3. Pressurized gravity feed systems

In this type of application (figure 11 ), the head Z ₀ is negative. The role of the pump is to increase an insufficient gravity flow and very often to regulate this additional flow according to the time of day, the season... etc., to avoid wasting water while satisfying needs.

In this type of application, the minimum flow rate is imposed; it is equal to the gravity flow rate of the system. At a lower flow rate, energy would be consumed purely as a waste: the pump would operate at a slightly negative head, in parallel with the bypass valve. The operating range is therefore a priori fixed, between the gravity flow q _G and the nominal flow Q _N...