High selector switch

High selector switch, 403, 404, 405 Hold elements, 558, 576-81 Hot spot, 405... 

HSS (see High selector switch) Hydraulics, of distillation trays, 72 Hydrodealkylation of toluene plant control system design, 519-29 description, 516-19... 

The control signals from the two pressure controllers go to a high-signal selector switch. When the pressure set by the wide-range system reaches a certain point, then, the narrow-range system takes over control. Control response charts are in Fig. 11.38. The situation is similar to that described for the chlorine system and shown in Fig. 11.20. 

The loader control panel, which may be mounted on the unit or at a remote point, contains motor starters, timers, high- and low-level switch lights and, on multiple silo systems, a selector switch to energize the proper high-level switch for automatic operation. When the operator wishes to change from loading one silo to another, the flex-hose connections to the material and vacuum line of the new tank must be changed and the tank selector switch on the control panel must be positioned to the new silo. The system is then ready to run. 

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). 

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