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1、Hydraulic and pneumatic pressure transmissionChapter 7 Basic Hydraulic Circuits 7.1 Pressure Control Circuits7.2 Speed Control Circuits 7.3 Directional Control Circuits7.4 Multi-actuator Control CircuitsChapter listIntroduction Any hydraulic system is constituted by several basic hydraulic circuits.
2、 A hydraulic basic circuit is a group of components. Lets classify: the functions in hydraulic system by: 1.pressure control circuits: control entire or partial operating pressure; 2.speed control circuits: control and regulate motion speed of actuator elements; 3.Directional control circuits: contr
3、ol and shift motion direction of actuator; 4.Multi-actuator control circuits: control and shift operating cycle between several actuators.7.1 Pressure Control Circuits 7.1.1 Pressure regulated circuits7.1.2 Pressure-venting circuits7.1.3 Pressure-reducing circuits7.1.4 Pressure-increasing circuits7.
4、1.5 Pressure counterbalance circuits7.1.6 Pressure-holding circuits Used to control and regulate the entire and partial pressure to realize a satisfied force and torque requirements, enhance working efficiency and improve the properties in a hydraulic system (six types shown in below) . 7.1.1 Pressu
5、re regulated circuits1. Pressure regulated from remote port Fig.7-1 a)Pressure regulated from remote port b)Multistage pressure regulated circuit c) Step less pressure regulated circuit 1-Relief-valve pilot 2,3-Pressure regulated valves 4-Directional valve 2. Multistage pressure regulated circuits A
6、s shown in Fig.7-1b.As shown in Fig.7-1c.3. Step less pressure regulated circuits7.1.2 Pressure-venting circuitsThe functionThe methods The function of a pressure venting circuit is to unload the pumping and to keep the pump idling when the hydraulic system is during the regular off-working, which i
7、t will realize to save the energy, reduce the heating and get a long life of use. There are two methods of unloaded pump: one is venting by pressure (pump operating under zero or near zero pressure, is called the pressure-venting) and the other is venting by flow rate (pump operating under zero or n
8、eat zero flow rates, is called flow-venting). 1. Pressure-venting by the neutral of a directional valveFig.7-2a Pressure-venting by the neutral of a directional valveFig.7-2b Pressure-venting by a solenoid operated relief valveFig.7-2c Pressure-venting by a pump limited pressure Fig.7-2d Pressure-ve
9、nting by an accumulator2. Pressure-venting by pilot -operated relief valve As shown in Fig.7-2b. 3. Pressure-venting by a pump limited pressure As shown in Fig.7-2c.4. Pressure-venting by an accumulatorAs shown in Fig.7-2d.7.1.3 Pressure-reducing circuits The function: Used to drop a stable branch c
10、ircuit pressure below the normal operating pressure of system. Usually a fixed pressure-reducing valve is installed to a branch circuit such as Fig. 7-3a. Fig. 7-3b is a two-stage pressure-reducing circuit. To ensure a stable working speed, the lowest pressure should not be less than 0.5MPa, and the
11、 highest setting pressure should be at least less than 0.5MPa of the system pressure. When the actuator elements speed in a reducing-circuit needs to be regulated, the speed-regulating valve should be installed in the latter of the reducing-valve in order to avoid the affection of speed during the w
12、orking.1,6- Pilot-operated pressure-reducing valve 2- Rated pressure-reducing valve 3- Check valve 4- Hydraulic cylinder 5-Two positions with two-ports directional valve Fig.7-3 a)One-stage pressure-reducing b) Two-stage pressure-reducing 7.1.4 Pressure-increasing circuits Fig.7-4 a)Single action pr
13、essure-increasing circuit b) Bi-action pressure-increasing circuit 1. A pressure-increasing circuits by a single action pressure-increasinga)b)2. A pressure-increasing circuit by a tandem circuit As shown in Fig.7-4b.1. Counter-balance circuits done by a combined of check- sequence valve7.1.5 Pressu
14、re counterbalance circuits a)b)c)Fig.7-5 a) Counter-balance circuits done by a combined of check- sequence valve b) Counter-balance circuits done by a hydraulicoperated check valve c) Counter-balance circuits done by a hydraulic -operated sequence valve 2. Counter control-balance circuits done by a
15、hydraulic control-operated check valve 3. Counter control-balance circuits done by a hydraulic-operated sequence valve As shown in fig.7-5b.As shown in fig.7-5c.7.1.6 Pressure-holding circuits 1. A pressure-holding circuit by the electric-contact pressure switchFig.7-6a A pressure-holding circuit by
16、 the pressure-relay Fig.7-6b A pressure-holding circuit by the accumulator Fig.7-6c A pressure-holding circuit by the auxiliary pump 2. A pressure-holding circuits by the accumulator As shown in fig.7-6b.3. A pressure holding by the auxiliary pumpAs shown in fig.7-6c.7.2 Speed Control Circuits 7.2.1
17、 The principles of speed-regulating and control 7.2.2 Throttle speed-regulating circuits by a invariable displacement pump 7.2.3 Volume speed-regulating circuits7.2.4 Fast-speed movement circuits7.2.5 Speed shift circuit Speed control circuits, are the important parts in a hydraulic system, aim at r
18、egulating the motion speed of the actuator elements. 7.2.1 The principles of speed-regulating and control The main types of actuators are hydraulic cylinders and motors in a hydraulic system. So there are two cases under the situations of oil compressibility and leakage are neglected:The speed of a
19、hydraulic cylinder is： The speed of a hydraulic motor is： For a hydraulic cylinder, the speed regulating can be done only by regulating the input flow rate of the cylinder. However for a hydraulic motor the speed regulating can be done by both of the two methods , i.e., input flow rate or exit displ
20、acement of motor. 1. Inlet throttle speed-regulating circuitsFig.7-7a)A inlet throttle speed-regulating circuit b)A outlet throttle speed-regulating circuit7.2.2 Throttle speed-regulating circuits by a invariable displacement pump a)b)（1 1）The features of speed-load The motion speed of a hydraulic c
21、ylinder is ： Flowing rate into the throttle orifice valve is: （7-1）（7-2）Then the force balance equation in piston is（7-3）If the oil flows directly to the reservoir， ，thenSubstituting into formula (7-2) we obtain, The formula（7-5）is the speed-load performance equation, the characteristic curves of th
22、e speed-load are shown in Fig. 7-8.（7-4）（7-5） From above, we know adjusting the area can realize the arbitrary speed-regulation. The range of speed regulation is very wide, Fig. 7-8 Speed-load performances of inlet throttle The character of speed variation with load can be described by speed rigidit
23、y as below,(7-6)Meanwhile from formula (7-5) and formula (7-6),(7-7)the overflow loss P1=pSq and the throttle loss P2=p1qL.The efficiency of circuit :(2) (2) Performance of power The outlet power of pump: Effective outlet power of the cylinder: the circuit power loss is （7-9） （7-8） 2. Outlet throttl
24、e speed-regulating circuits As shown in Fig.7-7b. In the same way, the performances of speed-load and the rigidity of speed are（7-10） （7-11） 3. Bypass throttle orifice speed-regulating circuitsFig.7-9a)A bypass throttle orifice speed-regulating circuitb) A speed-load performance of bypass throttle o
25、rifice speed-regulating circuit(1) Performance of speed-load（7-12） It is similar to the situation mentioned above,but here leaking flow rate should be added into the main flow rate from output of pump. Thus, the expression of speed isThe rigidity of speed is described as（7-13）(2) Characters of power
26、The output power from pumpThe output power from hydraulic cylinder （7-14）（7-15）Where The power loss is The efficiency of the circuit4.The comparisons for three throttle speed-regulating circuits（1）We compare formula (7-11) with formula (7-7). It is easy to find that they have the same speed-load cha
27、racteristics and the rigidity of speed. （2）There are two application differences between inlet and exit throttle orifice speed-regulating: firstly the throttle orifice valve in the exit circuit is used for engendering an against-pressure in the return chamber . Secondly the inlet throttle orifice sp
28、eed control circuit is easy to realize the pressure control. （3）The comparison of three circuits in rigidity . According toformula (7-12) we can draw a set of curves as shown in Fig.7-9b. （4）The comparisons of three circuits in power loss . There is only the throttle orifice loss without the overflo
29、w loss. So the bypass circuit has the advantage of lower power loss and higher efficiency than those of the inlet and outlet circuits. （5）Start-up performance after shut down. In outlet throttle orifice speed regulating circuits, the oil in the return chamber flows directly into the tank to make the
30、 work-machine impact ahead instantly duo to back pressure when starts-up. However, the start-up impact for the inlet throttle orifice speed regulating circuits can be avoided by regulating the inlet throttle orifice valve. 5. Improvement of the throttle orifice speed-regulating circuit Usually using
31、 the regulating speed valve (pressure-compensated) instead of the throttle orifice valve in order to improve circuit performances (p =constant, speed rigidity is higher, shown in Fig.7- 9b ). Similar to the throttle orifice valve, the circuits with regulating speed valve are (pressure-compensated) c
32、lassified into three positions of inlet, outlet and bypass as shown in Fig. 7-10 (a, b, and c). Here we need to pay attention to the pressure differential on two ends of the regulating speed valve which should be bigger than 0.5MPa for middle pressure systems and 1MPa for high pressure systems to in
33、sure the action of pressure-compensation.Fig. 7-10 Speed-regulating circuits with regulating speed valve (pressure-compensated)b)a)c)7.2.3 Volume speed-regulating circuit (by Vp or VM) 1. Regulating speed circuit by variable displacement pump and invariable displacement motorFig.7-11a)Circuit of var
34、iable displacement pump-fixed displacement motor b) Character curves Fig. 7-12 a) Circuit of variable displacement pump-variable displacement motor b) Character curves 2. Regulating speed circuit by variable displacement pump and variable displacement motor3. Volume - throttle speed-regulating circu
35、its (1) Volume-throttle speed-regulating circuit by pressure limiting variable displacement pump and speed-regulating valveAs show in fig.7-13a and 7-13b.Fig.7-13a) Volume - throttle speed-regulating circuit by pressure-limiting variable displacement pump and speed-regulating valve b) Character curv
36、es Working pressure in the cylinder would be（7-16）The efficiency of the circuit is（7-17） (2) Volume-throttle speed-regulating circuit by pressure-differential variable displacement pump and throttle valveFig. 7-14 Volume speed-regulating circuit by pressure-differential variable displacement pump an
37、d throttle valve Efficiency of circuit: This circuit possesses no overflow losses and the oil supply pressure of pump is increasing with the load changing. The circuit efficiency is only one term of throttle losses that is resulted from pressure difference . （7-18）7.2.4 Fast-speed movement circuitFi
38、g. 7-15 Fast-speed circuits by a differential area actuator 1. Fast-speed movement circuit by a differential area actuator2. Fast-speed movement circuit by double pumps oil supply Fig. 7-16 Fast-speed circuits by double pumps oil supply 3. Fast-speed movement circuits by increased-speed cylinder Fig
39、. 7-17 Fast-speed circuits by increased-speed cylinder 1- Increased-speed cylinder 2- Small chamber in the cylinder 3- Check valve4- Sequence valve 5- Big chamber in the cylinder 4. Fast-speed movement circuit by an accumulatorFig. 7-18 Fast-speed circuit by accumulator 1-Pump 2-Check 3-Directional
40、valve 4- Accumulator 5- Sequence valve 6-Hydraulic cylinder7.2.5 Speed shift circuit (1) Speed shift by distance valve (or solenoid pilot-actuated valve) Fig.7-19 a)Speed shift circuit by distance valve b) Speed shift circuit by parallel connection pumps 1. Speed shift between fast and slowa)b) (2)
41、Speed shift between two speeds by motorsAs shown in fig.7-19b.2. Speed shift of two slow speedsFig.7-20 a)Speed shift done by series connection of two speed-regulating valves. b) Speed shift done by parallel connection of two speed-regulating valvesa)b)7.3 Directional Control Circuits7.3.1 Direction
42、al circuit7.3.2 Locked cylinder A directional control circuit is used to control the actuator on operating or stopping or shifting flow direction of oil fluid. 7.3.1 Directional circuit A general directional valve can be connected between actuator and pump for a simple directional circuit. When a ci
43、rcuit needs to realize reciprocating motions continuously, the complex circuits are needed. So two types of directional circuits, i.e. directional shift controlled by time and by distance will be detailed in this section respectively.1. The directional circuit controlled by timeAs show in Fig.7-21.F
44、ig. 7-21 Directional valve circuit controlled by time The main oil line is only controlled by the main directional valve 2. If the pilot valve 3 moves towards left, the pressure control oil flows into the right of the main valve 2 via check and pushes the main valve movetowards left, and then the co
45、ntrol oil in the left chamber of the main valve 2 flows into tank via throttle valve . Here when the main directional valve 2 moves towards left, the brake taper surface T on it will close gradually the return oil port and make the piston in the cylinder move slowly. And after the main valve 2 moves
46、 a distance of the return oil port closes completely to make the piston stop. The half taper degree isand the brake long . 2. The directional circuit controlled by distanceFig.7-22 Directional valve circuit controlled by distance 1-Hydraulic cylinder 2-Main directional valve3- Pilot directional valv
47、e 4-Throttle valve 5-Relief valve7.3.2 Locked cylinder using pilot check valves The function：to lock the cylinder so that its piston cannot be moved due to external force acting on the piston rod. Fig. 7-23 Locked cylinder using pilot check valves 7.4 Multi-actuator control circuits7.4.1 Sequence ac
48、tion circuit7.4.2 Synchronization circuit7.4.3 Hands-off circuit7.4.1 Sequence action circuit Sequence action circuits allow several actuator motions to obey the setting scheduled actions in advance. There are two kinds of control methods: pressure and distance controls. Fig. 7-24 is a sequence acti
49、on circuit done by a sequence valve, such as the action sequence of a drill press is following (1) hold parts(2) aiguille squash in(3) aiguille exit(4) loosen parts. the pressure setting of the valve 4 should be more than the highest working pressure 1015, otherwise error actions will be happened.1.
50、 Sequence action circuit by pressure controlFig. 7-24 Sequence action circuit controlled by sequence valve 2. Sequence action circuit by distance controlFig.7-25a) Sequence action circuit by distance valveb) Sequence action circuit by distance switch7.4.2 Synchronization circuit Fig. 7-26 Synchroniz
51、ation circuit by speed-regulating valve 1. Synchronization circuit by a speed-regulating valve2. Synchronization circuit by series cylinder with compensation unitFig. 7-27 Synchronization circuit byseries cylinder with compensation unit 3. Synchronization circuits by synchronous cylinder or synchron
52、ous motorFig.7-28a) synchronization circuit by synchronous cylinder b) Synchronization circuit by synchronous motor a)b)4. Synchronization circuits by scale or servo valvesFig. 7-29 Synchronization circuits by scale or servo valves 7.4.3 Hands-off circuit This circuit is used to realize hands-off cy
53、linders motion during carrying their own poerating tasks. Fig. 7-30 is a hands-off circuit by two pumps supplying oil to the system. Hydraulic cylinder 1 and 2 finish automatically in a cycle motion of “fast extendsslow extendsfast retracts” respectively. Fig. 7-30 Multi-cylinder hands-off circuits
54、with fast and slow speed your suggestions are welcome!The EndFig.7-1a Pressure regulated from remote portFig.7-1b Multistage pressure regulated circuitFig.7-1c Stepless pressure regulated circuitFig.7-2a Pressure-venting by the neutral of a directional valveFig.7-2b Pressure-venting by a solenoid op
55、erated relief valveFig.7-2c Pressure-venting by a pump limited pressure Fig.7-2d Pressure-venting by an accumulationFig.7-3a one-stage pressure-reducing Fig.7-3b Two-stage pressure-reducing Fig.7-4a Single action booster circuitFig.7-4b Bi-action booster circuitFig.7-5a Counter-balance circuit done
56、by a combined of check- sequence valveFig.7-5b Counter-balance circuit done by a hydraulic control check valve Fig.7-5c Counter-balance circuit done by remote control counter-balance valveFig.7-6a A pressure-holding circuit by pressure-relay Fig.7-6b A pressure-holding circuit by accumulatorFig.7-6c
57、 A pressure-holding circuit by accumulatorFig.7-7a A inlet throttle speed-regulating circuitFig.7-7b A outlet throttle speed-regulating circuitFig.7-9a Bypass throttle orifice speed-regulating circuitsFig. 7-10a Speed-regulating circuits with regulating speed valve (pressure-compensated)Fig. 7-10b S
58、peed-regulating circuits with regulating speed valve (pressure-compensated)Fig. 7-10c Speed-regulating circuits with regulating speed valve (pressure-compensated)Fig.7-11a Circuit of variable displacement pump-fixed displacement motor Fig. 7-12 Circuit of variable displacement pump-variable displace
59、ment motorFig.7-13a Volume - throttle speed-regulating circuit by pressure-limiting variable displacement pump and speed-regulating valveFig. 7-14 Vloume speed-regulating circuit by pressure-differential variable displacement pump and throttle valve Fig. 7-15 Fast speed circuits by a differential ar
60、ea actuator Fig. 7-16 Fast speed circuits by double pumps oil supply Fig. 7-17 Fast speed circuits byincreased-speed cylinder Fig. 7-18 Fast-speed circuit by accumulator Fig.7-19a Speed shift circuit by distance valveFig.7-19b Speed shift circuit by parallel connection pumps Fig.7-20a Speed shift do
61、ne by series connection of two speed-regulating valves.Fig.7-20b Speed shift done by parallel connection of two speed-regulating valvesFig. 7-23 Locked cylinder using pilot check valves Fig. 7-24 Sequence action circuits by pressure control Fig.7-25a Sequence action circuit by distance valve Fig.7-2
62、5b Sequence action circuit by distance switchFig. 7-26 Synchronization circuit by speed-regulating valveFig. 7-27 Synchronization circuit by series cylinder with compensation unitFig.7-28a synchronization circuit by synchronous cylinder Fig.7-28b Synchronization circuit by synchronous motor Fig. 7-29 Synchronization circuits by scale or servo valves Fig. 7-30 Multi cylinder Hands-off circuits with fast and slow speed
