Single-Point Automatic Lubricators
When an automatic greaser is worth fitting, how to size it, and the five ways they fail · from the people who run the lubrication programme
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The problem is not that nobody greases. It is that nobody knows how much.
SKF put poor lubrication behind more than 36% of premature bearing failures. Almost none of that is neglect. It is grease going in at the wrong interval, in the wrong quantity, or of the wrong type — and the two failure modes look nothing alike.
Under-greasing is the one everyone pictures: the film thins, metal meets metal, the bearing runs hot and fails. Over-greasing is the one that surprises people, and it is more common. A packed housing has nowhere to put the excess, so the rolling elements churn it. Churning generates heat, the heat degrades the grease, the pressure pushes past the seal, and on an electric motor the escaping grease finds the windings. A bearing that was greased every week by a diligent fitter can fail sooner than one that was left alone.
The framework the lubrication trade uses for this is the five Rs: the right lubricant, in the right volume, at the right point, at the right interval, by the right method. A grease gun on a monthly round gets the point and the method right and leaves volume and interval to whoever is holding it.
Three drive types, and they are not interchangeable
Single-point lubricators all do the same job — push a measured amount of grease into one point over a set period. What separates them is how the piston is driven, and that decides everything about where each one belongs.
| Spring-driven | Gas / electrochemical | Motor-driven | |
|---|---|---|---|
| How it drives the piston | A wound spring pushes a plunger. | An electrochemical cell generates gas; the gas pressure drives the piston. | A battery-powered motor and gearbox drive the piston. |
| How the rate is set | Largely fixed by the spring and the grease. Little adjustment once fitted. | By the activator cell you choose at installation. Changing the rate means changing the cell. | By a switch or dial on the unit, changed at any time without opening the grease side. |
| Temperature sensitivity | Low, but grease stiffness at low temperature slows delivery. | High. Gas generation is a chemical reaction — it speeds up in heat and slows in cold, so the real dispense period drifts from the nominal one. | Low. The motor turns at the same rate whatever the ambient, within the unit’s rated range. |
| Working against back pressure | Weakest. Not for long feed lines or a stiff bearing. | Moderate, limited by the gas pressure the cell can raise. | Strongest — typically 5 to 10 bar, enough for a remote-mounted unit on a feed line. |
| Refill or replace | Usually a disposable unit. | Usually a disposable unit, or a replaceable cell and cartridge. | Drive unit is reused for years; you replace the grease cartridge and the battery. |
| Typical dispense period | Weeks to a few months. | 1 to 12 months, set by the cell. | 1 to 12 months, set on the unit. |
| Where it earns its place | Single low-cost points, short runs, where nobody will come back to adjust it. | Moderate point counts in stable ambient conditions, where the setting will not need changing. | Anything where the interval must be changed after the first review, where the ambient swings, or where the point is remote or hazardous. |
Sealing and certification vary by unit rather than by drive type: IP65 bodies and hazardous-location certification are both available. If the point is in a classified zone, the certificate on the specific unit is what matters, not the category.
Sizing: the number you are choosing is grease per day, not months
A dispense period of “six months” sounds like a maintenance interval. It is not. It is a rate — the reservoir divided by the period. A 150 ml unit set to six months is delivering under a millilitre a day; the same unit set to one month is delivering five. Sizing is deciding the daily rate the bearing wants and then picking a reservoir and period that give it.
Start from the bearing maker’s relubrication quantity and interval for that bearing at that speed, then adjust for what the plant actually does to it: shaft speed relative to the rating, operating temperature, vertical shafts (which lose grease faster), contamination and washdown, and continuous versus intermittent running. The output is a millilitres-per-day figure. Everything after that is arithmetic.
Then review it. The first setting is an estimate. Three months in, the evidence is on the bearing — temperature, purge at the seal, grease condition and colour. That review is what separates a lubrication programme from a box screwed onto a grease nipple.
Five ways they fail, all of them avoidable
Set once, never reviewed
The dispense period is chosen on the day of installation from an OEM figure, and then nobody goes back to it. Duty changes, ambient changes, the bearing beds in — and the setting does not. A lubricator on the wrong setting is a more reliable way of over-greasing a bearing than a grease gun is.
Nobody notices when it stops
A blocked feed line, an exhausted battery or a spent cell produces no noise and no alarm on most installations. The bearing runs dry for months while the plant believes it is on an automatic programme. Units with a blockage indicator help; a route that physically checks the dispensed level helps more.
Grease incompatibility on the refill
A lithium-complex unit topped up with a calcium sulphonate grease, or a polyurea motor grease crossed with lithium, can thicken, soften or separate in the cup. The failure looks like a lubricator fault and is a grease-selection fault. Keep one soap type per point and record it.
Remote mounting beyond the unit’s pressure
Mounting the unit off the machine on a length of tube is often the only way to reach a hot or guarded point — but the unit then has to push grease down that line. Spring and gas units run out of pressure quickly; a motor-driven unit rated to 5–10 bar will usually carry it. Match the drive to the line, not to the price.
Cold starts and hot rooms
Gas-driven units speed up in heat and slow in cold, because the drive is a chemical reaction. In a Telangana summer roof plant and an air-conditioned clean area, the same nominal setting will not give the same delivery. If the ambient swings, the drive type matters more than the setting does.
What we do about it
We run the lubrication side of plants for a living, which is the part of this that automatic lubricators do not solve on their own. Our shop-floor and plant maintenance programme starts with the asset register — every machine, its lubrication points, the correct grade for each point, the volume and the interval. That register is exactly the input a lubricator sizing needs, and most plants have never had it written down in one place.
And we supply what goes in them. Lithium complex, calcium sulphonate, polyurea and synthetic greases across Veedol, Balmerol, GS Caltex Kixx and SELCO — so the soap type in the cup and the soap type in the bearing are a decision somebody made, rather than whatever was in the store.
Send us the bearing list and we will size the points. Machine, bearing designation, speed, ambient, duty. You get back a written assessment of which points are worth automating, what daily rate each one wants, and which drive type suits the position — no commitment and no charge. If the answer for a point is “a fitter with a grease gun and a written quantity”, that is what it will say.
Related
- Shop-floor and plant maintenance — the asset register and the lubrication programme
- Oil analysis service — the same discipline applied to oil-lubricated equipment
- Gear oil change intervals — why calendar-based intervals mislead
- Industrial lubricants and greases — the range we stock in Secunderabad