Rexroth力士樂(lè)比例閥必須有一個(gè)配套的放大器，它接受來(lái)自于計(jì)算機(jī)，或者PLC，或者電位器（滑動(dòng)變阻器）的控制信號(hào)，把0-20毫安微弱的信號(hào)放大到0-800毫安。計(jì)算機(jī)的信號(hào)太弱了。然后，放大器把放大的信號(hào)傳送到電磁閥度，電磁閥依據(jù)傳來(lái)的信號(hào)大小，克服彈簧力，調(diào)節(jié)推桿的行程，輸出流量大約知1升/分鐘,壓力隨信號(hào)變化的控制油。再后，控制油到達(dá)主閥芯的兩端，依據(jù)不同的壓力，推動(dòng)閥芯移動(dòng)相應(yīng)的行程，因?yàn)殚y芯本身有錐度的臺(tái)階，與閥體組合，不同的行程得到不道同的過(guò)流面積，再入版口壓力穩(wěn)定的情況下，得到不同的流量。最終實(shí)現(xiàn)比例功能。比例閥是由計(jì)算機(jī)（或其他），放大器，比例電磁鐵，錐度臺(tái)階的閥芯，入口壓力補(bǔ)償閥（單聯(lián)可以不要），梭閥，內(nèi)置卸荷閥（把多余的流量送回油箱）等構(gòu)成的一個(gè)完整的體權(quán)系。才能真正實(shí)現(xiàn)比例功能。

Rexroth力士樂(lè)比例閥是一種新型的液壓控制裝置。在普通壓力閥、流量閥和方向閥上，用比例電磁鐵替代原有的控制部分，按輸入的電氣信號(hào)連續(xù)地、按比例地對(duì)油流的壓力、流量或方向進(jìn)行遠(yuǎn)距離控制。比例閥一般都具有壓力補(bǔ)償性能，輸出壓力和流量可以不受負(fù)載變化的影響.

(1）電磁式 電磁式是指采用比例電磁鐵作為電氣一機(jī)械轉(zhuǎn)換元件的比例閥，比例電磁鐵將輸入的電流信號(hào)轉(zhuǎn)換成力、位移機(jī)械信號(hào)輸出．進(jìn)而控制壓力、流量及方向等參數(shù)。

（2）電動(dòng)式 電動(dòng)式是指采用直流伺服電動(dòng)機(jī)作為電氣一機(jī)械轉(zhuǎn)換元件的比例閥，直流伺服電動(dòng)機(jī)將輸入的電信號(hào)．轉(zhuǎn)
換成旋轉(zhuǎn)運(yùn)動(dòng)轉(zhuǎn)速，再經(jīng)絲桿螺母、齒輪齒條或齒輪凸輪等減速裝置和變換機(jī)構(gòu)，輸出力與位移，進(jìn)一步控制液壓參數(shù)。

（3）電液式 電液式是指采用力矩馬達(dá)和噴嘴擋板的結(jié)構(gòu)為先導(dǎo)控制級(jí)的比例閥。對(duì)力矩馬達(dá)輸入不同的電信號(hào)，并通過(guò)同它連接在一起的擋板（有時(shí)力矩馬達(dá)的銜鐵就是擋板）輸出位移或角位移，改變擋板和噴嘴之間的距離，使噴嘴噴出的油液流阻產(chǎn)生變化，進(jìn)而控制輸小參數(shù)。
 

德國(guó)力士樂(lè)比例閥部分型號(hào)如下：

4WRA 4WRAE 比例閥
4WRE 4WREE 比例方向閥

R900245378 4WRA6E07-2X/G24N9K4/VL
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R900334921 4WRA6EA20-1X/24Z4/M
R900335832 4WRA6E1-20-1X/24NZ4/M
R900340833 4WRA6EB05-1X/24NZ4/M
R900343227 4WRA6E10-1X/24N9Z4/M
R900346618 4WRA6E05-1X/24NK4/M
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R900347307 4WRA6EB20-1X/24NZ4/M
R900347720 4WRA6E05-1X/12NZ4/M
R900351651 4WRA6E05-1X/24NZ4/V
R900351652 4WRA6E10-1X/24NZ4/V
R900353699 4WRA6EB20-1X/24Z4/M
R900357022 4WRA6EA05-1X/24NZ4/M
R900358926 4WRA6E05-1X/12NZ4/M
R900359586 4WRA6E20-1X/24Z4/V
R900361516 4WRA6E20-1X/24NZ4/V
R900369113 4WRA6E20-1X/24NJ/M
R900372595 4WRA6EA20-1X/24NZ4/V
R900373991 4WRA6E05-1X/24N9Z4/M
R900376358 4WRA6EA05-1X/24Z4/M
R900378517 4WRA6E20-1X/24N9Z4/M
R900382854 4WRA6E20-1X/24N9K4/M
R900384256 4WRA6EA10-1X/24NZ4/V
R900400005 4WRA6EA05-1X/24N9Z4/M
R900403084 4WRA6E10-1X/24Z4/V
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R900458113 4WRA6EB20-1X/24N9Z4/M
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R900488311 4WRA6E20-1X/24Z4/M
R900488312 4WRA6E05-1X/24NZ4/M
R900488515 4WRA6E20-1X/24NZ4/M
R900488591 4WRA6E10-1X/24NZ4/M
R900489020 4WRA6E1-20-1X/24Z4/M
R900498892 4WRA6EA10-1X/24NZ4/M
R900499932 4WRA6EA05-1X/24Z4/V
R900499956 4WRA6EB10-1X/24NZ4/M
R900520791 4WRA6E10-1X/24NZ4/MR
R900520897 4WRA6E05-1X/24Z4/MR
R900520898 4WRA6E10-1X/24Z4/MR
R900521234 4WRA6E05-1X/24N9Z4/V
R900523535 4WRA6E05-1X/24NZ4/MR
R900525288 4WRA6E05-1X/24Z4/V
R900535119 4WRA6E20-1X/24NZ4/MR
R900535570 4WRA6EA20-1X/24NJ/V
R900539607 4WRA6E1-10-1X/24Z4/M
R900548255 4WRA6E20-1X/24N9Z4/V
R900548263 4WRA6E1-10-1X/24N9Z4/V
R900550103 4WRA6E2-20-1X/24N9Z4/M
R900550178 4WRA6E1-10-1X/24NZ4/M
R900551851 4WRA6E15-2X/G24N9Z4/V
R900552258 4WRA6EA20-1X/24K4/VR
R900568684 4WRA6EB05-1X/24Z4/M
R900573107 4WRA6E05-1X/24NK4/M
R900573794 4WRA6E1-20-1X/24NK4/M
R900574608 4WRA6E30-2X/G24N9Z4/V
R900576426 4WRA6E10-1X/24N9Z4/V
R900591051 4WRA6E2-20-1X/24NZ4/M
R900592259 4WRA6EA20-1X/24N9Z4/M
R900594655 4WRA6EA05-1X/24Z4/V
R900702629 4WRA6EB20-1X/24NK4/M
R900703653 4WRA6EA05-1X/24K4/M
R900713549 4WRA6E1-07-2X/G24K4/V
R900728286 4WRA6EB15-2X/G24K4/V
R900737408 4WRA6EA07-2X/G24K4/V
R900902940 4WRA6E30-2X/G24N9K4/V
R900903242 4WRA6EA30-2X/G24N9Z4/V
R900904437 4WRA6E15-2X/G24Z4/V
R900904438 4WRA6E15-2X/G24K4/V
R900904439 4WRA6E30-2X/G24K4/V
R900906034 4WRA6E1-15-2X/G24N9K4/V
R900906262 4WRA6E07-2X/G24N9K4/V
R900907917 4WRA6E1-30-2X/G24N9Z4/V
R900910780 4WRA6E07-2X/G24K4/V
R900917701 4WRA6EB20-1X/24N9K4/M
R900918062 4WRA6EA15-2X/G24N9Z4/V
R900920557 4WRA6E15-2X/G24N9K4/V
R900922674 4WRA6EA30-2X/G24Z4/V
R900924377 4WRA6EB30-2X/G24N9K4/V
R900925363 4WRA6E10-1X/24K4/M
R900925553 4WRA6EA07-2X/G24N9K4/V
R900930396 4WRA6E20-1X/24K4/M
R900932055 4WRA6E1-07-2X/G24N9K4/V
R900933792 4WRA6EB15-2X/G24N9K4/V
R900934376 4WRA6E1-30-2X/G24N9K4/V
R900936935 4WRA6EA30-2X/G24N9K4/V
R900937718 4WRA6EA15-2X/G24N9K4/V
R900938512 4WRA6EA10-1X/24NK4/M
R900943643 4WRA6E20-1X/24NK4/MR
R900943644 4WRA6E10-1X/24NK4/MR
R900943662 4WRA6E05-1X/24NK4/MR
R900945901 4WRA6EA05-1X/24NK4/V
R900946353 4WRA6E15-2X/G24EXJ/V
R900947149 4WRA6E03-2X/G24N9K4/V
R900947693 4WRA6EB30-2X/G24K4/V
R900947835 4WRA6E1-30-2X/G24K4/V
R900952256 4WRA6EA30-2X/G24NJK31/V