Unit 19 Hydraulic Basic CircuitsContentslNew Words & Expressions lText & TranslationlComplex Sentence AnalysislKey to ExercisesNew Words & Expressions lpneumatic nju:mtik adj. 风动的， 气动的ldecompression di:kmpren n. 降压， 减压， 释放lregenerative ridenreitiv adj. 再生的， 新生的ltorque t:k n. 转矩，力矩，扭矩llubricator lu:brikeit n. 润滑剂, 加油器lmodification mdifikein n. 改装, 修订, 更改lcustomize kstmaiz v. 定制; 定做; 自定义lneutral nju:trl adj. 中立的, 中性的; 不确定的 n. 中位lpsi (pound per square inch) 气压单位（1 psi=6.89 kPa） New Words & Expressions lcylinder silind n. 气筒; 液压缸, 气缸lwelder weld n. 焊工; 电焊机lparallel prlel n. 平行, 平行线lsolenoid sulinid n. 螺线管lenergize endaiz v. 给与能量、电压, 使活跃lactuate ktjueit v. 开动（机器）, 驱动lcompensate kmpenseit v. 补偿, 赔偿ltraverse trv:s v. 横越, 转动, 在轴上旋转lmomentarily mumnterili adv. 短暂地, 临时地linitiate iniieit v. 开始; 创始Text & Translationl1Using schematic symbols as building blocks, you can construct a functional diagram showing piping arrangements and operation of any hydraulic or pneumatic circuit.lA number of circuits are used frequently in fluid power systems to perform useful functions. For example, metering circuits offer precise control of actuator speed without a lot of complicated electronics, decompression circuits reduce pressure surges within a hydraulic system by controlling the release of stored fluid energy, and pump-unloading and regenerative circuits make a system more energy efficient. Other circuits are designed for safety, sequencing of operations, and for controlling force, torque, and position. Still other circuits may enhance the application of specific components, such as pumps, motors, accumulators, filters, and airline lubricators.Text & TranslationlThe circuits appearing on the following pages are provided as a resource of general ideas. They may be used as: an educational resource to aid understanding of circuits already in use, a starting point for new designs, and as a modification to enhance operation of existing equipment.lThey certainly do not have to be implemented as shown. In fact, many of the circuits use purely mechanical components, so incorporating them into new or retrofit applications may involve integrating electronic feedback and control into the circuit as a modern alternative to mechanical control. 2However, many existing and new applications still gain the greatest benefit from mechanical controlespecially those applications where electricity could pose a threat to health and safety.Text & TranslationlHowever, whether using mechanical control or electronic, perhaps the greatest benefit may be gained by customizing one of these circuits to serve the specific requirements of an application.l1. Pressure-control circuitsl3When open- or tandem-center valves are used in circuits requiring pilot pressure to shift the valves, there must be a means of maintaining pressure when the valves are in neutral. One method is to install a backpressure check valve in the tank line. The check valve maintains a backpressure of, say, 50 psi.Text & TranslationlUsing two relief valves in this circuit gives two working pressures. On the up stroke of the cylinder, the low-pressure relief valve limits system pressure. During the down stroke, the high-pressure valve limits maximum press tonnage for doing work. Using the low-pressure relief on the up stroke saves power by supporting the cylinder with low-pressure fluid. Its illustrated by Fig. 19-1.Text & TranslationlIn a system with only one pump, reduced pressure for one branch of the circuit can be obtained with a pressure-reducing valve. 4This circuit is typical for a welder, which requires high clamping force to be set by the relief valve and reduced force on the welding gun to be set by the pressure-reducing valve. Placing the check valve in parallel with the pressure-reducing valve allows free return flow when the weld cylinder retracts. Its shown as Fig. 19-2.Text & TranslationFig. 19-1Two relief valves for two working pressures Text & TranslationFig. 19-2 Reduced pressure circuit for weldingText & Translationl2. Remote controllRegulating pump pressure from a remote station can be accomplished by using small, pilot relief valves connected to the systems main pilot-operated relief valve. In Fig. 19-3, with the 3-way solenoid valve de-energized, system pressure is limited to 1,500 psi in this circuit. Energizing the 3-way solenoid valve permits venting the relief valve to either 1,000 psi or 500 psi, depending on the position of the 4-way valve, which is determined by the pilot signal it receives.Text & TranslationFig. 19-3 Regulating pump pressure from a remote stationText & TranslationlIn Fig. 19-4, plot-operated relief valves provide two pressures for the mold-close cylinder and the injection cylinder of this plastic molding machine circuit. With the manual valve in neutral, the air-operated valves are actuated to extend the mold-close cylinder at a maximum pressure of 2,000 psi. Operating the manual valve to extend the injection cylinder vents the 400-psi relief to tank and vents the 2,000-psi relief at 400 psi. High-pressure fluid is held by the check valve.Text & TranslationFig. 19-4 Plot-operated relief valves in plastic molding machine circuitText & Translationl3. Pump-unloading circuitslWhen the open-center system is in neutral, pump output flows through the directional control valve to the tank. When this simple circuit handles only low flows and the directional valve spool has tapered lands, it proves to be very efficient. If several cylinders are used, the valve can be connected in seriesthat is, the tank port of one valve is connected to the pressure port of the next.Text & Translationl4. Pressure-compensated pumplA pressure-compensated, variable-volume pump is controlled by system pressure. As pressure increase, displacement of the pump decreases so that pump output at the preset pressure is only sufficient to make up for leakage. Used with a closed-center valve, the pump is stroked to minimum (zero) displacement when the valve is centered.Text & Translationl5. Hi-lo circuitlMany systems require a high volume at low pressure for rapid traverse of a vise or tool, and then low volume, high pressure for clamping or feeding. In Fig. 19-5, this can be accomplished by a hi-lo circuit using two pumps. During rapid traverse, both pumps supply the system. When pressure rises during clamping or feed, the large-volume main pump unloads, and the small pump maintains pressure. Output flow of the small pump is low enough to prevent heating of the oil. Instead of pilot operation, the unloading valve can be solenoid controlled and actuated by a pressure switch.Text & Translationl6. Sequencing circuitslCylinders may be sequenced by restricting flow to one cylinder. One method of restricting flow is with backpressure check valves. They prevent flow until a set pressure is reached. In this circuit as shown Fig. 19-6, cylinder 1 extends and retracts ahead of cylinder 2.lSeveral cylinders can be connected to move in sequence on forward and return strokes. In this circuit, a clamp must close before a drill descends. On the return stroke, the drill must pull out of the work before the clamp opens. The sequence valves are arranged to cause pressure buildup when one cylinder completes its stroke, the valve opens to allow flow to the other cylinder.Text & TranslationFig. 19-5Hi-lo circuit with both pumps Text & TranslationFig. 19-6Sequencing circuits and sequencing valve Text & Translationl7. Electrical controllLimit switches momentarily actuated by the cylinders control the solenoid valves to sequence this circuit. Solenoid is energized by a pushbutton to initiate movement 1. At the completion of movement 1, limit switch E is actuated to energize solenoid c, initiating movement 2. At the end of movement 2, limit switch F is actuated to energize solenoid b, initiating movement 3. At the end of this movement, limit switch G is actuated to energize solenoid d, initiating movement 4. The sequence valves prevent a pressure drop in either cylinder while the other operates. Its illustrated by Fig. 19-7.Text & TranslationFig. 19-7 Electrical circuit utilizing limit switches and solenoid valvesText & Translationl利用积木式的示意性符号，可以建立任意液压或者气压回路的管路系统和操作逻辑图。l大量的回路常常被用于液压系统中，以实现有效的功能。例如，在控制存储能量释放的液压系统中，测量回路为驱动器提供了精确的控制，不需要大量复杂的电路和减压回路来减少压力冲击，泵的卸载和循环回路使得系统具有更高的能量效率。其他回路的设计用来安全保护，顺序动作和控制压扭矩以及位置。还有一些其他回路可以用来提高特殊元件比如抽水泵、马达、压缩机、过滤器和线路润滑器的作用。Text & Translationl本文下面提到的这些回路主要作为一般概念的基础，这些回路可能用于：作为教育资源，辅助理解现有回路；作为新的回路设计的开端；同时也可以对已有设备进行修正，以提高其性能。l这些回路不是必须按照现实的那样来执行，事实上，很多回路纯粹是使用机械元件，所以把它们结合到新的或者改进的应用中，就会有除机械式控制外的另一个选择，那就是把集成电子反馈和控制包含到回路中。然而，许多存在的新的应用仍然从机械控制获得了最大的好处尤其是那些电气可能对健康和安全构成威胁时。Text & Translationl然而，是利用机械控制还是电气控制，在这些回路中定制去服务于某个应用的指定需要，或许可以获益最大。l1.压力控制回路压力控制回路l当在回路中用换向阀时，需要压力来开启阀，也就是阀在中位的时候必须要有一个保持压力。一个方法就是在油箱回油路上安装一个背压止回阀，这个止回阀保持一定的背压，比如每平方英寸50磅。Text & Translationl在回路中使用两个安全阀可以提供两个工作压力。在油箱的上升行程中，低压安全阀限制系统压力。在下降行程中，高压安全阀限制压力机工作过程中的最大吨位。在上升行程中使用低压安全阀可以提供液压缸低压液压油，以节省能量，如图19-1所示。l在只有一个液压泵的系统中，可以利用减压阀来减少回路中一个支路的压力。对于焊接装置来说，需要安装安全阀，以提供足够大的夹持力，同时用低压阀来降低焊枪的压力，此时减压回路就是典型的应用。将止回阀（单向阀）与减压阀平行安装，可以使焊接油缸自由平滑地缩回，如图19-2所示。Text & Translation图19-1两个减压阀提供两个工作压力 图19-2 焊接的减压回路Text & Translationl2.遥控遥控l与主回路先导阀相连接的小的先导阀可以在遥控站调节液压泵的压力。如图19-3所示，两位三通电磁阀失电，系统的压力被限制在每英寸1500磅。两位三通电磁阀得电导通，通过控制两位四通阀的换向，可以使安全阀的压力保持在每英寸1 000磅或者每英寸500磅。两位四通电磁阀的动作由它接收到的控制信号来决定。Text & Translation图19-3从遥控站调节泵压力Text & Translationl如图19-4所示，先导型安全阀为塑料模成型机的冲压油缸和注射油缸提供两种压力。手动换向阀处于中位时，开启气动两位二通换向阀，冲压油缸获得每英寸2000磅的最大压力。操纵手动换向阀，注射油缸获得每英寸400磅压力就会溢流回到油箱，同时主油路安全压力由每英寸2000磅降低到每英寸400磅，冲压油缸由单向阀保持高压力。Text & Translation图19-4 在塑料模成型机中的先导型安全阀Text & Translationl3.液压泵卸荷回路液压泵卸荷回路l当中位开式液压系统处于中位时，泵的输出流量通过方向控制阀回到油箱。当这个简单的回路仅仅在低流量下工作，方向控制阀的阀芯又是锥形的时候，中位开式液压系统效率会比较高。如果有多个油缸在工作，阀可以串连起来使用，也就是一个阀的回油口连到下一个阀的进油口。Text & Translationl4.压力补偿泵压力补偿泵l压力补偿变量泵是由系统压力控制的。当压力升高，泵的排量降低，这样液压泵在设定压力下的排量足够补偿泄露。使用一个中位闭式的阀，当阀处于中位时液压泵就能够将泵的压力调到最小或者零。Text & Translationl5.高低回路高低回路l工具或者夹具的快速行程，使得很多系统在低压下需要高流量，而在夹紧或者输送时，又需要高压低流量。如图19-5所示，这通过使用两个泵的高低回路来实现。快行程时，系统中两个泵工作。夹紧或输送时压力升高的时候，大流量主泵卸荷，小流量泵保持压力。小流量泵的输出流量足够防止油温的升高。相反在引导操作时，卸荷阀能够由电磁控制，利用压力开关驱动。Text & Translationl6.顺序回路顺序回路l一个液压缸的节流可以使多个液压缸顺序驱动。节流的一个方法就是背压止回阀（单向阀），它只有当压力达到一定的时候才会开始。如图19-6所示的回路中，液压缸1 在液压缸2之前伸长和缩回。Text & Translation图19-5 双泵高低回路 Text & Translation图19-6 顺序回路和顺序控制阀Text & Translationl几个液压缸可以连在一起按照进程和回路顺序运动。在这个回路中，在钻孔机下来之前夹具要夹紧。回程时，钻头必须在夹具松开之前拔出。顺序阀就是用来完成蓄压的，当一个油缸完成工作行程后，顺序阀打开，使液压油流向另一个油缸。l7.电控电控l由液压缸触发的限位开关控制电磁阀来完成顺序回路。一个按钮触发电磁铁动作开始动作1，动作1完成后，限位开关E触发使电磁铁c得电，开始动作2，在动作2完成的时候，限位开关F 触发使电磁铁b得电，开始动作3，动作3完成时，触发限位开关G使电磁铁d得电，开始动作4。在一个液压缸动作时，顺序阀防止另一个液压缸的压力降低，如图19-7所示。Text & Translation图19-7 利用限位开关和电磁铁的电控回路Complex Sentence Analysisl1 Using schematic symbols as building blocks, you can construct a functional diagram showing piping arrangements and operation of any hydraulic or pneumatic circuit. 利用积木式的示意性符号，可以建立任意液压或者气压回路的管路系统和操作逻辑图。l Using schematic symbols as building blocks：现在分词短语做状语, 表示条件, 相当于“If you use schematic symbols”l showing piping arrangements and operation：a functional diagram的后置定语，相当于“which shows piping arrangements and operation”Complex Sentence Analysisl2 However, many existing and new applications still gain the greatest benefit from mechanical control especially those applications where electricity could pose a threat to health and safety. 然而，许多存在的新的应用仍然从机械控制获得了最大的好处尤其是那些电气可能对健康和安全构成威胁时。l gain the benefit from：从 获得好处；获益l pose a threat to：对构成威胁。此外，pose 还可以与很多名词搭配，表示“提出，造成，引起”的意思Complex Sentence Analysisl3 When open- or tandem-center valves are used in circuits requiring pilot pressure to shift the valves, there must be a means of maintaining pressure when the valves are in neutral. 当在回路中用换向阀时，需要压力来开启阀，也就是阀在中位的时候必须要有一个保持压力。l requiring pilot pressure to shift the valves：circuits的后置定语，相当于“which require pilot pressure to shift the valves”Complex Sentence Analysisl 4 This circuit is typical for a welder, which requires high clamping force to be set by the relief valve and reduced force on the welding gun to be set by the pressure-reducing valve. 对于焊接装置来说，需要安装安全阀，已提供足够大的夹持力，同时用低压阀来降低焊枪的压力，此时减压回路就是典型的应用。l be typical for：对来说是典型的，具有代表性的l which requires high clamping force to be set：非限定性定语从句，先行词是welderKey to Exercisesl.Translate the following phrases into Chinese or English.l1. 液压基本回路l2. pneumatic circuit l3. 测量回路l4. decompression circuit l5. 循环回路l6. remote control l7. 先导安全阀 l8. pump-unloading circuit l9. 压力补偿泵l10. hi-lo circuitKey to Exercisesl.Mark the following statements with True (T) or False (F) according to the text.l1. F l2. T l3. T l4. Fl5. TKey to Exercisesl.Fill in the blanks with the suitable words or phrases given below.l1. obtainedl2. is typical forl3. setl4. in parallell5. retractsKey to Exercisesl.Translate the Chinese parts given in the brackets into English.l1. pump-unloading and regenerative circuits make a system more energy efficientl2. as a modification to enhance operation of existing equipmentl3. Regulating pump pressure from a remote station can be accomplishedl4. pump output at the preset pressure is only sufficient to make up for leakagel5. the large-volume main pump unloads, and the small pump maintains pressurelThe end!