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1、10 Hydraulic machinery and pump Hydraulic machinery are machines and tools which use fluid power to do work. Heavy equipment is a common example. In this type of machine, high-pressure liquid - called hydraulic fluid - is transmitted throughout the machine to various hydraulic motors and hydrau

2、lic cylinders. The fluid is controlled directly or automatically by control valves and distributed through hoses and tubes. The popularity of hydraulic machinery is due to the very large amount of power that can be transferred through small tubes and flexible hoses, and the high power density and w

3、ide array of actuators that can make use of this power. Hydraulic machinery is operated by the use of hydraulics, where a liquid is the powering medium. Pneumatics, on the other side, is based on the use of a gas as the medium for power transmission, generation and control. Hydraulic circuits For

4、 the hydraulic fluid to do work, it must flow to the actuator and or motors, then return to a reservoir. The fluid is then filtered and re-pumped. The path taken by hydraulic fluid is called a hydraulic circuit of which there are several types. Open center circuits use pumps which supply a continu

5、ous flow. The flow is returned to tank through the control valves open center; that is, when the control valve is centered, it provides an open return path to tank and the fluid is not pumped to a high pressure. Otherwise, if the control valve is actuated it routes fluid to and from an actuator and

6、tank. The fluids pressure will rise to meet any resistance, since the pump has a constant output. If the pressure rises too high, fluid returns to tank through a pressure relief valve. Hydraulic pumps supply fluid to the components in the system. Pressure in the system develops in reaction to the

7、load. Hence, a pump rated for 5,000 psi is capable of maintaining flow against a load of 5,000 psi.Pumps have a power density about ten times greater than an electric motor (by volume). They are powered by an electric motor or an engine, connected through gears, belts, or a flexible elastomeric coup

8、ling to reduce vibration. Common types of hydraulic pumps to hydraulic machinery applications are; Gear pump: cheap, durable, simple. Less efficient, because they are constant displacement, and mainly suitable for pressures below 20 MPa (3000 psi). Vane pump: cheap and simple, reliable (especial

9、ly in g-rotor form). Good for higher-flow low-pressure output. Axial piston pump: many designed with a variable displacement mechanism, to vary output flow for automatic control of pressure. There are various axial piston pump designs, including swashplate and checkball. The most common is the swa

10、shplate pump.Radial piston pump: A pump that is normally used for very high pressure at small flows. Piston pumps are more expensive than gear or vane pumps, but provide longer life operating at higher pressure, with difficult fluids and longer continuous duty cycles. Piston pumps make up one half

11、 of a hydrostatic transmission. Control valves Directional control valves route the fluid to the desired actuator. They usually consist of a spool inside a cast iron or steel housing. Directional control valves are usually designed to be stackable, with one valve for each hydraulic cylinder, and

12、 one fluid input supplying all the valves in the stack. The spool position may be actuated by mechanical levers, hydraulic pilot pressure, or solenoids which push the spool left or right. The main valve block is usually a stack of off the shelf directional control valves chosen by flow capacity a

13、nd performance. Some valves are designed to be proportional (flow rate proportional to valve position), while others may be simply on-off. The control valve is one of the most expensive and sensitive parts of a hydraulic circuit. Pressure relief valves are used in several places in hydraulic machin

14、ery; on the return circuit to maintain a small amount of pressure for brakes, pilot lines, etc... On hydraulic cylinders, to prevent overloading and hydraulic line rupture. On the hydraulic reservoir, to maintain a small positive pressure which excludes moisture and contamination. Pressure reducin

15、g valves reduce the supply pressure as needed for various circuits. Check valves are one-way valves, allowing an accumulator to charge and maintain its pressure after the machine is turned off, for example. Counterbalance valves are in fact a special type of pilot controlled check valve. Where

16、as the check valve is open or closed, the counterbalance valve acts a bit like a pilot controlled flow control. Hydraulic pump types Gear pumps Gear pumps (with external teeth) (fixed displacement) are simple and economical pumps. The swept volume or displacement of gear pumps for hydraulics will

17、 be between about 1 cm3 (0.001 litre) and 200 cm3 (0.2 litre). These pumps create pressure through the meshing of the gear teeth, which forces fluid around the gears to pressurize the outlet side. Some gear pumps can be quite noisy, compared to other types, but modern gear pumps are highly reliable

18、and much quieter than older models. Rotary vane pumps Rotary vane pumps (fixed and simple adjustable displacement) have higher efficiencies than gear pumps, but are also used for mid pressures up to 180 bars in general. Some types of vane pumps can change the centre of the vane body, so that a sim

19、ple adjustable pump is obtained. These adjustable vane pumps are in general constant pressure or constant power pumps: the displacement is increased until the required pressure or power is reached and subsequently the displacement or swept volume is decreased until an equilibrium is reached. Screw

20、pumps Screw pumps (fixed displacement) are a double Archimedes screw, but closed. This means that two screws are used in one body. The pumps are used for high flows and relatively low pressure (max 100 bar). They were used on board ships where the constant pressure hydraulic system was going throug

21、h the whole ship, especially for the control of ball valves, but also for the steering gear and help drive systems. The advantage of the screw pumps is the low sound level of these pumps; the efficiency is not that high. Bent axis pumps Bent axis pumps, axial piston pumps and motors using the bent

22、 axis principle, fixed or adjustable displacement, exists in two different basic designs. The Thoma-principle (engineer Hans Thoma, Germany, patent 1935) with max 25 degrees angle and the Wahlmark-principle (Gunnar Axel Wahlmark, patent 1960) with spherical-shaped pistons in one piece with the pisto

23、n rod, piston rings, and maximum 40 degrees between the driveshaft centerline and pistons (Volvo Hydraulics Co.). These have the best efficiency of all pumps. Although in general the largest displacements are approximately one litre per revolution, if necessary a two-liter swept volume pump can be b

24、uilt. Often variable-displacement pumps are used, so that the oil flow can be adjusted carefully. These pumps can in general work with a working pressure of up to 350–420 bars in continuous work. Axial piston pumps swashplate principle Axial piston pumps using the swashplate principle (fixed and a

25、djustable displacement) have a quality that is almost the same as the bent axis model. They have the advantage of being more compact in design. The pumps are easier and more economical to manufacture; the disadvantage is that they are more sensitive to oil contamination. Radial piston pumps Radial

26、 piston pumps (fixed displacement) are used especially for high pressure and relatively small flows. Pressures of up to 650 bar are normal. In fact variable displacement is not possible, but sometimes the pump is designed in such a way that the plungers can be switched off one by one, so that a sort

27、 of variable displacement pump is obtained. Peristaltic pumps Peristaltic pumps are not generally used for high pressures. Pumps for open and closed systems Most pumps are working in open systems. The pump draws oil from a reservoir at atmospheric pressure. It is very important that there is no

28、cavitation at the suction side of the pump. For this reason the connection of the suction side of the pump is larger in diameter than the connection of the pressure side. In case of the use of multi-pump assemblies, the suction connection of the pump is often combined. It is preferred to have free f

29、low to the pump (pressure at inlet of pump at least 0.8 bars). The body of the pump is often in open connection with the suction side of the pump. In case of a closed system, both sides of the pump can be at high pressure. The reservoir is often pressurized with 6-20 bars boost pressure. For closed

30、 loop systems, normally axial piston pumps are used. Because both sides are pressurized, the body of the pump needs a separate leakage connection. Multi pump assembly In a hydraulic installation, one pump can serve more cylinders and motors. The problem however is that in that case a constant pres

31、sure system is required and the system always needs the full power. It is more economic to give each cylinder and motor its own pump. In that case multi pump assemblies can be used. Gearpumps can often be obtained as multi pumps. The different chambers (sometimes of different size) are mounted in on

32、e body or built together. Also vane pumps can often be obtained as a multi pump. Gerotor pumps are often supplied as multi pumps. Screw pumps can be built together with a gear pump or a vane pump. Axial piston swashplate pumps can be built together with a second pump of the same or smaller size, or

33、can be built together with one or more gear pumps or vane pumps (depending on the supplier). Axial plunger pumps of the bent axis design can not be built together with other pumps. 翻譯 液壓機械及泵 液壓機械是機械和工具,它使用流體的力量去做的工作。重型設備是一種常見的例子。 在這種類型的機器，高壓液 - 所謂的液壓油 - 是整個傳送機各種液壓馬達和液壓缸。流體是直接控制或自

34、動通過控制閥，并通過軟管和管分配。 液壓機械的普及是由于應用非常的大量，可以通過小管和軟管轉移，高功率密度和廣泛的執(zhí)行機構，可以使這項技術廣泛的使用。 液壓機械是由水力學，其中以液體為介質供電使用。氣動，在另一邊，是基于一種氣體作為動力傳輸，發(fā)電和控制媒介的使用。 液壓回路 對于液壓油做的工作，它必須對執(zhí)行機構的馬達，然后返回到一個水庫。流體過濾，然后再抽水。由液壓油所采取的路徑稱為一個液壓回路，其中有幾種類型。開放中心電路用泵的供應源源不斷。流返回到油箱，通過控制閥的開放中心，也就是說，當控制閥為中心，它提供了一個開放的返回路徑坦克和流體是不是被泵到高的壓力。否則，如果控制閥的流體驅

35、動它的路線和從驅動器和坦克。流體的壓力將上升，以應付任何反抗，因為該泵具有恒定的輸出。如果壓力上升過高，流體返回艙通過泄壓閥。 液壓泵液供應系統(tǒng)中的組成部分。發(fā)展中的系統(tǒng)壓力與負載的反應。因此，5000磅額定泵是維持對5000 磅潮流有一個約十倍以上的電動馬達（體積比）的功率密度更大的能力。它們均采用了電動馬達或引擎，通過齒輪，皮帶，彈性聯(lián)軸器或柔性連接以減少振動。 液壓泵的常用類型轉換為液壓機械應用; 齒輪泵：便宜，耐用，操作簡單。效率較低，因為他們是恒位移，主要用于低于20兆帕（3000磅）的壓力下使用。 葉片泵：便宜，簡單，可靠（特別是在G -轉子的形式）。良好的高流量低壓力輸出

36、。 軸向活塞泵：很多人用一個變量的機制設計，來改變輸出流量的壓力自動控制。有各種軸向活塞泵的設計，包括斜盤。最常見的是活塞泵斜盤：通常是用于一個非常高的壓力容器用在小流量泵。 活塞泵比齒輪泵或葉片昂貴，但提供更長的運行在更高的生活壓力，困難的液體和更長的連續(xù)工作周期。活塞泵組成的一個靜液壓傳動的一半。 控制閥 方向控制閥路由到所需的驅動器的液體。它們通常由一個內部的鑄鐵或不銹鋼外殼閥芯。 方向控制閥通常設計成可堆疊每一個閥液壓缸和一個液體輸入提供所有堆棧中的閥門。 閥芯位置可能由機械驅動的杠桿，液壓試驗壓力或螺線管這推動閥芯左或右。 主閥塊通常是一堆現(xiàn)成的定向控制流量閥的容量和性

37、能選擇。有些閥門被設計成比例（流量成比例閥的位置），而其他可能會在過簡單。控制閥是液壓回路的最昂貴的和敏感的地區(qū)之一。 泄壓閥用于液壓機械在幾個地方;在回路保持剎車的壓力，中試線等少量..對液壓缸，防止超載和液壓管破裂。對液壓水庫，以維持一個小的正壓力，排除水分和污染。 減壓閥減少供應壓力，對各種電路的需要。 止回閥是單向閥，允許蓄電池充電和維持其壓力后機關閉，例如。 平衡閥的其實是一種液控單向閥的特殊類型。而單向閥打開或關閉，平衡閥的行為像一個飛行員控制流量控制位。 液壓泵類型 [編輯]齒輪泵 齒輪泵（帶外齒）（固定位移）既簡單又經(jīng)濟的泵。波及體積或液壓齒輪泵的排量將由約一

38、立方厘米（0.001升）和二百立方厘米（0.2升）。這些泵創(chuàng)建通過齒輪嚙合，這迫使各地的齒輪流體加壓出口側的壓力。一些齒輪泵可以很嘈雜，相對于其他類型，但現(xiàn)代的齒輪泵是非?？煽?，而且比舊型號更安靜。 旋片泵 旋片泵（固定和簡單的可調位移）比齒輪泵高效率，但也為中壓力高達180條的一般使用。有些種類的葉片泵可以改變身體中心的風向標，使一個簡單的調節(jié)泵獲得。這些可調葉片泵一般或恒功率恒壓泵：位移，直到所需的壓力或動力，隨后到達的位移或波及體積減小直至達到平衡增加。 螺桿泵 螺桿泵（固定位移）是一種雙重阿基米德螺旋，但收盤。這意味著兩個螺絲是在一個機構使用。該泵用于高流動和相對低的壓力（最大

39、100巴）。它們被用在船上其中常數(shù)壓力的液壓系統(tǒng)，通過全船去，特別是對球的控制閥門，同時也為舵機和幫助驅動系統(tǒng)。螺桿的泵的優(yōu)點是低這些泵聲級;效率不高。 彎軸泵 彎曲軸泵，軸向柱塞泵和馬達軸彎曲使用的原則，固定或可調位移，在兩個不同的基本設計存在。在托馬原則（工程師漢斯托馬，德國，專利1935年），最大25度角，原則球型活塞（貢納爾阿克塞爾，專利1960年）在一個與活塞桿，活塞環(huán)，最大一塊40驅動軸之間的中心線和活塞（沃爾沃液壓有限公司）學位。這些都對所有水泵最佳效率。雖然在一般的最大位移約一公升，每轉，如有需要兩升的有效容積泵可建成。常變排量泵的使用，使油流可仔細調整。這些泵可以在一般工

40、作與高達350-420帕工作在連續(xù)的工作壓力。 軸向柱塞泵斜盤原則 軸向柱塞泵斜盤使用原則（固定和可調位移）有質量，幾乎是作為模型彎曲軸相同。他們具有更加緊湊的設計優(yōu)勢。這些泵更輕松，更經(jīng)濟地制造;缺點是較為敏感的石油污染。 徑向柱塞泵 徑向柱塞泵（固定排量）用于特別是高壓力和相對較小的流動。高達650帕的壓力是正常的。其實可變排量是不可能的，但有時泵就是在這樣一個柱塞可以關閉一個接一個，這樣一變排量泵得到排序方式設計。 蠕動泵 蠕動泵一般不用于高壓力。 開啟和關閉系統(tǒng)的泵 大多數(shù)泵工作在開放系統(tǒng)。吸引了來自該泵在大氣壓力下油藏。這是非常重要的，沒有在泵的吸入側蝕。基于這個原因

41、，泵的吸入端連接在比端連接直徑大的壓力。在多泵組合使用的情況下，泵的吸連接往往是相結合。這是首選有自由流動的泵（泵在入口壓力至少0.8兆帕）。該泵的機構往往與泵的吸入端打開的連接。 在一個封閉的系統(tǒng)的情況下，泵，雙方可在高壓力。該水庫是經(jīng)常加壓6-20條增加的壓力。對于閉環(huán)系統(tǒng)，通常軸向柱塞泵的使用。由于雙方都加壓，泵的身體需要一個單獨的泄漏連接。 多泵總成 在液壓裝置，一臺泵可以為更多的缸和馬達。但問題是，在這種情況下，一恒壓系統(tǒng)是必要的，系統(tǒng)總是需要的全部功能。這是更經(jīng)濟，讓每個氣缸和運動本身的泵。在這種情況下多泵組件都可以使用。通?？蔀槎啾?。在（不同大小有時）安裝在不同的分庭一體或建在一起。此外葉片泵通?？勺鳛橐粋€多泵。泵通常提供的為多泵。螺桿泵可建同一個齒輪泵或葉片泵。斜盤式軸向活塞泵可建連同相同或更小尺寸的第二泵，也可以建立一個或多個齒輪泵或葉片泵（對供應商而定）在一起。設計彎曲軸的軸向柱塞泵不能建立同其他泵。 10