Once summer arrives, the oil purifier itself does not need any modification, but its running behaviour changes noticeably. The symptoms most often mentioned are that the vacuum level will not come up, that the water content comes down more slowly, and that the machine alarms and stops after a long period of continuous running. These symptoms share a common physical cause: the temperature throughout the system has risen, and vacuum degassing is very sensitive to temperature.
What the rise in temperature changes
Vacuum degassing depends on two things: heating the oil to a suitable temperature so that the stability of the dissolved gases is broken, and condensing the water vapour into water on a cold surface. Once the ambient temperature rises, the efficiency of the first step actually improves, because the oil temperature comes closer to the range in which degassing works; but the second step gets worse. The temperature rises everywhere in the system, the dew point rises with it, and water vapour that could previously be condensed no longer forms liquid water at the same vacuum level but stays in the system in the gas phase.
This produces what looks like a contradiction: at the higher temperature the gas leaves the oil faster, yet the water content indicator comes down more slowly. The water has become vapour but has not fallen as condensate and been drained away, and at the moment of testing it returns to the oil in dissolved form. The load on the vacuum pump becomes markedly heavier at this point, since it has to draw off both the dissolved gas in the oil and the increasing amount of water vapour in the system.
Deciding on a load reduction from the readings
Rather than deciding by season, look at a set of specific readings. The items below can all be seen directly on site, and taken together they largely show whether the equipment is adapting normally to the high temperature or already needs manual intervention. The principle is to look at the direction of change: the same figure means something different in a different season. The -0.08 MPa read on the same batch of oil in spring and autumn does not mean the same as the same figure read at the height of summer.
| Reading observed | What it indicates | Suggested action |
|---|---|---|
| The vacuum level stays around -0.08 MPa for a long time | The pump cannot pull, or the water vapour load in the system is high | Check the condensation and the temperature of the vacuum pump oil, and reduce the feed rate if necessary |
| The water content measured by GB/T 7600 comes down more slowly | The water vapour is not being condensed into liquid water | Reduce the throughput, extend the degassing time and improve the condensing conditions |
| The temperature of the vacuum pump oil rises noticeably | The viscosity of the pump oil falls and the pumping speed of the pump deteriorates | Stop the machine, let it cool, change the pump oil and start up again once it has recovered |
| The overpressure audible and visual alarm operates frequently | Insufficient condensation and heat dissipation raise the pressure on the gas side | Shorten the continuous running period and work in batches |
| The current of the circulation pump runs higher than usual | The resistance in the oil circuit has changed, possibly in relation to the condition of the element | Check the differential pressure of the element and confirm the state of the bypass valve |
A load reduction is not a shutdown
A load reduction means lowering the amount processed per unit of time, or shortening the continuous running period; it does not mean switching the machine off. The usual approach is to change long continuous processing into batch processing with intervals: process each batch until the set quantity is reached, then stop, leave the pump stopped and let the oil stand so that the temperature falls back into a range more favourable to condensation, then start the next batch. The total handled is unchanged, but the load in a single continuous run is much lower.
A second set of actions belongs on the environment side. Moving the machine out of direct sunlight, ensuring ventilation in the equipment room or the working area, cleaning the dust off the heat transfer surface of the condenser, and forcing air over the vacuum pump where necessary are all low-cost changes with a direct effect on the dew point and on the temperature of the pump oil. Many sites have not touched the machine settings at all and have simply moved the cabinet from outside to inside, and the situation has clearly been different since.
The temperature limit is a parameter, not a recommendation
It is worth repeating that the heating temperature has a definite range. Taking the TYA series as an example, the temperature control range is 45–80 °C, with the upper limit brought down to 70 °C where the water content is high, and the applicable ambient temperature range is -20–45 °C. In the hot season, if the site is already close to the upper limit of the ambient range, the machine has no additional heat dissipation margin for a higher ambient temperature, and the only option is to bring the feed rate down so that the system does not stay at high load for long periods.
- Re-plan the batch size against the highest ambient temperature of the day instead of keeping to the spring and autumn rhythm.
- Allow a settling time between the batches so that the temperature and the condensation return to a controllable range.
- Include the temperature of the vacuum pump oil and the amount of condensate drained off in the shift records, as a basis for deciding on a load reduction.
- After an alarm and a shutdown during continuous running, check the heat dissipation and the condensation first before considering increasing the vacuum extraction.
The problem in summer is not that the capability of the equipment is insufficient, but that the same capability has to deal at the same time with the oil temperature rising and the condensation becoming harder.