)都(dou)會出現明顯的(de)流(liu)(liu)-斷-流(liu)(liu)的(de)現象，即通(tong)(tong)常(chang)所說的(de)斷流(liu)(liu)現象。

圖1砼泵液壓系統原理圖

1-電動機；2-油箱；3-主(zhu)油泵；4-回(hui)油濾(lv)油器(qi)；5-空氣濾(lv)清器(qi)；6-溢流(liu)閥；7-壓(ya)力表；8-液動閥；9-分(fen)配閥油缸；10-主(zhu)油缸

砼斷流現象的(de)原(yuan)因有(you)三個：

①當主油(you)缸運行(xing)到接(jie)近行(xing)程終點時發出換(huan)(huan)(huan)向(xiang)(xiang)信號到換(huan)(huan)(huan)向(xiang)(xiang)油(you)缸換(huan)(huan)(huan)向(xiang)(xiang)，進(jin)而主系統油(you)路換(huan)(huan)(huan)向(xiang)(xiang)，主油(you)缸10向(xiang)(xiang)相反方向(xiang)(xiang)運動(dong)，此過程至少需0.2s；

②砼被(bei)吸入砼缸的吸入效率通常只(zhi)有85％～95％，不可避(bi)免地吸入一(yi)小段(duan)空氣，這將(jiang)是一(yi)小段(duan)空行程；

③換(huan)(huan)向時(shi)(shi)吸入砼缸的(de)砼在向外輸出時(shi)(shi)壓(ya)力(li)升(sheng)高，有(you)一(yi)定(ding)的(de)可壓(ya)縮性，這也是一(yi)小段(duan)空行(xing)程。由(you)于(yu)有(you)了(le)換(huan)(huan)向和(he)兩段(duan)空行(xing)程時(shi)(shi)間，因(yin)此砼泵送過程中出現了(le)斷流(liu)問題。

2、解決辦法

解(jie)決泵(beng)送過(guo)程(cheng)(cheng)中(zhong)(zhong)斷流現象的方法是盡可(ke)能縮短換(huan)(huan)(huan)向(xiang)時間和(he)(he)加快主油缸(gang)活塞在(zai)換(huan)(huan)(huan)向(xiang)開始階段的運(yun)行速度，在(zai)管(guan)道和(he)(he)分(fen)配閥中(zhong)(zhong)砼壓力完全釋(shi)放前實現砼連續泵(beng)送，以(yi)盡可(ke)能減少砼因斷流離析以(yi)及換(huan)(huan)(huan)向(xiang)過(guo)程(cheng)(cheng)中(zhong)(zhong)管(guan)道和(he)(he)分(fen)配閥中(zhong)(zhong)砼壓力釋(shi)放的反(fan)沖擊。

對(dui)于大多數泵(beng)送系(xi)統而言，可(ke)通過采用電(dian)比(bi)例控制(zhi)(zhi)(zhi)(zhi)恒功(gong)率(lv)柱塞(sai)泵(beng)來解(jie)決斷流(liu)問題。由(you)于電(dian)比(bi)例控制(zhi)(zhi)(zhi)(zhi)+恒功(gong)率(lv)控制(zhi)(zhi)(zhi)(zhi)是電(dian)控變(bian)量(liang)優先于恒功(gong)率(lv)控制(zhi)(zhi)(zhi)(zhi)，在低于功(gong)率(lv)雙曲線時(shi)排(pai)量(liang)受(shou)控制(zhi)(zhi)(zhi)(zhi)電(dian)流(liu)的調整，在換(huan)(huan)向(xiang)過程及換(huan)(huan)向(xiang)后(hou)(hou)油缸活塞(sai)推動管道中(zhong)的砼(tong)運動前，系(xi)統壓力通常低于泵(beng)送壓力，可(ke)以(yi)采用增大主油泵(beng)排(pai)量(liang)實(shi)現(xian)分配閥快速(su)換(huan)(huan)向(xiang)，減少(shao)換(huan)(huan)向(xiang)后(hou)(hou)到開始(shi)推動砼(tong)時(shi)間，實(shi)現(xian)砼(tong)流(liu)從表觀(guan)上不斷流(liu)。

通(tong)常(chang)可在油(you)缸(gang)(gang)和砼缸(gang)(gang)之(zhi)間的(de)(de)(de)水箱(xiang)中(zhong)設(she)置2個接近(jin)(jin)開(kai)(kai)關(guan)，根據主(zhu)油(you)泵(beng)(beng)排(pai)量和主(zhu)油(you)缸(gang)(gang)缸(gang)(gang)徑及行(xing)程設(she)置起始(shi)(shi)(shi)和截(jie)止(zhi)點取信(xin)(xin)口的(de)(de)(de)位置，這種控(kong)(kong)制的(de)(de)(de)關(guan)鍵是如何確定電比例(li)控(kong)(kong)制階段取信(xin)(xin)口的(de)(de)(de)開(kai)(kai)始(shi)(shi)(shi)和截(jie)止(zhi)位置，接近(jin)(jin)開(kai)(kai)關(guan)間的(de)(de)(de)距離通(tong)常(chang)為總行(xing)程的(de)(de)(de)5％～10％。接近(jin)(jin)開(kai)(kai)關(guan)得到起始(shi)(shi)(shi)信(xin)(xin)號后傳輸到可編程序控(kong)(kong)制器(qi)或(huo)保持繼電器(qi)，由控(kong)(kong)制器(qi)或(huo)繼電器(qi)控(kong)(kong)制發出使(shi)油(you)泵(beng)(beng)達到大(da)排(pai)量所需電流(通(tong)常(chang)幾百mA)到主(zhu)油(you)泵(beng)(beng)比例(li)電磁鐵，實(shi)現油(you)泵(beng)(beng)排(pai)量猛增，迅速換向和開(kai)(kai)始(shi)(shi)(shi)推送(song)(song)分配(pei)閥(fa)及管(guan)道中(zhong)的(de)(de)(de)砼。調整截(jie)止(zhi)接近(jin)(jin)開(kai)(kai)關(guan)位置，使(shi)油(you)缸(gang)(gang)開(kai)(kai)始(shi)(shi)(shi)推送(song)(song)分配(pei)閥(fa)及管(guan)道中(zhong)的(de)(de)(de)砼時停止(zhi)電控(kong)(kong)，繼續實(shi)現油(you)泵(beng)(beng)恒(heng)功率控(kong)(kong)制。實(shi)際使(shi)用中(zhong)取信(xin)(xin)口的(de)(de)(de)開(kai)(kai)始(shi)(shi)(shi)和截(jie)止(zhi)位置可根據砼泵(beng)(beng)的(de)(de)(de)實(shi)際情況做相(xiang)應調整，以保證大(da)程度(du)增加泵(beng)(beng)送(song)(song)中(zhong)砼流的(de)(de)(de)連續性。

在(zai)國外尤其是歐美各(ge)國由于(yu)多(duo)采用泵(beng)車，排量較大(da)(da)，砼(tong)骨料及(ji)(ji)級配控制比(bi)較嚴格，建(jian)筑規模(mo)和高(gao)度(du)都較小，斷(duan)流問題(ti)(ti)及(ji)(ji)危害(hai)不很(hen)明顯；而國內普遍使(shi)用拖泵(beng)，排量多(duo)在(zai)80m3/h以下，建(jian)筑規模(mo)和高(gao)度(du)都較大(da)(da)，斷(duan)流現象比(bi)較明顯。通(tong)過對主油泵(beng)控制方式的(de)選取和設置(zhi)，可以有效解(jie)決(jue)砼(tong)輸(shu)送中斷(duan)流問題(ti)(ti)，減少換向沖(chong)擊，大(da)(da)大(da)(da)提高(gao)砼(tong)泵(beng)泵(beng)送性能。