Improving Stability of Electronically Controlled Pressure-Reducing Valves through Gain Compensation

Abstract

This paper explains the root cause of instabilities that tend to arise in pressure-reducing valves (PRVs) under low-flow conditions. It was found that the loss of stability in PRVs is a direct result of an increase in the static valve-network gain as the valve position gets smaller, thus making pressure changes more sensitive to valve position adjustments. If the valve controller is tuned at medium valve openings characteristic of normal operating conditions, the increased gain at low valve openings can cause the control system to be too aggressive in its valve position adjustments, leading to oscillations. This paper provides a mathematical derivation of the gain equation for a simplified pipe-PRV-pipe model. The obtained gain equation curve was then used to derive the formula for a gain compensator whose purpose is to keep the static gain constant across an entire range of permitted valve openings. A simplified network transient model was then used to recreate a real-life PRV instability event and show the remedial effects of the gain compensator.