Four valve control

Simple two-valve controls suffice to effect the piston motions of the auxiliary equipment of the press - with the exception of the die-carrier shifting device - as the pullback ends of the pistons are suitably connected directly to the pressure water circuit (see p. 221). The sectional areas of the pistons of the shifting devices are of equal size and therefore require a four-valve control. 

Designing and calculating a control is preceded by the preparation of a hydraulic circuit diagram, based on the rule that one inlet- and one outlet valve each or one double-acting slide-valve each is required for one reciprocal motion of the plunger. Consequently, a four-valve control is to be provided for the advance and return motion or the up-and-down motion of the piston of a horizontal or vertical press respectively. Examples of this are the controls for the press and the die-carrier shifting device, illustrated in Fig. 92. 

The number of independent variables required to define the operation of an absorber or stripper may also be determined by applying the description rule, stated in Section 5.2.1. The number of trays or the column height is set by construction and may, in the design phase, be used as design variables. Since, by definition, the feeds are introduced at the top and bottom of the column, the feed locations are not variable. The feed compositions and thermal conditions are set outside the column region and are therefore beyond the operator s control. The operator can, however, control the valves on the two feeds and the two products. One of these four valves, usually the bottoms product valve, cannot be controlled independently since it must be set at steady state such as to maintain the required liquid level in the bottom of the column. The overhead valve is usually used to control the column pressure. The two feed valves may be controlled independently one controls the main process stream rate and the other controls the solvent or stripping gas flow rate. 

The heart has four valves— two atrioventricular (tricuspid and mitral) and two semilunar (pulmonic and aortic). Atrioventricular valves control bloodflow between the atria and ventricles. Semilunar valves control the bloodflow between the ventricles and the pulmonary artery and the aorta. 

Several of the control loops in Figure 21.35 are provided for inventory control, in three level-control loops and two pressure-control loops. Note, however, that the pressure in V-100 is assumed to be constant and loop PC-1 is not simulated by HYSYS.Plant. In contrast, pressure control is crucial to maintain stable internal flows in the column. Finally, because the feed flow rate and temperature controllers are decoupled from the rest of the process, they are not included in the C R analysis. Consequently, the interactions to be analyzed involve the four valves V-7, V-9, V-10, and V-12, and four controlled variables Xdj, JC/u (mole fractions of benzene in the distillate, MCB in the bottoms, and HCl in the absorber overhead stream, respectively) and Tg, the recycle temperature. Note that to improve the dynamic performance, the temperature of tray 4 is controlled rather than the distillate benzene mole fraction. 

Interaction analysis is performed using the steady-state RGA. To generate information to compute the RGA, the control loops are placed in manual mode, and the process is simulated to line-out the outputs at steady-state values. Then, one-by-one, step changes in the four valve positions are imposed, and new steady-state values of the outputs are recorded. Note that, for consistency, the step directions are chosen such that AC-1 changes in the same direction. The results are recorded in Table 21.10. Thus, for example, a 0.5% increase in the position of the reflux valve, V-7, leads to a decrease of 4.5°F in the temperature on tray 4. 

The catalytic tests with chromatographic analysis can be performed at atmospheric pressure in a fixed-bed quartz microreactor. The mass of catalyst used was 20 mg and a total flow of the reagents of 200mL/min, with a ratio CH4 C02 He of 1 1 18 (GHSV = 600,000 cm /hgcat). The gas flow of gases is monitored by the mass flow controllers with transducers valves connected to a four channel control panel (MKS), which allows an accurate dilution of the mixture reagents. 

This instrument uses a helium sparging device with four separately controlled solvent lines, ensuring optimal solvent degassing and improving check valve reliability at low flow rates, diminishing baseline disturbances at low ultraviolet (UV) wavelengths. 

Fig. 11.48 Four-way control valve bond graph model...

Granda J. J., Ferner E. Computer Simulation of a Hydraulic Four Way Control Valve. Transactions Journal of the Society for Computer Simulation 3(1), 67-81, January 1987. 

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