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8. Minimum stop frequency at 0 delivery (f min Q=0) during constant
pressure control.
Minimum stop frequency is the minimum frequency value that, while maintaining the p_set , water delivery is zero.
Below scheme graphically shows the function:
Progressively closing the water delivery valve reduces flow, causing VASCO to reduce the pump speed by reducing the output
frequency, to maintain a constant pressure (i.e. 3 bar).
Once the water flow stops (output completely closed), pump will run at minimum frequency to maintain the set pressure.
Upon determining that the water requirement has stopped, VASCO stops the pump to save energy. Thus, the pump will be
stopped when minimum frequency is reached.
Once the pump is stopped at min. frequency value, set pressure is maintained in the system.
To maintain the pressure on the pump output line, it is necessary to install a small pressure tank able to compensate for
minor water leakage and to limit the number of pump restarts.
It is important to pinpoint that a particular set pressure corresponds to a single value of min. stop frequency.
So, if the end user wants to change the set pressure, a new value of min. stop frequency should also be set.
9. Auxiliary pumps during constant pressure control
When the water needs vary considerably, it is advisable to share the water request between several pumps ensuring better
efficiency and reliability.
A first method consists of a single pump driven directly by VASCO and another 1 or 2 pumps directly connected to the mains
DOL (Direct On Line); DOL pumps are controlled by VASCO and connected to the mains through 1 or 2 contactors.
In this method, DOL pumps are not started and stopped smoothly with the corresponding increase in energy consumption
and mechanical wear (startup current). Also note that DOL pumps are not protected by VASCO.
A second method of sharing water demand (named COMBO mode) consists of using additional pumps in parallel (up to 8),
with each one driven by a VASCO.
