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液壓系統(tǒng)
一個(gè)完整的液壓系統(tǒng)由五個(gè)部分組成，即動(dòng)力元件、執(zhí)行元件、控制元件、無件和液壓油。動(dòng)力元件的作用是將原動(dòng)機(jī)的機(jī)械能轉(zhuǎn)換成液體的壓力能，指液壓系統(tǒng)中的油泵，它向整個(gè)液壓系統(tǒng)提供動(dòng)力。液壓泵的結(jié)構(gòu)形式一般有齒輪泵、葉片泵和柱塞泵。執(zhí)行元件(如液壓缸和液壓馬達(dá))的作用是將液體的壓力能轉(zhuǎn)換為機(jī)械能，驅(qū)動(dòng)負(fù)載作直線往復(fù)運(yùn)動(dòng)或回轉(zhuǎn)運(yùn)動(dòng)。 控制元件(即各種液壓閥)在液壓系統(tǒng)中控制和調(diào)節(jié)液體的壓力、流量和方向。根據(jù)控制功能的不同，液壓閥可分為村力控制閥、流量控制閥和方向控制閥。壓力控制閥又分為益流閥(安全閥)、減壓閥、順序閥、壓力繼電器等；流量控制閥包括節(jié)流閥、調(diào)整閥、分流集流閥等；方向控制閥包括單向閥、液控單向閥、梭閥、換向閥等。根據(jù)控制方式不同，液壓閥可分為開關(guān)式控制閥、定值控制閥和比例控制閥。 輔助元件包括油箱、濾油器、油管及管接頭、密封圈、壓力表、油位油溫計(jì)等。 液壓油是液壓系統(tǒng)中傳遞能量的工作介質(zhì)，有各種礦物油、乳化液和合成型液壓油等幾大類。
液壓的原理
它是由兩個(gè)大小不同的液缸組成的，在液缸里充滿水或油。充水的叫“水壓機(jī)”；充油的稱“油壓機(jī)”。兩個(gè)液缸里各有一個(gè)可以滑動(dòng)的活塞，如果在小活塞上加一定值的壓力，根據(jù)帕斯卡定律，小活塞將這一壓力通過液體的壓強(qiáng)傳遞給大活塞，將大活塞頂上去。設(shè)小活塞的橫截面積是S1，加在小活塞上的向下的壓力是F1。于是，小活塞對(duì)液體的壓強(qiáng)為P=F1/SI, 能夠大小不變地被液體向各個(gè)方向傳遞”。大活塞所受到的壓強(qiáng)必然也等于P。若大活塞的橫截面積是S2，壓強(qiáng)P在大活塞上所產(chǎn)生的向上的壓力F2=PxS2 ，截面積是小活塞橫截面積的倍數(shù)。從上式知，在小活塞上加一較小的力，則在大活塞上會(huì)得到很大的力，為此用液壓機(jī)來壓制膠合板、榨油、提取重物、鍛壓鋼材等。
液壓傳動(dòng)的發(fā)展史
液壓傳動(dòng)和氣壓傳動(dòng)稱為流體傳動(dòng)，是根據(jù)17世紀(jì)帕斯卡提出的液體靜壓力傳動(dòng)原理而發(fā)展起來的一門新興技術(shù)，1795年英國(guó)約瑟夫?布拉曼(Joseph Braman,1749-1814)，在倫敦用水作為工作介質(zhì),以水壓機(jī)的形式將其應(yīng)用于工業(yè)上,誕生了世界上第一臺(tái)水壓機(jī)。1905年將工作介質(zhì)水改為油,又進(jìn)一步得到改善。 第一次世界大戰(zhàn)(1914-1918)后液壓傳動(dòng)廣泛應(yīng)用,特別是1920年以后,發(fā)展更為迅速。液壓元件大約在 19 世紀(jì)末 20 世紀(jì)初的20年間,才開始進(jìn)入正規(guī)的工業(yè)生產(chǎn)階段。1925 年維克斯(F.Vikers)發(fā)明了壓力平衡式葉片泵,為近代液壓元件工業(yè)或液壓傳動(dòng) 的逐步建立奠定了基礎(chǔ)。20 世紀(jì)初康斯坦丁?尼斯克(G?Constantimsco)對(duì)能量波動(dòng)傳遞所進(jìn)行的理論及實(shí)際研究;1910年對(duì)液力傳動(dòng)(液力聯(lián)軸節(jié)、液力變矩器等)方面的貢獻(xiàn)，使這兩方面領(lǐng)域得到了發(fā)展。
第二次世界大戰(zhàn)(1941-1945)期間,在美國(guó)機(jī)床中有30%應(yīng)用了液壓傳動(dòng)。應(yīng)該指出,日本液壓傳動(dòng)的發(fā)展較歐美等國(guó)家晚了近 20 多年。在 1955 年前后 , 日本迅速發(fā)展液壓傳動(dòng),1956 年成立了“液壓工業(yè)會(huì)”。近20~30 年間，日本液壓傳動(dòng)發(fā)展之快，居世界領(lǐng)先地位。
液壓傳動(dòng)有許多突出的優(yōu)點(diǎn)，因此它的應(yīng)用非常廣泛，如一般工。業(yè)用的塑料加工機(jī)械、壓力機(jī)械、機(jī)床等；行走機(jī)械中的工程機(jī)械、建筑機(jī)械、農(nóng)業(yè)機(jī)械、汽車等；鋼鐵工業(yè)用的冶金機(jī)械、提升裝置、軋輥調(diào)整裝置等；土木水利工程用的防洪閘門及堤壩裝置、河床升降裝置、橋梁操縱機(jī)構(gòu)等；發(fā)電廠渦輪機(jī)調(diào)速裝置、核發(fā)電廠等等；船舶用的甲板起重機(jī)械（絞車）、船頭門、艙壁閥、船尾推進(jìn)器等；特殊技術(shù)用的巨型天線控制裝置、測(cè)量浮標(biāo)、升降旋轉(zhuǎn)舞臺(tái)等；軍事工業(yè)用的火炮操縱裝置、船舶減搖裝置、飛行器仿真、飛機(jī)起落架的收放裝置和方向舵控制裝置等。
液壓油作為動(dòng)力介質(zhì)廣泛應(yīng)用于油壓機(jī)械。油液類型包括合成化合物，礦物油，水和水基混合物。油液分布在機(jī)械設(shè)備的制動(dòng)系統(tǒng)和動(dòng)力轉(zhuǎn)向系統(tǒng)中。液壓系統(tǒng)是非常普遍的飛機(jī)飛行控制系統(tǒng)。
液壓系統(tǒng)，如上面提到的那些, 如果使用低壓縮,將最有效地利用工作液壓油。由于工業(yè)液壓系統(tǒng)快速循環(huán)運(yùn)行數(shù)百至數(shù)千次，導(dǎo)致氣溫達(dá)數(shù)百攝氏度，可能造成元件失靈，對(duì)系統(tǒng)造成嚴(yán)重傷害，因此液壓系統(tǒng)需要經(jīng)常維護(hù)。
為了財(cái)產(chǎn)安全要使用專門的耐火液體。飛機(jī)中使用的液壓系統(tǒng)中一般是始于制動(dòng)系統(tǒng)。[引文需要]飛機(jī)的性能提高于20世紀(jì)中葉，軍事所需的機(jī)械飛行控制成為難題，并介紹了液壓系統(tǒng)，以減少試點(diǎn)工作。液壓執(zhí)行器控制閥生產(chǎn)屬直接經(jīng)營(yíng)投入，由空勤人員（液壓機(jī)械）或由計(jì)算機(jī)管制（飛線），見飛行控制。
液壓動(dòng)力可以用于其他目的。它可以儲(chǔ)存在蓄電池啟動(dòng)輔助動(dòng)力單元（ APU ）中來自動(dòng)啟動(dòng)飛機(jī)的主引擎。許多飛機(jī)配備M61液壓動(dòng)力來驅(qū)動(dòng)火炮系統(tǒng)，提高了可靠行，不易引起火災(zāi)。
液壓系統(tǒng)自身的動(dòng)力來源于泵驅(qū)動(dòng)，泵與發(fā)動(dòng)機(jī)相連直接供電。當(dāng)液壓系統(tǒng)操作存在問題時(shí)可以直接關(guān)閉發(fā)動(dòng)機(jī)，對(duì)系統(tǒng)維護(hù)非常有用。
飛機(jī)液壓油有各種規(guī)格：
? ? 液壓油經(jīng)常暴露于工作場(chǎng)所。某些動(dòng)物吞咽或吸入酷似飲用水的液壓油可造成神經(jīng)損傷，甚至導(dǎo)致死亡。有些類型的液壓油會(huì)刺激你的皮膚或眼睛。在這些油液中發(fā)現(xiàn)了國(guó)家環(huán)境保護(hù)署（ EPA ）確定的1428中有害物質(zhì)中的至少10種 。
? ? 什么是液壓油？液壓油是多種化學(xué)物質(zhì)組成的液體。它們被用于汽車的自動(dòng)變速箱，或叉車、拖拉機(jī)、推土機(jī)、工業(yè)機(jī)械和飛機(jī)的制動(dòng)系統(tǒng)和動(dòng)力轉(zhuǎn)向系統(tǒng)。三種最常見類型的液壓油是礦物油型，合成油型以及水液型 。一些液壓油的商品說明中說自己的產(chǎn)品已經(jīng)通過了國(guó)際上的許多檢驗(yàn)，但并不意味著此種液壓油不含有毒物質(zhì)。??
? ? 液壓油是由原油和某些材料生產(chǎn)，因此有些液壓油是溫和的，有的有油膩味有的沒有任何氣味，有些易燃有些不會(huì)燃燒。
液壓油進(jìn)入環(huán)境時(shí)會(huì)發(fā)生什么變化？當(dāng)液壓油從機(jī)械或從儲(chǔ)存區(qū)和廢物場(chǎng)地中泄露出去后，如果蔓延到土壤，液壓油中的某些化學(xué)物質(zhì)可能分解在空氣、土壤或水中，但分解了多少目前尚不清楚；某些成分將繼續(xù)滲透到地下水，沉淀在底部，足以呆在那里一年之久。 魚類如果生活在受污染的水中，那么他們體內(nèi)可能含有一些液壓油成分。
? ? 人是怎么接觸到液壓油的呢？當(dāng)你生活在被污染的水或土壤以及危險(xiǎn)廢物場(chǎng)地或工業(yè)設(shè)施附近時(shí)，空氣中存在大量的揮發(fā)性的液壓油分子，當(dāng)吸入這些揮發(fā)性的液壓油分子后，類似于間接的觸摸或吞咽液壓油。由于液壓油實(shí)際上是化學(xué)品的混合物，人很難在空氣中發(fā)覺出來。吸入大量的某些類型的液壓油可引起肺炎，腸出血，甚至死亡。如果對(duì)此知之甚少很可能會(huì)影響您的健康。
吞食或吸入液壓油能影響動(dòng)物的神經(jīng)系統(tǒng)。家兔吸入某種非常高成分的液壓油造成肺部擁擠，出現(xiàn)呼吸困難，并表現(xiàn)為昏昏欲睡。如果有動(dòng)物吞食了液壓油，會(huì)立即全身震顫，腹瀉，出汗，呼吸困難，一段時(shí)間內(nèi)四肢無力，甚至幾個(gè)星期后癱瘓。這都是液壓油的直接影響造成的，因?yàn)橐簤河湍芷茐捏w內(nèi)行動(dòng)的某些酶。沒有報(bào)告說人吞咽或呼吸此種類型的液壓油，會(huì)造成這些影響。當(dāng)某些類型的液壓油不慎進(jìn)入眼中或接觸到皮膚，在很短的時(shí)間內(nèi)，會(huì)有發(fā)紅和腫脹的現(xiàn)象發(fā)生。目前還不清楚液壓油是否會(huì)導(dǎo)致出生缺陷或?qū)ι秤杏绊憽?
? ? 是否有醫(yī)療測(cè)試，以查看我們有沒有接觸到液壓油？血液，尿液或糞便中不能測(cè)試液壓油含量，但液壓油中的某些化學(xué)成分是可測(cè)量的。一些液壓油阻止某些酶的活性，通過測(cè)試血液中這些酶的含量可以間接衡量。然而，許多其他化學(xué)物質(zhì)也可能造成這種效果。這個(gè)測(cè)試在醫(yī)院的普通化驗(yàn)室很難測(cè)量，只有在特殊實(shí)驗(yàn)室的專用設(shè)備下才可以辦到。
? ???聯(lián)邦政府是否已經(jīng)提出了一些措施，以保護(hù)人類健康？對(duì)于可能造成不良影響的主要液壓油，聯(lián)邦政府已經(jīng)有明確的規(guī)定和限制場(chǎng)合，以保證人類健康。例如，礦物油，一種類型的液壓油的主要化學(xué)成分，分屬于石油餾分類化學(xué)品，有規(guī)章嚴(yán)格限制這些化學(xué)品。 職業(yè)安全及健康管理（ OSHA ）建立了一個(gè)接觸限值為2000毫克每立方米（毫克/立方米）石油蒸餾的8小時(shí)工作日， 40小時(shí)工作制。國(guó)立職業(yè)安全及健康（ NIOSH ）建議的石油蒸餾工作日限制為350毫克/立方米10小時(shí)， 40小時(shí)工作制。
液壓技術(shù)被引入工業(yè)領(lǐng)域已經(jīng)有一百多年的歷史了，隨著工業(yè)的迅猛發(fā)展，液壓技術(shù)更日新月異。伴隨著數(shù)學(xué)、控制理論、計(jì)算機(jī)、電子器件和流體力學(xué)的發(fā)展，出現(xiàn)了液壓伺服系統(tǒng)，并作為一門應(yīng)用科學(xué)已經(jīng)發(fā)展成熟，形成自己的體系和一套行之有效的分析和設(shè)計(jì)方法。
下面是液壓系統(tǒng)設(shè)計(jì)的方法和注意問題：液壓機(jī)的總體布局和工藝要求，包括采用液壓傳動(dòng)所完成的機(jī)床運(yùn)動(dòng)種類、機(jī)械設(shè)計(jì)時(shí)提出可能用的液壓執(zhí)行元件的種類和型號(hào)、執(zhí)行元件的位置及其空間的尺寸范圍、要求的自動(dòng)化程度等；液壓機(jī)的工作循環(huán)、執(zhí)行機(jī)構(gòu)的運(yùn)動(dòng)方式，以及完成的工作范圍。液壓執(zhí)行元件的運(yùn)動(dòng)速度、調(diào)速范圍、工作行程、載荷性質(zhì)和變化范圍；各部件的動(dòng)作順序和互鎖要求，以及各部件的工作環(huán)境與占地面積等；液壓系統(tǒng)的工作性能，如工作平穩(wěn)性、可靠性、換向精度、停留時(shí)間和沖出量等方面的要求；其它要求，如液壓裝置的質(zhì)量、外形尺寸和經(jīng)濟(jì)性等。
? ???設(shè)計(jì)液壓傳動(dòng)系統(tǒng)的步驟：明確對(duì)液壓傳動(dòng)系統(tǒng)的工作要求，是設(shè)計(jì)液壓傳動(dòng)系統(tǒng)的依據(jù)，由使用部門以技術(shù)任務(wù)書的形式提出；擬定液壓傳動(dòng)系統(tǒng)圖，根據(jù)工作部件的運(yùn)動(dòng)形式，合理地選擇液壓執(zhí)行元件；根據(jù)工作部件的性能要求和動(dòng)作順序，列出可能實(shí)現(xiàn)的各種基本回路。此時(shí)應(yīng)注意選擇合適的調(diào)速方案、速度換接方案，確定安全措施和卸荷措施，保證自動(dòng)工作循環(huán)的完成和順序動(dòng)作和可靠。
液壓傳動(dòng)方案擬定后，應(yīng)按國(guó)家標(biāo)準(zhǔn)規(guī)定的圖形符號(hào)繪制正式原理圖。圖中應(yīng)標(biāo)注出各液壓元件的型號(hào)規(guī)格，還應(yīng)有執(zhí)行元件的動(dòng)作循環(huán)圖和電氣元件的動(dòng)作循環(huán)表，同時(shí)要列出標(biāo)準(zhǔn)元件及輔助元件一覽表。計(jì)算液壓系統(tǒng)的主要參數(shù)和選擇液壓元件；計(jì)算液壓缸的主要參數(shù)；計(jì)算液壓缸所需的流量并選用液壓泵；選用油管；選取元件規(guī)格；計(jì)算系統(tǒng)實(shí)際工作壓力；計(jì)算功率，選用電動(dòng)機(jī)；發(fā)熱和油箱容積計(jì)算；
液壓系統(tǒng)油溫升高的原因、后果及解決措施
液壓系統(tǒng)在工作中有能量損失，包括壓力損失、容積損失和機(jī)械損失三方面，這些損失轉(zhuǎn)化為熱能，使液壓系統(tǒng)的油溫升高。一般液壓系統(tǒng)的油溫應(yīng)控制在（30-60）℃范圍內(nèi)，最高不超過（60-70）℃。
油溫升高會(huì)引起一系列不良后果：（1）使油液粘度下降，泄漏增加，降低了容積效率，甚至影響工作機(jī)構(gòu)的正常運(yùn)動(dòng)；（2）使油液變質(zhì)，產(chǎn)生氧化物雜質(zhì)，堵塞液壓元件中的小孔或縫隙，使之不能正常工作；（3）引起熱膨脹系數(shù)不同的相對(duì)運(yùn)動(dòng)零件之間的間隙變小，甚至卡死，無法運(yùn)動(dòng)；（4）引起機(jī)床或機(jī)械的熱變形，破壞原有的精度。
保證液壓系統(tǒng)正常工作溫度的措施：當(dāng)壓力控制閥的調(diào)定值偏高時(shí)，應(yīng)降低工作壓力，以減少能量損耗；由于液壓泵及其連接處的泄漏造成容積損失而發(fā)熱時(shí)，應(yīng)緊固各連接處，加強(qiáng)密封；當(dāng)油箱容積小、散熱條件差時(shí)，應(yīng)適當(dāng)加大油箱容積，必要時(shí)設(shè)置冷卻器；由于油液粘度太高，使內(nèi)磨擦增大而發(fā)熱時(shí)，應(yīng)選用粘度低的液壓油；當(dāng)油管過于細(xì)長(zhǎng)并彎曲，使油液的沿程阻力損失增大、油溫升高時(shí)，應(yīng)加大管徑，縮短管路，使油液通暢；由于周圍環(huán)境溫度過高使油溫升高時(shí)，要利用隔熱材料和反射板等，使系統(tǒng)和外界隔絕；高壓油長(zhǎng)時(shí)間不必要地從溢流閥回油箱，使油溫升高時(shí)，應(yīng)改進(jìn)回路設(shè)計(jì)，采用變量泵或卸荷措施
空氣侵入到液壓系統(tǒng)的不良后果主要有：使油液具有一定的壓縮性，致使系統(tǒng)產(chǎn)生噪聲、振動(dòng)和引起運(yùn)動(dòng)部件的爬行，破壞了工作的平穩(wěn)性；易使油液氧化變質(zhì)，降低油液的使用壽命。
解決措施：
1、空氣由油箱進(jìn)入系統(tǒng)的機(jī)會(huì)較多，如油箱的油量不足；液壓泵吸油管侵入油中太短；吸油管和回油管在油箱中距離太近或沒有用隔板隔開；回油飛濺，攪成泡沫；液壓泵吸入空氣；回油管沒有插入油箱，使回油沖出油面和箱壁，在油面上會(huì)產(chǎn)生大量氣泡，使空氣與油一起吸入系統(tǒng)。因此，油箱的油面要經(jīng)常保持足夠的高度；吸油管和回油管應(yīng)保證在最低油面以下，兩者要用隔板隔開；
2、由于密封不嚴(yán)或管接頭處和液壓元件接合面處的螺釘擰得不緊，外界空氣就會(huì)從這些地方侵入；系統(tǒng)中低于大氣壓部分，如液壓泵的吸油腔、吸油管和壓油管中油流速度較高（壓力低）的局部區(qū)域；在系統(tǒng)停止工作，系統(tǒng)中回油腔的油液經(jīng)回油管返回油箱時(shí)，也會(huì)形成局部真空的區(qū)域，在這些區(qū)域空氣最容易侵入。因此，要盡量防止各處的壓力低于大氣壓力；各個(gè)密封部件均應(yīng)使用良好的密封裝置，管接頭和各接合面處的螺釘應(yīng)擰緊；經(jīng)常清洗液壓泵吸油口處的過濾器，以防止吸油阻力增大而把溶解在油中的空氣游離出來進(jìn)入系統(tǒng)；
3、液壓設(shè)備的液壓缸上最好設(shè)有排氣裝置，以排除系統(tǒng)中的空氣
由于液壓泵流量不足，致使系統(tǒng)中流量不足時(shí)，應(yīng)檢查液壓泵零件是否有損壞情況，及時(shí)地更換或修復(fù)損壞超差件；如果因泵內(nèi)吸入空氣影響了液壓泵的流量，則要采取措施，防止空氣吸入，變量泵由于變量機(jī)構(gòu)工作不良影響泵的流量，應(yīng)對(duì)變量機(jī)構(gòu)拆卸、清洗或修理、更換；壓力分配閥工作不良引起流量不足時(shí)，應(yīng)修理或更換；因油液粘度不合適而影響流量時(shí)，要更換粘度適當(dāng)?shù)挠鸵?，并注意油溫?duì)粘度的影響；溢流閥工作不良影響流量時(shí)，應(yīng)采取措施，使其工作正常；由于液壓缸、閥等元件泄漏嚴(yán)重，造成流量不足時(shí)，應(yīng)針對(duì)不同情況采取相應(yīng)的措施；流量控制閥的調(diào)節(jié)機(jī)構(gòu)工作不正常時(shí)，應(yīng)根據(jù)零件損壞情況予以修復(fù)或更新、或拆開清洗，使調(diào)節(jié)機(jī)構(gòu)動(dòng)作靈活，工作正常。
液壓系統(tǒng)中噪聲產(chǎn)生原因及解決措施
空氣侵入液壓系統(tǒng)是產(chǎn)生噪聲的主要原因。因?yàn)橐簤合到y(tǒng)侵入空氣時(shí)，在低壓區(qū)其體積較大，當(dāng)流到高壓區(qū)時(shí)受壓縮，體積突然縮小，而當(dāng)它流入低壓區(qū)時(shí)，體積突然增大，這種氣泡體積的突然改變，產(chǎn)生“爆炸”現(xiàn)象，因而產(chǎn)生噪聲，此現(xiàn)象通常稱為“空穴”。針對(duì)這個(gè)原因，常常在液壓缸上設(shè)置排氣裝置，以便排氣。另外在開車后，使執(zhí)行件以快速全行程往復(fù)幾次排氣，也是常用的方法；
液壓泵或液壓馬達(dá)質(zhì)量不好，通常是液壓傳動(dòng)中產(chǎn)生噪聲的主要部分。液壓泵的制造質(zhì)量不好，精度不符合技術(shù)要求，壓力與流量波動(dòng)大，困油現(xiàn)象未能很好消除，密封不好，以及軸承質(zhì)量差等都是造成噪聲的主要原因。在使用中，由于液壓泵零件磨損，間隙過大，流量不足，壓力易波動(dòng)，同樣也會(huì)引起噪聲。面對(duì)上述原因，一是選擇質(zhì)量好的液壓泵或液壓馬達(dá)，二是加強(qiáng)維修和保養(yǎng)，例如若齒輪的齒形精度低，則應(yīng)對(duì)研齒輪，滿足接觸面要求；若葉片泵有困油現(xiàn)象，則應(yīng)修正配油盤的三角槽，消除困油；若液壓泵軸向間隙過大而輸油量不足，則應(yīng)修理，使軸向間隙在允許范圍內(nèi)；若液壓泵選用不對(duì)，則應(yīng)更換；
溢流閥不穩(wěn)定，如由于滑閥與閥孔配合不當(dāng)或錐閥與閥座接觸處被污物卡住、阻尼孔堵塞、彈簧歪斜或失效等使閥芯卡住或在閥孔內(nèi)移動(dòng)不靈，引起系統(tǒng)壓力波動(dòng)和噪聲。對(duì)此，應(yīng)注意清洗、疏通陰尼孔；對(duì)溢流閥進(jìn)行檢查，如發(fā)現(xiàn)有損壞，或因磨損超過規(guī)定，則應(yīng)及時(shí)修理或更換；
換向閥調(diào)整不當(dāng)，使換向閥閥芯移動(dòng)太快，造成換向沖擊，因而產(chǎn)生噪聲與振動(dòng)。在這種情況下，若換向閥是液壓換向閥，則應(yīng)調(diào)整控制油路中的節(jié)流元件，使換向平穩(wěn)無沖擊。
??在工作時(shí)，液壓閥的閥芯支持在彈簧上，當(dāng)其頻率與液壓泵輸油率的脈動(dòng)頻率或與其它振源頻率相近時(shí)，會(huì)引起振動(dòng)，產(chǎn)生噪聲。這時(shí)，通過改變管路系統(tǒng)的固有頻率，變動(dòng)控制閥的位置或適當(dāng)?shù)丶有钅芷?，則能防振降噪。
機(jī)械振動(dòng)，如油管細(xì)長(zhǎng)，彎頭多而未加固定，在油流通過時(shí)，特別是當(dāng)流速較高時(shí)，容易引起管子抖動(dòng)；電動(dòng)機(jī)和液壓泵的旋轉(zhuǎn)部分不平衡，或在安裝時(shí)對(duì)中不好，或聯(lián)軸節(jié)松動(dòng)等，均能產(chǎn)生振動(dòng)和噪聲。對(duì)此應(yīng)采取的措施有：較長(zhǎng)油管應(yīng)彼此分開，并與機(jī)床壁隔開，適當(dāng)加設(shè)支承管夾；調(diào)整電動(dòng)機(jī)和液壓泵的安裝精度；重新安裝聯(lián)軸節(jié)，保證同軸度小于0.1MM等。
液壓系統(tǒng)在制造、試驗(yàn)、使用和儲(chǔ)存中都會(huì)受到污染，而清洗是清除污染，使液壓油、液壓元件和管道等保持清潔的重要手段。生產(chǎn)中，液壓系統(tǒng)的清洗通常有主系統(tǒng)清洗和全系統(tǒng)清洗。全系統(tǒng)清洗是指對(duì)液壓裝置的整個(gè)回路進(jìn)行清洗，在清洗前應(yīng)將系統(tǒng)恢復(fù)到實(shí)際運(yùn)轉(zhuǎn)狀態(tài)。清洗介質(zhì)可用液壓油，清洗時(shí)間一般為2-4小時(shí)，特殊情況下也不超過10小時(shí)，清洗效果以回路濾網(wǎng)上無雜質(zhì)為標(biāo)準(zhǔn)。一般液壓系統(tǒng)清洗時(shí)，多采用工作用的液壓油或試車油。不能用煤油、汽油、酒精、蒸氣或其它液體，防止液壓元件、管路、油箱和密封件等受腐蝕。為了防止外界濕氣引起銹蝕，清洗結(jié)束時(shí)，液壓泵還要連續(xù)運(yùn)轉(zhuǎn)，直到溫度恢復(fù)正常為止，清洗后要將回路內(nèi)的清洗油排除干凈。
詞匯
添加劑：物質(zhì)添加到另一個(gè)少量以提高其性能。
中科院：化學(xué)文摘社。
致癌性：能夠?qū)е掳┌Y。
石油餾分：化學(xué)部分石油。
Hydraulic System
A complete hydraulic system consists of five parts, namely, power components, the implementation of components, control components, no parts and hydraulic oil. The role of dynamic components of the original motive fluid into mechanical energy to the pressure that the hydraulic system of pumps, it is to power the entire hydraulic system. The structure of the form of hydraulic pump gears are generally pump, vane pump and piston pump. Implementation of components (such as hydraulic cylinders and hydraulic motors) which is the pressure of the liquid can be converted to mechanical energy to drive the load for a straight line reciprocating movement or rotational movement. Control components (that is, the various hydraulic valves) in the hydraulic system to control and regulate the pressure of liquid, flow rate and direction. According to the different control functions, hydraulic valves can be divided into the village of force control valve, flow control valves and directional control valve. Pressure control valves are divided into benefits flow valve (safety valve), pressure relief valve, sequence valve, pressure relays, etc.; flow control valves including throttle, adjusting the valves, flow diversion valve sets, etc.; directional control valve includes a one-way valve , one-way fluid control valve, shuttle valve, valve and so on. Under the control of different ways, can be divided into the hydraulic valve control switch valve, control valve and set the value of the ratio control valve. Auxiliary components, including fuel tanks, oil filters, tubing and pipe joints, seals, pressure gauge, oil level, such as oil dollars. Hydraulic oil in the hydraulic system is the work of the energy transfer medium, there are a variety of mineral oil, emulsion oil hydraulic molding Hop categories.
Hydraulic principle
It consists of two cylinders of different sizes and composition of fluid in the fluid full of water or oil. Water is called "hydraulic press"; the said oil-filled "hydraulic machine." Each of the two liquid a sliding piston, if the increase in the small piston on the pressure of a certain value, according to Pascal's law, small piston to the pressure of the pressure through the liquid passed to the large piston, piston top will go a long way to go. Based cross-sectional area of the small piston is S1, plus a small piston in the downward pressure on the F1. Thus, a small piston on the liquid pressure to P = F1/SI, Can be the same size in all directions to the transmission of liquid. "By the large piston is also equivalent to the inevitable pressure P. If the large piston is the cross-sectional area S2, the pressure P on the piston in the upward pressure generated F2 = PxS2 ,Cross-sectional area is a small multiple of the piston cross-sectional area. From the type known to add in a small piston of a smaller force, the piston will be in great force, for which the hydraulic machine used to suppress plywood, oil, extract heavy objects, such as forging steel.
History of the development of hydraulic
And air pressure drive hydraulic fluid as the transmission is made according to the 17th century, Pascal's principle of hydrostatic pressure to drive the development of an emerging technology, the United Kingdom in 1795 Joseph (Joseph Braman ,1749-1814), in London water as a medium to form hydraulic press used in industry, the birth of the world's first hydraulic press. Media work in 1905 will be replaced by oil-water and further improved. World War I (1914-1918) after the extensive application of hydraulic transmission, especially after 1920, more rapid development. Hydraulic components in the late 19th century about the early 20th century, 20 years, only started to enter the formal phase of industrial production. 1925 Vickers (F. Vikers) the invention of the pressure balanced vane pump, hydraulic components for the modern industrial or hydraulic transmission of the gradual establishment of the foundation. The early 20th century Constantine (G ? Constantimsco) fluctuations of the energy carried out by passing theoretical and practical research; in 1910 on the hydraulic transmission (hydraulic coupling, hydraulic torque converter, etc.) contributions, so that these two areas of development.
The Second World War (1941-1945) period, in the United States 30% of machine tool applications in the hydraulic transmission. It should be noted that the development of hydraulic transmission in Japan than Europe and the United States and other countries for nearly 20 years later. Before and after in 1955, the rapid development of Japan's hydraulic drive, set up in 1956, "Hydraulic Industry." Nearly 20 to 30 years, the development of Japan's fast hydraulic transmission, a world leader.
Hydraulic transmission There are many outstanding advantages, it is widely used, such as general workers. Plastic processing industry, machinery, pressure machinery, machine tools, etc.; operating machinery engineering machinery, construction machinery, agricultural machinery, automobiles, etc.; iron and steel industry metallurgical machinery, lifting equipment, such as roller adjustment device; civil water projects with flood control the dam gates and devices, bed lifts installations, bridges and other manipulation of institutions; speed turbine power plant installations, nuclear power plants, etc.; ship deck crane (winch), the bow doors, bulkhead valves, such as the stern thruster ; special antenna technology giant with control devices, measurement buoys, movements such as rotating stage; military-industrial control devices used in artillery, ship anti-rolling devices, aircraft simulation, aircraft retractable landing gear and rudder control devices and other devices.
Hydraulic fluids are a large group of fluids used as the motive medium in hydraulic machinery. Fluid types include synthetic compounds, mineral oil, water, and water-based mixtures. The fluids are found in machinery and equipment ranging from brakes, power steering systems. Hydraulic systems are very common in aircraft flight control systems.
Hydraulic systems like the ones mentioned above will work most efficiently if the hydraulic fluid used has low compressibility.Because industrial hydraulic systems operate at hundreds to thousands of PSI and temperatures reaching hundreds of degrees Celsius, severe injuries and death can result from component failures and care must always be taken when performing maintenance on hydraulic systems.
Fire resistance is a property available with specialized fluids.The use of hydraulic systems in aircraft almost certainly began with braking systems.[citation needed] As aircraft performance increased in mid-20th century, the amount of force required to operate mechanical flight controls became excessive, and hydraulic systems were introduced to reduce pilot effort. The hydraulic actuators are controlled by valves; these in turn are operated directly by input from the aircrew (hydro-mechanical) or by computers obeying control laws (fly by wire). See flight controls.
Hydraulic power is used for other purposes. It can be stored in accumulators to start an auxiliary power unit (APU) for self-starting the aircraft's main engines. Many aircraft equipped with the M61 family of cannon use hydraulic power to drive the gun system, permitting reliable high rates of fire.
The hydraulic power itself comes from pumps driven by the engines directly, or by electrically driven pumps. Electric pumps can provide both redundancy and the means of operating hydraulic systems without starting the engines, which can be very useful during maintenance.
Aircraft hydraulic fluids fall under various specifications:
Exposure to hydraulic fluids occurs mainly in the workplace. Drinking certain types of hydraulic fluids can cause death in humans, and swallowing or inhaling certain types of hydraulic fluids has caused nerve damage in animals. Contact with some types of hydraulic fluids can irritate your skin or eyes. These substances have been found in at least 10 of the 1,428 National Priorities List sites identified by the Environmental Protection Agency (EPA).
What is hydraulic fluids?
Hydraulic fluids are a large group of liquids made of many kinds of chemicals. They are used in automobile automatic transmissions, brakes, and power steering; fork lift trucks; tractors; bulldozers; industrial machinery; and airplanes. The three most common types of hydraulic fluids are mineral oil, organophosphate ester, and polyalphaolefin. Some of the trade names for hydraulic fluids include Durad®, Fyrquel®, Skydrol®, Houghton-Safe®, Pydraul®, Reofos®, Reolube®, and Quintolubric®. (Use of trade names is for identification only and does not imply endorsement by the Agency for Toxic Substances and Disease Registry, the Public Health Service, or the U.S. Department of Health and Human Services.)
Some hydraulic fluids have a bland, oily smell and others have no smell; some will burn and some will not burn. Certain hydraulic fluids are produced from crude oil and others are manufactured.
What happens to hydraulic fluids when it enters the environment? Hydraulic fluids can enter the environment from spills, leaks in machines that use them, or from storage areas and waste sites. If spilled on soil, some of the ingredients in hydraulic fluids will stay on top and others will sink into the groundwater. In water, some hydraulic fluids' ingredients will transfer to the bottom and can stay there for more than a year. Certain chemicals in hydraulic fluids may break down in air, soil, or water, but how much breaks down isn't known. Fish may contain some hydraulic fluids if they live in contaminated water.
How might I be exposed to hydraulic fluids?
Touching or swallowing hydraulic fluids. Breathing hydraulic fluids in the air near machines where hydraulic fluids are used. Touching contaminated water or soil near hazardous waste sites or industrial manufacturing facilities that use or make hydraulic fluids.
How can hydraulic fluids affect my health?
Little is known about how hydraulic fluids can affect your health. Since hydraulic fluids are actually mixtures of chemicals, some of the effects seen may be caused by additives in the hydraulic fluids.
In people, the effects of breathing air with high levels of hydraulic fluids are not known. Drinking large amounts of some types of hydraulic fluids can cause pneumonia, intestinal bleeding, or death in humans. Weakness of the hands was seen in a worker who touched a lot of hydraulic fluids.
Rabbits that inhaled very high levels of one type of hydraulic fluid had trouble breathing, congested lungs, and became drowsy. The nervous systems of animals that swallowed or inhaled other hydraulic fluids were affected immediately with tremors, diarrhea, sweating, breathing difficulty, and sometimes several weeks later with weakness of the limbs, or paralysis. The immediate effects are caused because hydraulic fluids stop the action of certain enzymes, called cholinesterases, in the body. There are no reports of people swallowing or breathing the types of hydraulic fluids that cause these effects. When certain types of hydraulic fluids were put into the eyes of animals or allowed to touch the skin of people or animals for short periods of time, redness and swelling occurred. It is not known whether hydraulic fluids can cause birth defects or reproductive effects.
Is there a medical test to show whether I've been exposed to hydraulic fluids?
Hydraulic fluids can't be measured in blood, urine, or feces, but certain chemicals in the hydraulic fluids can be measured. Some of the hydraulic fluids stop the activity of certain enzymes, called cholinesterases, in blood and this activity can be measured. However, many other chemicals also cause this effect. This test isn't available at most doctors' offices, but can be done at special laboratories that have the right equipment.
Has the federal government made recommendations to protect human health?
There are no federal government recommendations to protect humans from the health effects of the major hydraulic fluids. However, mineral oil, the major chemical ingredient of one type of hydraulic fluid, is part of the petroleum distillate class of chemicals and there are regulations for these chemicals.
The Occupational Safety and Health Administration (OSHA) has set an exposure limit of 2,000 milligram per cubic meter (mg/m³) petroleum distillates for an 8-hour workday, 40-hour workweek. The National Institute for Occupational Safety and Health (NIOSH) recommends an exposure limit of 350 mg/m³ petroleum distillates for a 10-hour workday, 40-hour workweek.
Hydraulic technology has been the introduction of industry have a history of more than one hundred years. With the rapid development of industrial, hydraulic technology with each passing day. Along with mathematics, control theory, computers, electronic devices and the development of fluid mechanics, a hydraulic servo system. And as an applied science that has come of a