A machine with a flow rate of 6000 L/h that runs only on the few days of the year when it is needed and a machine that runs continuously have completely different cost structures. During the purchase the figures that stick in the mind are the flow rate and the price, while what really sets the pace of the payback is the utilisation: how much of the time the machine is available is it actually running, and whether it is running at full load during that time.
Utilisation is two ratios, one of time and one of flow
Utilisation can be split into two ratios. One is the time utilisation: the hours the machine actually runs divided by the total hours it is available on site. The other is the flow utilisation: the oil actually treated divided by the theoretical treatment calculated from the rated flow multiplied by the running time. The two ratios point at two different kinds of waste. A low time utilisation means the machine stands still for most of the time it is there; a low flow utilisation means it does not run at full load even while it is running. The rated flow rate of the ZYD-100 is 6000 L/h, the ZYD-200 12000 L/h and the ZYD-300 18000 L/h, and the same machine can produce very different values for the two ratios at different sites.
Why the utilisation of the same machine differs so much
The difference comes mainly from three places. The first is the type of work: a site that purifies continuously has a high time utilisation, a site that treats oil in batches during maintenance windows has a low one. The second is the standby relationship. A machine that is held as standby naturally has a time utilisation close to zero, but it has to take over as soon as the main machine stops, so the value of a standby machine cannot be measured by utilisation; it has to be measured by how fast it can respond. The third is how well the amount of oil matches the size of the machine: a 6000 L/h machine that only ever handles small batches can have a high time utilisation and a low flow utilisation at the same time, and since every start carries a fixed stretch of heating and vacuuming, the fixed part weighs more heavily when the batches are small.
When utilisation is low, look at the schedule or at the machine first
A low utilisation has two possible causes and they need opposite treatment. One is a scheduling problem: there is simply little oil, the work is spread out and the fixed cost of every start takes a large share. Concentrating the work into fewer running periods is then often more effective than changing the machine. The other is a machine problem: the treatment rate is larger than the site actually needs, the machine runs at a low load most of the time and the fixed losses cannot be spread. The flow utilisation is what tells them apart: if the flow utilisation is low as well, the work is spread out; if the flow utilisation is close to the rated value while the time utilisation is low, the machine is too big.
How the utilisation lands in the accounts
In the accounts the utilisation affects three sums of money: the spreading of the depreciation, the rhythm at which consumables such as filter elements and vacuum pump oil are changed, and the hidden cost of waiting for parts and for a window. Taking 6000 L/h as the example, the same annual treatment spread over more hours carries a higher fixed cost per hour. So when a machine is selected, besides confirming that it can meet the peak demand, it is worth establishing how many hours in the year it will really have to work at full load.
| Feature of the site | Time utilisation | Flow utilisation | Which one to work on first |
|---|---|---|---|
| Continuous purification with a stable load | High | High | Keep it, and stock consumables to the rhythm |
| Work spread out in small batches | Low | Low | Concentrate the schedule first |
| The machine runs at a low load for a long time | High | Low | Check first whether the machine is too large |
| The machine is held as standby | Low | Not applicable | Look at the response time, not the utilisation |
- Record the start and stop time and the quantity treated for every run; both ratios are worked out from those two sets of figures.
- When utilisation is low, look at the schedule before considering a new machine; the other way round leads to the wrong purchase.
- Work out the replacement rhythm of consumables from the hours actually run, not from the calendar.
- Keep a separate record for standby machines; what is assessed there is the response, not the hours.
Utilisation is not a figure on paper; it decides how much work the machine actually did for the site over the year.
