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In this method, energy consumption and reliability of the pumping system is maximized: VASCO monitors and protects each
pump. It is possible to assemble a booster system composed of pumps connected in COMBO mode and another 1 or 2 DOL
pumps to cover additional water demand (menaged only by master).
9.1 DOL pumps
Each DOL pump is switched on by a contactor controlled by the digital output DOL1 and DOL2 present in the VASCO.
Two pumps are connected in parallel, with one pump (pump 1, P1) run by the inverter, while the second pump (pump 2, P2)
is directly connected to the main power (“Direct On Line” connection). Start/Run of the second pump is controlled by the
relay DOL1 (allowing a third pump to be controlled by the relay DOL2).
If pump 1 (P1) is already running to maintain the desired set pressure (red line) , an additional water request changes the
system curve from C1 to C2 ; since pump 1 (P1) is running at maximum speed, it is not possible to maintain the set pressure
by increasing the speed, so the system pressure will drop till reaching the new working point 2.
If pressure at the point 2 is (p_set – delta start pres), VASCO will run the DOL by relay DOL1. The DOL pump will run at its
nominal speed while the pump 1 will drop it speed equal to the P1 pattern to maintain set pressure.
If water demands decreases, returning to the system curve C1, pump 1 will reduce the pump speed to maintain constant
pressure in the system. When pump 1 reaches a frequency equivalent to the minimum frequency, while still maintaining set
pressure, the DOL pump will be switched off and pump 1 will increase the speed to maintain the p_set in the system.
VASCO relays driving the DOL pumps are relays with no voltage contacts. Max voltage to the contacts is
250 V, max current 5 A.
C1
C2
P2
P1@f min Q=0
P1+P2
C1
C2
P2
P1
P1+P2
delta start pres.
1
2
3
Q
H
Q
H
