When the cost of running an oil purifier is assessed, the easiest way to go wrong is to fix a depreciation period first, for instance five or eight years out of habit, and then divide the purchase price by that number. The annual cost that comes out looks tidy, but it rarely matches the rate at which the machine actually consumes things. The approach that is closer to reality is to first see which parts of the machine really are consumed, and then let the rate of consumption lead to the number of years.
Start by separating what is consumed
The parts of a machine fall roughly into three groups. The first is consumed by running: filter elements and vacuum pump oil, and these are what really decide how long the machine can work continuously. The fine filtration stage of the ZYD-100 is built from five 150-500-5 fine filter elements in parallel, and coarse elements 150-250-50 and 110-250-50 and the secondary element 110-400-20 are among the other specifications available; the rate at which elements have to be changed is set directly by the condition of the oil and by the filtration accuracy required.
The second group is consumed by movement: seals, couplings and the gaskets at the pipe connections. The third group is consumed by time: ageing rubber parts and ageing electrical components.
| Category of part | What it decides | How it is observed |
|---|---|---|
| Filter elements | Whether continuous throughput and filtration accuracy can be maintained | Differential pressure records and accumulated running hours |
| Vacuum pump oil | Whether the ultimate vacuum holds at ≤5 Pa | The condition of the pump oil and the vacuum reading |
| Seals and gaskets | Whether the system leaks oil or air | Inspection during shutdown and leakage records |
| Electrical components | Whether the control system and the protection functions are reliable | Protection operations and alarm records |
| Heating and vacuum parts | Whether the temperature range and the vacuum range can be maintained | The temperature display and the vacuum reading |
Work back from the life of the consumables
Put the element replacement interval and the accumulated running hours side by side, then set them against the actual annual workload of the machine, and the number you get is more reliable than one worked back from the calendar. The point of this method is not that it is more precise, but that it follows the actual use: in a year with a high workload the consumables go faster and the depreciation is faster, and in a year of long idle time the consumables go slower and the book value is naturally retained for longer.
It has to be said that what this method produces is the service life in a usable state, which is not the same as the depreciation period used for accounting. The difference between the two has to be closed by management decisions and not by changing the method.
The accounts of this machine fall into three parts
- The first is the consumables account: elements, pump oil and seals. This one follows the workload and not the calendar.
- The second is the energy account: the total power of the ZYD-100 is 72 + 5 kW, and this one follows the running hours and the oil temperature and is directly linked to the way the machine is used.
- The third is the cost of standing still: the machine occupies floor space and it occupies the maintenance window, and it produces nothing while it is stopped. This cost is incurred during the shutdown as well.
A common mistake in the estimate
The most common mistake is to treat "it has not broken" as "it is still usable". Changing elements only once the differential pressure alarm has tripped, and changing the pump oil only once the ultimate vacuum has fallen away, both keep the machine running at an efficiency that is lower than it should be: the book life does not get shorter, but the real working cost keeps climbing. Replacing consumables on condition rather than on the calendar is the first step towards bringing the depreciation estimate and the real cost together.
The number of years grows out of the rate at which the consumables are used up and is not cut out of the calendar; the calendar only records, it does not decide.
