At commissioning, most automatic lubrication controllers ask the same question in one form or another: how long should the pause be between lubrication cycles? On many units that value can be entered either in hours or in minutes.
It looks like a formatting choice. It is not, because the two settings count different clocks. On a machine that does not run around the clock, the difference can be a multiple of the grease you intended to deliver.
Setting the interval is the automated version of a question maintenance teams have asked for as long as machines have had bearings: how often should this point be greased? What follows covers what each setting counts, when the distinction matters, how to turn a manufacturer’s recommendation into a setting, and how to check afterwards that the machine receives what was planned.
What the two settings actually count
A minute-based setting measures elapsed time. The timer runs from power-up and does not care whether the machine is producing or standing still. When the count reaches the set value, the controller starts a lubrication cycle.
An hour-based setting normally measures accumulated machine hours. Depending on the controller and how it is wired, the counter either advances only while a run signal is present, or it follows pulses from a machine-hour meter.
That difference matters more than the unit printed on the display. The label “hours” is not a statement about the clock. It is a statement about what the counter is allowed to count.
Because naming varies between manufacturers, confirm the behavior of the actual unit before relying on it. Two questions settle it: does the timer keep advancing when the machine stops, and is the counter linked to a run signal from the machine or to an internal clock?
The same setting can deliver three times the planned grease
Take a lubrication point that requires 0.12 cm³ every four operating hours, on a machine that runs a single eight-hour shift.
Configured as machine hours, the counter reaches four hours half way through the shift and again at the end. The point receives two doses a day, 0.24 cm³ in total, which is what the calculation assumed.
Configured as elapsed time, the same four hours continue to pass through the sixteen hours when the machine is stopped. The controller fires six times a day and delivers about 0.72 cm³. The machine receives three times the intended quantity, and most of the extra grease goes in while nothing is turning.
The multiplier is the calendar hours in a day divided by the hours the machine actually runs. An eight-hour shift gives a factor of three. A two-shift operation running sixteen hours gives 1.5. Continuous plant running twenty-four hours gives one, which is why this problem stays hidden on continuous processes and appears on mobile equipment, batch plants and anything with a shift pattern.
There is a second effect to be aware of. When the machine is stopped, some controllers suspend the lubrication cycle while the timer keeps running, so the next cycle begins the moment the machine restarts. Others continue cycling. Either way, the delivered quantity per operating hour is higher than the calculation assumed.
The table below summarizes the choice for common duty patterns.
| Machine duty | Elapsed-time (minutes) setting | Run-time (hours) setting |
|---|---|---|
| Continuous, 24 hours a day | Matches the calculation | Matches the calculation |
| Single 8-hour shift | Delivers about 3 times the planned quantity | Delivers the planned quantity |
| Two shifts, 16 hours a day | Delivers about 1.5 times the planned quantity | Delivers the planned quantity |
| Seasonal or occasional use | Continues cycling, or queues cycles, while the machine is idle | Resumes from where the counter stopped |
The interval cannot be shorter than the cycle time
Before choosing a unit for the interval, it helps to know how long one lubrication cycle takes, because that sets the floor.
A lubrication cycle is not the same as a motor run time. During a cycle the pump elements deliver grease, pressure builds through the main line, the distribution components complete their sequence and the system reaches its end-of-cycle condition. In a progressive lubrication system that sequence is what proves every outlet has moved. The pause that follows has to be long enough for all of it to finish.
If the pause is set shorter than the cycle time, the controller starts the next cycle before the previous one has completed. The pump then runs almost continuously, the grease is churned rather than delivered, and the indication that normally proves a completed sequence loses its meaning.
Cycle time depends on several things that have nothing to do with the controller: how far the grease must travel and through what bore, how stiff it is, how cold the machine is, how many outlets open at the same time and what backpressure the bearings present. A cycle that takes forty seconds on a warm afternoon can take several minutes on a cold morning start, particularly on long main lines.
The practical sequence is to measure actual cycle completion at the lowest ambient temperature the machine will see, then set the pause with margin above it. If the controller offers a cycle-completion timeout, set that as well, so an incomplete cycle raises an alarm instead of quietly repeating.
This is also why both units exist on the same controller. Small machines and oil systems often complete a cycle in seconds, and minutes are the natural unit. Grease systems on large equipment usually need long pauses, and hours describe them better. A progressive lubrication pump driving a circuit of several hundred meters of line has a very different cycle time from a single-line system on a compact machine.
Turning a manual recommendation into a setting
Maintenance manuals rarely phrase intervals the way a controller expects. They say 15 g per bearing every 500 operating hours, or grease daily, or lubricate each shift.
The word doing the work in those sentences is “operating”. A daily task on a machine that ran four hours is a different requirement from a daily task on one that ran sixteen.
A workable order of operations:
- Find the interval and establish its basis. Is it operating hours, calendar time, or a maintenance task?
- Convert the quantity into a volume using the density of the grease actually in use.
- Divide the requirement into doses the metering device can deliver.
- Determine the shortest interval the system tolerates, from cycle time plus margin.
- Select the clock that matches the basis found in step one.
- Record the reasoning, so the next person can check the logic rather than guess.
Steps two and three are covered in detail in how to calculate grease quantity for each lubrication point. The sequence behind them, from lubrication point schedule to pump output, is set out in how to size an automatic lubrication system.
Changing the interval changes the dose at every point on the circuit
On a shared circuit, points fed by the same divider or the same injector block use one interval. Shortening it to help a single under-lubricated point raises the delivered volume at every other point on that circuit by the same proportion.
That is not a reason to avoid the change, but it is a reason to calculate the side effect first. A point that was already receiving its full requirement can be pushed into over-lubrication, which brings its own problems: higher running temperature, churning losses and additional load on the seals. Where points on the same machine have markedly different requirements, grouping them into zones is usually a better answer than compromising one shared interval.
Checking the setting in the field
The arithmetic behind an interval is easy to get wrong silently, so it is worth one verification after commissioning.
- Work out the expected consumption over a week, from the configured interval, the dose per event and the expected operating hours.
- Note the reservoir level, or read the low-level signal, over the same period.
- Compare the two figures.
If actual consumption is close to the calculated one, the clock and the interval agree with the machine’s duty.
If actual consumption is higher than calculated by roughly 24 divided by the daily operating hours, the controller is counting elapsed time on a machine that does not run continuously. That single ratio is usually enough to identify the problem, and it is a reason to keep consumption figures after commissioning rather than only during it.
Consumption monitoring covers the other direction as well. A drop in consumption can mean a blocked divider outlet or a leaking line. The equipment that detects it is the same equipment that holds the interval. Progressive dividers with piston detection and cycle confirmation turn a lubrication schedule into something the controller can report on. An automatic lubrication system controller with low-level and cycle-completion inputs gives you both the interval setting and the evidence that it is being honoured.
Common mistakes
- Choosing the clock that matches the maintenance roster rather than the way the machine is used.
- Setting “every shift” on equipment that runs for part of a shift.
- Treating minutes as the more precise option, when the unit has nothing to do with precision.
- Copying an interval between two machines that have different duty cycles but similar lubrication points.
- Lengthening or shortening the interval without recalculating the quantity per point.
- Assuming the machine can be lubricated whenever the timer says so. On equipment that stops, the pump can only work while the machine runs, so the achievable interval is always bounded by the duty cycle.
FAQ
Should I set hours or minutes?
Match the setting to the basis of the requirement. If the requirement is written in operating hours, use the run-time counter. Elapsed-time settings suit machines that run continuously, and systems whose complete cycle takes only seconds.
My controller only offers minutes. Can I still hold an operating-hours interval?
Only if the timer stops when the machine stops. Convert the requirement into operating minutes and check whether the controller’s counter follows the run signal. On a machine that runs continuously, elapsed minutes and operating minutes behave the same way. On a machine that runs one shift, they do not.
The machine runs two shifts, five days a week. What should I work in?
Operating hours. Eighty hours a week is a different duty from one hundred and sixty-eight, and the delivered quantity per production hour differs accordingly.
Can I shorten the interval instead of increasing the dose?
Often yes. Smaller doses at shorter intervals are gentler than large infrequent ones, provided the interval stays comfortably above the cycle time and the component manufacturer has not set a maximum interval. Recalculate delivery for every point sharing the circuit before making the change.
Does temperature affect the interval?
It affects the cycle time, and therefore the shortest interval you can use. Cold grease takes longer to travel through the same line, and a pump element delivers less per unit of time. Measure cycle completion at the lowest expected temperature rather than at commissioning temperature.
The machine may sit idle for several weeks. What should the setting be?
Decide deliberately. With an elapsed-time setting the controller keeps running its schedule, or queues the next cycle, while the machine is idle. A run-time counter resumes where it left off, so the first event after a long stop may come quickly or after several hours, depending on where the counter stood. If the machine needs lubrication on every start, that is a start-up function rather than an interval setting, and it should be specified separately.
Setting the interval with the machine, not the calendar
Most interval problems come from one assumption: that time on the controller and time on the machine are the same thing. They are not, and the gap between them is the ratio of calendar hours to operating hours.
Confirm what the counter counts, keep the interval above the cycle time at the coldest start, recalculate the quantity whenever the interval changes, and check consumption once after commissioning. Those four steps cover the setting itself and the evidence that it is working.
If you are specifying a system and the interval requirement is still written as a maintenance task, send INA the machine’s duty cycle, the lubrication point schedule and the manufacturer’s recommended quantities. The sizing sequence starts from the machine, and the interval falls out of it.