机械专业毕业设计外文翻译流量控制阀容积控制

1、外 文 翻 译 姓 名： 学 号：200540401234 班 级：机械05-2 指导老师： 二零零九年四月一号 流量控制阀容积控制容积或流量控制阀用于调整速度。油缸的速度依靠单位时间内进入的油液的多少。通过各种各样的活塞泵或柱塞泵，流量调整是可能的，但是在许多回路当中，最常用到的是活塞泵或柱塞泵的复合型或调整流量的容积控制阀。 流量控制方法有三种应用容积控制阀来控制油缸速度的基本方法。它们是：进口节流、出口节流和旁路节流。进口节流式回路 在压力管路中的液压调节操作中，流量控制阀被放在泵和油源中间。通过这种方式，它控制流入油缸的液体数量。泵传输的多余的油液流经溢流阀流入油箱。通过安装有流量控制

2、阀的缸套看出，在某一方面的流量是可以控制的。流量控制当中必须包括单向阀或单向阀被并联在回油管路中。如果希望在两个方向控制速度，流量控制阀应安装在泵的出口管道中优于定向阀。进口节流的方式是最精确的。它用在油缸持续负载的情况中。例如，提升加载的垂直放置的液压缸或者在一定速度下推动的负载。出口节流式回路 出口节流控制用在负载可能突然撤消的情况中。这种流量控制元件被安装在需要抑制从油缸中排进流量的地方。两个方向调整速度的阀被安装在油箱管路中不同于定向阀。出口节流控制经常在单方向调整速度中用到，它在管路中被放在油箱和定向阀之间。为使油缸快速回程，这里要求配置一个旁路单向阀。旁路节流式回路 在回路节流装置

3、中，流量控制位于泵的供给的三通下方。它通过计算泵输出到油箱的量的大小决定油缸的速度。优点是泵在工作中获得的压力下工作，即使有过量的液体通过流量控制阀而不是溢流阀流回油箱。 缺点是：采用旁路节流时，被控制量是进入油箱的流量，而不是进入液压缸的流量，因而，由于工作载荷的变化，泵对液压缸的供液量也会发生变化。 旁路节流回路不应该安装在负载突然消失的装置中。 流量控制类型 流量控制阀分为两种基本类型：压力补偿型和非压力补偿型。后者常用在负载压力相对稳定。进给速度要求不严格的地方，它们与固定节流孔或可调节针阀一样简单，尽管包括了更多复杂的元件甚至一个可以反向自由流动的单向阀。非压力补偿阀的应用回受到某种

4、程度的限制。既然通过它流经节流口后的压力损失与平方根成比例关系。这意味着工作负载的任一明显变化将会影响进程速度。压力补偿流量控制阀又进一步分为节流型和旁通型。这两个类型的压力补偿流量控制阀都是通过调节节流阀，利用差动安置或液压静力学来维持一个恒定的压力损失。图3-22所示为通过压力补偿控制流量的旁通联合过载保护装置。它有一个常闭的液压静力学部件，当超过节流阀的调整值时，其打开使液体流回油箱。通过工作载荷获得的压力在液压静力学部件上方的工作腔里被感觉到，并且通过一个刚度较小的弹簧使旁通型的压力补偿流量阀关闭。液压静力学部件下方工作腔里的压力增加时将导致节流阀节流，和引起的多余的流量引入油箱，当不

5、同的压力足够克服弹簧的作用功。不同的是，它能保持20psi的压力。不管工作载荷多大，通过节流阀可获得一个稳定的流量。由于泵的运转仅需20psi，超过工作载荷的压力，节省了一些功能。 图 3-22 进口节流阀通过调节加载提动阀芯的弹簧限制液压静力学部件上方的最大压力来实现过载保护，不论什么时候工作载荷超过调定值时，它会产生一种和复合式溢流阀相同的功能。旁通流量控制阀只被用在进口节流回路。如果用在出口节流回路，排出的油液不会通过节流阀，而将会流回油箱，使得载荷消失。依靠液压静力学部件时，通过节流阀，节流型流量控制装置也可保持一个稳定的差动压力。图3-23在这个阀中，液压静力学部件是常开的。阻断超过

6、节流阀调定流量，将会关闭。在这些部件中，工作载荷压力与液压静力学装置上方的刚度教小的弹簧共同使用使阀常开。节流阀入口和液压静力学下方的压力使其关闭，仅允许油液进入20psi通过的节流阀。 图 3-23 节流型流量控制装置当流量超过节流阀的调定值时，它们将会关闭。所以节流型压力补偿流量控制阀可能会被用在进口节流、出口节流和旁路节流回路。不象旁通型，两个或更多的节流型阀会被用在相同的泵中，既然多余的泵输出量通过溢流阀流回油箱。给液压缸管路布置一个整体的单向阀任意地给回程提供流量（图3-24）。当它们用在旁路节流回路中，或者在供给线路和定向阀的油箱管路中，它是不能实现的。温度补偿流量控制阀流经压力补

7、偿流量控制阀油掖温度必定会有不同程度的变化。后来维氏设计的具有温度补偿的特性的阀。尽管当油温升高时，油液自由流动，但当油温升高时要获得稳定的流量必须减小节流阀孔口面积。这是通过补偿杆在油温升高变长，油温降低时变短来完成的。节流阀是一个简单的，可以移进和移出控制孔口的滑阀。这个补偿杆被安装在节流阀和调节器之间。这个设计在反向自由流动单向阀中也适合。远程流量控制阀 远程流量控制阀通过电信号来调节节流阀孔口的尺寸。节流滑阀与力矩马达的电枢连接。当力矩马达对信号产生反应时就会转动。与压力补偿流量控制阀的操作是相同的。 图 3-24 流量控制阀和单向阀 flow-control valvesvolume

8、 controlsvolume or flow control valves are used to regulate speed. the speed of an actuator depends on how much oil is pumped into it per unit of time. it is possible to regulate flow with a variable displacement pump, but in many circuits it is more practical to use a fixed displacement pump and re

9、gulate flow with a volume control valve.flow control methodsthere are three basic methods of applying volume control actuator speeds. they are meter-in, meter-out and bleed-off.meter-in circuit in meter-in operation, the flow control valve is placed between the pump and actuator. in this way, it con

10、trols 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 in the cylinder line as shown, flow is controlled in one direction. a check valve must be included in the flow control or p

11、laced in parallel with it for return flow. if it is desired to control speed in both directions, the flow control can be installed in the pump outlet line prior to the directional valve.the meter-in method is highly accurate. it is used in applications where the load continually resists movement of

12、the actuator, such as raising a vertical cylinder load or pushing a load at a controlled speed.meter-out circuit meter-out 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 regular speed in both directions,

13、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 directional valve. here too a bypass check valve would be required for a rapid return stroke.bleed-off circuit in a bleed-off a

14、rrangement, the flow control is teed off the supply line from the pump and determines the actuator speed by metering 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 inste

15、ad of through the relief valve.its disadvantage is some loss of accuracy because the measured flow is to tank rather than into the cylinder, making the latter subject to variations in the pump delivery due to changing work loads.bleed-off circuits should not be used in applications where there is a

16、possibility of the load running away.types of flow controlsflow control valves fall into two basic categories: pressure compensated and non-pressure compensated. the latter being used where load pressures retain relatively constant and feed rates are not too critical. they may be as simple as a fixe

17、d orifice or an adjustable needle 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 limited, since flow through an orifice is essentially proportional to the square root of the pressure d

18、rop (p) across it. this means that any appreciable change in the work load would affect the feed rate.pressure compensated flow controls are further classified as restrictor and by-pass types. both utilize a compensator or hydrostat to maintain a constant pressure drop across an adjustable throttle.

19、the by-pass type-combines overload protection with pressure compensated control of flow (fig.3-22). it has a normally closed hydrostat which opens to divert fluid, in excess of the throttle setting, to the tank. pressure required by the work load is sensed in the chamber above the hydrostat and toge

20、ther with a light spring tends to hold it closed. pressure in the chamber below the hydrostat increases due to the restriction of the throttle and causes it to raise diverting any excess flow to tank when the difference in pressure is sufficient to overcome the spring. this difference, usually 20 ps

21、i, is maintained across the throttle providing a constant flow regardless of the work load. some horsepower saving is accomplished in that the pump need operate at only 20 psi above work load pressure.overload protection is provided by an adjustable spring loaded poppet which limits the maximum pres

22、sure above the hydrostat, causing it to function as a compound relief valve whenever work load requirement excess its setting. the by-pass flow control can only be used in a meter-in circuit. if used for metering out, exhaust oil which could not get through the throttle would be diverted to tank per

23、mitting the load to run away. figure 3-22 flow control and relief valve meter in figure 3-23 pressure compensated restrictor type flow controlthe restrictor type flow control-also maintains a constant 20 psi differential across its throttle by means of a hydrostat (fig.3-23). in this valve, the hydr

24、ostat is normally open and tends to close off blocking all flow in excess of the throttle setting. in these units, the work load pressure acts with a light spring above the hydrostat to hold it open. pressure at the throttle inlet and the hydrostat tends to close it, permitting only that oil to ente

25、r the valve that 20 psi can force through the throttle.because of their tendency to close off when flow tried 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, two or more restrictor valves may be used with same

26、 pump since the excess pump delivery returns to tank through the relief valve.when placed in cylinder lines an integral check valve is optional to provide free flow for a rapid return stroke (fig.3-24). 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.temperature compensated flow control valveflow through a pressure compensated flow control valve is subject to change with variations in oil temperature. later de