Question: Consider the compressor shown in Fig. PI0049-6. This two-stage compressor has two different suction points. In each suction line there is a volumetric flow meter calibrated at 0°C and 1 atm, a pressure transmitter, and a temperature transmitter. An important consideration in the control of the compressor is to avoid the surge condition, Figure shows a curve indicating the minimum inlet flow, in ACFM (actual ft3/min) required, for a given inlet pressure, to avoid surge. Each stage can go into surge independently. Under normal operating conditions, the operator sets the position to each suction valve. However, for safety reasons,

the operator must not close the valves below the surge limit. Design a control strategy to avoid closing the valves below the surge limit. Also as a result of safety considerations, although it is permissible to open the valves very fast, closing the valves must be done slowly. Design this constraint into your previous design.