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目(mu)前混(hun)凝土輸送泵(beng)(beng)(beng)已(yi)廣泛應用于砼(tong)(tong)(tong)工(gong)(gong)程施工(gong)(gong)中。所用砼(tong)(tong)(tong)泵(beng)(beng)(beng)主要為雙缸驅動砼(tong)(tong)(tong)泵(beng)(beng)(beng)，其在泵(beng)(beng)(beng)送換向(xiang)瞬間普遍存在砼(tong)(tong)(tong)斷流(liu)(liu)現(xian)象(xiang)。這(zhe)種斷流(liu)(liu)現(xian)象(xiang)具有兩大危害，一是(shi)容(rong)易導(dao)致砼(tong)(tong)(tong)離析，部分砼(tong)(tong)(tong)脫水成干硬砼(tong)(tong)(tong)造成堵管，尤其在泵(beng)(beng)(beng)送低坍落度的砼(tong)(tong)(tong)時(shi)更是(shi)如(ru)此；二是(shi)換向(xiang)瞬間管路(lu)及分配閥中砼(tong)(tong)(tong)壓(ya)力(li)釋放，對砼(tong)(tong)(tong)泵(beng)(beng)(beng)液壓(ya)系統產生沖擊，造成某些零部件損(sun)壞并增(zeng)加能量(liang)損(sun)耗(hao)。斷流(liu)(liu)對垂直向(xiang)上(shang)尤其是(shi)向(xiang)50m以上(shang)高(gao)度泵(beng)(beng)(beng)送時(shi)危害很明(ming)顯。

1、原因分析

如(ru)下圖1為(wei)一(yi)種開式(shi)液(ye)壓(ya)系統(tong)的(de)(de)(de)雙缸(gang)(gang)(gang)驅(qu)動砼(tong)泵(beng)送(song)系統(tong)的(de)(de)(de)液(ye)壓(ya)原理(li)圖。該(gai)泵(beng)為(wei)全液(ye)控砼(tong)泵(beng)，恒(heng)功率(lv)主(zhu)油(you)泵(beng)通過液(ye)動閥(fa)(fa)8-1、8-2向主(zhu)油(you)缸(gang)(gang)(gang)10-1、10-2和分(fen)配閥(fa)(fa)油(you)缸(gang)(gang)(gang)9供油(you)。主(zhu)油(you)缸(gang)(gang)(gang)插裝閥(fa)(fa)和分(fen)配閥(fa)(fa)油(you)缸(gang)(gang)(gang)分(fen)別發出信號控制液(ye)動閥(fa)(fa)換(huan)向，使(shi)主(zhu)油(you)缸(gang)(gang)(gang)和分(fen)配閥(fa)(fa)油(you)缸(gang)(gang)(gang)的(de)(de)(de)動作順(shun)序(xu)相互協調，實現(xian)砼(tong)泵(beng)送(song)循環，其中主(zhu)油(you)缸(gang)(gang)(gang)10雙缸(gang)(gang)(gang)交替地(di)吸-排砼(tong)實現(xian)砼(tong)的(de)(de)(de)連(lian)續(xu)泵(beng)送(song)。每次換(huan)向過程中砼(tong)流通常(chang)都會(hui)出現(xian)明顯的(de)(de)(de)流-斷-流的(de)(de)(de)現(xian)象，即通常(chang)所說的(de)(de)(de)斷流現(xian)象。

圖1砼泵液壓系統原理圖

1-電動機；2-油(you)(you)(you)箱；3-主(zhu)油(you)(you)(you)泵(beng)；4-回油(you)(you)(you)濾油(you)(you)(you)器；5-空氣濾清器；6-溢(yi)流閥(fa)(fa)；7-壓(ya)力表；8-液動閥(fa)(fa)；9-分(fen)配閥(fa)(fa)油(you)(you)(you)缸；10-主(zhu)油(you)(you)(you)缸 

砼斷(duan)流現(xian)象的原因有三個：

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

②砼被吸入(ru)砼缸(gang)的吸入(ru)效率(lv)通(tong)常只有85％～95％，不(bu)可避免地吸入(ru)一小段空氣，這將是(shi)一小段空行程；

③換(huan)向(xiang)時(shi)吸入(ru)砼缸(gang)的砼在向(xiang)外輸出時(shi)壓力(li)升高，有(you)一定的可(ke)壓縮性，這也(ye)是一小段(duan)空(kong)行程。由于有(you)了(le)換(huan)向(xiang)和(he)兩(liang)段(duan)空(kong)行程時(shi)間，因此砼泵送過程中出現了(le)斷(duan)流問題。

2、解決辦法

解決泵(beng)送過(guo)(guo)程中斷流現象(xiang)的方法(fa)是盡可能(neng)縮短換向時間和(he)加(jia)快主油缸活塞在(zai)換向開始階段(duan)的運行速(su)度，在(zai)管道和(he)分配閥中砼(tong)壓(ya)力(li)完全釋放(fang)(fang)前實現砼(tong)連續泵(beng)送，以盡可能(neng)減少砼(tong)因斷流離析(xi)以及換向過(guo)(guo)程中管道和(he)分配閥中砼(tong)壓(ya)力(li)釋放(fang)(fang)的反沖擊(ji)。

對于(yu)(yu)大多數泵送(song)系(xi)統(tong)而言，可(ke)通(tong)過(guo)采(cai)用電(dian)(dian)比例控(kong)制(zhi)(zhi)(zhi)恒功(gong)率柱(zhu)塞(sai)泵來解決斷流(liu)問(wen)題(ti)。由于(yu)(yu)電(dian)(dian)比例控(kong)制(zhi)(zhi)(zhi)+恒功(gong)率控(kong)制(zhi)(zhi)(zhi)是(shi)電(dian)(dian)控(kong)變量(liang)優(you)先于(yu)(yu)恒功(gong)率控(kong)制(zhi)(zhi)(zhi)，在低于(yu)(yu)功(gong)率雙曲線(xian)時(shi)排(pai)量(liang)受控(kong)制(zhi)(zhi)(zhi)電(dian)(dian)流(liu)的(de)(de)調(diao)整，在換(huan)向(xiang)(xiang)過(guo)程及換(huan)向(xiang)(xiang)后(hou)油缸活塞(sai)推(tui)動(dong)管道中的(de)(de)砼(tong)(tong)運動(dong)前，系(xi)統(tong)壓力通(tong)常低于(yu)(yu)泵送(song)壓力，可(ke)以(yi)采(cai)用增大主油泵排(pai)量(liang)實(shi)現(xian)分(fen)配(pei)閥快(kuai)速換(huan)向(xiang)(xiang)，減(jian)少(shao)換(huan)向(xiang)(xiang)后(hou)到(dao)開始推(tui)動(dong)砼(tong)(tong)時(shi)間，實(shi)現(xian)砼(tong)(tong)流(liu)從表觀(guan)上不斷流(liu)。

通常(chang)可在(zai)油(you)(you)缸(gang)和(he)砼(tong)缸(gang)之間的(de)(de)水(shui)箱中(zhong)(zhong)設(she)置2個(ge)接(jie)近(jin)開(kai)(kai)(kai)關(guan)(guan)(guan)，根(gen)據主油(you)(you)泵排量(liang)(liang)和(he)主油(you)(you)缸(gang)缸(gang)徑及行程設(she)置起始(shi)和(he)截止(zhi)點取(qu)信口的(de)(de)位置，這種(zhong)控(kong)(kong)制(zhi)(zhi)(zhi)的(de)(de)關(guan)(guan)(guan)鍵是如何確定(ding)電(dian)比例(li)控(kong)(kong)制(zhi)(zhi)(zhi)階段取(qu)信口的(de)(de)開(kai)(kai)(kai)始(shi)和(he)截止(zhi)位置，接(jie)近(jin)開(kai)(kai)(kai)關(guan)(guan)(guan)間的(de)(de)距(ju)離通常(chang)為總行程的(de)(de)5％～10％。接(jie)近(jin)開(kai)(kai)(kai)關(guan)(guan)(guan)得到(dao)(dao)起始(shi)信號(hao)后傳輸到(dao)(dao)可編程序控(kong)(kong)制(zhi)(zhi)(zhi)器或保持繼電(dian)器，由控(kong)(kong)制(zhi)(zhi)(zhi)器或繼電(dian)器控(kong)(kong)制(zhi)(zhi)(zhi)發出(chu)使油(you)(you)泵達到(dao)(dao)大(da)排量(liang)(liang)所(suo)需電(dian)流(通常(chang)幾(ji)百mA)到(dao)(dao)主油(you)(you)泵比例(li)電(dian)磁(ci)鐵，實(shi)現油(you)(you)泵排量(liang)(liang)猛增(zeng)，迅速(su)換向和(he)開(kai)(kai)(kai)始(shi)推送(song)分配(pei)閥及管道中(zhong)(zhong)的(de)(de)砼(tong)。調整截止(zhi)接(jie)近(jin)開(kai)(kai)(kai)關(guan)(guan)(guan)位置，使油(you)(you)缸(gang)開(kai)(kai)(kai)始(shi)推送(song)分配(pei)閥及管道中(zhong)(zhong)的(de)(de)砼(tong)時停止(zhi)電(dian)控(kong)(kong)，繼續實(shi)現油(you)(you)泵恒(heng)功率控(kong)(kong)制(zhi)(zhi)(zhi)。實(shi)際(ji)使用中(zhong)(zhong)取(qu)信口的(de)(de)開(kai)(kai)(kai)始(shi)和(he)截止(zhi)位置可根(gen)據砼(tong)泵的(de)(de)實(shi)際(ji)情況做相應調整，以保證大(da)程度增(zeng)加(jia)泵送(song)中(zhong)(zhong)砼(tong)流的(de)(de)連續性。

在國(guo)外(wai)尤其是歐美各國(guo)由于多采(cai)用泵(beng)車，排量較(jiao)大(da)，砼(tong)骨料及(ji)級配控(kong)制比較(jiao)嚴(yan)格，建(jian)筑(zhu)規模(mo)和高(gao)(gao)度都較(jiao)小，斷流問題及(ji)危害不很(hen)明(ming)(ming)顯(xian)；而國(guo)內普遍使用拖泵(beng)，排量多在80m3/h以下(xia)，建(jian)筑(zhu)規模(mo)和高(gao)(gao)度都較(jiao)大(da)，斷流現(xian)象比較(jiao)明(ming)(ming)顯(xian)。通過(guo)對主油泵(beng)控(kong)制方式的選取和設置，可以有效解(jie)決砼(tong)輸送中斷流問題，減少換向沖擊，大(da)大(da)提高(gao)(gao)砼(tong)泵(beng)泵(beng)送性能。