BIZOMAT MAKEOS · Engineering
Thrust Pad Bearing Check (Unit Load, PV, Friction Loss, Oil Flow)
Is this thrust bearing’s unit load and PV within limits, how much power does friction waste, and how much oil must flow through it to carry the heat away?
Check of a flat or tilting-pad thrust bearing: pad area from the ring and pad coverage, unit load, mean sliding velocity and PV (as the thrust bearing pad tool) against your allowable values, friction power loss from the friction coefficient, and the oil flow needed to remove that heat for the allowed oil temperature rise (as the coolant flow for a heat load tool) against the oil supply.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Outside diameter | mm | Outside diameter of the thrust ring. |
| Inside diameter | mm | Inside diameter of the thrust ring. |
| Pad coverage of the ring | % | Share of the ring covered by pads (the rest is oil grooves). |
| Thrust load | N | Axial load on the bearing. |
| Speed | rpm | Shaft speed. |
| Friction coefficient | Friction coefficient of the running bearing (from its type and lubrication). | |
| Oil | ||
| Allowed oil temperature rise | K | Rise in oil temperature you accept through the bearing. |
| Oil specific heat | kJ/(kg·K) | Specific heat of the oil. |
| Oil density | kg/m³ | Density of the oil. |
| Limits | ||
| Allowable unit load | MPa | Allowable unit load for the bearing material and type. |
| Allowable PV | MPa·m/s | Allowable PV for the bearing material and type. |
| Oil supply available | L/min | Oil flow available to the bearing. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Outside diameter
- What it is
- The outside diameter of the ring of thrust pads.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 150 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A larger outside diameter increases the pad area and the mean sliding speed.
What this means: Inside diameter
- What it is
- The inside diameter of the ring of thrust pads.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 100000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- A smaller inside diameter increases the pad area.
What this means: Pad coverage of the ring
- What it is
- The share of the ring’s area actually covered by bearing pads; the rest is oil grooves or gaps between pads.
- Units and format
- Enter a number in %: percent: the number is read as a percentage, so type 8 for 8 %. The form accepts 1% to 100%. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 80% as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pad area, and so unit load, scale directly with it.
- Get it right
- Measure from the drawing: total pad area divided by the full ring area.
What this means: Thrust load
- What it is
- The axial thrust load the bearing carries in service.
- Units and format
- Enter a number in N: newtons. The form accepts 0.000001 N or more. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20000 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Unit load, PV and friction loss rise in proportion to it.
- Get it right
- Use the total axial load on the bearing, not the load per pad.
What this means: Speed
- What it is
- The rotational speed of the shaft and thrust collar.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 1000000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1500 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sliding speed, PV, friction loss and oil flow rise in proportion to speed.
What this means: Friction coefficient
- What it is
- The friction coefficient of the bearing while running, which depends on its type, lubrication regime and speed, from the bearing maker or test data.
- Units and format
- Enter a plain number with no unit. The form accepts 0.0001 to 0.5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 0.005 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Friction loss and oil flow rise in proportion to it.
Oil
What this means: Allowed oil temperature rise
- What it is
- The largest rise in oil temperature you accept between the bearing inlet and outlet.
- Units and format
- Enter a number in K: kelvin (a difference of 1 K equals 1 °C). The form accepts 0.000001 K to 100 K. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 15 K as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Oil flow needed is inversely proportional to the allowed rise.
- Get it right
- A temperature difference, not the outlet temperature.
What this means: Oil specific heat
- What it is
- The specific heat capacity of the lubricating oil, from the oil supplier’s data.
- Units and format
- Enter a number in kJ/(kg·K): kilojoules per kilogram per kelvin. The form accepts 0.000001 kJ/(kg·K) to 10 kJ/(kg·K). Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.88 kJ/(kg·K) as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Oil flow needed is inversely proportional to it.
- Get it right
- Enter kilojoules, not joules, per kilogram per kelvin.
What this means: Oil density
- What it is
- The density of the lubricating oil at its working temperature, from the oil supplier’s data.
- Units and format
- Enter a number in kg/m³: kilograms per cubic metre. The form accepts 0.000001 kg/m³ to 2000 kg/m³. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 870 kg/m³ as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Limits
What this means: Allowable unit load
- What it is
- The largest average pressure on the pads you accept, from the bearing material supplier or bearing maker for this bearing type.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 1000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
What this means: Allowable PV
- What it is
- The largest product of unit load and sliding speed the bearing material and type can run at, from the bearing material supplier.
- Units and format
- Enter a number in MPa·m/s: MPa·m/s. The form accepts 0.000001 MPa·m/s to 10000 MPa·m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 20 MPa·m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Check the units of the limit: megapascals times metres per second.
What this means: Oil supply available
- What it is
- The oil flow your lubrication system can deliver to this bearing.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0.000001 L/min to 100000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
Method and formulas
- Area = π (D_o² − D_i²) ÷ 4 × coverage; P = W ÷ area; V = π (D_o + D_i) ÷ 2 × n; PV (as the thrust bearing pad tool).
- Friction loss = μ W V.
- Oil flow = loss ÷ (ρ c_p ΔT) (as the coolant flow for a heat load tool).
- Example: 1.9771 MPa, PV 17.857; friction wastes 903.21 W, needing 2.2089 L/min of oil.
Limitations
- Uniform load over the pads; misalignment concentrates load on some pads.
- The friction coefficient must suit the regime (boundary, mixed or full film).
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a thrust collar or pad bearing
- Size the oil supply for a thrust bearing
- Compare pad areas for a new load
Who it is for
- Design engineers
- Maintenance engineers
- Lubrication engineers
What you get
- Pad area, unit load, velocity and PV
- Friction power loss
- Oil flow needed
Interpreting the result
- If PV is too high, more pad area or a lower speed helps; if the oil flow is short, raise the allowed rise only within the oil’s limits.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2338–2356, 371–374. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
Thrust bearings
In Plain Bearings by the Numbers
What it covers: Check a thrust face's area, unit load, sliding speed and PV, estimate its friction heat and oil flow with the BIZOMAT thrust tools, and see why tapered lands and tilting pads carry load.
BIZOMAT tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.
Open the Thrust Pad Bearing Check (Unit Load, PV, Friction Loss, Oil Flow) calculator