A sliding bearing may operate within its individual load and speed limits yet still experience excessive wear or temperature rise when load and sliding speed occur together. This is why engineers use the PV value to evaluate the severity of a sliding bearing application.

PV combines two important operating parameters:

• P — bearing pressure

• V — sliding velocity

The basic relationship is:

PV = P × V

However, PV should not be treated as a universal pass/fail value. Actual bearing performance also depends on factors such as temperature, shaft surface condition, running clearance, motion type, lubrication, environment, and the specific bearing material and grade.

What Is Bearing PV Value?

For a typical cylindrical radial plain bearing under radial loading, bearing PV value is calculated from bearing pressure and sliding velocity.

Bearing PV Formula

PV = P × V

Where:

• PV = pressure-velocity value

• P = bearing pressure

• V = sliding velocity

For a cylindrical radial bearing, the projected bearing area is commonly approximated as:

A = D × L

Where:

• A = projected bearing area

• D = bearing inside diameter

• L = bearing length

Bearing pressure is then:

P = F / (D × L)

Where:

• F = applied radial load

• D = bearing inside diameter

• L = bearing length

When force is expressed in newtons and dimensions in millimeters:

1 N/mm² = 1 MPa

Therefore, bearing pressure calculated in N/mm² can be directly expressed in MPa.

These equations apply to the stated cylindrical radial-bearing case. Thrust washers, flanged bearings, spherical bearings, and applications involving combined axial, radial, or moment loads may require different projected-area definitions or additional engineering analysis.

Why Is PV Important for Sliding Bearings?

Load and speed affect a sliding bearing in different ways, but evaluating them separately does not always represent the severity of the actual application.

A bearing may tolerate a certain load at low speed or a certain speed at low load. When load and sliding speed occur simultaneously, however, frictional heat generation and wear conditions can become more severe.

This is why PV is useful as a screening parameter during bearing selection.

PV can help engineers:

• quantify the combined effect of pressure and sliding velocity;

• compare an application with manufacturer-published material data;

• identify operating conditions that may require further evaluation;

• determine whether a particular bearing material or grade should be investigated further.

PV is not, by itself, a bearing life prediction or a complete suitability calculation.

How to Calculate Bearing PV Value Step by Step

For a typical cylindrical radial sliding bearing, the calculation can be organized as:

Load → Projected Area → Bearing Pressure → Sliding Velocity → PV

Step 1: Determine the Bearing Load

Use the load actually experienced by the bearing under the relevant operating condition.

Depending on the application, this may include:

• continuous operating load;

• dynamic load;

• peak load;

• shock load;

• transient load.

If the bearing experiences significantly different load conditions during a cycle, using only the nominal average load may underestimate the actual operating severity.

Step 2: Calculate the Projected Bearing Area

For a cylindrical radial bearing:

A = D × L

For example, if:

• D = 40 mm

• L = 40 mm

then:

A = 40 × 40 = 1,600 mm²

Step 3: Calculate Bearing Pressure

Using:

P = F / (D × L)

If the radial load is 8,000 N:

P = 8,000 / 1,600 = 5 N/mm² = 5 MPa

The bearing pressure is therefore:

P = 5 MPa

Step 4: Calculate Sliding Velocity

The velocity calculation depends on the type of bearing motion.

Rotary Motion

For continuous rotary motion:

V = πDn / 60

Where:

• V = sliding velocity in m/s

• D = bearing diameter in meters

• n = rotational speed in rpm

For example:

• D = 40 mm = 0.04 m

• n = 300 rpm

Then:

V = π × 0.04 × 300 / 60 ≈ 0.628 m/s

Oscillating Motion

For oscillating bearings, the definition of oscillation angle should be stated clearly.

Let θ be the one-side oscillation angle measured from the center position.

One complete oscillation cycle is:

−θ → +θ → −θ

For a cylindrical bearing with diameter D, the approximate sliding distance per complete cycle is:

Distance/cycle ≈ 2 × θ × πD / 360

Where θ is expressed in degrees and D is expressed in meters.

If the oscillation frequency is f cycles per second:

Average V ≈ Distance/cycle × f

This gives an average sliding velocity based on the total sliding distance per cycle.

For non-uniform oscillating motion, however, instantaneous velocity may be significantly higher than the cycle-average value. Acceleration, deceleration, dwell time, and the actual motion profile should therefore be considered when evaluating demanding applications.

Reciprocating Motion

For reciprocating motion, let S be the stroke length.

One complete cycle consists approximately of:

Forward stroke + return stroke

Therefore:

Distance/cycle ≈ 2S

If the reciprocating frequency is f cycles per second:

V ≈ 2Sf

As with oscillating motion, the average velocity does not describe the complete motion profile. Peak velocity, acceleration, dwell time, and transient conditions may need to be considered for engineering evaluation.

Step 5: Calculate the Bearing PV Value

Once bearing pressure and sliding velocity are known:

PV = P × V

Using the example above:

• P = 5 MPa

• V ≈ 0.628 m/s

Therefore:

PV ≈ 5 × 0.628 = 3.14 MPa·m/s

The calculated bearing PV value is approximately:

3.14 MPa·m/s

How Should You Interpret a Bearing PV Value?

A calculated PV value should be compared with the current technical data for the specific bearing material or grade, under conditions relevant to the application.

For example, a calculated value of:

PV ≈ 3.14 MPa·m/s

does not automatically prove that the bearing is suitable or unsuitable.

The engineering evaluation should also consider:

• operating temperature;

• shaft material and hardness;

• shaft surface condition and roughness;

• running clearance;

• motion type and velocity profile;

• lubrication condition;

• contamination and environment;

• duty cycle and required service life.

For a specific PTFE composite bearing such as MG-1, the calculated PV should therefore be checked against the manufacturer's current technical data and evaluated together with the actual load, speed, temperature, shaft condition, clearance, and operating environment.

Generic PV values found online should not be treated as universal acceptance limits.

What Does the PV Limit Mean?

A PV limit represents an operating boundary or recommended/allowable PV range established under defined material, test, or application conditions.

PV data may distinguish between:

• continuous PV conditions for sustained operation;

• short-term or peak PV conditions for temporary operating periods.

A short-term PV allowance should not be assumed simply because a calculated value is above a published continuous value. Any permitted short-term or peak condition should come from the relevant manufacturer's technical data or application evaluation.

There is no single universal PV limit that applies to every sliding bearing material, grade, geometry, or operating environment.

What Happens When the PV Limit Is Exceeded?

When PV increases, the sliding interface may experience more severe operating conditions.

A simplified engineering chain is:

Higher PV / more severe sliding
→ potentially higher friction and heat generation
→ higher bearing temperature
→ changes in material behavior, wear rate, or clearance
→ possible surface or transfer-film instability
→ accelerated wear, scoring, or, under severe conditions, seizure

The actual failure mechanism depends on the bearing material, shaft condition, lubrication, temperature, motion profile, contamination, and other application-specific factors.

Therefore, exceeding a published PV value should be treated as a trigger for engineering evaluation rather than as proof of a specific failure mode.

Factors That Affect Actual Bearing PV Performance

The same calculated PV value can produce different results in different applications. Important factors include:

• Temperature: Higher operating temperatures can change material properties, friction, wear behavior, and clearance.

• Shaft surface: Shaft material, hardness, roughness, and surface finish can strongly influence the sliding interface.

• Running clearance: Clearance affects contact conditions, thermal behavior, and bearing operation.

• Motion type: Continuous rotation, oscillation, and reciprocation produce different velocity and load profiles.

• Lubrication: Dry-running, grease-lubricated, oil-lubricated, and other conditions can produce different friction and wear behavior.

• Environment: Water, chemicals, dust, contamination, and other environmental conditions may affect actual performance.

How Does PV Differ by Bearing Material?

PV performance is material- and grade-specific. The following comparison is qualitative and should not be used as a substitute for manufacturer technical data.

The PV behavior of one bearing material should not automatically be transferred to another material or grade.

How to Use PV for Bearing Selection

PV should be used as one part of a broader engineering selection process.

A practical sequence is:

1. Calculate the application PV.

2. Compare it with current manufacturer data for the specific bearing material or grade.

3. Check operating temperature.

4. Verify shaft material and hardness.

5. Check shaft surface condition and roughness.

6. Evaluate running clearance.

7. Confirm the actual motion and velocity profile.

8. Consider lubrication, contamination, chemicals, and other environmental conditions.

9. Evaluate duty cycle and required service life.

The key principle is:

PV is a bearing selection parameter, not a standalone suitability or life calculation.

Common Mistakes When Calculating Bearing PV

Several calculation and interpretation errors occur frequently.

1. Multiplying Load Directly by Speed

PV is not simply:

Load × rpm

Pressure must first be calculated from the appropriate projected area, and sliding velocity must be expressed in a consistent unit.

2. Using the Wrong Projected Area

For the cylindrical radial-bearing case described here:

A = D × L

Other bearing geometries may require different area definitions.

3. Mixing Units

Check:

• diameter units;

• length units;

• force units;

• pressure units;

• velocity units.

For the rotary velocity equation, diameter must be converted to meters if the required velocity unit is m/s.

4. Using Average Speed for Every Motion Type

For oscillating and reciprocating bearings, average sliding velocity may not represent peak velocity or the actual motion profile.

5. Ignoring Peak or Transient Loads

Using only nominal load can underestimate PV when the application includes shock, acceleration, or short-duration peak loading.

6. Treating a Published PV Value as a Universal Limit

PV data is material-, grade-, test-, and application-dependent. A published number should be interpreted within its stated conditions.

7. Using PV as a Direct Life Prediction

Two applications with the same PV can have different wear rates and service lives because temperature, shaft condition, clearance, environment, and motion profile may differ.

8. Ignoring Shaft Condition and Clearance

A mathematically acceptable PV value does not eliminate the need to verify the mating shaft and running clearance.

Bearing PV Calculation Checklist

Use the following information when performing a preliminary PV calculation or preparing a bearing engineering inquiry.

This information can also be used as the basis for an engineering inquiry or RFQ.

When Should You Ask a Bearing Manufacturer?

Manufacturer evaluation is particularly useful when:

• calculated PV is close to the published range;

• the application combines high load and low speed;

• the bearing operates at high sliding frequency;

• oscillating or reciprocating motion is demanding;

• operating temperature is high;

• water, chemicals, or contamination are present;

• running clearance is tightly controlled;

• the application uses custom bearing dimensions;

• the bearing is part of an OEM design with defined service-life requirements.

For an application review, provide as much of the following information as possible:

• shaft diameter;

• bearing dimensions;

• operating load;

• rotational speed or motion frequency;

• motion type;

• operating temperature;

• shaft material and hardness;

• shaft surface condition;

• running clearance;

• lubrication and environmental conditions;

• duty cycle and required service life.

The manufacturer can then evaluate the calculated PV together with the actual application conditions.

Frequently Asked Questions

What is bearing PV value?

Bearing PV value is the product of bearing pressure and sliding velocity:

PV = P × V

It is commonly used as a screening parameter for evaluating the severity of sliding bearing operating conditions.

What is a good PV value for a sliding bearing?

There is no single PV value that can be considered universally good for every sliding bearing. The appropriate range depends on the specific bearing material or grade and the actual operating conditions.

Does a higher PV rating mean a better bearing?

Not necessarily. PV performance is only one engineering parameter. Bearing selection also depends on temperature, shaft condition, clearance, motion, lubrication, environment, and required service life.

What is the difference between PV and bearing load capacity?

Bearing load capacity describes how much load a bearing can support under specified conditions. PV combines bearing pressure with sliding velocity and is used to assess the combined severity of load and sliding motion.

Can a bearing operate above its continuous PV rating for a short time?

In some applications, short-term or peak operating conditions may be permitted, but this should not be assumed. Any allowable short-term condition should be confirmed using the manufacturer's technical data or application-specific engineering evaluation.

Does PV apply to oscillating and reciprocating bearings?

Yes. PV can be used as a screening parameter for oscillating and reciprocating applications, but the sliding velocity must be calculated from the actual motion. Peak velocity, acceleration, dwell time, load variation, and the complete motion profile may need to be considered.

From PV Calculation to Engineering Evaluation

A practical bearing PV evaluation can be summarized as:

1. Determine the actual operating load.

2. Calculate the appropriate projected bearing area.

3. Calculate bearing pressure.

4. Determine sliding velocity from the actual motion.

5. Calculate PV.

6. Compare the result with current manufacturer data for the specific material or grade.

7. Review temperature, shaft condition, clearance, environment, duty cycle, and service-life requirements.

The key point is that PV is an engineering selection parameter, not a standalone bearing life or suitability calculation.

For demanding applications, a more useful engineering workflow is:

PV Calculation → Material Data → Application Review → PV Evaluation → RFQ

If you are selecting a PTFE composite bearing or another sliding bearing for an OEM application, providing the actual load, speed, motion, temperature, shaft condition, clearance, and environment allows the bearing supplier to evaluate the application more accurately.

Request Engineering Evaluation | Send Your RFQ

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• PTFE Composite Bearing Selection Guide

• How Sliding Speed Impacts PTFE-Based Bearing Performance

• How Shaft Surface Roughness Determines PTFE Bearing Life

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• MG-1 PTFE Composite Bearings