In the configuration data for the ZYD-100, the line for the 150-500-5 fine filter element holds two fields that have nothing to do with filtration performance: filtration accuracy 1~5 μm and a differential pressure alarm value of 0.35 MPa. The first answers how large a particle this batch of oil can hold back, the second answers at what differential pressure this batch of oil has to stop. The second number is often treated as a configuration remark, but it is in fact the trigger point of a protective action.
0.35 MPa is a limit given with the product
The filter media of this fine element is imported HPM deep-layer filter media, the machine it is fitted on is the ZYD-100 two-stage vacuum oil purifier (5 elements), and the cleanliness achievable is NAS class 5. The differential pressure alarm value of 0.35 MPa is the boundary given together with it, corresponding to the range over which the media keeps normal flow at the rated flow rate. Its advantage is that the alarm action and the performance decay fall on the same moment, so the site no longer has to make a second judgement on whether to stop.
The ZYD-100 itself carries an over-pressure sound and light alarm with shutdown. The machine stopping when the differential pressure reaches 0.35 MPa is the defined action of that protection, not a fault. This limit should therefore be treated as a shutdown line, not as a reference value that may be crossed slightly.
Below the limit: the differential pressure is the only visible indicator of the element load
Below 0.35 MPa the element is still working, but its condition does not display itself. The contaminants are held back inside the media and the operator sees no indication at all. The differential pressure is the only quantity that shows it: the resistance of the oil flowing through the media rises as the dirt holding capacity increases, and the reading rises monotonically with it.
So below the limit the differential pressure acts as an indicator. Whenever the differential pressure is read, the oil temperature has to be recorded with it, because viscosity is part of it as well: when the oil is cold and the viscosity high, the same flow has to cross a greater differential pressure, and that part of the rise comes from the viscosity and not from the element becoming dirty. Only when the temperature is normal and the differential pressure still rises monotonically does it mean that the dirt holding capacity is at work.
Above the limit: why the shutdown is the correct result
The alarm and shutdown after the differential pressure has crossed 0.35 MPa raises the question of why the machine is not simply kept running. There are two reasons. The first is that the accuracy can no longer be relied on: once the media is filled with contaminants its holding capacity falls, and both the filtration accuracy of ≤1 μm and the cleanliness of NAS 1638 class 5 of the ZYD-100 are hard to maintain. The second is that the condition of the whole machine is dragged down: when the filtration stage has an abnormal flow the pump and the heater both work at high load, and the capabilities of working vacuum -0.08 ~ -0.0999 MPa and ultimate vacuum ≤5 Pa all rest on the premise that the filtration stage flows normally.
What this limit really holds back is the stretch of operation in which the efficiency is falling but the machine is still running. That stretch is the hardest to handle, because the machine shows no obvious abnormality while the throughput drops and the indicators fall back, and by the time the oil is found to be out of specification the deviation has been building up for some time. The shutdown cuts the process at this point; the cost is a period of downtime, and the return is an oil specification that can still be relied on.
| Combination of differential pressure reading and oil temperature | Explanation | Response |
|---|---|---|
| Differential pressure below 0.35 MPa and rising monotonically with the dirt holding capacity | The element is decaying normally and is still within the usable range | Record the differential pressure and the oil temperature, and schedule the element change against the differential pressure |
| Differential pressure close to 0.35 MPa, but the oil temperature clearly low | Viscosity accounts for a substantial part of the reading | Raise the oil temperature to the set value and read it again; do not change the element on the strength of this reading |
| Differential pressure has crossed 0.35 MPa | Sound and light alarm with shutdown; the flow through the media is already beyond its limit | Stop, replace the fine filter element, then restart |
| TYA series pressure >0.3 MPa | The value of the same kind of judgement on another model | Clean the filter or replace the element |
Five in parallel, and another 0.3 MPa limit
The fine filtration stage of the ZYD-100 consists of five 150-500-5 elements in parallel. The parallel arrangement shares the total flow across the five elements, each of them carries less flow, and at the same dirt holding capacity the differential pressure rises more slowly and the alarm triggers later. In other words, the parallel arrangement lengthens the usable stretch of the differential pressure curve; it does not raise the alarm value.
The TYA series is a different value: cleaning and element replacement are required at pressure >0.3 MPa. The two limits do not contradict each other. One is the alarm value given with the fine element on the ZYD-100, the other is the operating convention given with the TYA machine as a whole; they apply to different models and different components, and neither can be substituted for the other. The TYA series carries automatic backwash filter elements, so cleaning is part of the remedial action; the 150-500-5 is imported HPM deep-layer filter media, and the corresponding action is replacement.
The condition of the upstream elements is written into the same curve. The dirt held by the coarse elements 150-250-50 and 110-250-50 and by the second stage element 110-400-20 determines the particle load entering the fine filtration stage, and the dirtier the incoming oil, the faster the differential pressure of the fine stage rises. Before deciding whether the fine element should be changed, first confirm whether the upstream stage has already failed.
- Treat 0.35 MPa as a shutdown line, not as a recommended value: running on past it means the cost of the accuracy loss and the pump load is carried by the quality of the oil.
- Whenever the differential pressure is read, record the oil temperature with it; the rise caused by a low oil temperature falls back once the oil has reached the set value, and that is not a reason to change the element.
- Look at the trend of the differential pressure; a single reading says nothing: the rise caused by the dirt holding capacity is monotonic, while the offset caused by the viscosity stays largely unchanged once the temperature has settled.
- The 0.3 MPa of the TYA and the 0.35 MPa of the ZYD-100 are values for different models and different components; check the model and the component before applying either of them.
The 0.35 MPa line does not mark how good the element is; it marks the boundary of continued operation. The consequence of crossing it is carried by the quality of the oil, which is why the shutdown is the correct result.
