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附錄A
英文部分：
The commonly used sources of power in hydraulic systems are pumps and accumulators .
Similarly,accumulator connected to atmosphere will dischange oil at atmosphere pressure until it empty. only when connected to a system having resistance to flow can pressure be developed.
Three types of pumps find use in fluid-power systems: 1,rotary,2,reciprocating,3,or piston-type,and 3,centrifugal pumps.
Simple hydraulic system may use but one type of pump . The trend is to use pumps with the most satisfactory characteristics for the specific tasks involved . In matching the characteristics of the pump to the requirements of the hydraulic system , it is not unusual to find two types of pumps in series . For example , a centrifugal pump may be to supercharge a reciprocating pump , or a rotary pump may be used to supply pressurized oil for the contronls associated with a reversing variabledisplacement pumps .
Most power systems require positive displacement pumps . At high pressure , reciprocating pumps are often preferred to rotary pumps .
Rotary pumps
These are built in many differnt designs and extremely popular in modern fluid power system . The most common rotay-pump designs used today are spurgear , internal gear ,generated rotor , sliding vane ,and screew pumps . Ehch type has advantages that make it most suitable for a given application .
Gear pumps
Gear pumps are the simplest type of fixed displacement hydraulic pump available . This type consists of two external gear , generally spur gear , within a closed-fitting housing . One of the gear is driven directly by the pump drive shaft . It ,in turn , then drives the second gear . Some designs utilize helical gears ,but the spur gear design predominates . Gear pumps operate on a very simple principle , illustration Fig.7.3 . As the gear teeth unmesh , the volume at the inlet port A expands , a partial vacuum on the suction side of the pump will be formed . Fluid from an external reservoir or tank is forced by atmospheric pressure into the pump inlet . The continuous action of the fluid being carried from the inlet to the discharge side B of the pump forces the fluid into the system .
Pressure rise in a spur-gear pump is produced by the squeezing action on the fluid as it is expellde from between the meshing gear teeth and the casing . Fluid from the discharge side is prevented from returing to the inlet side by the clearance between the gears and houseing .
Vane pumps
The vane pump ,illustration 7.4 , consists of a housing that is eccentric or offset with respect to the drive shaft axis . In some models this inside surface consists of a cam ring that can be rotated to shift the relationship between rotor are rectangular and extend radially from a center radius to the outside diameter of the rotor and from end to end . A rectangular vane that is essentially the same size as the slot is inserted in the slot and is free to slide in and out .
As the rotor turns , the vanes thrust outward , and the vane tips track the inner surface of the housing , riding on a thin film of fluid . Two port or end plates that engage the end face of the ring provide axial retention .
Centrifugal force generally contributes to outward thrust of the vane . As they ride along the eccentric housing surface , the vane move in and out of the rotor slots . The vane divide the area between the rotor and casing into a series of chambers .The sides of each chamber are formed by two adjacent vanes ,the port or end plates , the pump casing and the rotor . These chambers change in change in volume depending on their respective position about the shaft .
As each chamber approaches the inlet port , its vanes move outward and its volume expands , causing fluid to flow into the expanded chamber . Fluid is then carried within the chamber around to the dischange port . As the chamber approaches the discharge port , its vanes are pushed inward ,the volume is reduced , and the fluid is forced out the discharge port .
The variable-volume vane pump can be adjusted to discharge a different volume of fluid while running at constant speed , simply by shifting the cam ring with respect to the rotor .When the pump components are in position such that the individual chambers achieve their maximun volume as they reach the inlet port , the maximum volume of fluid will be moved . If the relationship between housing and rotor is changed such that the chambers achieve their minmum of zero volume as they reach the inlet port , the pump delivery will be reduced to zero .
Since the vane pump housing or cam ring must be shifted to change the eccentricity and vary the output , variable-displacement vane pumps cannot have the closed end fit common to fixed-displacement vane pumps . Volumetric efficiency is in the range of 90% to 95% . These pumps retain their efficiency for a considerable length of time since compensation for wear between the vane ends and the housing is automatic .As these surfaces wear , the vanes move farther outward from their slots to maintain contact with the housing .
Vane pump speed is limited by vane peripheral speed . High peripheral speed will cause cavitation in suction cavity . which results in pump damage and reduced flow .
An imbalance of the vanes can cause the oil film between the vane tips and the cam ring to break down , resulting in metal-to-metal contact and subsequent increased wear and slipage . One metheod applied to eliminate high vane thrust loading is a dual-vane construction .
In the dual-vane construction , two independent vanes are located in each rotor slot . Chambered edges along the sides and top of each vane from a channel that essentially force causes the vane to follow the contour of each pair of vanes . Centrifugal force causes the vane to follow the contour of the cam-shaped ring . There is just sufficient seal between the vanes and ring without destroying the thin oil film .
Piston-type pump
Two basic types of piston or reciprocating pumps are the radial piston and the axial typese , both are available as fixed or variable displacement models . Axial piston pumps may be further divided into in-line and bent axis types .
All piston pumps operate by allowing oil to flow into a pumping cavity as a piston retreats and then forcing the oil out into another chamber as the piston advances . Design differences among pumps lie primarily in the methods of separating inlet from outlet oil .
In-line piston pump
The siplest typeof axial piston pump is the swash plate in-line design , illustration 7.5 .The cylinder are connected though piston shoes and a retracting ring , so that the shoes beat anainst an angled swash plate . As the block turns ,the piston shoes follow the swash plate ,causing the piston to reciprocate . The ports are arranged in the valve plate so that the pistons pass the inlet port as they are being pulled out and pass the outlet port as they are being forcing back in .
The angle of the swash plate controls the delibery . Where the swash plate is fixed , the pump is of the constant-displacement type . In the variable-displacement , inline piston pump , the swash plate is moumted on a pivoted yoke . As the swash plate angle is increased , the cylinder stroke is increase , resulting in a greater flow . A pressure compensator control can position the yoke automatically to maintain a constant output pressure .
Operation of he inline pump compensator control is shown schematically in Fig.7.6 .The control can position the yoke automatically in Fig.7.6 . The control consists of a compensator valve balanced between load pressure and the force of a spring , a yoke piston controlled by the compensator valve to move the yoke , and a yoke retun spring .
With no outlet pressure , the yoke return spring moves the yoke to the full delibery position .As pressure builds up ,it acts against the end of the valve spool .When the pressure is high enough to overcome the valve spring , the spool is displaced and oil enters dis placement . If the pressure falls off , the spool moves back , oil is discharged from the piston to the inside of the pump case , and the spring returns the yoke to a greater angle .
The compensator thus adjusts the pump output to whatever is required to develop and maintain the preset pressure . This prevents excess power losses bu relief valve operation at full pump volume during holding or clamping .
There compensator thus adjusts the pump output to whatever is required to develop and maintain the preset pressure . This prevents excess power losses by relief valve operation at full pump volume during holding or clamping .
There is a variation of the swash plate in-line pump . It is a design where the swash plate turns , but the cylinder barrel remains stationary . The plate is canted so that it wobbles as it turns . This action pushes the pistons in and out the stationary cylingder barrel .
This type of in-line pump contains a separate inlet and outlet check valve for each piston since the pistons do not move past the inlet and outlet port .
BENT-axis piston pump
Illustration 7.7 show a bent-axial piston pump , which contatins a cylinder block assembly in which the pistons are equally spaced around the cylinder block axis . Cylinder bores are parallel to the axis . The cylinder block turns with the drive shaft , but at an offest angle . The piston rods are attaached to the drive shaft flange by ball joints . A universal link keys the cylinder block to the drive shaft to maintain alignment and assure that they turn together . The link does not transmit force except to accelerate and decceltate the cylinder block and to overcome resistance of the block revolving in oil filled housing .
As the shaft roates , distance between any one piston and the valving surface changes continually . Each piston moves away from the valving surface during one half of the revolution and toward the valving surface during the other half . The inlet chamber is in line as the pistons move away , and the outletr chamber is in line as the pistons move closer , thus drawing liquiring in during one half of the inlet chamber as the pistons are moving away from the pintle . Thereforce , during rotation , pistons draw liquid into the cylinder bores as they pass the inlet side of the pinntle and force that liquid out of the bores as they pass the outlet side of the pintle . The displacement of this pump varies with the offset angle , the maximum angle being 30 degree ,the minimum zero . Fixed displacement models are usually avaiable with 23 degree angle .In the variable displacement construction a yoke with an external control is used to change the angle . With some contronls , the yoke can be moved over center to reverse the direction of flow from the pump .
Pump/system interaction
Frequently , hydraulic system designers choose off-the-shelf pumps with little cocern other than supplying sufficient flow at available input power . Early enphasis that positive displacement pumps supply only flow and that pressure is developed by the system suggests that , as a minmum , the pump should be chosem in light of several overall requirements and with system detailed design and the nature of the working fluid well in mind .
Positive displacement pumps generate flow . In a fixed delivery pump , provisions must be made to dissipate flow or system pressure will rise until a rupture occurs . The usual means of accomplishing flow control is to place a relief valve inthe high pressure line . When the pressure rise above an established amoumt ,the relief valve will vent excess flow back to the reservoir . In such systems , pump flow and relief valve capacity must be carefully matched to assure proper venting . Flow from a high pressure line through a relief valve to a low pressure element is wasted hydraulic horsepower , which can be calculated from the following relationship :
hp=PQ/1714
Where : Q = flow in gpm
This wasted horsepower is converted to heat in the hydraulic system . If not properly removed , the heat can damage the fluid , elastomer seals , and other organic material in the system .
Pressure-compensated variavle delivery pumps do not require a relief valve in the high pressure line . The pressure compensation feature eliminates the need for the relief valve . In nearly all working systems ,however , at least one is used on just-in-case basis . The use of a pressure compensator , while avoiding dependence on a relief valve , brings on its own problems . The actuator -spring-spool arrangement in the compensator is a dynamic , damped-mass-spring arrangement . However , when the system calls for a chang in axhieve their maxmum volume as they reach the inlet port , the maximum volume of fluid will ve moved . If the relationship between housing and rotor is changed such that the chambers achieve their minimum of zero volume as they reach the inlet port , the pump delivery will be reduced to zero .
Since the vane pump housing or cam ring must be shifted to change the eccentricity and vary the output , variable-displacement vane pumps cannot have the closed end fit common to fixed-displacement pumps . Volumetric efficiency is the range of 90% to 95% . These pumps retain their efficiency for a considerable length of time since compensation for wear between the vane ends and the housing is automatic . As these surfaces wear , the vanes move farther outward from their slots to maintain contact with the housing .
Vane pump speed is limited by vane peripheral speed . High peripheral speed will cause cavitation in suction cavity , which results in pump damage and reduced flow .
An imbalance of the vanes can cause the oil film between the cane tips and the cam ring to break down , resulting in metal-to-metal contact and subsequent increased wear and slipage . One method applied to eliminate high vane thrust loading is a dual-vane construction .
In the dual-vane construction , tow independent vanes are located in each totor slot chmbered edges along the sides and top of each vane from a channel that essentially balances the hydraulic pressure on the top and bottom of each pair of vanes .
Centrifugal force cause the vane to follow the contour of the cam-shaped ring .There is just sufficient seal between the vanes and ring without destroying the thin oil film .
附錄B
中文部分：
常用的液壓系統(tǒng)的動(dòng)力源是泵和蓄能器。
一般情況下，一個(gè)蓄能器在正常的大氣壓力下，連續(xù)的向各系統(tǒng)中壓入液壓油，直至將所儲(chǔ)存的能量全部用完為止。 只有當(dāng)其連接的系統(tǒng)中，具有抗流壓力時(shí)才能夠得到補(bǔ)充。
在液壓系統(tǒng)和液力系統(tǒng)中，常使用液壓泵有三種類型：
1、回轉(zhuǎn)式，
2、往復(fù)式，
3、活塞式或者離心式。
簡(jiǎn)單液壓系統(tǒng)一般使用的都是第一類液壓泵。 目前的發(fā)展趨勢(shì)是針對(duì)具體的工作任務(wù)和工況，選用最佳的液壓泵類型。在符合特性和要求的液壓泵中，找到兩種不同類型的液壓泵式很常見的。 例如，離心泵，往復(fù)泵都可以可對(duì)系統(tǒng)增壓，旋轉(zhuǎn)泵和變量液壓泵聯(lián)合使用也可以提供高壓的液壓油。 大部分動(dòng)力系統(tǒng)還需要采取容積式液壓泵泵。而在較高的體統(tǒng)壓力下，往復(fù)泵往往要優(yōu)于回轉(zhuǎn)泵。
回轉(zhuǎn)泵
這些形式的液壓泵因?yàn)榫哂性S多不同的設(shè)計(jì)形式而極受歡迎，在現(xiàn)代流體動(dòng)力系統(tǒng)。 最常見的旋轉(zhuǎn)泵的設(shè)計(jì)形式，包括內(nèi)部使用齒輪的、內(nèi)部使用轉(zhuǎn)子的、內(nèi)部采用滑動(dòng)葉片的和使用螺桿的。 其中，每一種類型都有其獨(dú)特的優(yōu)點(diǎn)，都有其最適合的一定的應(yīng)用場(chǎng)合。
齒輪泵
齒輪泵是可以提供的最簡(jiǎn)單的一種液壓泵。 這一類型的液壓泵一般包括兩個(gè)外嚙合的齒輪，一般是圓柱直齒輪，安裝在一個(gè)密封的殼體里面。 其中一個(gè)齒輪由液壓泵的傳動(dòng)軸直接驅(qū)動(dòng)， 第一個(gè)齒輪然后再推動(dòng)第二輪。還有一些設(shè)計(jì)中利用螺旋齒輪，但是一般以齒輪設(shè)計(jì)為主。 齒輪泵的動(dòng)作的原理非常簡(jiǎn)單，如插圖7.3 所示。 由于在齒輪的輪齒在脫開嚙合時(shí)，進(jìn)氣道擴(kuò)大， 液壓泵將會(huì)形成局部真空的具有吸力的空腔。 流體在系統(tǒng)的壓力下被從外部油箱或罐體中壓入， 連續(xù)運(yùn)動(dòng)的液壓油在液壓泵的作用下，從真空的吸力空腔中被送入排出液壓油的一
側(cè)——B側(cè)。
直齒輪泵內(nèi)的液壓油被從脫開嚙合的輪齒和套管之間不斷的排出，這種擠壓運(yùn)動(dòng)使得齒輪泵內(nèi)的壓力上升，從排油一側(cè)來的液壓油由于被阻止，不能返回進(jìn)油一側(cè)的輪齒的間隙和空腔。
葉片泵
如插圖7.4所示，葉片泵一般是由一個(gè)相通的腔體，是偏心或抵消對(duì)傳動(dòng)軸軸線。在一些模型內(nèi)的表面設(shè)有一個(gè)凸輪環(huán)，一個(gè)可旋轉(zhuǎn)移動(dòng)的長(zhǎng)方形的轉(zhuǎn)子，轉(zhuǎn)子的徑向延長(zhǎng)，從一個(gè)中心，半徑為外徑的轉(zhuǎn)子，到末端結(jié)束。 上面是尺寸大小相同的插槽，矩形葉片一般插入到插槽中，并且可以自如的滑入和滑出。
當(dāng)轉(zhuǎn)子轉(zhuǎn)動(dòng)時(shí)，葉片被向外甩出， 而葉片尖端則貼緊其運(yùn)動(dòng)軌道空腔的內(nèi)表面， 處于液壓油的薄膜的上面。 兩個(gè)油口或端板，向環(huán)形的端面提供軸向的存儲(chǔ)。
通常離心有助于葉片的向外推出。當(dāng)葉片處于偏心空腔的表面上時(shí)，葉片從轉(zhuǎn)子的縫隙中甩出和甩。 葉片將套管和轉(zhuǎn)子之間的區(qū)域分成一系列的小空腔。每一個(gè)小空腔都是由兩個(gè)相鄰葉片，油口或者端盤，液壓泵殼體和轉(zhuǎn)子形成。 這些空腔的容積的變化取決于他們相對(duì)于軸的相對(duì)位置。
當(dāng)每個(gè)廳內(nèi)靠近進(jìn)內(nèi)氣孔的時(shí)候，其葉片向外移動(dòng)，其空腔的容積膨脹， 造成液壓油流入擴(kuò)大空腔。 流體隨后被帶入圍繞著排油孔的空腔內(nèi)。當(dāng)這些空腔靠近排油孔時(shí)，葉片被甩入腔內(nèi)，空腔的容積減小，液壓油隨即被壓出排油孔。
變量葉片泵，可以進(jìn)行調(diào)整，以適應(yīng)不同的流體排量，當(dāng)在定常速度下運(yùn)行時(shí)， 只需要改變把凸輪環(huán)相對(duì)于對(duì)轉(zhuǎn)子的位置即可。當(dāng)液壓泵的部件的處于各自的空腔在靠近吸油孔時(shí)達(dá)到最大的位置的時(shí)候，流體的最大排量就將會(huì)改變。 如果腔體和轉(zhuǎn)子的相對(duì)關(guān)系改變，則空腔在他們到達(dá)吸油孔的時(shí)候就達(dá)到了他們的最小容積————零容積，此時(shí)，液壓泵的排油量也減少到零。
由于葉片泵的空腔或凸輪圈必須變化從而改變偏心率即改變輸出量， 變量葉片泵沒有相應(yīng)于普通固定位移葉片泵的固定端， 容積效率范圍是90%至95% 。 這些液壓泵能夠在一個(gè)相當(dāng)長(zhǎng)的時(shí)間里保持其效率，因?yàn)槿~片兩端和空腔之間摩擦補(bǔ)償是自動(dòng)的。 正是由于這些表面的摩擦， 才使得葉片泵的葉片能夠向外面甩出同時(shí)又不會(huì)脫離插槽。
葉片泵的速度一般要受到葉片圓周速度的限制。 過高的圓周速度將導(dǎo)致空腔內(nèi)出現(xiàn)負(fù)壓，從而導(dǎo)致液壓泵損壞和流量減小。
一個(gè)不平衡的葉片將會(huì)引起葉片頂端和凸輪環(huán)之間的油膜的破壞，從而進(jìn)一步導(dǎo)致金屬和金屬之間的直接接觸，因而增加了磨損和葉片泵的動(dòng)力傳動(dòng)損耗 。消除這種葉片泵的葉片的高推力負(fù)荷的方法之一就是采用雙葉片結(jié)構(gòu)。
在雙葉式結(jié)構(gòu)中，每?jī)蓚€(gè)互相獨(dú)立的葉片是分別設(shè)置在每個(gè)轉(zhuǎn)子槽中的。腔室的邊緣兩旁和頂部葉片每一個(gè)渠道，基本上形成了一個(gè)十字狀，每個(gè)一雙葉片等高。 在離心力的作用下，使得葉片隨著凸輪環(huán)的外部輪廓的變化而變化。 當(dāng)葉片和凸輪環(huán)之間形成了足夠大的間隙的時(shí)候，將會(huì)破壞油膜。
活塞式泵
兩種基本類型的活塞液壓泵或者是往復(fù)式液壓泵都是活塞徑向和軸向類型的， 兩者均可作為定量泵或可變排量泵模型。 其中，軸向柱塞泵，又可以進(jìn)一步分為線性柱塞泵和彎曲軸型柱塞泵兩種類型。
所有的活塞式液壓泵的運(yùn)行原理，都是通過液壓油流入泵腔而推動(dòng)活塞向后面移動(dòng)，然后活塞再向前移動(dòng)，從而將液壓油排出，使得液壓油進(jìn)入泵的另一個(gè)腔室中。 不同的泵的設(shè)計(jì)差異泵主要在于活塞進(jìn)入和推出從而將液壓油分離的方法。
直軸式柱塞泵
最簡(jiǎn)單的軸向柱塞泵是將沖板進(jìn)行線性化設(shè)計(jì)，如插圖7。5 所示，氣缸與活塞的回縮盤之間相連， 使移動(dòng)的回縮盤成傾斜式。 當(dāng)傾斜圓盤轉(zhuǎn)動(dòng)的時(shí)候，柱塞的端腳斜盤上運(yùn)動(dòng)，從而使得活塞桿不斷的往復(fù)的運(yùn)動(dòng)，同時(shí)因?yàn)橛涂诜謩e安排在閥板上，能夠使活塞通過進(jìn)氣道，當(dāng)它們運(yùn)動(dòng)到一定的位置時(shí)，通過油口將液壓油推出排油口。
斜盤的傾斜角度決定了柱塞泵的排量。在這里，斜盤的位置是固定的，而泵的位移是恒定的。 在變量的線性柱塞泵中，逆止閥活塞泵，沖板是裝在一個(gè)鉸鏈的枷鎖。 由于沖板角度的增大，氣缸沖程增加，形成了更大的流量。 由于壓力補(bǔ)償控制位置的作用，自動(dòng)保持恒定輸出壓力。
線性柱塞泵的運(yùn)行原理就是如插圖7.6所示 。 在圖中，能夠自動(dòng)的控制枷鎖的定位。 這種控制由一個(gè)補(bǔ)償閥來平衡負(fù)載壓力和系統(tǒng)的壓力，枷鎖活塞由補(bǔ)償閥移動(dòng)另一個(gè)枷鎖來實(shí)現(xiàn)控制。
由于壓力無法卸載， 枷鎖回位彈簧的推動(dòng)枷鎖直到臨界的位置。 由于壓力的累積，它的動(dòng)作是組織閥芯末端。當(dāng)壓力高至足以克服閥的彈簧力的時(shí)候，閥芯就會(huì)變換位置，同時(shí)，液壓油也會(huì)進(jìn)入原來的空腔中。假如壓力下降，閥芯向后移動(dòng)， 液壓油被活塞排出而進(jìn)入液壓泵的管道。系統(tǒng)就會(huì)使枷鎖回到一個(gè)更大的角度。
補(bǔ)償器調(diào)節(jié)泵的輸出量，從而達(dá)到任何要求達(dá)到的更高的壓力或者保持原來預(yù)置的壓力。這使得過剩的動(dòng)力損失得以通過節(jié)流閥的在滿載的時(shí)候的保持和收緊作用而被部分保留和利用。
在直軸式的柱塞泵中，有一個(gè)可以變化的斜盤。 這是一個(gè)設(shè)計(jì)中的斜盤式的轉(zhuǎn)折，但缸筒依然保持了其平穩(wěn)。 斜板是傾角回轉(zhuǎn)的。 這一動(dòng)作推動(dòng)活塞進(jìn)入和推出較為平穩(wěn)的缸筒。
這種類型的直軸式柱塞泵在每一個(gè)位置上都包括一個(gè)單獨(dú)的進(jìn)油口檢測(cè)閥和一個(gè)單獨(dú)的出油口檢測(cè)閥。因此，柱塞才不會(huì)在移動(dòng)的時(shí)候超出進(jìn)油口和排油口。
斜軸式柱塞泵
如圖7.7所示，說明了斜軸式柱塞泵的工作原理， 裝配中的活塞包含缸體也同樣以缸體的軸線為基準(zhǔn)間隔排列在四周， 缸孔平行于軸線?；钊敉ㄟ^法蘭盤和球關(guān)節(jié)連接在傳動(dòng)軸上。
一個(gè)普遍的鏈接鍵缸體的傳動(dòng)軸一定要保持對(duì)準(zhǔn)，并且要保證他們一起轉(zhuǎn) 。缸體和克服阻力的旋轉(zhuǎn)座因?yàn)榧铀俨粋鬟f力矩而使得液壓油充入空腔。 同時(shí)，由于軸的旋轉(zhuǎn)，其距離任何一個(gè)活塞和閥門表面的距離在不斷變化。 每個(gè)活塞逐漸遠(yuǎn)離閥門的表面，直到達(dá)到總路程的一半時(shí)產(chǎn)生了質(zhì)的變化。進(jìn)油室是呈線性的遠(yuǎn)離線為活塞， 而出油室則是線性的向活塞靠攏， 因此所繪制出的流體都是在進(jìn)氣道空腔內(nèi)的中間處遠(yuǎn)離活塞 。這一期間，活塞輪換提取液壓油進(jìn)入缸孔，他們通過進(jìn)氣道的一側(cè)和高壓力使液壓油流出鉆孔，同時(shí)，它們通過插座一側(cè)的樞軸，這種泵的位移隨著偏移角的變化而變化， 其最大角度為30度，最低為零。 固定位移模式通常每周以23度的傾角。 在變排量施工的枷鎖與外聘 控制是用來改變角度。 一些控制，枷鎖可以移到中心逆向流動(dòng)的方向由泵。
泵/系統(tǒng)頻繁互動(dòng)
液壓系統(tǒng)設(shè)計(jì)者選擇現(xiàn)成的水泵幾乎關(guān)于除供應(yīng)足夠的流量，可輸入功率。在早期的液壓泵的結(jié)構(gòu)中，正位移泵供應(yīng)只有流量和壓力是由系統(tǒng)顯示， 作為最小的一個(gè)， 泵應(yīng)選擇參照若干總體要求和系統(tǒng)的詳細(xì)設(shè)計(jì)和性質(zhì) 工作流體好記。 正位移泵產(chǎn)生的流量。 在一個(gè)固定輸送泵， 必須作出規(guī)定，以分散水流或系統(tǒng)的壓力將上升，直至出現(xiàn)破裂。 通常的辦法實(shí)現(xiàn)流量控制，是把一個(gè)閥耐高壓線路。 當(dāng)壓力超過既定額度，溢流閥會(huì)發(fā)泄過剩回流庫區(qū)。 在這種制度下，泵的流量和閥容量必須仔細(xì)匹配，以保證適當(dāng)?shù)男埂?液壓油的液流從高壓線路通過溢流閥，以直到液壓馬達(dá)，變成了低氣壓?？梢杂?jì)算出這一過程服從以下關(guān)系:
hp= pq/1714
這里: q=油路中的流量
液壓系統(tǒng)中由于電流階躍引起部分能量被轉(zhuǎn)化為熱量二浪費(fèi)掉了。 如果不妥善解決，熱量會(huì)破壞液壓系統(tǒng)、油管、橡膠密封件，和其它有機(jī)物質(zhì)的東西。
壓力補(bǔ)償式變量泵不需要在高壓線路安裝溢流閥。 壓力補(bǔ)償功能也不需要安全閥。 在幾乎所有的工作系統(tǒng)中，一般至少有一個(gè)是用屬于特殊的情況。 使用壓力補(bǔ)償，同時(shí)避免依賴溢流閥而帶來的系統(tǒng)本身的問題。 動(dòng)力-彈簧閥芯排列中的補(bǔ)償是動(dòng)態(tài)的，即阻尼-彈簧-安裝排列。其落點(diǎn)量達(dá)到進(jìn)氣道， 最高流體體積就能夠達(dá)到。
如果空腔和轉(zhuǎn)子之間的關(guān)系發(fā)生了改變，空腔會(huì)調(diào)整自己的流量，其最低流量一般為零。當(dāng)葉片到達(dá)進(jìn)氣道時(shí)，液壓泵的輸送量將減少到零。 由于葉片泵住房或凸輪圈必須轉(zhuǎn)向改變偏心率和不同的輸出， 可變位的葉片泵沒不能有封閉式，如果需要封閉式，則需要選用普通的固定泵。
葉片泵的容積效率范圍為90%至95% 。 這種液壓泵能夠保留其高效率達(dá)到相當(dāng)長(zhǎng)的時(shí)間，因?yàn)槿~片兩端和空腔之間的補(bǔ)償磨損是自動(dòng)的。正是由于這些表面磨損，當(dāng)葉片處于遠(yuǎn)離其插槽的位置時(shí)，才能夠保證葉片與葉片之間的空腔。
葉片泵的速度是有限的，其速度決定于葉片轉(zhuǎn)動(dòng)時(shí)的圓周速度。 過高的圓周速度將導(dǎo)致空腔內(nèi)產(chǎn)生負(fù)壓，從而導(dǎo)致液壓泵的損壞，也會(huì)導(dǎo)致流程的縮短。一個(gè)失去平衡的葉片能造成葉片的尖端和凸輪環(huán)之間的油膜被破壞，從而導(dǎo)致金屬和金屬的直接接觸，因而增加了磨損和動(dòng)力傳遞的損耗。
用于消除高壓葉片的推力負(fù)荷的一種方法就是采用雙葉片構(gòu)造。在雙葉式構(gòu)造中， 每一片獨(dú)立的葉片設(shè)置在相應(yīng)的每個(gè)飛輪插槽的邊沿線兩側(cè)和頂部之間。離心力造成葉片隨著凸輪形盤的輪廓轉(zhuǎn)動(dòng)、變化。因此能夠有足以密封性能， 葉片之間的薄油膜也不會(huì)被破壞。