An automatic oiler supplies lubricant without repeated hand oiling. The mechanism shown uses a driven eccentric, connecting rod and plunger to draw oil from a reservoir and deliver a charge through check valves. Use the calculator to compare ideal delivery, stroke timing and reservoir duration from the entered speed, drive ratio and volume per stroke.
Automatic Oiler Interactive Calculator
Vary engine speed, drive ratio, oil volume per stroke and reservoir size to compare ideal delivery, stroke timing and reservoir duration.
Equation Used
The automatic oiler is modeled as a positive-displacement plunger pump. Engine speed divided by the drive ratio gives pump strokes per minute, and multiplying by the metered oil volume per stroke gives oil delivery in cc/min.
- One metered oil charge is delivered per plunger stroke.
- No leakage past the plunger and no check-valve backflow.
- A pump stroke is a delivery event; visible drop size and drop count are not calculated.
- Engine speed and adjustment remain constant.
The interval is seconds per pump stroke, not seconds per visible drop. Actual drop size is not an input. Ideal delivery assumes the entered displaced volume reaches the outlet.
How the plunger delivers oil
The eccentric turns rotary input into reciprocating plunger motion. During suction, the inlet check admits oil from the reservoir while the outlet check prevents return flow. During delivery, the inlet closes and the outlet opens toward the lubrication point.
The drawing follows one pump cycle. Its speed is slowed for viewing, while the numerical results use the entered engine speed and reduction ratio. Oil markers show flow direction; they do not measure visible drops.
Parts and functions
- Reservoir: holds the available oil supply.
- Drive and eccentric: determine pump frequency and reciprocating motion.
- Plunger and chamber: displace the entered oil volume during each delivery stroke.
- Inlet and outlet checks: direct flow through the pump.
- Delivery line: carries lubricant to the served point.
Clearances, seals, valve opening pressure and maximum speed belong to a particular pump design. They cannot be specified from the four inputs here. Actual delivery also depends on complete filling, leakage, viscosity and outlet pressure.
Where automatic lubrication is useful
Automatic lubrication can supply machine bearings, sliding surfaces or other friction points at controlled intervals. A mechanically driven pump ties its frequency to shaft speed. Electrically, pneumatically and gas-driven lubricators use other means of driving or metering the lubricant.
These arrangements are not interchangeable. The served component determines the required lubricant and replenishment quantity. The pump and delivery network must also work against the application’s pressure and temperature conditions.
SKF’s VectoLub VTEC is a manufacturer example of volumetric micropumps supplying small oil quantities to friction points. Its nozzle delivery arrangement differs from this simple plunger-and-line drawing. Product-specific data, rather than a generic stroke-volume example, should be used for actual selection.
Delivery and timing equations
Let N be engine revolutions per minute, R be engine revolutions per pump stroke, Vs be oil volume per stroke in cc, and Vres be reservoir volume in cc. One cc is one cm³ or one mL.
- Pump stroke rate n = N/R strokes/min.
- Ideal oil delivery Q = n × Vs cc/min.
- Stroke interval = 60/n seconds/stroke.
- Reservoir duration = Vres/Q minutes.
The entered Vs is treated as the volume reaching the outlet on each stroke. For an ideal cylindrical plunger, swept volume is area × stroke. If using measured net delivery per stroke, enter that value directly; the calculator does not apply a separate volumetric-efficiency factor.
Reservoir duration assumes constant delivery and that the entered volume is available. A real installation may need a low-level reserve. Visible drop timing additionally requires the actual volume per drop, which this tool does not specify.
Worked example: a small metered supply
With N = 600 rpm, R = 20 rev/stroke, Vs = 0.05 cc/stroke and Vres = 100 cc, the pump makes 600/20 = 30 strokes/min. Delivery is 30 × 0.05 = 1.5 cc/min. The interval is 60/30 = 2 seconds per stroke, and the ideal reservoir duration is 100/1.5 = 66.6667 minutes.
At 300 rpm with the other inputs fixed, there are 15 strokes/min and 0.75 cc/min. The interval becomes 4 seconds and reservoir duration 133.3333 minutes.
At the original speed but Vs = 0.10 cc/stroke, frequency remains 30 strokes/min. Delivery doubles to 3 cc/min, duration halves to 33.3333 minutes, and stroke timing stays at 2 seconds. This distinguishes changing the amount per stroke from changing how often strokes occur.
These values demonstrate arithmetic. They do not establish a suitable oil feed for a particular bearing, cylinder or saw chain.
Comparing lubrication arrangements
| Arrangement | How oil reaches the surface | What requires attention |
|---|---|---|
| Mechanically driven metering pump | Repeated displaced charges follow the drive motion. | Net volume per stroke, speed, filling and discharge pressure. |
| Splash lubrication | Moving parts distribute oil from a sump. | Machine-specific oil level, geometry and operating conditions. |
| Pressure-fed circulating system | A pump circulates oil through passages and returns. | Flow, pressure regulation, filtration and heat removal. |
The systems serve different designs. The calculated volume from a force-feed pump is not a bearing-film thickness, a wear prediction or a substitute for the machine’s lubrication specification.
Automatic-oiler questions
No. A stroke delivers the entered volume. A sight-feed drop has its own volume, affected by the outlet and oil conditions; no drop volume is entered here.
With a fixed drive ratio and volume per stroke, more revolutions produce more pump strokes and a higher ideal flow.
It is engine revolutions per pump stroke. Increasing it reduces pump frequency at the same engine speed.
No. It assumes that the entered oil volume reaches the outlet on every stroke. Actual net delivery must be established for the pump and conditions.
It calculates the supply implied by the inputs. The machine’s lubrication requirements must come from its manufacturer or an application-specific assessment.
Use the lubricant specified for both the equipment and its lubrication system. A generic choice based only on pump type cannot establish viscosity or material compatibility.
No. A loss of visible flow may have several causes, and appearance alone does not prove delivery at the served point. Follow the equipment’s shutdown and diagnostic procedure before continued operation.
No. The cycle is slowed for viewing; the displayed rate and interval come from the entered numbers.
Manufacturer reference
SKF, VectoLub VTEC, describes a volumetric micropump system for small-quantity oil delivery. Its product data applies to that equipment, not to the example mechanism drawn here.
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