The JL series portable oil filter trolley is often treated as simple equipment: a hand-pushed trolley frame with filter elements fitted to it, pushed by one person, and able to fill as well as to filter. Its position in the purification line, however, often determines the final result of the whole line.
10~25 μm is the range designed for pre-filtration
The filtration accuracy of the JL series is 10~25 μm. That figure is neither low nor high; it sits exactly between large particles and fine filtration: much coarser than the filtration accuracy of ≤1 μm of the ZYD-100, and much finer than a direct oil inlet with no filtration at all. There are three reasons for choosing this range. First, what it has to intercept is large debris such as iron filings, sand grains and fragments of sealing material, which would damage the pump, score the valve trim and block the medium, and 10 μm is already sufficient. Second, the interception area is left to collect the dirt, so that the element does not saturate within a few hours. Third, the medium can be washed and used again, which keeps the consumable cost per run low.
Where it sits in the line
- First stage: one pass before the oil enters the machine, holding the large particles outside the vacuum system.
- Middle stage: filtering and filling in one operation when oil is transferred between tanks, with no additional equipment needed.
- Final stage: a last coarse screening when a tank is topped up, so that the contaminants carried in with the new oil do not contaminate the system first.
What the absence of a power supply brings, in adaptability and in cost
The trolley frame structure filters by hand power alone, with no motor, no heater and no control cabinet. This looks like a compromise, but in practice it is the machine's greatest advantage in adaptability: many places where filtration is needed have no power supply, or it is not worth running a cable for a short job. On-site maintenance, temporary transfers and the topping up of peripheral oil tanks are places where a machine needing three-phase 380V / 50Hz simply cannot go. The cost is equally clear: the flow rate is limited, the oil cannot be heated to reduce its viscosity, and once the medium is blocked there is nothing to judge by but feel rather than an instrument reading.
What goes wrong if it is used directly as the fine filtration stage
If the output of the JL is treated directly as oil that is fit to go back into service, the problem is generally not with the JL itself but with the criteria being applied. Its 10~25 μm interception capacity will hold a 20 μm particle, but it will not hold the finer particles below a few tens of microns that are even harder to see, and it makes no attempt at all on water, dissolved gas or oxidation products. Oil that has been through it and is then filled into a transformer still has essentially its original water content and gas content, and the breakdown voltage does not recover simply because the oil has been through the trolley. Treating pre-filtration as fine filtration has one direct consequence: the oil looks clean while the problem is pushed on to the machine behind it, and sometimes on to the period after commissioning.
The other consequence is in the consumables and the working time. All the fine particles that the fine filtration stage was supposed to remove are pushed on to the stage behind it, so the differential pressure of the elements there rises much faster. In the other direction, if somebody changes the specification of the JL medium in pursuit of accuracy, the consumable cost goes up while the service life still does not compare with that of a real fine filtration stage.
| Comparison | JL series | ZYD-100 fine filtration stage |
|---|---|---|
| Filtration accuracy | 10~25 μm | ≤1 μm |
| Main duty | Hold back large particles and protect the stage behind | Collect fine particles and control the cleanliness |
| Power supply required | None, pushed by hand | Three-phase 380V / 50Hz |
| Water and gas | Not treated | Water content ≤3 ppm, gas content ≤0.01% |
| Cleanliness | Not used as an acceptance criterion | NAS 1638 class 5 |
The value of pre-filtration is not in how fine it filters, but in that it holds back the particles that would damage the equipment before the expensive machine behind it starts work.