Reservoir, pneumatic system

Directional control valves for hydraulic and pneumatic systems are similar in design and operation. However, there is one major difference. The return port of a hydraulic valve is ported through a return line to the reservoir. Any other differences are pointed out in the discussion of these valves. 

Figure 8.14. Schematic diagram of a pneumatic system retrofitted to a capillary electrophoresis instrument for capillary electrochromatography with simultaneous pressurization of the column inlet and outlet reservoirs.

For engineers to use pneumatics, they must design a pneumatic system. As we noted in Chapter 2, a system is a group of related components that work together to achieve a process. A typical pneumatic system consists of a compressor, a reservoir, transmission lines, control valves, and actuators. These components are shown in Figure 11-13. 

The compressor is a device that increases the pressure of air and pumps the compressed air into a tank. The compressed air tank is called a reservoir. The compressed air is then routed to the desired location through transmission lines. Transmission lines are tubing through which the compressed air flows. Control valves regulate the flow of gases. The pneumatic system uses a cylinder with a movable piston to convert its fluid power into mechanical power in the form of linear motion. 

The components of a hydraulic system are similar to those of the pneumatic system. Figure 11-14 shows the components of a hydraulic system. The pressure of the hydraulic fluid is provided by the system s pump. The hydraulic pump is a device that creates flow in the system. The reservoir stores the hydraulic fluid before it is pressurized by the pump. Transmission lines carry the pressurized hydraulic fluid to the control valve and actuators. The control valves regulate the flow and pressure of the hydraulic fluid. The actuators transfer the fluid power into mechanical power. 

The major attraction of pneumatic systems for prosthetics applications is their inherent compliance, which tends to give these systems a very natural look and feel. While pneumatic systems did find some measure of success in prosthetics, hydraulic systems did not. Hydraulics tended to be messy, with hydraulic units leaking hydraulic fluid. In addition, a fluid reservoir and fluid are required, adding to the total weight of the mechanism. 

Figure 3 (A) Robot system for lipofection screening (A) Worktable with racks for microplates, buffer reservoirs, plastic, and glass vials. (B) Four tip liquid handling arm. (C) Gripper for transport of microplates and glass test tubes. (D) High power water bath sonicator. ( ) Nitrogen evaporator. (F) Microplate washer. (G) Absorbance reader. (H) Luminescence reader. (/) Transparent hood. (/) CO2 incubator with pneumatic door (from the rear, front view in B). (B) Self-constructed robotic conveyor for the transport of cell culture plates from the incubator to the worktable.

TTiese include an IBM PC/AT computer that functions in conjunction with a Zymate System V Controller located beneath the table top. Other devices located on this table include an autotitrator with solvent/titrant reservoirs, a pneumatic solvent switching valve, a metering pump, and a Zymark Power and Event Controller (PEC). A bar code printer provides labels for sample vials, and a printer is used for hard copy report generation. The devices mounted on the robot table (approximately 90x 1 SO cm) are listed in Table 6.S. 

The experimental setup can be seen in Figure 8. It mainly consists of the gas-liquid two-phase flow loop and three UVP-DUO systems. The pipe loop is made of plexiglass and has an inner diameter D of 40 mm. It consists of a water reservoir, a water pump controlled by a frequency inverter, liquid- and gas-phase flow meters, a pneumatic valve, and the... 

LEI as an analytical technique thus requires a tunable laser, an atom reservoir, a galvanic detection system and read-out electronics including a boxcar integrator. It was first realized experimentally with a flame as the atom reservoir using pneumatic nebulization for sample uptake [670]. 

Fig. 5. Diagram of Varian Model 8500 pumping system, a = valve to pressurize the reservoir, c = solvent reservoir, -flow valve, f = pressure transducer, g = pneumatic valve...

Generally in commercial apparatus, no device is used to prevent solvent back--flow. In the Perkin-Elmer system, a small glass bead column is used on each solvent line to limit this back-flow to the reservoir, but it cannot prevent it completely. The Varian pumps can be supplied with a pneumatic valve which suppresses back-flow and reduces the inconveniences. 

Pressure-control valves have a third port to vent excess pressure and prevent it from affecting the downstream piping. The bypass, or exhaust, port has an internal flow-control device, such as a diaphragm or piston, that opens at predetermined set-points to permit the excess pressure to bypass the valve s primary discharge. In pneumatic circuits, the bypass port vents to the atmosphere. In hydraulic circuits, it must be connected to a piping system that returns to the hydraulic reservoir. 

I. C systems for process plants depend for their safe and continuous operation, under normal and abnormal conditions, on independent dedicated electrical, pneumatic and possibly hydraulic sources of power. These power sources should be installed, inspected, tested and made operational as early as practicable, so as to be available for the inspection, testing, calibration and adjustment of the components and ensembles constituting the plant s I. C systems. Batteries provide DC power directly or provide secure AC power through an inverter. Instrument air is produced by oil free compressor sets delivering to an air receiver via filters and air dryers. In an application where hydraulic power is required, the necessary pump sets, filters, reservoir and accumulator, can be integrated into a self-contained power pack. 

It should perhaps be noted here that these pneumatic pumps can however only operate for a limited time before re-filling of the solvent reservoir is necessary. Further, whilst they are excellent devices for operating HPLC columns in the isocratic mode they are not suitable for gradient mode elution. In spite of these drawbacks, the simplicity and cheapness of this type of eluant-pressurizing system make them very attractive to a number of laboratories and especially those on limited budgets. 

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