Dynamic Air Consumption of Control Valves
When comparing new automobiles, would you rely on fuel consumption data measured only while the engines were idling?? Probably not, but that is equivalent to the static air consumption data used today by purchasers and vendors of control valve positioners.? Static energy consumption can be misleading, particularly for pneumatic positioners with low bleed rates, in process loops where the input signal changes frequently.
??????????? Energy consumption of the control systems is part of the operating cost of a process plant.? However, attempting to minimize energy consumption by restricting energy flow to the final control element may compromise the purpose of the control loop.? Degrading the performance of the control loops reduces product quality, reduces plant output, or wastes process fluids far more valuable than the instrument air.? The operating cost of the control valve must be weighed against the control valve's effect on the control loop.
Please see below link for more details on it.