液壓閥畢業(yè)設(shè)計(jì)外文翻譯

1、<p><b>　　閥</b></p><p>　　液壓回路中的壓力控制閥是用來(lái)確保回路中不同部分的壓力達(dá)到我們的預(yù)期值。壓力控制閥通過(guò)以下幾種方式實(shí)現(xiàn)我們的預(yù)期值：（1）把高壓回路中的流體通過(guò)低壓區(qū)，來(lái)限制高壓區(qū)的壓力：（2）分流到其他區(qū)域。這類閥可分為安全閥、溢流閥、平衡閥、順序閥和卸荷閥。分流型閥是可以減壓的。</p><p>　　壓力閥也可以定義為常

2、閉式或者常開式的兩通閥，溢流閥、順序閥、卸荷閥、和平衡閥是常閉式的，兩通閥處于常開或半開狀態(tài)以完成其工作任務(wù)。減壓閥是一種常開閥，可以限止最終阻止油液進(jìn)入出口回路。任何一種類型閥工作，都能自動(dòng)調(diào)節(jié)阻尼孔的大小進(jìn)行壓力控制。當(dāng)閥依靠外線先導(dǎo)油液進(jìn)行控制時(shí)，并不需要阻尼孔調(diào)節(jié)。卸荷閥沒有自我調(diào)節(jié)的能力，主要依靠外部油源的信號(hào)進(jìn)行調(diào)節(jié)。而節(jié)流閥、減壓閥、平衡閥和順序閥是完全自動(dòng)進(jìn)行調(diào)節(jié)的。本章我們將研究不同種類的壓力閥，學(xué)習(xí)這些閥如何應(yīng)用于不

3、同的回路中。</p><p><b>　　壓力閥的類型</b></p><p>　　下面是幾種常用的動(dòng)力控制元件：</p><p>　　安全閥通常用提動(dòng)型兩通閥，當(dāng)流體的壓力達(dá)到設(shè)定值時(shí)，釋放流體進(jìn)入出口，這種閥保護(hù)管路和設(shè)備，以免由于壓力過(guò)大而損壞。</p><p>　　溢流閥這種閥在回路中可以在所連接的部分限制其

4、最大壓力。</p><p>　　單向平衡閥這種閥維持油液一個(gè)方向的流體阻力，而另一個(gè)方向自由流動(dòng)。</p><p>　　順序閥引導(dǎo)油液順次流向回路的各個(gè)部分。</p><p>　　卸荷閥該閥允許壓力升到某一調(diào)定值，然后只要控制油源在控制口處保持事先調(diào)定的壓力值，它就使液流旁路通過(guò)。</p><p>　　減壓閥 此閥不管進(jìn)油口的壓力值有

5、多大，都能保持其出口降低壓力值。</p><p>　　液壓保險(xiǎn) 此閥中安裝了易碎的薄片，當(dāng)系統(tǒng)中的壓力達(dá)到預(yù)設(shè)值時(shí)，薄片破碎。</p><p>　　壓力開關(guān) 由油液的壓力進(jìn)行控制，同時(shí)也能對(duì)油液的壓力的變化做出相應(yīng)的反應(yīng)。</p><p><b>　　先導(dǎo)式溢流閥</b></p><p>　　國(guó)際標(biāo)準(zhǔn)的簡(jiǎn)化液壓符號(hào)，

6、已經(jīng)廣泛的應(yīng)用了。因此，用在普通液壓回路中的溢流閥和其輔助裝置的一些連接件，在液壓圖中很少表達(dá)出來(lái)。因?yàn)檫@些簡(jiǎn)單的液壓符號(hào)表達(dá)只是閥的基本元件，比如壓力輸入，液壓油箱連接，閥芯彈簧等，偏置箭頭表明此種閥屬于常閉閥。溢流閥的先導(dǎo)閥彈簧上標(biāo)有一個(gè)斜箭頭。如果該閥是可調(diào)的，特別是該元件對(duì)回路的控制很大影響時(shí)，則在閥的簡(jiǎn)化圖中，也可以在閥芯彈簧加一個(gè)同樣的斜箭頭。先導(dǎo)式溢流閥的完全符號(hào)，包括基本部分和相關(guān)控制。如點(diǎn)劃線框所包含的有5個(gè)接口，分別

7、是進(jìn)油口、接油箱口、遠(yuǎn)程控制口、測(cè)試口，以及先導(dǎo)閥的在特殊情況中才使用的外泄口。</p><p>　　進(jìn)油口和油箱接口是主油道，流人測(cè)試口和遠(yuǎn)程控制口的流量，只需要供這兩個(gè)部分工作就夠了。測(cè)試口的作用是測(cè)量管中油液的壓力，其中并不一定要有油液流過(guò)。遠(yuǎn)程控制回路油液需要通過(guò)其閥芯的固定阻尼孔，流量取決于主閥芯彈簧。如果是有外泄回路的溢流閥，通過(guò)其阻尼孔的油液并不比通過(guò)內(nèi)部固定阻尼孔的多。</p>&l

8、t;p>　　圖示的是復(fù)合(先導(dǎo)式)溢流閥的剖面圖。主閥芯與上面的彈簧相連，處于一定的位置，阻止來(lái)自進(jìn)油口的油液流回油箱。</p><p>　　進(jìn)油口與位于彈簧下面的主閥芯底部直接相通，控制油與彈簧腔之間的連接管路上有阻尼孔的限制。主閥芯上下端面的面積是相同的。在某些設(shè)計(jì)上，也有可能不完全相等。某一端面積稍大，可以完成特定功能。工作時(shí)如果先導(dǎo)油液無(wú)法從調(diào)節(jié)口通過(guò)，主閥由于面積相同處于平衡狀態(tài)，閥芯在彈簧的作用

9、下，處于封閉進(jìn)油口和出油口的位置。如果主閥芯上端的彈簧腔的壓力升高，作用在錐閥上的作用力超過(guò)彈簧力時(shí)，部分先導(dǎo)壓力油流回油箱。當(dāng)這部分壓力油的流量大于阻尼孔的最大可通流量時(shí)，作用于閥芯上端的力就會(huì)小于下端的力，此時(shí)，閥芯的上下端面所受到的壓力不等，處于不平衡狀態(tài)。當(dāng)作用于閥芯下端壓力繼續(xù)上升時(shí)，通過(guò)調(diào)節(jié)口的先導(dǎo)流量增大，主閥上下腔壓力不平衡程度加大，形成的壓力差超過(guò)彈簧的預(yù)緊力。這就產(chǎn)生了一個(gè)從輸入壓力油口到回油箱口的通道，這與直動(dòng)式彈

10、簧溢流閥的通道形成過(guò)程極其相似。</p><p>　　調(diào)壓彈簧A在彈簧B處于不工作狀態(tài)時(shí)，會(huì)提供一個(gè)最大的預(yù)緊力。當(dāng)調(diào)節(jié)彈簧B處于工作狀態(tài)時(shí)，主閥芯又會(huì)受到一個(gè)附加的作用力，最小開啟壓力取決于彈簧力A。此壓力不會(huì)低于彈簧A的力。如果其他支路的阻力比較小，則回路中的壓力比較低。由彈簧B對(duì)先導(dǎo)閥所產(chǎn)生力，一般被認(rèn)為是對(duì)調(diào)壓彈簧A所產(chǎn)生的附加力。在很多閥中，主閥芯彈簧是不可調(diào)節(jié)的。</p><p&g

11、t;　　主閥芯和彈簧所在的腔叫做控制腔，我們應(yīng)該熟記這個(gè)術(shù)語(yǔ)，因?yàn)樗鼜V泛的應(yīng)用于工業(yè)液壓系統(tǒng)中。注意閥體左側(cè)上部的一個(gè)連接口，連接到控制腔可允許其中的油液自由的流回油箱。因此，對(duì)主閥芯彈簧不會(huì)產(chǎn)生任何附加力。</p><p>　　如果在遠(yuǎn)控口布置一個(gè)小溢流閥，則最大的壓力值由此閥來(lái)決定。</p><p><b>　　流量控制閥</b></p><p

12、>　　容積或流量控制閥常用來(lái)調(diào)節(jié)速度。由前述已經(jīng)知道，油缸的速度取決于單位時(shí)間內(nèi)泵輸入的油量?？梢杂靡粋€(gè)變量泵調(diào)節(jié)流量，而在許多回路中是用定量泵調(diào)節(jié)流量的，所以常用流量控制閥調(diào)節(jié)流量。</p><p>　　流量調(diào)節(jié)方法：實(shí)現(xiàn)用流量調(diào)節(jié)閥來(lái)控制油缸速度的方法有三種，分別是：進(jìn)口節(jié)流、出口節(jié)流和旁路節(jié)流。</p><p>　　進(jìn)口節(jié)流回路 在回路中，節(jié)流閥串聯(lián)在泵和液壓缸之間，用這種方

13、式，可以控制流人液壓缸的油量。泵輸送的多余的油通過(guò)溢流閥回油箱。由于節(jié)流閥安裝在液壓缸油路上，油液只能朝一個(gè)方向流動(dòng)，所以在節(jié)流閥內(nèi)或并聯(lián)安裝了單向閥，使倒流油液通過(guò)。如果希望油液雙向控制速度，節(jié)流閥必須安裝在泵出口方向閥的前面。節(jié)流控制的控制精度比較高，常用在液壓缸有常負(fù)載的回路中，例如，在負(fù)載作用下做垂直上升運(yùn)動(dòng)的液壓缸，或以某控制速度推動(dòng)液壓缸。</p><p>　　出口節(jié)流回路 出口節(jié)流回路多用在負(fù)載元

14、件可能會(huì)出現(xiàn)速度失控的情況。節(jié)流閥在此處的作用就是限制液壓缸的油液流盡。為了能雙向調(diào)速，節(jié)流閥多被安裝在方向閥和油箱之間。更常見的是只需要一個(gè)方向需要控制，控制閥安裝在方向閥與液壓缸之間。為了能使液壓缸能快速回程，此處也可以設(shè)置一個(gè)旁路單向閥。</p><p>　　旁路節(jié)流調(diào)速回路 在旁路節(jié)流回路中，節(jié)流閥安裝在泵的出油口處的旁路，調(diào)節(jié)從旁路把油分流回油箱的流量，從而調(diào)節(jié)液壓缸的速度。其優(yōu)點(diǎn)在于泵是在工作壓力下

15、進(jìn)行調(diào)節(jié)，多余的油是通過(guò)節(jié)流閥而不是溢流閥流回油箱的。缺點(diǎn)是調(diào)節(jié)精度比較差，原因在于精確分流的油液是回到油箱，而未流經(jīng)液壓缸，這樣由于工作負(fù)載的變化，使泵的輸出不穩(wěn)定。旁路節(jié)流調(diào)速回路在負(fù)載失控的情況下不能應(yīng)用。</p><p><b>　　節(jié)流調(diào)節(jié)的類型</b></p><p>　　節(jié)流閥閥有兩種基本類型：壓力補(bǔ)償型和非壓力補(bǔ)償型。后者常用在負(fù)載壓力相對(duì)穩(wěn)定，運(yùn)動(dòng)速

16、度要求不太嚴(yán)格的地方。盡管其構(gòu)件比較復(fù)雜，甚至包含有為油液反向自由流動(dòng)的單向閥，這種方法就像一個(gè)固定節(jié)流口或可調(diào)節(jié)的針閥一樣，仍然是非常簡(jiǎn)單的。非壓力補(bǔ)償型應(yīng)用受到了一定的限制，這是因?yàn)橥ㄟ^(guò)阻尼孔的流量與流經(jīng)它所產(chǎn)生的壓力差平方根成比例。這表明工作負(fù)載的巨大變化會(huì)影響到運(yùn)動(dòng)速度。</p><p>　　壓力補(bǔ)償型節(jié)流閥可進(jìn)一步劃分為調(diào)速閥型和溢流節(jié)流型。兩者都利用一個(gè)補(bǔ)償器或穩(wěn)定器來(lái)穩(wěn)定通過(guò)可調(diào)節(jié)流口而產(chǎn)生的壓力差

17、。</p><p>　　溢流節(jié)流型節(jié)流閥是帶過(guò)載保護(hù)裝置的壓力補(bǔ)償控制閥，它有一個(gè)常閉的節(jié)流口，當(dāng)打開它時(shí)，可以使油液流到油箱。工作負(fù)載所需的壓力值由位于上腔內(nèi)的傳感器探測(cè)，該壓力與一根輕彈簧共同使閥口處于常閉狀態(tài)。節(jié)流口下端的腔內(nèi)壓力由于受到節(jié)流閥的阻力而不斷增加，當(dāng)其上下端受到的壓力差達(dá)到足以克服彈簧力時(shí)，多余的油液就會(huì)流回油箱。這個(gè)壓力差，通常為20psi，不管工作負(fù)載有多大，都會(huì)由于確定量的油液經(jīng)過(guò)節(jié)流口

18、而形成穩(wěn)定值。</p><p>　　過(guò)載保護(hù)裝置由一個(gè)可調(diào)節(jié)的彈簧提供，以限制節(jié)流口上腔的最大壓力值，只要工作負(fù)載超過(guò)設(shè)定值，它就相當(dāng)于一個(gè)溢流閥。溢流節(jié)流型控制閥只用在進(jìn)口節(jié)流調(diào)速回路。如果用在出口節(jié)流調(diào)速回路中，回油不能通過(guò)節(jié)流閥流回油箱，而無(wú)法抑制引起的負(fù)載失控。</p><p>　　調(diào)速閥型流量控制閥依靠的是穩(wěn)定器使油液通過(guò)節(jié)流閥維持20psi的壓力差。這種閥的閥芯處于常開狀態(tài)，可

19、以自動(dòng)關(guān)小節(jié)流口以阻止過(guò)多的油液流過(guò)。在閥中，工作負(fù)載和閥芯上端的一根彈簧共同使閥芯處于開啟狀態(tài)。節(jié)流口進(jìn)口和閥芯下端的壓力欲使其關(guān)閉，僅允許油液進(jìn)入閥內(nèi)，維持通過(guò)節(jié)流閥20psi的壓力差。</p><p>　　當(dāng)油液達(dá)到節(jié)流閥的設(shè)定值時(shí)，閥口有關(guān)閉的趨勢(shì)。調(diào)速閥型節(jié)流閥可以安置在進(jìn)油口，出油口和旁路節(jié)流調(diào)速回路上。與溢流節(jié)流型節(jié)流調(diào)速不同，調(diào)速閥型可以在一個(gè)泵源中使用兩個(gè)或多個(gè)節(jié)流閥，泵輸出的多余油液通過(guò)溢流閥

20、返回油箱。</p><p>　　當(dāng)設(shè)置節(jié)流閥在液壓缸回路上時(shí)，為能迅速反向回流，應(yīng)該選擇整體式單向閥。而單向閥不允許設(shè)置在主供油管路，方向閥的回油箱管路以及旁路節(jié)流調(diào)速中。</p><p><b>　　溫度補(bǔ)償型節(jié)流閥</b></p><p>　　流經(jīng)壓力補(bǔ)償節(jié)流控制閥的流量易于受溫度變化的影響。威格士公司后期設(shè)計(jì)的閥，采用了溫度補(bǔ)償型節(jié)流閥的

21、結(jié)構(gòu)。油液溫度升高時(shí)，油液流動(dòng)阻力小。當(dāng)溫度升高時(shí)，通過(guò)減小節(jié)流閥的開口尺寸仍能維持流量的穩(wěn)定，這可以通過(guò)一個(gè)能熱脹冷縮的補(bǔ)償桿來(lái)實(shí)現(xiàn)。節(jié)流閥芯是一個(gè)能來(lái)回進(jìn)出的柱塞。溫度補(bǔ)償桿就安裝在節(jié)流閥和調(diào)節(jié)器之間，這種設(shè)計(jì)也可以設(shè)置一個(gè)可反向自由流動(dòng)的單向閥來(lái)實(shí)現(xiàn)。</p><p>　　遠(yuǎn)程流量控制閥遠(yuǎn)程流量控制閥允許通過(guò)電信號(hào)調(diào)節(jié)節(jié)流閥的開口大小，節(jié)流閥芯和扭距馬達(dá)的轉(zhuǎn)子相連，并且能對(duì)扭距馬達(dá)的電信號(hào)做出反應(yīng)，其操作

22、原理與壓力補(bǔ)償調(diào)速閥是一樣的。</p><p>　　本文引自《機(jī)械給工程專業(yè)英語(yǔ)》216～220頁(yè)，賀自強(qiáng)主編 北京理工大學(xué)出版社 1989.8</p><p><b>　　Valves</b></p><p>　　Pressure-Control Valves</p><p>　　Pressure-control va

23、lves are used in hydraulic circuits to maintain desired pressure levels in various parts of the circuits. A pressure-control valves maintains the desired pressure levels by diverting higher-pressure fluid to a lower-pres

24、sure area . Thereby limiting the pressure in the higher-pressure area. restricting flow into another area. Valve that divert fluid can be safety, relief, counterbalance, sequence, and unloading types. Valves that restri

25、ct flow into another area can be of the r</p><p>　　A pressure-control valve may also be defined as either a normally closed or normally open two-way valve. Relief , sequence , unloading and counterbalance va

26、lves are normally closed , two-way valves that are partially or fully open valve that restricts and finally blocks fluid flow a secondary. With either type of operation, the valve can be said to create automatically an o

27、rifice to provide the desired pressure control An orifice is nit always created unloading valve. It is piloted from an exte</p><p>　　Types of Pressure-Control Valves</p><p>　　Eight popular devi

28、ces for pressure-control are:</p><p>　　Safety valve Usually a poppet-type two-way valve intended to release fluid to a secondary area when the fluid pressure approaches the set opening pressure of the valve

29、. This type of valve protects piping and equipment from excessive pressure.</p><p>　　Relief valve Valve which limits the maximum pressure that can be applied in that portion of the circuit to which it is co

30、nnected.</p><p>　　Counterbalance valve Valve which maintains resistance against flow to one direction but permits free flow in the other direction.</p><p>　　Sequence valve Valve which directs

31、flow to more than one portion of a fluid circuit, in sequence.</p><p>　　Unloading valve Valve which allows pressure to build up to an adjustable setting, then bypasses the flow as long as a remote source

32、maintains the preset pressure on the pilot port. </p><p>　　Pressure-reducing valve Valve which maintains a reduced pressure at its outlet regardless of the higher inlet pressure.</p><p>　　Hydra

33、ulic fuse Device equipped with a frangible disk which establishes the maximum pressure in a hydraulic circuit by rupturing at a preset pressure valve.</p><p>　　Pressure switch Switch operated by fluid pre

34、ssure and responsive to arise or fall in fluid pressure.</p><p>　　Compound Relief Valves</p><p>　　In the study of ISO hydraulic symbol, it was stated that simplified symbol are widely used. Beca

35、use of this , pressure-relief valves used in common hydraulic circuits are rarely shown complete with all auxiliary devices and connections. Instead, the simplified symbol shows only the basic relief valve, pressure inpu

36、t tank connection, valve spring , and the offset arrow indicating that the valve is normally closed. A slash arrow as shows on the bias spring of the pliot-relief valve if the valve is</p><p>　　The input pre

37、ssure and tank connection provide the major flow through the valve. Only enough fluid need flow to the test-station and remote-control connection for the respective function. The test station is generally used for a gaug

38、e connection to check fluid pressure. This does not require a flow of fluid. The remote-control connection passes the quantity of fluid coming through the fixed internal orifice at the rate established by the spring in t

39、he main relief element. An external drain from </p><p>　　Figure shows a cutaway view of compound relief valve. Note that the main spool is held by the spring in a position that blocks the passage from the pr

40、essure input port to the tank port, just as the symbol in Figure shows.</p><p>　　Input pressure is directed to the bottom of the spool below the spring cavity without restriction. The supply line to the spri

41、ng cavity is restricted by an orifice in the line . The area of the main spool is she same. In certain poppet designs; The areas may not be exactly equal. One end may have a larger area to ensure certain function actions

42、. In operation, if fluid cannot escape through adjustment port, a balance is provided by the equal areas at each end of the spool. The spring then maintai</p><p>　　Adjustment A would provided a specific maxi

43、mum relieving pressure if adjustment B were completely relaxed. Where adjustment B is in use, providing an additive pressure to the main-spool spring, the minmum relieving providing will be fixed by adjustment A . The re

44、lieving pressure can never be less than that established by adjustment A in the valve. Pressure in the circuit could be less if there were relaxation through some other path. Resistance to pliot-flow created by adjustmen

45、t B may be consid</p><p>　　The pocket containing the main-spool spring is called the control chamber. It will be well to remember this term, as it widely used in industrial hydraulics. Note the auxiliary ven

46、t connection in the upper left side of the valve in Figure. This port permits the escape of fluid directly to the tank without restriction. Thus, there can be no hydraulic additive pressure to the main spool spnng.</p

47、><p>　　If a small relief valve is placed in the circuit with a connection to the reliving pressure will be established by this additive at a remote point.</p><p>　　Volume Control</p><p&g

48、t;　　Volume or flow control valves are used to regulate speed. An was developed in earlier chapters, the speed of an actuator depends on how much oil is pumped into it per unit of time. It is possible to regulate flow wit

49、h a variable displacement pump, but in many circuits it is more practical to use a fixed displacement pump and regulate flow with a volume control valve.</p><p>　　Flow Control Methods</p><p>　　T

50、here are three basic methods of applying volume control actuator speeds. They are meter-in, meter-out and bleed-off.</p><p>　　Meter-In Circuit In meter-in operation, the flow control valve is placed between

51、 the pump and actuator. In this way, it control the amount of fluid going into the actuator. Pump delivery in excess of the metered amount is diverted to tank over the relief valve. With the flow control valve installed

52、in the cylinder line as shown, flow is controlled in one direction. A check valve must be included in the flow control or placed in parallel with it for return flow. If it is desired to control direc</p><p>

53、　　Meter-Out Circuit Meter-out control control is used where the load might tend to "run away". The flow control is located where it will restrict exhaust flow from the actuator. To regulate speed in both direc

54、tions, the valve is installed in the tank line from the directional valve. More often control is needed in only one direction and it is placed in the line between the actuator and direction valve. Here too a bypass chec

55、k valve would be required for a rapid return stroke.</p><p>　　Bleed-Off Circuit In a bleed-off arrangement, the flow control is bleed off the supply line from the pump and determines the actuator speed by m

56、etering a portion of the pump delivery to tank. The advantage is that the pump operates at the pressure required by the work, since excess fluid returns to tank through the flow control instead of through the relief valv

57、e. Its disadvantage is some less of accuracy because the measured flow is to tank' rather into the cylinder, making the latter subject </p><p>　　Types of Flow Controls</p><p>　　Flow control

58、valves fall into two basic categories: pressure compensated and non-pressure compensated. The latter being used where load pressure remain relatively constant and feed rates are not too critical. They may be as simple as

59、 a fixed orifice or an adjustable needle for free valve, although more sophisticated units may even include a check valve for free flow in the reverse direction. Use of non-pressure compensated valves is somewhat limite

60、d, since flow through an orifice is essentially</p><p>　　Pressure compensated flow controls are further classified as restrictor and by-pass types. Both utilize a compensator or hydrostat to maintain a const

61、ant pressure drop across an adjustable throttle.</p><p>　　The By-Pass Type-combines overload protection with pressure compensated control of flow. It has a normally closed hydrostat which opens to divert flu

62、id, in excess of the throttle setting, to the tank. Pressure required by the work load is sensed in the chamber above the hydrostat and together with a light spring tends to hole it closed. Pressure in the chamber below

63、the hydrostat increase duo to restriction of the throttle and cause is to raise diverting any excess flow to tank when the differen</p><p>　　Overload protection is provided by an adjustable spring loaded pop

64、pet which limits the maximum pressure above the hydrostat, causing it to function as a compound relief valve whenever work load requirement exceed its setting. The by-pass flow control can only be used in a meter-in circ

65、uit. If used for metering out, exhaust oil which could not get through the throttle would be diverted to tank permitting the load to run away.</p><p>　　The Restrictor Type Flow Control-also maintain a consta

66、nt 20 psi differential across its throttle by means of a hydrostat. In this valve, the hydrostat is normally epen and tends to close off blocking all flow in excess of the throttle setting. In these units the work load p

67、ressure acts with a light spring above the hydrostat to hold it open. Pressure at the throttle inlet and under the hydrostat tend to close it, permitting only that oil to enter the valve that 20 psi can force through the

68、 thro</p><p>　　Because of their tendency close off when flow tales to exceed the throttle setting, restrictor type valves may be used in meter-in, meter-out and bleed-off circuits. Unlike the by-pass type ,

69、two or more restrictor valves may be used with the same pump since the excess pump delivery returns to tank through the relief valves.</p><p>　　When placed in cylinder lines an integral check valve is option

70、al to provide free flow for a rapid return stroke. One would not be required for valves placed in the main supply line, the tank line of a directional valve or when they are used in bleed-off circuits.</p><p&g

71、t;　　Temperature Compensated Flow Control Valve</p><p>　　Flow through a pressure compensated flow control valve is subject to change with variations in oil temperature. Later design Vickers valves incorporate

72、 a temperature. Although oil flows more freely when it is hot, constant flow can be maintained by decreasing the size of the throttle opening as the temperature rises. This is accomplished through a compensating rod whi

73、ch lengthens with heat and contracts when cold. The throttle is a simple plunger that is moved in and out of the control port. Th</p><p>　　Remote Flow Control Valves Remote flow control valves permit adjust

74、ment of the throttle size by an electrical signal. The throttle spool is linked to armature of a torque motor and moves in response to signal to the torque motor. Operation is otherwise the same as a pressure compensated