The standard configuration of the ZYD-100 is five 150-500-5 fine filter elements in parallel. The five elements sit in five housings and each forms an independent path. After the oil enters the filtration section it is split into five streams, each passing through one element, and the streams join again at the next section. The advantage of the arrangement is direct: once the total flow is shared, each element carries only one fifth of the flow it carried before, the pressure drop rises more slowly, and the element life is extended.
The price of a parallel bank is an insensitive pressure drop
A parallel arrangement has a side effect: the pressure reading no longer reflects the real burden. The total pressure drop is set by the path with the least resistance. In other words, when the pressure drop of one element rises, as long as another path is more open than it is, the pointer on the main pressure gauge hardly moves.
In the extreme case one element is almost blocked and the other four are still open. The flow moves by itself onto those four, and the total pressure drop sits only a little above the normal value. The gauge looks entirely healthy, yet the result has changed: in number, five elements are still working; from the point of view of filtration, the oil in the area served by the nearly blocked element is being forced through the gaps, and the filtration accuracy no longer holds on that path.
That is the second risk carried by the parallel arrangement. The first is element life, the second is an invisible failure. The dangerous moment is not the one when the pressure alarm sounds, but the stage in which the pressure still shows little sign of a problem and one element has already failed.
Why five elements may all need changing when the alarm comes
The pressure alarm value for a fine filter element is 0.35 MPa. Once the pressure reaches that value, the overall resistance of the filtration section has become high. Under a parallel arrangement, a high overall resistance means that most of the paths are close to saturation. The remedy is then normally to change the whole group of elements rather than the single one. What the site finds on inspection is that some elements still look clean while others have been pressed into a hard crust.
| Stage | Total pressure drop | Actual condition |
|---|---|---|
| Normal | Low and steady | All five paths open |
| One element nearly blocked | Almost no change | Flow moves to the remaining four |
| Several elements saturating in turn | Starts to rise slowly | More than one element has failed |
| Close to the alarm value | Reaches 0.35 MPa | The whole group needs changing |
Read together with the point above, the conclusion is clear. A parallel arrangement extends the element life; what it does not change is the way elements are replaced. Unless each element has been measured on its own, there is no way to know which one failed first, and by the time the group is changed the cost has already been incurred.
How the site weighs the five elements one by one
- Use the inlet and outlet isolation on each housing, close the other paths one at a time and leave a single element running, then read the pressure drop of that element.
- Measure all five and enter them in one table, so that there is a baseline to compare against at the next change.
- Carry out the isolated measurement with the machine stopped and the oil circuit depressurised; do not force a changeover while it is running.
- Record which housing and which element number each measurement belongs to, so that the next change does not have to guess either.
The procedure is not complicated. What it costs is a planned shutdown, and what it returns is the option to change only the element that is actually saturated, or to find the failure before it develops into the loss of a whole group.
The parallel arrangement dulls the pressure reading, and what it dulls is exactly the information the site needs.
