It is a Combination of valves AS-A/Y-40 (booster) and AS-A/Y-30 or AS-A/Y-35 (surge control valves).
When the pump starts the electric current never exceeds the nominal pump current. The best way to start a pum is with all turns at once expecially for submersible pumps. The hydraulic system of valves AS-A/Y-40 και AS-A/Y-30 ή AS-A/Y-35 remains closed when the pump starts. In that way when the pum starts the current equals the current of losses. From an open contact we give current to the booster valve, which gradually and smoothly starts the pump without exceeding the nominal pump current. Meanwhile the valve AS-A/Y-30 or AS-A/Y-35 eliminates the overpressure waves and in cases of small consumption it returns the released water to the pumping tank.