Plain Bearing PV Value Calculator
Calculate the PV value of a plain bearing from specific load p and sliding speed v – a common but on its own insufficient indicator of thermal duty.
Formula
PV = p * v
The product of specific load and sliding speed correlates with the frictional heat generated per unit area, and is therefore used as an approximate indicator of the thermal-tribological duty of a plain bearing, especially for dry-running or boundary-lubricated polymer and sintered bearings.
What this model does not show
A low PV value alone is not an approval. p and v each have their own independent limits: a very high specific load at very low speed can give a low PV yet still overload locally (e.g. risk of seizure); conversely very high speed at low load can trigger other failure mechanisms (wear, heating) that a PV limit alone does not capture. There is no universal, material-independent PV limit.
Worked example
With p = 2.5 MPa (from the Plain bearing specific load calculator) and v = 3.927 m/s (from the Plain bearing sliding speed calculator, d = 50 mm, n = 1,500 rpm): PV = 2.5 MPa x 3.927 m/s = 9.82 MPa*m/s. Since 1 MPa*m/s = 1 W/mm2, this corresponds to an area-specific frictional power density of 9.82 W/mm2 -- a value to be checked against an actual datasheet for the material pairing used, not a rule of thumb.
Common mistakes
- Checking only the PV value while forgetting to also check p and v individually against their own limits.
- Using a 'generic' PV limit found online that applies to a different material pairing or lubrication type.
- Misreading MPa*m/s and W/mm2 as different physical statements instead of recognizing they are numerically identical.
Frequently asked questions
Is meeting a PV limit sufficient proof by itself?
No. A PV limit is necessary but not sufficient. p and v must also each individually stay within the permissible values for the actual material pairing.
Why do MPa*m/s and W/mm2 give the same number?
1 MPa = 1e6 Pa = 1e6 N/m2. Multiplied by 1 m/s that gives 1e6 (N/m2)(m/s) = 1e6 W/m2 = 1 W/mm2 -- the units are numerically interchangeable even though written differently.
For which bearing types does the PV value matter most?
Mainly for dry-running or boundary-lubricated plain bearings (e.g. polymer or sintered bearings), where frictional heat is barely carried away by a load-bearing oil film and thermal duty dominates.
Where do I get a permissible PV limit?
Only from an actual manufacturer datasheet for the material pairing, lubrication, ambient temperature and duty type used -- there is no material-independent standard value.
Can a low PV value still cause damage?
Yes. Very high specific load at very low speed can cause local seizure despite a low PV; very high speed at low load can trigger other wear mechanisms. The PV product alone does not fully capture these cases.
What comes after the PV value?
For a full hydrodynamic assessment (instead of an approximate PV estimate), the Plain bearing Sommerfeld number and Plain bearing operating clearance calculators give a more differentiated basis.