In this application, the flare valve will need to open quickly in response to high pressures, but the compressor suction valve will need to move much more slowly to prevent instability in the compressors. The main problem with split range control is that the controller only has one set of tuning parameters. If the controller is tuned to be fast acting to optimise the performance of the flare valve, the suction valve will also move rapidly to produce unstable gas flows to the compressors. If the controller is tuned slower to stabilise the compressors, then the flare valve will not open fast enough as the pressure rises. A further issue is that the process response of the route to flare generally differs to the process response of the route to the compressors, so both routes will anyway require very different tuning for optimal control. The solution is to replace the split range controller with two independent controllers, both reading the same pressure transmitter, but one controlling the flare valve and the other the suction valve. Not only can each controller be tuned correctly for its dedicated service, but different setpoints can also be used to prevent the flare valve from