"Automatic pump switch" covers both the mechanical pressure switch and the electronic controller, although the two are not the same. A comparison table and which one suits you.
In the Iranian market the phrase "automatic pump switch" covers two different things: the mechanical pressure switch and the electronic controller. The two are not the same. An automatic switch, in the general sense, is any device that starts and stops the pump without the user intervening; a smart controller is a subset of that which reads the pump current and the unit temperature as well as the pressure.
Why the ambiguity matters
When a seller says "automatic switch", the meaning may be a cheap part with a spring and a diaphragm, or a unit with a display and fault codes. The price gap is wide and the gap in what they do is wider. Ask which one it is before buying.
What a mechanical pressure switch does
A spring and a diaphragm make and break the contact at a set pressure. That is all. The part does not know how much current the pump draws, whether water is reaching it, or how hot it has become. The pressure is set with a screw and a spring, not with a number.
What a smart controller adds
An electronic controller measures the line pressure continuously with a sensor and decides from that figure. HYDROSET PM821 starts and stops the pump and also reads the pump current, stopping the pump in three dangerous conditions: dry running, over current, and a rise in the unit's internal temperature.
| Subject | Mechanical pressure switch | HYDROSET PM821 controller |
|---|---|---|
| Pressure setting | By spring, approximate | Numeric — F1 and F2 on the display |
| Pump start | Abrupt | Soft, over the F11 time |
| Pump stop | Abrupt | Soft, over the F12 time |
| Dry running | Not detected | By current (F4) or pressure (F10) |
| Over current | No protection | Stops above the F3 current |
| Over temperature | No protection | Stops, then returns automatically |
| Status display | None | Four-digit display with fault codes |
| Retry | None | Automatic, every F6 minutes |
Why the soft start matters
When a pump starts abruptly, the column of water in the pipe accelerates and water hammer follows. Over time that shock loosens fittings and wears valves. On HYDROSET PM821 the soft-start time is set with F11 and the soft-stop time with F12, and the factory value of both is 0.2 seconds.
Which one suits you
If the only issue in the building is starting and stopping the pump, and the pump never runs out of water, a mechanical pressure switch does that job for less money.
If any of these are also in play, a smart controller covers all three:
- Pressure swings on the upper floors
- Water hammer in the pipework
- The risk of the pump burning out when the supply is cut
Replacing it is not difficult
The controller takes the place of the pressure switch directly: the sensor screws onto the pipe after the check valve, and the incoming supply and the pump output go to the unit's terminals. No pipework changes. The full steps are in the installation guide.
The full comparison table is on the controller vs pressure switch page. To choose a model from the pump's nameplate current, see PM821-8 up to 8 A and PM821-16 up to 16 A.
