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,
![1160_11-7.png](https://secure.tutorsglobe.com/CMSImages/1160_11-7.png)
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.