M15.5 Summary

We have seen that a direct-acting valve might be used to compensate for the orifice plate nonlinearity if no square root extractor is used. We also noted that a linear valve should be used if the pressure drop across the valve is constant (say, the upstream and downstream headers are maintained at constant pressure, and there is negligible pressure drop through the piping). We notice that an equal-percentage valve should be used if a substantial amount of the pressure drop at high flow rates is due to piping, while most of the pressure drop at low flow rates is across the valve.

Many industrial controllers use proportional band rather than proportional gain. You can still use any of the techniques presented in this text to find the proportional gain, and simply convert to PB using PB = 100/k_c.