A filter element is a consumable, and when it arrives only two things are usually done: count the quantity and check the model. Once that is done it goes straight onto the machine, and if the differential pressure turns out to be high and the flow rate will not rise, going back to look into it afterwards often makes it impossible to say which step caused the problem. The value of an incoming inspection does not lie in picking out defective items, but in establishing a baseline for this batch of elements against which later readings can be compared, so that when the differential pressure has to be judged, there is a basis for deciding whether it is due to loading or was already high.
First establish what you have received
The first step of the inspection is to check the specification, not the quantity. Different specifications of element are used on the same machine: the common coarse elements are 150-250-50 and 110-250-50, the second stage element is 110-400-20, and the fine elements come as 110-600-5 and 150-500-5. The three groups of figures in the specification correspond to the outer diameter, the length and the filtration accuracy; leave one out and it does not match.
Take the ZYD-100 as an example. The standard configuration is 5 fine elements 150-500-5 fitted in parallel, and the corresponding differential pressure alarm value is 0.35 MPa. In other words, any differential pressure abnormality anywhere on this machine has to be judged against the reference of that alarm value, rather than described as high or low from impression.
| Element specification | Position in the process | What the inspection has to confirm |
|---|---|---|
| Coarse element 150-250-50 / 110-250-50 | First stage at the oil inlet | Outer diameter and length, whether the pleats are damaged, whether the end face sealing surface is flat |
| Second stage element 110-400-20 | Intermediate filtration stage | Whether the batch is consistent, whether there is any deformation under pressure |
| Fine element 150-500-5 | Fine filtration at the oil outlet | The matching relationship of the 5 parallel elements and the corresponding differential pressure alarm value |
The most valuable item in the inspection: the initial differential pressure
Fit an element that has never been used, measure the differential pressure once, and that reading is the starting point of this element. Deep-bed media from different batches differ in fibre distribution and grammage, so the initial differential pressure cannot be identical. Record the initial differential pressure of this batch, and every differential pressure measured afterwards can be expressed as an increase relative to the starting point, which gives the reading a reference.
Without this baseline, differential pressure management can only be judged by experience as to whether the figure counts as high. With the baseline, the judgement becomes a comparison: if the differential pressure on one element is far above its initial value, it is loading up normally; if the differential pressure is still high after a new element has been fitted, the problem is most likely in the pipework, the valves or the sealing of the machine itself, and has nothing to do with the element.
The first batch and the last batch need to be looked at separately
The inspection samples individual items, and in a bulk delivery the easiest ones to miss are the two ends: the first few elements that have just arrived, and the last few left over at the end of the installation. The former sets the baseline level of the whole batch; the latter has been in its packaging for a long time, and whether the storage conditions were met is only known on arrival, because the risk of moisture ingress or deformation under pressure sits in this part.
- After opening the packaging, look at the end face first: whether the sealing surface has indentation, burrs or foreign matter, because an uneven end face affects the sealing once the element is fitted into the housing.
- Look at the pleats: the pleats of deep-bed media should be evenly upright, and an element whose pleats have clearly collapsed or folded over will lose flow rate from the start once it is fitted.
- Look at the outer surface: an element deformed by being crushed in transit is likely to have the media crack at the fold during subsequent operation.
- Retain a duplicate: keep one element from the batch that is not fitted to the machine, as the reference sample for any later dispute.
What goes into the inspection record also matters. Writing only the word "passed" leaves nothing that can be rechecked later; writing the specification, the quantity, the number of elements inspected, the initial differential pressure reading and the date gives a record that can actually be used. Retaining a duplicate costs almost nothing in the purchasing stage, and yet it provides the most direct evidence when a differential pressure dispute arises.
The real output of an incoming inspection is not the four words inspected and passed, but a set of baseline data that can be compared over the long term.
