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Laboratory analysis of a piston actuated pressure reducing valve under low flow conditions
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1  Department of Engineering, University of Ferrara, 44122 Ferrara, Italy


Pressure reducing valves (PRVs) are widely used in water distribution networks for optimal pressure management. Several studies and field applications prove the effectiveness of PRVs for water loss reduction, but some recent studies have also highlighted some problems and operational limitations. In this study, we analyse the functioning of a piston actuated pressure reducing valve (where the regulating device operates in a parallel direction to the flow) with a mechanical pilot which is subjected to low flow regimes, a condition that is often observed in the real distribution networks. The analyses are carried out by means of laboratory tests featuring two sets of experiments, i.e. a) by testing the behaviour of the PRV when a pre-established initial value and subsequent variation of flow rate occurs in the system and b) by testing the PRV in face of a temporal series of flow rates observed at the inlet section of a real hydraulic district. The first set of tests highlighted different field behaviour of the PRV corresponding to well defined ranges of flow rate, and in particular that for some flow rates the PRV tends not to respect the imposed set-point value and, under certain flow rate values, an unstable behaviour characterised by significant pressure oscillations occurs. The second set of laboratory tests has shown that the anomalous behaviour identified in the first set of tests can occur in ordinary operational conditions of a network, implying potential technical and economic consequences in terms of damage to pipes and hydraulic devices.

Keywords: pressure reducing valve (PRV); anomalies; instability; low flow
Comments on this paper
Cristina Verde
control issue
The experiment shows a practical issue of a valve, when the operation point of the pipeline is not considered. This is a problem from control point of view.
Valentina Marsili
Thank you for comment. We agree that the focus is on the control of the piston of the valve that, through its opening degree, fixes the pressure value downstream the valve itself. Indeed, the analysed PRV does not have an electronic control system as the piston is mechanical and controlled through the pilot by the pressure value occurring in the pipeline in the section immediately upstream the valve itself. The behaviour of the valve thus depends on the pressure and on the flow in the pipe where the valve is located. In fact, for flow rate greater than 0.7 L/s the pressure control mechanism seems to work correctly. Some problems occur when the flow rate becomes lower than 0.7 L/s with the occurrence of an important instability for flow rate lower or equal to 0.2 L/s, range of flow rates not uncommon for real hydraulic districts. We remain totally available for further clarifications.

Valentina Marsili