The motor does not always start from the pump station, what is the reason?

Hello. Nikolay, it would be nice to know the details of your problem. It is difficult to answer questions accurately when information is given superficially.

Please note, here are additional questions, if you feel like it, answer them in the comments:

1. How is it buzzing? How does the pump usually buzz, with wheezing, interruptions, or what?
2. “There are cases” - how often?
3. “After some time, begins to pump water” - after how much and how is everything with water, clean, jerky or normal?
4. What is the model of the pumping unit?

But still, we will try to resolve your situation:

1. The first thing you need to do is pick up the instructions from your station and read the section “Possible problems and methods for their elimination”.
2. You hear a buzz, but the impeller of the motor makes no movements. And then the motor starts suddenly, not always at regular intervals. We clarified this moment, you measured the voltage, everything is fine.
3. Check valve or impeller clogged / salted - remove, clean.
4. There is a problem with the capacitor running to start. This happens when it is oxidized, there are breakdowns in the motor winding and so on. It is necessary to very carefully check whether the rotor spins in the off state of the pump and the station.
5. The problem with the bearings. When a similar problem occurs, the impeller of the motor will rotate heavily. This can happen even if it is salted or there is dirt on it, very often this option also occurs with prolonged stagnation of the mechanism or when the equipment is in the well compartment.
6. There are breakdowns or weaknesses on connections, hoses, etc., that is, the pump is not equipped with a “dry run” system (and this is not always a reliable design), it begins to “breathe”.
7. Breakdowns, a breakthrough in the membrane of the station (though then there will most likely be other symptoms).
8. Water has gone, and the suction depth has increased to critical for the pump, since then it needs acceleration to set.

If you are not confident in your abilities, call a specialist.