Pneumatic actuators

IX]- T ffo-way valve -C Three-way valve -lx]- Bulterfly valve -tSD- Non-relLirn valve -txj- Valve with control trim T Diaphragm valve actuator (pneumatic)... 

Manual and automatic valves of the diaphragm, butterfly, or ball type are commonly used of a construction suited to the application. Automatic valves may be actuated pneumatically, hydraulically, or electrically and where large engineered plants are concerned separate valves are ascribed to discrete functions. Smaller packaged units often employ a single multiport valve mounted on the top or the side of the vessel. 

Fig. 11.1). The test foot is applied against the test surface, the actuating (pneumatic) cylinder causes swinging (slippage) motion of the test foot, and the instrument displays the slip index on its protractor scale. It ensures consistent operation by the application of uniform force for each test, and permits reliable metering of inclined surfaces such as ramps. The application of vertical and horizontal forces is simultaneous, thus avoiding residence -time and permitting reliable measurement of wet surfaces.

In order to transport fluids in microfluidic systems with a liquid flow layer and a pneumatic control layer, a pneumatic pump typically consists of three pneumatic actuators (pneumatic microvalves) in the pneumatic control layer and a microfluidic channel in the liquid flow layer, as schematically shown in Fig. 1 [1]. The two layers are separated by an elastic membrane, such as a film of PDMS materials. The time-phased deflection of elastic membranes at the top of pneumatic actuators along the microchannel length can generate a peristaltic effect which drives the fluid from the inlet to outlet along the microfluidic channel in the liquid flow layer. The deflection of elastic membranes and the actuatirm... 

Quake and coworkers [16] developed a PDMS microfluidic device (shown in Fig. 4c) for nucleic acid purification from a small number of bacterial or mammalian cells. This multilayer device contained fluidic channels and a system of membrane-actuated pneumatic valves and pumps, which enabled precise control of buffers, lysis agents, and cell solution and also allowed for parallel processing. Bacterial cells, dilution buffer, and lysis buffer are first introduced into the chip and then transferred into the rotary mixer. Once mixed, the lysate is flushed over a DNA affinity column and drained. The DNA... 

The general metal capacity of squaring shears range from thin materials, up to a l- /2-in. mild-steel plate, and are able to cut virtually all types of alloy and steel that are within the rated, mild-steel capacity of the shear. Squaring shears derive their power source from either manual actuation, pneumatics, hydraulics, or mechanical drive systems, with each power source providing unique advantages that meet the needs of specific shearing applications. 

Tendon or residual muscle movement has been used to actuate pneumatic sensors when interposed between a prosthetic socket and the superficial tendons and/or muscle. These sensors can be used for prosthesis control. The Vaduz hand, which was developed by a German team headed by Dr. Edmund Wilms in Vaduz, Liechtenstein, following World War II, used muscle bulge to increase pneumatic pressure to operate a switch-controlled, voluntary-closing, position-servo hand. This hand can be considered to be a forerunner of the pneumatic Otto Bock Hands of the 1970s and the electrically powered Otto Bock Hands of today. 

Pneumatically (air) operated—This is the most common type of actuator. Pneumatic actuators convert air pressure to mechanical energy and can be found in three designs (1) diaphragm, (2) piston, and (3) vane. 

Conventional tactile displays could hardly control delicate tactile sensation, because it was difficult to make fine distributed stimuli on a human skin under the limitations of their actuators, such as magnetic oscillators, piezoelectric actuators, shape memory alloy actuators, pneumatic devices, and so on. EAP materials have many attractive characteristics as a soft and light actuator for such a stimulation device. 

Figure 24.3 Examples of active hand systems equipped with different types of actuators pneumatic devices ((a) adapted from [6] Copyright (2004) IEEE, (b) Rutgers MU glove, adapted from 17] Copyright (2002) IEEE) electromagnetic motors ((c) Cyber grasp/Cyber glove, adapted from [7] Copyright (2002) IEEE) and shape memory alloy wires ((d) adapted from [9]).

E. A. Mayer, Electro-Pneumatic Control Valve for EGRfATC Actuation, SAE 810464, Society of Automotive Engineers, Warrendale, Pa., 1981. 

Hydraulic The design of typical hvdraiilic actuators is similar to double-acting piston pneumatic types. One kev advantage is the high pressure (yvpicallv35 to 70 bar [500 to 1000 psi]), vvFich leads to high thrust in a smaller paclcage. The incompressible nature of the... 

As most throttling control valves are still operated bv pneumatic actuators, the control-valve device descriptions that follow relate primarily to devices that are used with pneumatic actuators. The function of hydraulic and electrical coimteiparts are very similar. Specific details on a particular valve-control device are available from the vendor of the device. 

Transducers The ciirrent-to-pressiire transducer (I/P transducer) is a conversion interface that accepts a standard 4-20 rnA input current from the process controller and converts it to a pneumatic output in a standard pneumatic pressure range (normally (),2-L0 bar [3-15 psig] or, less frequently, 0,4-2,0 bar [6-30 p.sig]). The output pressure generated by the transducer is connected directly to the pressure connection on a spring-opposed diaphragm actuator or to the input of a pneumatic valve positioner. 

The flow capacity of the transducer can be increased bv adding a booster relav like the one shown in Fig, 8-7.3/ , The flow capacity of the booster relav is nominally fiftv to one hundred times that of the nozzle amplifier shown in Fig, 8-7.3 3 and makes the combined trans-diicer/booster suitably responsive to operate pneumatic actuators. This type of transducer is stable into all sizes of load volumes and produces measured accuracy (see Instrument Society of America [ISA]-S5l, 1-1979, Process Instrumentation Terminology for the definition of measured accuracy) of 0,5 percent to 1,0 percent of span. 

FIG. 8-74 Positioner/actiiators (a) generic block diagram (h ) an example of a pneumatic positioner/actuator. 

Figure 8-74b is an example of a pneumatic positioner/actuator. The input signal is a pneumatic pressure that (1) moves the summing beam, w ch (2) operates the spool valve amplifier, which (3) provides flow to and from the piston actuator, which (4) causes the ac tuator to move and continue moving until (5) the feedback force returns the beam to its original position and stops valve travel at a new position. Typical positioner operation is thereby achieved. 

The stiffness characteristic of the positioner/actuator varies with frequency. Figure 8-75Z indicates the stiffness of the positioner/actu-ator is high at low frequencies and is directly related to the locked-stem pressure gain provided by the positioner. As frequency increases, a dip in the stiffness curve results Trom dynamic gain attenuation in the pneumatic amplifiers in the positioner. The value at the bottom of the dip is the sum of the mechanical stiffness of the spring in the actu-... 

FIG. 8-75 Frequency response curves for a pneumatic positioner/actuator (a) input signal to stem travel for a 69-inch spring and diaphragm actuator with a 1.5-inch total travel and. 3-15 psig input pressure (h ) dynamic stiffness for the same positioner/actuator. 

Positioner Application Positioners are widelv used on pneumatic valve actuators, VIore often than not, thev provide improved process-loop control because thev reduce valve-related nonlinearitv, Dvnarnicallv, positioners maintain their abilitv to improve control-valve performance for sinusoidal input frequencies up to about one half of the positioner bandwidth. At input frequencies greater than this, the attenuation in the positioner amplifier netvv ork gets large, and valve nonlinearitv begins to affect final control-element performance more significantlv. Because of this, the most successful use of the positioner occurs when the positioner-response bandwidth is greater than twice that of the most dominant time lag in the process loop. 

Solenoid Valves The electric solenoid valve has tw o output states. Wlien sufficient electric current is supplied to the coil, an internal armature moves against a spring to an extreme position. This motion causes an attached pneumatic or hvdraiilic valve to operate. Wlien current is removed, the spring returns the armature and the attached solenoid valve to the deenergized position. An intermediate pilot stage is sometimes used when additional force is required to operate the main solenoid valve. Generallv, solenoid valves are used to pressurize or vent the actuator casing for on/off control-valve application and safetv shutdown applications. 

FIG. 10-53 Pneumatically actuated diaphragm pump for slurry service. (Coutiesy of Dotr-Olvier Inc.)... 

Gas compressor anti-surge (GM-OFF) control circuit, comprising transmitters, computers and pneumatic control valve Reverse flow protection (on axnal compressors only) as supplementary protection device against surging, working independently of the control circuit Expander emergency stop valve with pneumatic actuator and solenoid valve... 

Expander bypass (stack) valve with pneumatic actuator and solenoid valve... 

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