One number on the pump nameplate picks the model. Selection tables by pump current, by floors and units, by circuit breaker, and the pressure suggested for each building height.
Chosen correctly, a pump controller keeps building water pressure steady and makes the pump last longer. Chosen wrongly, one of two things happens: the unit keeps reporting an over-current fault and stopping the pump, or it runs beyond its rating. This guide settles which HYDROSET model suits your building in a few minutes.
The only number you really need
The current, in amperes, is printed on the pump's metal nameplate. That single figure decides the model.
| Current on the pump nameplate | Pump power | Suitable model |
|---|---|---|
| up to 8 A | up to 1.5 hp | PM821-8 |
| 8 to 16 A | up to 3 hp | PM821-16 |
| up to 25 A | up to 4 hp | PM821-25 |
If the pump current exceeds the model's rating, the unit reports over current (E1) and stops the pump. Always pick a model rated at or above the nameplate current.
If the nameplate is unreadable
In older buildings the nameplate is often worn away. Use the number of floors and units instead. This table shows the pump normally fitted in such a building and the matching model.
| Floors | Units | Typical pump | Suitable model |
|---|---|---|---|
| 1 to 2 | 1 to 2 | 0.5 to 1 hp | PM821-8 |
| 3 to 4 | 3 to 6 | 1 to 1.5 hp | PM821-8 |
| 5 to 6 | 6 to 10 | 2 hp | PM821-16 |
| 7 to 8 | 10 to 14 | 2.5 hp | PM821-16 |
| 9 to 10 | 14 to 20 | 3 hp | PM821-16 |
The right circuit breaker
The circuit must be protected by a correctly sized miniature circuit breaker. One that is too small will trip when the pump starts.
| Model | Pump power | Miniature circuit breaker |
|---|---|---|
| PM821-8 | up to 1 hp | C16 |
| PM821-8 | 1.5 hp | C10 to C16 |
| PM821-16 | 2 hp | C16 to C20 |
| PM821-16 | 2.5 hp | C20 to C25 |
| PM821-16 | 3 hp | C25 to C32 |
Suggested pressure by building height
After installation you set two main parameters: F1, the pressure at which the pump stops, and F2, the pressure at which it starts. The right values depend on the height of the building.
| Building height | Suggested F1 | Suggested F2 |
|---|---|---|
| 10 m (3 floors) | 3.0 bar | 1.5 bar |
| 15 m (5 floors) | 3.5 bar | 2.0 bar |
| 20 m (7 floors) | 4.0 bar | 2.5 bar |
| 30 m (10 floors) | 5.0 bar | 3.5 bar |
The gap between F1 and F2 should not be too small. A narrow gap means the pump switches on and off constantly, which wears out its switch and capacitor sooner.
Points that get overlooked at purchase
- The unit works with and without a pressure vessel; it makes no difference to model selection.
- If the output drives a contactor, the pump current does not pass through the unit. Detect dry running by pressure rather than by current in that case.
- The supplied pressure sensor covers 0 to 20 bar and has a G1/4 female thread.
- Every unit's sensor is calibrated at the factory, so no initial adjustment is needed.
In short
For most residential buildings up to four floors, PM821-8 is enough. From five to ten floors choose PM821-16, and for higher-power pumps up to 4 hp choose PM821-25. If you are still unsure, tell us the nameplate current or the number of floors and units and we will suggest the right model.
