The habit on many sites when an alarm comes is: the lamp is lit, look at it once, the sound goes off, press the reset, the machine carries on running. For an overpressure alarm that habit is dangerous, because overpressure is not a prompt but a warning given before the last stage of the protection chain.
First link: at a pressure above 0.3 MPa the element has reached the point where it needs attention
Taking the TYA series as an example, a pressure above 0.3 MPa means the element has to be cleaned or replaced. The figure of 0.3 MPa is not chosen at random: once the contaminants trapped on the surface of the filtration medium have built up to a certain thickness, the oil needs a higher pressure to pass through, and a pressure that keeps rising means the build-up is still getting worse. If the machine only alarms and does not stop at that point, the element continues to work at a higher differential pressure, the contaminants are compacted into the deeper layers of the medium, the pressure rises faster and eventually the medium ruptures or the bypass opens, and the treatment quality runs out of control.
Second link: the audible and visual alarm brings someone to site
The purpose of the audible and visual overpressure alarm is to bring a person to the machine while it is still within a controllable range. It carries two layers of information: on the one hand that the pressure has reached a level worth paying attention to, and on the other hand where specifically to look, whether the filtration element needs cleaning and replacement or whether the pressure fluctuation comes from the oil inlet side. Both channels are provided because a single channel is easy to defeat: relying on the figure on the screen alone, with long intervals between night-shift inspections, a person may not see it for hours; relying on the sound alone, it cannot be heard in a noisy workshop. The two channels complement each other, and if one is weakened by the environment the other still backs it up.
- When the alarm appears: stop the oil feed, look at the pressure gauge and the level first, and establish whether the problem is on the oil inlet side.
- When an element change is confirmed: stop the machine, release the pressure, remove the elements in order and clean or replace them.
- Resetting and running on: this amounts to skipping the second link, leaving only the last gate on the protection chain.
Third link: the stop protection is the last gate
The purpose of the automatic stop protection is to stop the machine when nobody has responded in time. It catches several specific situations: the element is completely blocked and the pressure keeps climbing; a mistake on the oil inlet side closes a valve and the pressure builds up with nowhere to go; the heating runs away or the condensate is abnormal and the pressure inside the tank rises abnormally. Once the machine has stopped the pressure is released and the machine stands in a relatively safe static state, waiting for someone to deal with it. The automatic stop is not meant to let the machine recover by itself, but to stop the risk where it is.
What happens if it is reset and run on
Resetting and running on after an alarm carries the risk up a chain: the differential pressure is not dealt with, so the pressure climbs back to the alarm value; the medium is compacted further under the high differential pressure; the filtration element ruptures or the bypass opens and the particles that were not held back pass into the downstream side; the cleanliness of the outlet oil falls while the machine shows everything normal, and by the time the user notices, the problem has changed from replacing one element to reprocessing the whole batch of oil. The other common consequence is that the heating and the vacuum system keep working under an abnormal pressure, with a higher load on the vacuum pump and fluctuating oil temperature, and the treatment indicators drift away from their values.
The correct sequence is: stop the oil feed first, release the pressure, and establish whether the element or the oil inlet side is the cause; where it is the element, clean or replace it and start again, watching how fast the pressure rises in the first few minutes; where it is the inlet side, remove the cause and then restart. The alarm record is itself a basis for judgement: the same alarm recurring means the conditions themselves have to be adjusted, rather than each time changing an element and leaving it at that.
| Link | Trigger condition | What it catches | Action on site |
|---|---|---|---|
| Threshold check | Pressure above 0.3 MPa | The early signs of a failing filtration element | Stop the oil feed and check the element |
| Audible and visual alarm | The limit exceeded and sustained | The absence of information when nobody is on site | Go to site and confirm the pressure and the level |
| Automatic stop | The limit exceeded and not reset | The continued deterioration when nobody responds | Stop, release the pressure and investigate |
| Return to service | The cause has been removed | Running with a fault still present | Watch the rate of rise of the differential pressure in the first few minutes |
The logic of the protection chain is that the threshold detects, the alarm calls someone, and the stop backs it up; resetting straight away and skipping the middle link means treating the last gate as the only one.