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15/05/2024

Pressure switch. The fuel pressure switch on the boiler has failed. What is an abnormal fire?

Greetings! Today our fuel pressure sensor on the boiler failed. We found out about this as a result of the malfunction of the boiler and the alarm “Abnormal fire” on the panel. This problem is quite critical and requires an immediate solution.

Pressure switch. The fuel pressure switch on the boiler has failed. What is an abnormal fire?

According to the instructions, the pressure in the line to the fuel spray nozzles should be about 20 kg, the pressure switch setting should be about 14 kg (low pressure protection).

Below I propose to figure out what this problem is and what it can lead to in the future.

What is an abnormal fire?

When the pressure switch is triggered, the fuel supply is cut off and the boiler stops. If this does not happen, then at low pressure in the line (14 kg and below), the fuel will not be immediately cut off, but will be incorrectly sprayed (poured) into the firebox and “torn” pieces of flame will form. For this reason, the "Abnormal fire" alarm will sound and the boiler will stop.

Another problem may arise if the burner has nozzles without non-return valves; in such situation, if the pressure switch is not working, small amount of fuel will leak to the boiler furnace, which can lead to fire and flame pops.

Old pressure switch (calibration attempt)
Old pressure switch (calibration attempt)
Fuel pressure gauge (about 20 kg)
Fuel pressure gauge (about 20 kg)

This problem was discovered as a result of the “Abnormal fire” alarm, which is a general alarm and the engineer on duty for a long time could not understand what the “wrong flame” problem was. This could be a lack or, on the contrary, a large amount of air supplied to the nozzles, it could be a problem with the photocell, temperature or fuel pressure (but there is no low pressure alarm and at the same time the engineer did not pay attention to the pressure gauge, which already had insufficient pressure).

Operation of the pressure switch on the circuit diagram
Operation of the pressure switch on the circuit diagram
Low fuel pressure protection

Low fuel pressure protection

Low fuel pressure protection helps the engineer quickly understand the problem, but even if it does not work, there is still the end protection for the “wrong flame” in the boiler furnace.

New pressure switch
New pressure switch

As a result, it was not possible to restore the old pressure switch, and calibration also did not help. Therefore, I had to replace the pressure switch with a new one. The pressure setting according to the instructions should be 14 kg and the differential should be about 1 kg.

After installing a new pressure switch, the low fuel pressure protection was tested with a positive result.

Boiler model: Miura GK-2230-1400.

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