Background
The main aqueduct in Costa Rica is operated by the Costa Rican Institute of Aqueducts and Sewers (AYA). It feeds some of the most populated zones in the metropolitan area.
Challenge
High level water losses
Leakage and pipe rupture-related water losses in the system reached about 50% of the total input volume. Due to varying demand and long pipelines from the installation point to the ends of the supplied system, the system’s operators had to set inlet pressure at a level high enough to overcome friction head losses during maximal demand. At night, when demand flow is low and there is less friction, pressure in supplied zones increased which, in turn, produced higher leakage rates and pipe ruptures.
An old valve on the main aqueduct in Costa Rica
Solution
Modulating water pressure
In this gravitational aqueduct, pressure control and management were considered to be the most immediate and effective form of intervention to reduce water losses and reduce the rate of new pipe breaks. The idea of implementing a sophisticated regulation system powered by electricity was rejected, due to frequent power cuts in the area. Battery-operated control was also rejected, as it requires a high level of operator skill, and is considered less reliable in the long run, compared to hydromechanical control.
The required solution had to be simple, easy to operate and more effective than other systems that control pressure to a fixed value, or control it according to time of day.
With guidance and support from Dorot’s local distributor, R&M Costa Rica, a hydraulically flow-modulated pressure-reduction system was selected as the best solution, specifically the 24″/600 mm Dorot model 32-24-PRM (HyMod) – a pilot operated pressure-reducing valve with flow-modulated set-value. It is 100% hydromechanical, with no special mechanisms nor moving elements that may fail, making it highly reliable. Using no electronic controllers and requiring no battery or external power source, the PRM (HyMod) uses standard pressure-reducing pilot valves as its only control devices.
24"/600 mm Dorot model 32-24-PRM (HyMod) - a pilot operated pressure-reducing valve with flow-modulated set-value
Results
Minimum required pressure guaranteed
The system was installed, commissioned and adjusted to modulate between 50 psi downstream-pressure at minimal demand flow, to around 60 psi at maximal flow, guaranteeing a minimum required pressure at the supplied zones during periods of both low and high consumption.
