Chapter 13 Applying Hydraulic Power Typical Circuits and Systems 1
Objectives Name common, basic subsystems that compose complex hydraulic systems and describe their function. Compare the design and operation of basic pressure control circuits. Contrast the operating characteristics of meterin, meter-out, and bleed-off flow control circuits. Goodheart-Willcox Co., Inc. 3 Objectives Compare the design and operation of several typical lflow control circuits. it Compare the design and operation of basic motion control circuits. Describe the design and operation of rapid- advance-to-work circuits. Goodheart-Willcox Co., Inc. 4 2
Objectives Describe various hydraulic circuits designed to provide for operator safety and the protection ti of system components. Goodheart-Willcox Co., Inc. 5 Basic Circuits and Their Use in System Analysis and Design Hydraulic systems involve a group of components that closely work together to produce a desired performance Pressure control Flow control Motion control Miscellaneous functions A hydraulic system typically includes several of these segments Goodheart-Willcox Co., Inc. 6 3
Design and Operation of Basic Pressure-Related Circuits Basic pressure-control circuits limit the maximum operating pressure of a hydraulic system Variations of this function include circuits that can: Control pressure from a remote location Provide for the selection of multiple pressures in a single circuit Goodheart-Willcox Co., Inc. 7 Design and Operation of Basic Pressure-Related Circuits A basic pressure-control circuit Goodheart-Willcox Co., Inc. 8 4
Design and Operation of Basic Pressure-Related Circuits Remote pressure control in a circuit Goodheart-Willcox Co., Inc. 9 Design and Operation of Basic Pressure-Related Circuits Multiple operating pressures can be achieved for a system by using a compound relief valve The venting feature is combined with additional low-flow-capacity, direct-operated relief valves Goodheart-Willcox Co., Inc. 10 5
Design and Operation of Basic Pressure-Related Circuits Multiple pressures in a circuit Goodheart-Willcox Co., Inc. 11 Design and Operation of Basic Pressure-Related Circuits Reduced pressure in a circuit Goodheart-Willcox Co., Inc. 12 6
Design and Operation of Basic Pressure-Related Circuits With open- and tandem-center directional control valves, a spring-loaded check valve may be placed in the return line to create low back pressure Maintains low system pressure necessary to operate pilot-controlled functions This variation still produces an energy-efficient circuit that is a feature of these valve center designs Goodheart-Willcox Co., Inc. 13 Design and Operation of Basic Pressure-Related Circuits Back-pressure check valve Goodheart-Willcox Co., Inc. 14 7
Design and Operation of Basic Three basic flow control circuits are used in hydraulic systems: Meter in Meter out Bleed off These basic circuits meet the varying flowcontrol demands for systems with positive and negative loads Goodheart-Willcox Co., Inc. 15 Design and Operation of Basic The meter-in flow control design places the flow control valve between the pump and the inlet of the actuator Should only be used for positive loads Cannot provide accurate control under a negative load condition The prime mover is always operating against the maximum pressure setting of the system relief valve Goodheart-Willcox Co., Inc. 16 8
Design and Operation of Basic Basic meter-in circuit Goodheart-Willcox Co., Inc. 17 Design and Operation of Basic The meter-out flow control design places the flow control valve between the actuator t outlet t and the reservoir Can provide accurate control for positive and negative loads The prime mover is always operating against the maximum pressure setting of the system relief valve Goodheart-Willcox Co., Inc. 18 9
Design and Operation of Basic Basic meter-out circuit Goodheart-Willcox Co., Inc. 19 Design and Operation of Basic The bleed-off flow control design places the flow control valve in a tee in the working line between the directional control valve and the actuator inlet Outlet of the flow control is directly connected to the reservoir Measured flow is diverted to the reservoir while remaining flow operates the actuator The prime mover operates against a pressure only high enough to move the load Goodheart-Willcox Co., Inc. 20 10
Design and Operation of Basic Basic bleed-off circuit Goodheart-Willcox Co., Inc. 21 Design and Operation of Basic Meter-in and meter-out circuits provide the most accurate actuator speeds Both meter fluid flow delivered directly to or from the actuator The meter-out circuit is the best method for negative loads that may pull the actuator Goodheart-Willcox Co., Inc. 22 11
Design and Operation of Basic The bleed-off flow control circuit is less accurate than either the meter-in or meter-out t system Flow is metered back to the reservoir while the remaining pump output establishes actuator speed The remaining flow can vary because of pump efficiency and system leakage Flow control valve metering accuracy under varying load conditions is also a factor Goodheart-Willcox Co., Inc. 23 Design and Operation of Basic The bleed-off circuit is the most energy- efficient i design This is due to the fact the prime mover operates at a pressure only high enough to move the load Goodheart-Willcox Co., Inc. 24 12
Design and Operation of Other Several other circuit designs can also be used to control lflow to a circuit itactuator t High-low pump circuit Regenerative-cylinder-advance circuit Rapid-advance-to-work circuit Goodheart-Willcox Co., Inc. 25 Design and Operation of Other The high-low pump circuit allows a system to use two pumps in tandem Provides high-volume flow during low-pressure demand Provides low-volume flow during high-pressure demand Lowers equipment costs by reducing prime mover size and cuts ongoing system energy consumption Goodheart-Willcox Co., Inc. 26 13
Design and Operation of Other High-low pump circuit Goodheart-Willcox Co., Inc. 27 Design and Operation of Other A regenerative-cylinder-advance circuit provides a rapid advance to the point where a load is encountered Fluid is recirculated from the rod end into the blind end and coupled with pump output to increase flow into the blind end, thus increasing cylinder extension speed Recirculation is possible due to the difference in area between the cylinder piston ends Goodheart-Willcox Co., Inc. 28 14
Design and Operation of Other Regenerative-cylinder-advance circuit Goodheart-Willcox Co., Inc. 29 Design and Operation of Other During the rapid-extension phase of a regenerative circuit, it the effective force is limited to the maximum pressure setting of the system multiplied by the cross-sectional area of the cylinder rod Goodheart-Willcox Co., Inc. 30 15
Design and Operation of Other A mechanically activated deceleration valve is often used in rapid-advance-to-work d circuits it This controls the rate at which the advancing cylinder is slowed from the rapid-advance speed to the slower feed rate Goodheart-Willcox Co., Inc. 31 Design and Operation of Other Application of a deceleration valve Goodheart-Willcox Co., Inc. 32 16
Design and Operation of Basic Motion-Related Circuits Sequence circuits operate actuators in a specific order Two common methods for actuator sequencing are: Spring-loaded check valves Specially designed sequence valves Goodheart-Willcox Co., Inc. 33 Design and Operation of Basic Motion-Related Circuits Check valves are inexpensive Valves designed for specific sequence control provide more accurate movement Goodheart-Willcox Co., Inc. 34 17
Design and Operation of Basic Motion-Related Circuits Sequencing with spring-loaded check valves Goodheart-Willcox Co., Inc. 35 Design and Operation of Basic Motion-Related Circuits Specially constructed pressure control valves can be used to sequentially block fluid flow to actuators When a preselected pressure is reached, these valves open to allow fluid flow to the actuator This provides the order of operation Check valves allow reverse flow around these pressure control valves Goodheart-Willcox Co., Inc. 36 18
Design and Operation of Basic Motion-Related Circuits Sequencing with special valves Goodheart-Willcox Co., Inc. 37 Design and Operation of Basic Motion-Related Circuits Synchronizing the movement of cylinders requires accurately metering fluid idflow into the actuators Accurate flow control valves Other metering devices, such as mechanically connected hydraulic motors Goodheart-Willcox Co., Inc. 38 19
Design and Operation of Basic Motion-Related Circuits Synchronization with accurate flow control valves Goodheart-Willcox Co., Inc. 39 Design and Operation of Basic Motion-Related Circuits Synchronization with mechanically coupled motors Goodheart-Willcox Co., Inc. 40 20
Design and Operation of Circuits with Other Functions Two factors that are basic to motor operation are: Fluid flow rate establishes motor speed Pressure establishes torque output Other factors must also be considered: Motor freewheeling Motor braking Goodheart-Willcox Co., Inc. 41 Design and Operation of Circuits with Other Functions Motor control circuits with a three-position directional control valve can allow a hydraulic motor to: Rotate with full speed and torque capability Freewheel using the inertia of the load to sustain rotation Brake to a stop under controlled conditions Goodheart-Willcox Co., Inc. 42 21
Design and Operation of Circuits with Other Functions Circuit allowing a motor to be powered, braked, or to freewheel Goodheart-Willcox Co., Inc. 43 Design and Operation of Circuits with Other Functions Decompression circuits release the pressures from the expansion and contraction ti of components and the external loading of actuators These high pressures can exist even when the power unit is not operating Decompression is for both operator safety and the continued functioning of the system Goodheart-Willcox Co., Inc. 44 22
Design and Operation of Circuits with Other Functions Decompression circuits often use staged, pilot-operated tdcheck valves Pressurizing the first stage opens a small orifice that quickly reduces the high system pressure The pilot mechanism continues to open the check valve, exposing a larger orifice that allows the rapid movement of system fluid to the reservoir Goodheart-Willcox Co., Inc. 45 Design and Operation of Circuits with Other Functions Decompression circuit on a platen press Goodheart-Willcox Co., Inc. 46 23
Design and Operation of Circuits with Other Functions Safety is always a factor when designing hydraulic circuits it High pressures High fluid flow rated Substantial forces Rapid movement of system components Inappropriate use of any of these elements can produce a dangerous work situation for a machine operator Goodheart-Willcox Co., Inc. 47 Design and Operation of Circuits with Other Functions Safety-related circuits ensure: Equipment can be operated without injury Equipment cannot unexpectedly operate Costly equipment is protected against excessive pressure and operating rates Goodheart-Willcox Co., Inc. 48 24
Design and Operation of Circuits with Other Functions Two-hand safety circuit for machine operator safety Goodheart-Willcox Co., Inc. 49 Review Question Remote control of pilot-operated relief valves can be easily achieved dby using the feature of the valve. vent Goodheart-Willcox Co., Inc. 50 25
Review Question A maximum pressure lower than the system relief valve setting may be obtained in a portion of a circuit by using a(n) valve. pressure-reducing Goodheart-Willcox Co., Inc. 51 Review Question Name the three characteristics of basic flow control circuits it that tneed dto be considered d when selecting a design for use in a hydraulic system. A. Accuracy of flow control, B. operating efficiency, and C. ability to control varying loads. Goodheart-Willcox Co., Inc. 52 26
Review Question Which flow control circuit is considered the most energy efficient? i Bleed-off circuit. Goodheart-Willcox Co., Inc. 53 Review Question Describe two methods that may be used to synchronize the movement of ftwo or more hydraulic cylinders. A. Use of two hydraulic motor with a mechanical coupling between their output shafts and B. use of accurate pressurecompensated flow control valves. Goodheart-Willcox Co., Inc. 54 27
Review Question How is rapid cylinder advance created in a regenerative-cylinder-advance d circuit? it? Fluid from the rod end of the cylinder is directed to the blind end to increase the amount of fluid flow available to extend the cylinder. Goodheart-Willcox Co., Inc. 55 Review Question Name three factors that hydraulic safety circuits ensure. A. Equipment can be operated without injury, B. equipment cannot unexpectedly operate, and dc. Costly equipment is protected against excessive pressure and operating rates. Goodheart-Willcox Co., Inc. 56 28
Glossary Back-pressure check valve A spring-loaded d check valve used with some pilotcontrolled hydraulic systems to maintain sufficient pressure during the idle portion of the cycle to shift directional control valves. Goodheart-Willcox Co., Inc. 57 Glossary Bleed-off circuit A hydraulic speed-control circuit in which the required flow rate to the actuator is set by returning unneeded pump output directly to the reservoir through a flow control valve. Goodheart-Willcox Co., Inc. 58 29
Glossary Deceleration valve A control valve specifically designed to allow maximum, deceleration, and feed flow rates. The valves often use mechanical activation and a check valve that allows an unrestricted return flow rate. Goodheart-Willcox Co., Inc. 59 Glossary High-low pump circuit A circuit using two fixed-displacement pumps. The pumps are connected, with appropriate pressure control valves, to provide a high-volume flow at low pressure and a low-volume flow when high pressure is required to operate a system. Goodheart-Willcox Co., Inc. 60 30
Glossary Maximum operating pressure The highest pressure recommended for operation of a hydraulic or pneumatic system. Meter-in circuit A fluid power flow-control circuit in which fluid is metered into an actuator to control operating speed. Goodheart-Willcox Co., Inc. 61 Glossary Meter-out circuit A fluid power flow-control circuit in which fluid is metered out of an actuator to control operating speed. Goodheart-Willcox Co., Inc. 62 31
Glossary Rapid-advance-to-work circuit A fluid power circuit design that allows a tool or other machine element to rapidly move to a preset position, slow to a point where machining is to occur, and then move at an accurate cutting speed. May also allow rapid retraction of the work elements. Goodheart-Willcox Co., Inc. 63 Glossary Regenerative-cylinder-advance circuit A hydraulic circuit design in which fluid discharged from the rod end of a cylinder combines with pump delivery and is directed to the cylinder blind end. The design results in increased cylinder extension speed, but reduced force capability. Goodheart-Willcox Co., Inc. 64 32
Glossary Remote location A location for control components that is beyond the distance usually used for placement of components on machines. Sequence The order in which various valve and actuator functions occur in a fluid power circuit. Goodheart-Willcox Co., Inc. 65 Glossary Synchronization The timing of one movement or operation with another, such as the identical movement of two actuators operating in a fluid power circuit. Goodheart-Willcox Co., Inc. 66 33
Glossary Two-hand safety circuit A fluid power circuit in which machine activation and continued operation requires both hands of the machine operator to continuously depress control valves. Goodheart-Willcox Co., Inc. 67 34