Half of the decision about the oil change interval is already settled at the moment the oil has been purified to the required state. The purification quality is often treated as a one-off acceptance indicator: it is measured once as the oil leaves the tank, and if it passes, the job is closed. But the oil keeps serving in the equipment after purification, and how much residual contaminant it carries into that service decides how much work those contaminants can still do. So how far the interval can be extended by a cleaner batch ultimately comes down to the state left behind at the start.
What purification leaves behind is what the service period has to live with
Purification has to deal with three things: water, gas and particles. The work of the three does not stop at the moment the oil leaves the tank; after they enter the service period they go on acting by their own mechanisms.
- In the service period the water goes on migrating into the oil-paper insulation and the metal parts, and the lower the initial residue, the lower the starting point available for that migration.
- In the service period the gas goes on coming off and gathering in the gas phase at the top of the tank, and the initial gas content decides the state that space starts in.
- After entering the service period the particles go on migrating inside the equipment and along the oil circuit, and the lower the initial cleanliness, the higher the starting point in the early hours of operation.
These three are not three separate judgements standing side by side; they are three continuations of the same thing into the service period. Purification pushes each of them down to its target position, and the service period afterwards is the process of letting them carry on from that position.
Where the three indicators set the starting point
The targets the ZYD-100 sets for the treated oil are: water content ≤3 ppm (GB/T 7600), gas content ≤0.01% (GB/T 423), cleanliness NAS 1638 class 5, breakdown voltage ≥65 kV (GB/T 507), filtration accuracy ≤1 μm. Taken together these figures describe the actual state of the oil as it leaves the machine, not the way the machine is described in advertising.
Two kinds of figure have to be told apart here. The filtration accuracy of ≤1 μm is the retention capability of the filter media, something the machine does; cleanliness of NAS 1638 class 5 is the cleanliness class measured on the treated oil sample, and that is a result. The accuracy of the machine sets the lower limit of the result, while what actually has to be re-checked at acceptance is the result itself. The same applies to the water content and the gas content: both are measured by standard methods and describe a specific state attached to this batch of oil.
| Item | Basis | Target value for the ZYD-100 | The starting state it describes |
|---|---|---|---|
| Water content | GB/T 7600 | ≤3 ppm | How much water is left in the oil |
| Gas content | GB/T 423 | ≤0.01% | How much dissolved gas is left in the oil |
| Cleanliness | NAS 1638 | class 5 | How many particles are left in the oil |
| Breakdown voltage | GB/T 507 | ≥65 kV | The ability of the oil to withstand an electric field |
| Filtration accuracy | Machine capability | ≤1 μm | How large a particle the filter media can hold back |
How the quality carries through to the interval
The interval is not a fixed number; it is decided by several things together, and the purification quality is the one that is quoted again and again. The first is how clean the starting point is: oil with a low water content, a low gas content and good cleanliness leaves less room for contaminants to keep working during the service period, and it degrades more slowly under the same operating conditions.
The second is the operating conditions themselves. Load, voltage level, temperature and running hours all accelerate the degradation, and none of these conditions changes because the earlier purification was good. The third is the disturbance caused by topping up: the fresh oil that is brought in, the condition of the oil that is added and the amount of air that the topping-up action carries in all add on to the existing state. So how far the interval can be extended depends on the combined weight of these items and not on any single indicator on its own.
Set the interval from your own records
Since the interval has to be set from your own data, what is needed is not a single acceptance result but a few continuous records.
- After each purification, measure once by GB/T 7600, once by GB/T 423 and once by NAS 1638, write the three figures down and treat them as the starting point of that batch.
- Append the data from every test of the oil with the same batch number during the service period to the starting point, and see which way it moves and how fast.
- Record the running hours, the load and the temperature alongside it, so that the part of the degradation caused by the earlier quality can be told apart from the part caused by the operating conditions.
- Register the source and the quantity of every top-up separately; it is an additional segment on top of the starting point and cannot be mixed into the same record.
- Use the history of the same oil rather than a fixed interval to decide the next replacement, and let the trigger condition take precedence over the calendar.
The interval is not set from the calendar; it is the curve measured from the state of the oil sample on the day of purification right through to the end of the service period.
