The idea of a small or medium-sized company purifying its own oil is a natural one: a machine does not look expensive and the money saved on oil seems to come back quickly. But when the figures are worked out, the amount that can be saved on the oil is the thing most easily overestimated, and the continuing costs of floor space, power and labour are the ones most easily underestimated. Spread them out and do the arithmetic once, and the conclusion is usually clearer than the intuition.
First, how much oil a major overhaul actually involves
The starting point for the economics is the quantity of oil, not the price of the machine. The total oil in the hydraulic station of a medium-sized workshop may be only a few tonnes, while the oil in a main transformer can amount to more than ten tonnes. A difference of an order of magnitude in quantity gives a completely different conclusion. Add up every oil storage point in the plant: the hydraulic stations, the gearboxes, the oil tanks, the transformers and the reserve oil drums, and that gives the upper limit of the annual volume to be processed.
Then there is the frequency. One major overhaul a year and four planned oil changes a year make a very large difference to how well the machine is used. The same machine used four times a year spreads its cost over a smaller volume than one used once a year. Conversely, if the quantity is small and scattered and the machine is used only once or twice a year, most of the time an owned machine stands idle while its depreciation, its electricity, its floor space and the management cost are still paid.
How to compare owning the machine with having the work done by a third party
The cost of owning the machine is not only the quotation; it normally includes the items below. Leaving any one of them out makes the calculation come out too low, and the conclusion naturally favours buying the machine, while the part that actually has to be paid is often the part that was left out. Spread these over a year and divide by the volume actually processed, and only then do you have a unit cost that stands up. This calculation is more useful than looking at the equipment price itself.
- The investment in the machine itself, together with the consumables that keep being used: filter elements, vacuum pump oil, seals.
- Dedicated floor space: the machine itself plus the oil tanks and the buffer tanks, with room left for access and for working around the equipment.
- The power supply: an independent circuit of three-phase 380V / 50Hz; in most smaller plant areas the capacity has to be calculated separately.
- People: at least one person who can read a vacuum level, who knows when to change the filter element and who can understand an oil sample report.
- Time: the working window usually falls in a shutdown and maintenance period, and the opportunity cost of that period is often higher than the cost of the machine.
Having the work done by a third party has exactly the opposite characteristics: the cost per job is high, but there is no capital outlay, no floor space and no dedicated staff, and the responsibility for maintaining the equipment passes to somebody else. Where the quantity is not large and the frequency is not high, the unit cost of having the work done is usually lower than the share of the cost of a machine standing idle for long periods, provided the cost per job and the depreciated fixed costs are compared on the same basis.
At what scale it starts to pay
There is no universal threshold, because the cost of electricity, of oil, of labour and of floor space differs a great deal from place to place. The conditions for the decision can, however, be set out. The annual volume processed has to be stable, which in other words means the machine must not stand idle for long periods. The site needs an independent three-phase supply and floor space for the machine and the oil tanks. There have to be one or two people willing to take this work on. And the oils treated must not be too scattered, otherwise the configuration has to be made separately for each medium.
Working this framework through, the general case is that a fixed machine is worth owning when the annual volume processed across the plant is steadily in the tens of tonnes or more and there is a fixed place and the people to do the work. Where the quantity is between a few tonnes and more than ten tonnes and the work is concentrated in a few maintenance windows, hiring a mobile machine is usually more flexible; a mobile vacuum oil purifier such as the TYG-100 at 6000 L/h is ready for use on arrival, and there is no need to solve the long-term occupation of a fixed site.
There is an intermediate option that is worth considering: hire a machine, work through several overhauls with it, record the real oil quantities, the time each job takes, the labour involved and the consumption of the consumables, and only then decide whether to buy. This costs little, but it turns an estimate into measured data, and what it records is precisely the variables that decide the threshold above. That fits the site better than any external estimate.
A hidden cost that should not be overlooked
Once the machine is owned, the oil treatment capability creates new demand. A machine on which new oil could simply be fitted is now first purified and then used; oil that was changed once a year may now be changed more often because the treatment is convenient. This is usually not a bad thing, but it pushes the volume processed beyond the original estimate. The assessment should include how much extra volume the machine will bring once it is in the workshop, instead of extrapolating only from the past oil change records.
Whether owning the machine pays does not depend on whether the machine is expensive, but on how many days in the year it can actually be put to use.