The vacuum level is the most direct indication of the condition of a vacuum oil purifier. The working vacuum range of the ZYD-100 is -0.08 ~ -0.0999 MPa and the ultimate vacuum is ≤5 Pa. The vacuum level that will not reach its value is reported from site in two forms: the reading sticks near -0.05 MPa and will not go lower, or it reaches -0.08 MPa at start-up and then falls back slowly after a few minutes. The two point to different causes, and the order of investigation is different as well.
Work through the five gates below in order: pump and pump oil → leaks in the pipework and the joints → booster stage → oil temperature → feed rate. The first three are on the equipment side, the last two are on the operating condition side. If the previous gate has not been cleared, measuring the ones after it means nothing.
First gate: the vacuum pump itself and the pump oil
The pump oil is the lifeblood of the vacuum pump. Emulsified, blackened or carbonised pump oil, a viscosity that is not right, or an insufficient oil level all reduce the pumping speed. The ultimate vacuum of ≤5 Pa is a figure for the no-load condition and cannot be reached under load, so the point is not the figure itself but two other things: whether the condition of the pump oil is normal, and whether the difference between the no-load ultimate vacuum and the reading under load is still the same.
Some of the confirmation can be done without dismantling the machine. After stopping it, look at the oil level in the sight glass and whether it is within range, whether the oil has gone cloudy or black, and whether the pump body is noticeably hotter than the other equipment; then carry out a no-load vacuum test as described in the machine manual and see whether the reading settles at a stable value. If the level does not come up even with no load, the problem is in the pump or the pump oil and there is no need to go on to the pipework.
Second gate: leaks in the pipework and the joints
This is the most common case and also the easiest to check yourself. The typical signs are that the reading falls steadily during a no-load vacuum test and recovers after the machine has been stopped and left standing for a while, or that after start-up it can only reach about -0.05 MPa and will not go any lower.
The way to confirm it is a soap solution made up on site: dilute washing-up liquid with water to a slightly viscous solution, and brush or swab it onto every joint, flange, seal ring, sight glass and pump port of the vacuum pipework, then let the system build up the negative pressure slowly. Where a continuous string of bubbles appears is the leak. This has to be done with the machine stopped, depressurised and cooled; do not break a joint while the machine is under pressure and energised. Wipe the soap solution off afterwards, because the residual moisture on its own contaminates the pump oil.
Third gate: has the booster stage failed?
The ZYD-100 uses a combination of a rotary vane pump and a JRP-500 Roots blower, with the Roots blower acting as the booster: it compresses the gas drawn by the first stage and passes it on to the rotary vane pump. If the Roots blower is not working or its efficiency has dropped, the system is effectively one compression stage short, the achievable vacuum level is markedly worse, and the machine shows that it cannot pull: the vacuum level falls away quickly once the oil is admitted.
Two points tell it apart on site: whether the running sound and the running current of the Roots blower are clearly different from those of the other pumps; and whether, with the system isolated as described in the machine manual and an ultimate vacuum test carried out, the vacuum level comes up. If it does, the pipework and the seals are sound and the problem lies in the way the stages of the pump set are matched.
Fourth gate: has the oil temperature reached its set value?
The boiling point of water changes with temperature, and if the oil does not come up to temperature the water vapour in the vacuum chamber does not vapourise and separate easily, the vapour partial pressure stays high, and the vacuum level appears not to come up either. The temperature control range is 45–80 °C, with the upper limit brought down to 70 °C where the water content is high. Staying below the lower limit, or having the heating capacity taken away by the large amount of moisture that vapourises, both show up as a poor vacuum level. The way to judge it is to check the actual oil temperature against the set value, rather than looking only at the heater indicator lamp.
Fifth gate: does the feed rate exceed the degassing capability?
The last gate is the operating condition. As the feed rate rises, the oil level in the tank rises and the exposure time of each drop of oil shortens, so the degassing is incomplete; at the same time the gas load rises. Both pull the vacuum level down. The way to judge it is a step test: reduce the feed rate by one step, hold it for ten minutes or so and see whether the vacuum level recovers. If it recovers, the machine was overloaded and the rate that recovers is the usable rate under the present condition. If it does not, one of the earlier gates has not been resolved.
| Gate | Typical symptom | How to confirm | Action |
|---|---|---|---|
| Pump and pump oil | The vacuum level does not come up even with no load | Check the pump oil colour, the oil level and the pump body temperature, and carry out a no-load test | Stop the machine, disconnect the power, change the pump oil and check the pump set |
| Pipework joints | The reading falls slowly and recovers after the machine is stopped | Apply the soap solution point by point and look for a continuous string of bubbles | Stop the machine, release the pressure, then tighten up or replace the seals |
| Booster stage | The vacuum level drops out of -0.08 MPa quickly once the oil is admitted | Compare the sound and the current of the Roots blower, and carry out an isolated test | Stop the machine and check the Roots blower and the drive |
| Oil temperature | The vacuum level is low and the oil temperature is below the set value | Check the actual oil temperature against the set value | Check the supply to the heater and the temperature control probe |
| Feed rate | The vacuum level recovers after the feed rate is reduced by one step | Reduce the rate in steps and compare | Run at the usable rate, or change to a model with a larger throughput |
The safety preconditions for the leak check and for dismantling
The soap solution leak check has to be done with the machine stopped, depressurised and cooled; dismantling the pump, changing the pump oil and working on the seals all require the power to be disconnected first and the lock-out tag applied. If any one of those steps is not carried out properly, the conclusions drawn afterwards are not reliable. Checking for leaks under pressure can cause an oil spray accident, and it can also cause a leak to be missed because the seal is temporarily held closed.
When the vacuum level will not come up, first establish whether it is not coming up at all or whether it has fallen away: if it is not coming up, check the pump and the pump oil; if it has fallen away, check for leaks and for the feed rate.