Reverse-acting

Figure 7-8M. Ultrex Reverse Acting Rupture Disc providing instantaneous full opening, non-reclosing. By permission. Continental Disc Corporation.

For flow tested combinations, see a few typical data in Table 7-12. Note, for example, that using a Continental disk reverse acting knife blade rupture disc with a Crosby JOS/JBS pressure relief valve that the combined effect is to multiply the rated capacity of the Crosby valve by a multiplier of 0.985 for a set pressure in the 60-74 psig range... 

Note Zap is a reverse-acting rupture disk using replaceable knife blades. Patented. Other disk and valve manufacturers have tested their own combinations to obtain combination capacity factors. 

Figure 12-31. Capacity control suction valve unloaders are available in either of two designs with pneumatic operators (A) direct-acting (air to unload) (B) reverse-acting or fail safe (air to load), which automatically unloads the compressor in the event of control air failure (C) an innovation in manually operated unloaders. Here, the lever cam arrangement provides positive loading or unloading, eliminating the requirement to turn a handwheel completely in or out. (Used by permission Bui. 9-201B, 1991. Cooper-Cameron Corporation.)...

DNA from one reversibly acting nucleophile to the next (Fig. 9.5). This migration is currently under investigation in our laboratory, but the consequences of repetitive capture and release of a QM have already been observed from the extended lifetime of a QM in the presence of strong and reversibly acting nucleophiles as described below. 

Figure 24 Effects of Disturbance on Reverse Acting Controller. 35...

The proportional controller is reverse-acting so that the control valve throttles down to reduce steam flow as the hot water outlet temperature increases the control valve will open further to increase steam flow as the water temperature decreases. 

At time tb the measured variable increases by 100°F, or 50%, of the measured variable span. This 50% controller input change causes a 100% controller output change due to the controller s proportional band of 50%. The direction of the controller output change is decreasing because the controller is reverse-acting. The 100% decrease corresponds to a decrease in output for 15 psi to 3 psi, which causes the control valve to go from fully open to fully shut. 

Figure 29 Effect of Disturbance on Proportional Plus Rate Reverse Acting...

Next we look at the temperature transmitter. It is direct acting (when the process temperature goes up, the transmitter output signal, PM, goes up). Now if PM increases, we want to have less steam. This means that the controller output must decrease since the valve is AO. Thus the controller must be reverse-acting and have a positive gain. 

If an operator saw this problem developing, he would switch the temperature loop into manual and cut back on the steam flow. The control system in Fig. 8,4fl will perform this "override control automatically. The low selector (LS) sends to the steam valve the lower of the two signals. If the steam valve is air-to-open, the valve will be pinched back by cither high temperature (through the reverse-acting temperature controller) or by low base level (through the low-base-level override controller). 

Note that the gain of the controller is chosen to be positive (reverse-acting) so the controller output decreases as temperature increases, which increases cooling-water flow through the AC valve (this makes the gain of the control valve negative). 

Liquid level can be detected (inferred) by measuring a d/p. The high-pressure side of the d/p cell is connected to the bottom of the vessel, and the low-pressure side (reference) to the vapor space is connected above the liquid (pressurized tanks) or is vented to the atmosphere (atmospheric tanks). In atmospheric HTG, the low-pressure side reference leg must produce a constant head either by a column of fluid of fixed height (reference leg) or by a gas-filled reference leg. The sensor can be direct-acting (0 to 100%) d/p or reverse-acting (100 to 0%), and the densities (therefore temperatures also) of both process and reference liquids must be constant. 

R/A Reverse acting RCP Recycle compressor RFC Reversible fuel cell R/P Resource to production ratio... 

Desoxypeganine hydrochloride, (II), a reversibly acting cholinesterase and inhibitor monoamine oxidase, was determined by Asmussen (2) to be useful in the treatment of alcohol dependence. The cholinesterase inhibitor identified by Opitz (3), galathamine, (III), was also effective in treating chronic alcoholism. 

This nonmonotonic behavior can lead to feedback control instability. On one side of the hump the controller should be direct acting. On the other it should be reverse acting. So we must be careful when applying differential temperature control structures. 

FIG. 11 -69 Typical central-station air-conditioning unit and control system. On a rising room wet-bulb temperature, the wet-bulb branch-line air pressure increases through the reverse-acting outdoor-air wet-bulb temperature-limit thermostat Ti to open gradually the maximum outdoor-air damper Di and simultaneously closr return-air damper Dg, then gradually open chilled-water valve Vi- On a rising room dry-bulb temperature, the dry-bulb branch-line air... 

---