The typical symptom is like this: the same vacuum oil purifier processes the same batch of oil and the water content at the inlet and at the outlet differs very little; after several hours of continuous running, the sample sent for testing still sits near the 3 ppm (GB/T 7600) acceptance line. The most common reaction on site is to change the filter element at once, change the pump oil and suspect that the machine has had it, and as a result the time is spent on the least likely places.
The order to follow is this: the water content of the incoming oil itself → whether the condensate is draining off properly → whether the vacuum level has really reached its value → and only then the machine itself. The first two steps do not require dismantling, the third is a matter of reading the instruments, and only the fourth involves dismantling with the machine stopped and the power disconnected. In this order the cost of the investigation runs from high to low, and the machine is not opened up at the outset.
First step: confirm how high the water content of the incoming oil is
If there is a large amount of free water in the incoming oil, the machine is actually doing the job of carrying the water away from the oil, not of extracting the water from it. The way to judge this is direct: take one sample at the inlet and one at the outlet and measure the water content with the same method at the same time. If the incoming oil is already far above 3 ppm, the first thing to do is staged pre-treatment: let the oil stand or pass it through a coarse filter to take the free water out first, and only then feed it into the vacuum chamber, rather than increasing the vacuum further.
Another variable that is easily overlooked is temperature. Oil with a high water content that stays above 80 °C for a long time vapourises a large amount of water, the gas load in the tank rises sharply, the load on the vacuum pump increases and the degassing efficiency falls. This is why the temperature control upper limit is brought down to 70 °C when the water content is high: a little speed is given up in exchange for a stable vacuum system.
Second step: confirm that the condensate is really being drained off
Dehydration depends on vapourising the water, recovering it as a liquid in the condensing section and draining it away. If it is not drained away the water circulates in the system, and the water content naturally does not come down. There are three common points at which it stops: the drain channel is blocked by dirt or sludge; a float type or solenoid drain valve is stuck, with the float held up by dirt so that it cannot close, or held down by debris so that it cannot suck the water out; or the drain line is connected the wrong way round or forms a siphon, so the liquid cannot get out and air is drawn into the vacuum system instead.
- Look at the amount and the frequency of the water drained off: if almost nothing is drained during a shift while the incoming oil is clearly wet, the water is not being separated out at all.
- Look at the appearance of the drained water: if it is cloudy, carries oil or contains flocculent matter, the water that was separated carries oil with it and the drain channel is dirty as well.
- Listen near the drain outlet: a continuous gurgling sound or a pipework that is drawn flat indicates a siphon or a reverse flow under negative pressure.
Third step: confirm that the vacuum level has really reached its value
The vacuum level is a direct reflection of the degassing capability. The working vacuum of the ZYD-100 is -0.08 ~ -0.0999 MPa and the ultimate vacuum is ≤5 Pa. When judging it, do not rely on the instantaneous value on the panel: the reading naturally fluctuates while the machine is taking in oil, heating or switching between operating states, so watch it for several minutes in steady running. If the steady value clearly fails to reach -0.08 MPa, the investigation turns to the leaks, the pump oil and the pump set.
Fourth step: and only then the machine itself
| Symptom | Most likely cause | How to confirm | How to deal with it |
|---|---|---|---|
| The incoming oil is dry and the water content at the outlet is still high | The condensate is not draining off | Check the amount drained off, the appearance of the drained water and the action of the drain valve | Stop the machine, release the pressure, clear the drain channel and clean the float or the drain valve |
| The water content of the incoming oil is extremely high | The gas load exceeds the degassing capability | Measure the water content of the incoming oil and see whether the vacuum level frequently drops out of -0.08 MPa | Pre-treat in stages and bring the temperature control upper limit down to 70 °C |
| The vacuum level does not come up and falls continuously | A leak in the pipework or at a joint | Apply the soap solution to the joints and see whether bubbles form continuously | Stop the machine, release the pressure, then tighten up or replace the seals |
| The vacuum level fluctuates and the note of the pump becomes coarse | The pump oil is emulsified or the oil level is low | Look at the transparency of the pump oil, the level and the pump body temperature | Stop the machine, disconnect the power, change the pump oil and top up the level |
| The oil temperature does not come up and the vacuum level is low | Insufficient heating capability | Check the actual oil temperature against the set value | Check the supply to the heating element and the temperature control probe |
The safety preconditions before any work is carried out
In the checks above, every step that involves opening the pressure gauge, removing a drain valve or handling the pump oil requires the machine to be stopped, depressurised and disconnected from the power, in that order. Dismantling under pressure sprays the oil out, and incomplete depressurising brings residual pressure out the moment the cover is opened; the power is disconnected so that the heating circuit and the pump cannot start by themselves during the work. If the order is reversed, at best a seal is left out and leaks once the machine is reassembled, and at worst someone is burned.
When the water content does not come down, do not change the filter element yet. Measure the water content of the incoming oil once, then look at the drain once; those two actions rule out more than half of the possibilities.