applied sciences Article Application of Time-Controlled Critical Point in Pressure Reducing Valves: A Case Study in North Spain  
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Departamento de Fisica Aplicada, Radiologia y Medicina Fisica, Universidad de Cordoba, Campus de Rabanales, 14071 Cordoba, Spain; ggl2 orba@ucos (A.O.-B. ); [EMAIL_ADDRESS] (D.M.-R.); [EMAIL_ADDRESS] (M.-J.-A.-U.) GS Inima Environment, C. Gobelas, 41, 28023 Madrid, Spain; [EMAIL_ADDRESS]  
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network [15; 16]. The PRVs are placed in the WDN working under different schemes: fixed outlet (FO), time-controlled (TC), flow modulation (FM) and critical point control (CPC) [17], with the main objective of reducing excess pressure which generates water leakage and water losses [18]. FO is the simplest and most common scheme and only requires the installation of the PRV. It is suitable mainly for areas with uniform supply features and low headloss. The main limitation of this type of control is the inability to adapt to a variable demand pattern, common of areas with seasonal demand. The rest of the schemes, TC, FM and CPC, bring additional benefits to the operation of the network, but their installation is more complex, costly, requires additional equipment and the operator workforce must be well trained to support the installation, operation and maintenance [19]. TC consists of setting different values of pressure at the outlet of the PRV according to the time of the day. TC might be achieved by the addition of hydromechanical parts to the control trim of the PRV or by the utilization of electronic controllers. The most common application is double set-point, where pressure during the minimum consumption period, usually night time, is lowered to reduce leakage and kept at a higher value during peak demand time to satisfy customer demand. Despite this method being widely employed, the literature does not contain too many references about how to select the right settings of the valve. [PERSON] et al. [20] developed a model to calculate time schedules at the outlet of the PRV utilizing a nonlinear programming problem. The use of a genetic algorithm for this purpose was later introduced by [PERSON] et al. [21]. FM pressure-controlled systems rely on a flow signal generated by a flow meter, usually a pulse output or a 4-20 mA signal [22]. This system dynamically adjusts the pressure at the outlet of the PRV according to the flow, following a set-point table introduced by the user. While FM has remarkable benefits, such as being an effective method to address background leakage [23] and the possibility to adapt to real time demand [24], it also encounters some inconveniences, mainly from an operational point of view. These restrictions relate to the unavailability of a working flow meter at the installation site: sometimes it is not an option to install a flow meter due to lack of budget or because there is not enough space at the installation site.