After an oil purifier has been delivered, three standard numbers often appear together on the acceptance sheet: GB/T 7600, GB/T 423 and GB/T 507. Many people read them as "three stricter indicators", but the three standards govern three different things, they measure different physical quantities, and the samples are handled in different ways. Read together on one sheet, it is easy to arrive at a "pass" without being able to say which requirement was actually met.
Which item each standard governs
GB/T 7600 governs the water content of the oil, that is how much water is left in it. GB/T 423 governs the gas content of the oil and measures the gas dissolved in it expressed as a volume fraction. GB/T 507 governs the breakdown voltage and measures the ability of the oil to withstand an electric field, using a defined electrode gap and a defined way of applying the voltage. The corresponding figures for the ZYD-100 are ≤3 ppm (GB/T 7600), ≤0.01% (GB/T 423) and ≥65 kV (GB/T 507).
| Indicator | Basis standard | Figure for the ZYD-100 | What it answers |
|---|---|---|---|
| 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 |
| Breakdown voltage | GB/T 507 | ≥65 kV | How high a voltage the oil can withstand in an electric field |
| Cleanliness | NAS 1638 | class 5 | How many particles are left in the oil |
| Filtration accuracy | Machine capability figure | ≤1 μm | How large a particle the medium can hold back |
Passing is not the same thing in each case
Water content, gas content and breakdown voltage are related, but they do not correspond one to one. A water content that passes does not mean the gas content passes: a batch of oil can be dried down to ≤3 ppm and still hold dissolved gas, and the other way round a batch of oil can have a very low gas content and a high water content. More important, the breakdown voltage is the result that emerges from several conditions at once. It is influenced by the water content, the gas content and the particle state, so a pass says something about the combined condition and not about any single item.
This is also why a passing breakdown voltage cannot be turned round into a passing water content, and the other way round just as little. All three have to be measured separately, written separately and judged separately.
What writing the standard numbers into the contract saves
Most arguments at acceptance are not about the machine being unable to do something; they are about the two sides using different criteria. Putting the standard numbers into the contract actually settles three things: which quantity is being measured, which method is used, and which threshold decides the result.
- Water content written as GB/T 7600 and ≤3 ppm gives both sides one definition of "water content".
- Gas content written as GB/T 423 and ≤0.01% fixes the method the figure belongs to, so a number produced by a different method cannot simply be compared with it.
- Breakdown voltage written as GB/T 507 and ≥65 kV fixes the electrode gap and the way the voltage is applied, which avoids two parties reporting numbers from different electrode sizes.
- Cleanliness written as NAS 1638 and class 5 is kept as a separate item from the filtration accuracy of ≤1 μm: the first measures a result, the second measures the capability of the machine.
The sampling responsibility has to be written down as well: who takes the sample, in what container, when it is sent for testing, and from which point in the line it is taken. If that step is left open, the standard numbers can be written as precisely as you like and the two sides will still not agree.
There is another case in which both sides simply follow their own habit and the figures come out different. Take water content: one party seals the sample and sends it immediately, the other leaves it in the drum for a while before taking it. The difference between those two steps is enough to put the results into different acceptance bands. Writing the practice down removes more later disagreement than adding one more parameter would.
Three standard numbers printed side by side do not mean the standards are stricter; the three things they govern could never replace one another in the first place.
