Once the oil has been heated to a set temperature it is fed into the vacuum chamber, where the pressure is drawn down to the working vacuum of -0.08 ~ -0.0999 MPa and the oil mist flashes at that pressure. The gas that was dissolved in the oil and part of the water are released at that point. Once released they do not disappear; they have to leave the machine along the pumping path. Many sites treat this section as "pumped away and done", but as soon as the mixture enters the pumping path it splits into two destinations that are handled in completely different ways.
What actually flashes out
What comes out is not a single substance but a mixture: the gas that was dissolved in the oil, the part of the water present as vapour, and a small amount of air carried in with the oil. The targets the ZYD-100 sets for the treated oil are gas content ≤0.01% (GB/T 423) and water content ≤3 ppm (GB/T 7600). Both figures describe what is left in the oil, which means the substance of degassing is to drive these components out of the oil phase and then out of the machine.
Driving them into the gas phase is only the first step. Once the mixture enters the pumping path it splits again: the part that can return to the liquid phase when it cools, and the part that can only be drawn off. That dividing line is not set by the machine; it is determined by the temperature and the pressure at the time, which is why the same machine behaves differently at different oil temperatures.
The first route: the part that can be condensed back
As the mixture travels along the pumping path, the pipe wall is cooler than the gas stream and heat exchange begins. Water vapour condenses into droplets on the wall, and a small amount of oil carried in the gas stream is separated out as well. The purpose of this section is to recover first everything that can turn back into a liquid, and only then let the remaining gas take up the pumping speed of the vacuum pump. Without that step the pump has to handle the whole load directly.
To judge on site whether this section is working, look at two places: first, whether liquid is being discharged at the drain, and second, whether there is condensation or oil film on the outside of the pipework. Both places are normally in the pipe run between the chamber and the pump. If there is a lot of water on the outside of the chamber while the drain is dry, the liquid has most probably condensed on the chamber wall and has not yet entered the pumping path.
The second route: the gas that can only be drawn off
The remaining gas consists mainly of dissolved gas, water vapour and air. At a working vacuum of -0.08 ~ -0.0999 MPa it cannot be liquefied, so it can only be removed by the vacuum pump. The vacuum system of the ZYD-100 consists of the X-100 vacuum pump and the JRP-500 roots blower, the front stage extracting and the rear stage boosting, which pushes the ultimate vacuum down to ≤5 Pa. When something goes wrong on this route it usually shows up as the vacuum level failing to reach the working range, or as the pumping speed falling noticeably as the run continues.
| What you see on site | The more likely cause | How to confirm it |
|---|---|---|
| The vacuum builds up, but after a running period it becomes harder and harder to reach the working range | Oil mist has accumulated in the pumping path, or the water vapour load has stayed high | Check whether liquid is being discharged at the drain and review the condition of the vacuum pump oil |
| Water is discharged at the drain, but the water content of the oil will not come down | The condensing section is working; the problem lies in the degassing performance itself | Re-test the water content to GB/T 7600 and check that the temperature control is inside the 45~80 °C range |
| The ultimate vacuum does not reach ≤5 Pa and the pump oil turns cloudy | The mixture carrying oil mist has gone straight into the pump casing | Drain and replace the pump oil, then watch the state of what comes out of the drain |
| Heavy condensation on the outside of the chamber, while the outside of the pipework is dry | The condensation is taking place on the chamber and has not reached the pipe run | Record where the condensation appears on the chamber and on the pipework separately |
Why the two routes have to be looked at separately
If the mixture carrying oil mist goes straight into the vacuum pump, the pump oil is contaminated and the ultimate vacuum falls with it. If the condensing section fails to condense the water and a large volume of water vapour hits the pump chamber, the pumping load on the pump increases noticeably. This is why the condition of the pump oil, the gas content of the oil and the ultimate vacuum have to be read together; a conclusion drawn from any one of them on its own is easily wrong.
- When judging the condensing section, what comes out of the drain is a more reliable indication than the outside of the chamber, because the latter is strongly affected by the ambient humidity.
- When judging the pumping section, whether the ultimate vacuum holds at ≤5 Pa is a more sensitive indication than the working vacuum gauge.
- If both figures fall, verify them one at a time; do not change the pump oil and the pipework together, or there is no way to tell which of them made the difference.
Condensing takes back the part that can turn into a liquid and exhausting removes the rest; mix the two together and the condition of the pump can never be pinned down.
