BIZOMAT MAKEOS · Engineering
Plain Bearing Pressure, Velocity and PV
Are the pressure, sliding speed and PV of this bushing within the material’s limits?
Projected bearing pressure, sliding velocity and PV value of a plain (sleeve) bearing or bushing, compared with the limits of the bearing material.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Radial load | N | Radial load on the bearing. |
| Shaft diameter | mm | Shaft (journal) diameter. |
| Bearing length | mm | Bearing length in contact. |
| Speed (or equivalent for oscillation) | rpm | Shaft speed; for oscillation use the equivalent speed from the bearing maker’s method. |
| Maximum pressure of material | MPa | Static or dynamic pressure limit from the bearing material maker. |
| Maximum sliding speed of material | m/s | Sliding speed limit from the maker (lubricated or dry as applicable). |
| Maximum PV of material | MPa·m/s | PV limit from the maker for the lubrication condition. |
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: Radial load
- What it is
- The radial force carried by the plain bearing, from a shaft reaction calculation.
- 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 2000 N as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pressure and PV rise in proportion.
- Get it right
- Enter the load on this bearing, not the total shaft load.
What this means: Shaft diameter
- What it is
- The diameter of the shaft (journal) running in the bearing.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 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 shaft lowers pressure but raises sliding speed.
- Get it right
- Use the shaft diameter at the bearing, not the bearing outside diameter.
What this means: Bearing length
- What it is
- The axial length of the bearing surface in contact with the shaft.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.000001 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 30 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Pressure and PV fall in proportion; sliding speed is unchanged.
- Get it right
- Subtract chamfers and oil grooves that carry no load.
What this means: Speed (or equivalent for oscillation)
- What it is
- The rotational speed of the shaft. For oscillating motion, the equivalent continuous speed from the bearing maker’s method.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0 rpm to 1000000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 200 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 and PV rise in proportion.
- Get it right
- For oscillation do not enter the cycle rate; convert it with the maker’s method.
What this means: Maximum pressure of material
- What it is
- The highest projected pressure the bearing material allows, from the bearing material maker.
- Units and format
- Enter a number in MPa: megapascals (1 MPa = 1 N/mm²). The form accepts 0.000001 MPa to 10000 MPa. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 MPa as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Check whether the maker gives a static or a dynamic limit and use the one that matches the duty.
What this means: Maximum sliding speed of material
- What it is
- The highest sliding speed the bearing material allows, from the maker, for the lubrication condition.
- Units and format
- Enter a number in m/s: metres per second. The form accepts 0.000001 m/s to 1000 m/s. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 2.5 m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Dry-running and lubricated limits differ; use the one that applies.
What this means: Maximum PV of material
- What it is
- The highest product of pressure and sliding speed the bearing material allows, from the maker, which limits heating.
- 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 1.6 MPa·m/s as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Get it right
- Use the PV limit for the actual lubrication condition.
Method and formulas
- P = W ÷ (d L) (projected area).
- V = π d n ÷ 60 000.
- PV = P × V; compare each with the material limits.
- Example: 2000 N on a 30 × 30 mm bush at 200 rpm gives P = 2.2222 MPa, V = 0.31416 m/s and PV = 0.69813.
Limitations
- PV limits depend on lubrication, temperature and duty; they are screening values, not a hydrodynamic design.
- Fully hydrodynamic journal bearings need a film thickness (Sommerfeld) analysis.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Select a bronze, polymer or sintered bush
- Check a pivot or slow shaft bearing
- Compare bush lengths
Who it is for
- Design engineers
- Maintenance engineers
What you get
- Projected pressure
- Sliding velocity
- PV value
- Utilisation of each limit
Interpreting the result
- A length-to-diameter ratio of about 0.5 to 1.5 is common for bushes.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2314–2337. 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
Unit load, sliding speed and PV
In Plain Bearings by the Numbers
What it covers: Calculate a bearing's unit load, sliding speed and PV, check a bush against its material limits with the BIZOMAT PV tool, handle oscillating motion, and see why PV does not rate a full-film bearing.
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.