机械 外文翻译 外文文献 英文文献 液压机械及泵

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 hydraulic 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 wide 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 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

continuous flow. The flow is returned to tank through the control valve's 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 tank. The fluid's 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 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 coupling 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 (especially 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 swashplate 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 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 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 and 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 machinery; 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 reducing 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. Whereas 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 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 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 simple 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 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 through 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 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 piston 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 built. 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 adjustable 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 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 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 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 flow 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 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 pressure 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 one 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 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.

翻译

液压机械及泵

液压机械是机械和工具,它使用流体的力量去做的工作。重型设备是一种常见的例子。

在这种类型的机器，高压液- 所谓的液压油- 是整个传送机各种液压马达和液压缸。流体是直接控制或自动通过控制阀，并通过软管和管分配。

液压机械的普及是由于应用非常的大量，可以通过小管和软管转移，高功率密度和广泛的执行机构，可以使这项技术广泛的使用。

液压机械是由水力学，其中以液体为介质供电使用。气动，在另一边，是基于一种气体作为动力传输，发电和控制媒介的使用。

液压回路

对于液压油做的工作，它必须对执行机构的马达，然后返回到一个水库。流体过滤，然后再抽水。由液压油所采取的路径称为一个液压回路，其中有几种类型。开放中心电路用泵的供应源源不断。流返回到油箱，通过控制阀的开放中心，也就是说，当控制阀为中心，它提供了一个开放的返回路径坦克和流体是不是被泵到高的压力。否则，如果控制阀的流体驱动它的路线和从驱动器和坦克。流体的压力将上升，以应付任何反抗，因为该泵具有恒定的输出。如果压力上升过高，流体返回舱通过泄压阀。

液压泵液供应系统中的组成部分。发展中的系统压力与负载的反应。因此，5000磅额定泵是维持对5000 磅潮流有一个约十倍以上的电动马达（体积比）的功率密度更大的能力。它们均采用了电动马达或引擎，通过齿轮，皮带，弹性联轴器或柔性连接以减少振动。

液压泵的常用类型转换为液压机械应用;

齿轮泵：便宜，耐用，操作简单。效率较低，因为他们是恒位移，主要用于低于20兆帕（3000磅）的压力下使用。

叶片泵：便宜，简单，可靠（特别是在G -转子的形式）。良好的高流量低压力输出。

轴向活塞泵：很多人用一个变量的机制设计，来改变输出流量的压力自动控制。有各种轴向活塞泵的设计，包括斜盘。最常见的是活塞泵斜盘：通常是用于一个非常高的压力容器用在小流量泵。

活塞泵比齿轮泵或叶片昂贵，但提供更长的运行在更高的生活压力，困难的液体和更长的连续工作周期。活塞泵组成的一个静液压传动的一半。

控制阀

方向控制阀路由到所需的驱动器的液体。它们通常由一个内部的铸铁或不锈钢外壳阀芯。

方向控制阀通常设计成可堆叠每一个阀液压缸和一个液体输入提供所有堆栈中的阀门。

阀芯位置可能由机械驱动的杠杆，液压试验压力或螺线管这推动阀芯左或右。主阀块通常是一堆现成的定向控制流量阀的容量和性能选择。有些阀门被设计成比例（流量成比例阀的位置），而其他可能会在过简单。控制阀是液压回路的最昂贵的和敏感的地区之一。

泄压阀用于液压机械在几个地方;在回路保持刹车的压力，中试线等少量..对液压缸，防止超载和液压管破裂。对液压水库，以维持一个小的正压力，排除水分和污染。

减压阀减少供应压力，对各种电路的需要。

止回阀是单向阀，允许蓄电池充电和维持其压力后机关闭，例如。

平衡阀的其实是一种液控单向阀的特殊类型。而单向阀打开或关闭，平衡阀的行为像一个飞行员控制流量控制位。

液压泵类型

[编辑]齿轮泵

齿轮泵（带外齿）（固定位移）既简单又经济的泵。波及体积或液压齿轮泵的排量将由约一立方厘米（0.001升）和二百立方厘米（0.2升）。这些泵创建通过齿轮啮合，这迫使各地的齿轮流体加压出口侧的压力。一些齿轮泵可以很嘈杂，相对于其他类型，但现代的齿轮泵是非常可靠，而且比旧型号更安静。

旋片泵

旋片泵（固定和简单的可调位移）比齿轮泵高效率，但也为中压力高达180条的一般使用。有些种类的叶片泵可以改变身体中心的风向标，使一个简单的调节泵获得。这些可调叶片泵一般或恒功率恒压泵：位移，直到所需的压力或动力，随后到达的位移或波及体积减小直至达到平衡增加。

螺杆泵

螺杆泵（固定位移）是一种双重阿基米德螺旋，但收盘。这意味着两个螺丝是在一个机构使用。该泵用于高流动和相对低的压力（最大100巴）。它们被用在船上其中常数压力的液压系统，通过全船去，特别是对球的控制阀门，同时也为舵机和帮助驱动系统。螺杆的泵的优点是低这些泵声级;效率不高。

弯轴泵

弯曲轴泵，轴向柱塞泵和马达轴弯曲使用的原则，固定或可调位移，在两个不同的基本设计存在。在托马原则（工程师汉斯托马，德国，专利1935年），最大25度角，原则球型活塞（贡纳尔阿克塞尔，专利1960年）在一个与活塞杆，活塞环，最大一块40驱动轴之间的中心线和活塞（沃尔沃液压有限公司）学位。这些都对所有水泵最佳效率。虽然在一般的最大位移约一公升，每转，如有需要两升的有效容积泵可建成。常变排量泵的使用，使油流可仔细调整。这些泵可以在一般工作与高达350-420帕工作在连续的工作压力。

轴向柱塞泵斜盘原则

轴向柱塞泵斜盘使用原则（固定和可调位移）有质量，几乎是作为模型弯曲轴相同。他们具有更加紧凑的设计优势。这些泵更轻松，更经济地制造;缺点是较为敏感的石油污染。

径向柱塞泵

径向柱塞泵（固定排量）用于特别是高压力和相对较小的流动。高达650帕的