Adjusting The Zero Point - Grundfos DMX 221 Installations- Und Bedienungsanleitung

3.6 Adjusting the zero point

Make sure the pump was installed and started up correctly.
50
60 40
70 30
80
20
90 10
100% 0
The zero point is factory-set to a counterpressure of 3 bar. If the operating counterpressure at the
outlet valve deviates considerably from this value, we recommend that you readjust the zero point
to obtain more precise values.
1. Install a transparent hose with dosing medium in the inlet valve, or use the scaled pulsation
damper, if installed on the inlet side.
2. For pumps with level control unit, deactivate the function.
3. Start dosing.
4. Set the dosing flow to 15 %.
5. Turn the adjusting knob slowly towards the zero point until the dosing flow stops.
The medium level stops falling in the transparent hose.
6. Stop dosing.
7. Unscrew the locking screw below the stroke-length adjusting knob.
8. Without changing the position of the adjusting knob, remove the plug placed in the middle of
the adjusting knob.
9. Unscrew the screw in the adjusting knob together with the spiral spring.
10. Gently and without turning it, pull off the adjusting knob.
11. Fit it back in such a way that the arrow on the adjusting knob is pointing to zero on the dial.
12. Refit the spiral spring and the screw in the adjusting knob. Tighten the screw until the spring
is slightly preloaded.
Even when turning the adjusting knob to 100 %, the spiral spring must remain preloaded.
13. Screw in the locking screw below the stroke-length adjusting knob.
Related information
• 3.2 Safety instructions and requirements for startup
• 9.6 Dosing curves
WARNING
Chemical hazard
Death or serious personal injury
● Wear protective clothing when working on the dosing head, connections or
lines.
● Collect and dispose of all chemicals in a way that is not harmful to persons or
the environment.
Only adjust the stroke length while the pump is running.
DMX 221 | | 16