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

PV combines two important operating parameters: bearing pressure (P) and sliding velocity (V). However, PV should not be treated as a universal pass/fail number. Actual bearing performance also depends on temperature, shaft surface condition, clearance, motion type, lubrication, environment, and the specific bearing material or grade.

In this guide, we explain how to calculate bearing PV value, how to interpret PV limits, and how to use the result together with other application conditions when selecting a sliding or self-lubricating bearing.

What Is Bearing PV Value?

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

PV = P × V

Where:

• P = bearing pressure

• V = sliding velocity

PV is commonly used as an indicator of the combined severity of load and sliding motion in plain and sliding bearing applications.

Bearing Pressure

For a typical cylindrical radial plain bearing, the projected bearing area can be approximated as:

A = D × L

Where:

• A = projected bearing area

• D = bearing inside diameter

• L = bearing length

The average projected bearing pressure is then:

P = F / (D × L)

Where:

• F = radial load

• D = bearing inside diameter

• L = bearing length

When F is in newtons and D and L are in millimeters, pressure is obtained in N/mm², which is numerically equivalent to MPa:

1 N/mm² = 1 MPa

This projected-area calculation is appropriate for a typical cylindrical radial bearing. Other bearing geometries, load directions, or combined loading conditions may require a different load and contact analysis.

Sliding Velocity

Sliding velocity depends on the type of motion.

Common motion types include:

• Rotary motion

• Oscillating motion

• Reciprocating motion

For a rotating shaft, the basic sliding velocity is:

V = πDn / 60

where D is in meters and n is in rpm, giving V in m/s.

PV Value

Once bearing pressure and sliding velocity have been determined:

PV = P × V

For example, if:

• P = 5 MPa

• V = 0.628 m/s

then:

PV = 5 × 0.628 ≈ 3.14 MPa·m/s

The exact numerical result may vary slightly depending on rounding.

Why Is PV Important for Sliding Bearings?

Load Alone Does Not Tell the Whole Story

Load is an important bearing design parameter, but it does not fully describe the severity of a sliding application.

Consider two bearings operating at the same average pressure. One operates at low speed while the other operates at substantially higher speed. The higher-speed application generally introduces more sliding per unit time and may generate more frictional work and heat.

Therefore, pressure should not be evaluated in isolation.

Speed Alone Does Not Tell the Whole Story

The same principle applies to speed.

Two bearings may operate at the same sliding velocity but under very different loads. The higher-load application can produce substantially different contact conditions, frictional behavior, wear, and heat generation.

Velocity therefore should not be evaluated independently of bearing pressure.

PV Combines Pressure and Sliding Speed

PV provides a convenient way to express the combined severity of pressure and sliding motion:

Pressure × Velocity = Operating Severity Indicator

This makes PV particularly useful during the early stages of bearing selection and application review.

However, PV is an engineering indicator—not a complete bearing life calculation or a standalone suitability test.

How to Calculate Bearing PV Value Step by Step

Step 1: Determine the Bearing Load

Start with the actual load acting on the bearing during operation.

Depending on the application, this may include:

• Radial load

• Axial load, where applicable

• Static load

• Dynamic load

• Shock or peak load

Do not automatically use only the nominal machine load. If the application contains acceleration, impact, vibration, or changing load conditions, the relevant peak or representative operating condition should also be considered.

For a typical cylindrical radial bearing, the simple PV calculation described in this article assumes that the relevant radial load can be represented by an average projected bearing pressure.

Step 2: Calculate the Projected Bearing Area

For a typical cylindrical radial plain bearing:

A = D × L

For example, if:

• D = 40 mm

• L = 40 mm

then:

A = 40 × 40 = 1,600 mm²

The average projected pressure is:

P = F / A

If the radial load is 8,000 N:

P = 8,000 / 1,600 = 5 N/mm²

Therefore:

P = 5 MPa

The calculation can be summarized as follows:

Step 3: Calculate Sliding Velocity

For rotary motion:

V = πDn / 60

Make sure the diameter used in the velocity calculation is converted to meters when the required velocity unit is m/s.

For example:

• D = 40 mm = 0.04 m

• n = 300 rpm

Therefore:

V = π × 0.04 × 300 / 60

V ≈ 0.628 m/s

For oscillating or reciprocating bearings, the velocity calculation needs to reflect the actual motion rather than simply using rotational speed.

Oscillating Motion

For a simplified oscillating calculation, the sliding distance depends on the shaft diameter and angular travel.

If θ is the one-side oscillation angle measured from the center position, and one complete cycle is defined as movement from −θ to +θ and back to −θ, a simplified estimate of the total sliding distance per cycle is:

Sliding distance per cycle ≈ 2 × θ × πD / 360

where:

• θ = one-side oscillation angle in degrees

• D = shaft diameter

Average sliding velocity can then be estimated as:

Average V ≈ sliding distance per cycle × cycle frequency

where cycle frequency is expressed in cycles per second.

This is a simplified average-velocity estimate. Actual motion profiles may produce significantly different instantaneous or peak velocities, particularly when acceleration, dwell periods, or non-uniform motion are involved.

Reciprocating Motion

For a reciprocating bearing with a stroke length S, the total sliding distance during one complete cycle is approximately:

2S

If the cycle frequency is f, expressed in cycles per second, the simplified average sliding velocity can therefore be estimated as:

V ≈ 2Sf

This calculation provides an average velocity over the complete cycle. Actual instantaneous velocity may be significantly higher or lower depending on the motion profile.

Step 4: Calculate PV

Once pressure and velocity are known:

PV = P × V

For the example:

• P = 5 MPa

• V ≈ 0.628 m/s

Therefore:

PV ≈ 5 × 0.628

PV ≈ 3.14 MPa·m/s

The calculated value is an important input for bearing selection, but it should not be interpreted by itself as proof that a bearing will operate safely.

Bearing PV Calculation Example

Consider a cylindrical sliding bearing with the following operating conditions:

• Shaft diameter: 40 mm

• Bearing length: 40 mm

• Radial load: 8,000 N

• Rotational speed: 300 rpm

Step 1: Projected Area

A = D × L

A = 40 × 40 = 1,600 mm²

Step 2: Bearing Pressure

P = F / A

P = 8,000 / 1,600

P = 5 MPa

Step 3: Sliding Velocity

Convert the diameter:

D = 40 mm = 0.04 m

Then:

V = π × 0.04 × 300 / 60

V ≈ 0.628 m/s

Step 4: PV

PV = P × V

PV = 5 × 0.628

PV ≈ 3.14 MPa·m/s

Engineering Interpretation

A calculated PV of approximately 3.14 MPa·m/s does not automatically mean that the bearing is suitable or unsuitable.

The result must be evaluated against the current technical data for the specific bearing material and grade, together with conditions such as:

• Operating temperature

• Shaft material and hardness

• Shaft surface roughness

• Bearing clearance

• Motion type

• Lubrication condition

• Environmental exposure

• Expected operating life

A generic PV value found online should not be used as a universal acceptance limit. For example, when evaluating a PTFE composite bearing such as MG-1, the calculated PV should be checked against the manufacturer's current technical data together with the actual load, speed, temperature, shaft and clearance conditions.

What Does the PV Limit Mean?

A bearing manufacturer's PV information generally describes an operating range under defined test or application conditions. It should therefore be treated as application guidance rather than as a universal material constant.

Continuous PV Limit

A continuous PV limit generally refers to conditions under which the bearing is expected to operate continuously within the specified application and test conditions.

Continuous operation is important because frictional heat has more time to accumulate and affect the bearing system.

Short-Term or Peak PV Limit

Some bearing materials may tolerate higher PV conditions for short periods than they can sustain continuously.

However, a short-term PV allowance must come from the manufacturer's technical data or application guidance. Engineers should not assume that exceeding a continuous value is acceptable simply because the high-PV condition is temporary.

The duration, frequency, thermal conditions, and motion profile can all affect the result.

Why PV Limits Are Not Universal

PV performance varies between bearing materials and grades.

Examples include:

• PTFE composite bearings

• Filament-wound bearings

• Bi-metallic bearings

• Engineering plastic bearings

Even within the same material family, performance can change with:

• Temperature

• Shaft surface condition

• Load

• Sliding speed

• Motion type

• Lubrication

• Environmental conditions

Therefore:

Always use the manufacturer's current technical data for the specific bearing grade when evaluating allowable PV.

What Happens When the PV Limit Is Exceeded?

Exceeding a recommended PV condition does not necessarily produce an immediate catastrophic failure. However, it can increase thermal and wear-related risks.

A typical engineering chain may be:

Higher PV / more severe sliding conditions

↓

Potentially higher friction and heat generation

↓

Higher bearing temperature

↓

Changes in material behavior, wear rate, or clearance

↓

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, clearance, load profile, and other application factors.

This is why a PV calculation should be followed by a broader application review rather than treated as a single pass/fail test.

Factors That Affect Actual Bearing PV Performance

Temperature

Temperature is one of the most important factors in sliding bearing performance.

Friction generates heat, while the bearing system dissipates heat through conduction, convection, and other mechanisms. As temperature rises, material properties, thermal expansion, clearance, and wear behavior may change.

The basic relationship can be viewed as:

Load + Speed → Friction → Heat Generation → Temperature Rise → Material and Clearance Changes → Bearing Performance

PV is useful for describing operating severity, but PV alone does not determine the final bearing temperature or thermal equilibrium.

Shaft Surface Condition

The shaft is part of the sliding interface, so its surface condition directly affects bearing performance.

Important parameters may include:

• Surface roughness

• Surface hardness

• Surface finish

• Surface damage

• Material compatibility

A bearing with an acceptable calculated PV may still experience accelerated wear if the mating shaft surface is unsuitable. For more on this, see our article How Shaft Surface Roughness Determines PTFE Bearing Life.

Bearing Clearance

Correct running clearance is essential to bearing performance.

A PV calculation can be mathematically correct while the actual bearing application remains unsuitable because of excessive or insufficient clearance.

Thermal expansion, shaft size, housing dimensions, bearing material, and operating temperature should therefore be considered when determining clearance.

Motion Type

PV behavior can differ substantially between:

• Rotary motion

• Oscillating motion

• Reciprocating motion

Continuous rotary motion, low-angle oscillation, and high-frequency reciprocation can produce different wear mechanisms and heat-generation patterns even when a simplified PV calculation gives a similar numerical value.

For non-rotary applications, the actual motion profile should therefore be considered. See our guide How Sliding Speed Impacts PTFE-Based Bearing Performance.

Lubrication Conditions

Sliding bearings may operate under different lubrication conditions, including:

• Dry running

• Initial lubrication

• Boundary lubrication

• Oil-lubricated environments

• Grease-lubricated environments

A self-lubricating bearing should not automatically be interpreted as a bearing that can never be exposed to additional lubrication. The effect of lubrication depends on the specific bearing construction and application.

Contamination and Environment

Environmental conditions can significantly affect bearing performance.

Examples include:

• Dust

• Water

• Moisture

• Chemicals

• Corrosive media

• Foreign particles

The calculated PV should therefore be considered together with the actual operating environment.

How PV Differs by Bearing Material

Different bearing constructions have different performance characteristics. A general comparison can help during the initial selection stage:

These are general characteristics rather than universal performance limits.

Actual allowable PV values should always be taken from the manufacturer's current technical data for the specific bearing grade.

This distinction is especially important when comparing products from different manufacturers or when evaluating a new OEM application. For material-specific PV data, refer to the current product datasheet.

How to Use PV When Selecting a Self-Lubricating Bearing

PV is most useful when it forms part of a broader bearing-selection process.

Step 1: Determine the Load

Identify the actual radial or applicable bearing load, including relevant peak or dynamic conditions.

Step 2: Calculate Projected Pressure

For a typical cylindrical radial bearing:

P = F / (D × L)

Step 3: Calculate Sliding Velocity

For rotary motion:

V = πDn / 60

For oscillating or reciprocating applications, calculate velocity according to the actual motion profile.

Step 4: Calculate PV

PV = P × V

Step 5: Compare PV With Manufacturer Data

Compare the calculated PV with the technical data for the specific bearing material and grade.

At the same time, check:

• Operating temperature

• Shaft material and hardness

• Shaft roughness

• Bearing clearance

• Motion type

• Lubrication

• Environment

• Expected service life

The key principle is:

PV should be treated as a selection parameter, not a standalone suitability or life calculation.

This approach is much more reliable than selecting a bearing based on pressure, speed, or PV alone.

If the application requires an estimate of bearing life, PV alone is not sufficient. A structured life estimate should also consider the bearing material, operating conditions, motion profile, wear behavior, and manufacturer-specific data.

Common Mistakes When Calculating Bearing PV

1. Using the Wrong Load

Using only the nominal or average machine load can underestimate the actual bearing condition when shock, acceleration, or peak loads are present.

2. Using the Wrong Diameter

Diameter must be used consistently in the relevant calculation and with the correct unit.

For projected area, define the bearing geometry clearly. For rotary sliding velocity, the diameter must be expressed in meters when calculating velocity in m/s.

3. Forgetting Unit Conversion

Common errors include mixing:

• mm and m

• mm/s and m/s

• rpm and revolutions per second

Always check units before calculating PV.

4. Treating Rotational Speed as Sliding Velocity

Rotational speed in rpm is not the same quantity as sliding velocity in m/s.

For rotary applications, sliding velocity depends on both shaft diameter and rotational speed:

V = πDn / 60

5. Comparing PV With the Wrong Material Data

A PV value should be compared with data for the actual bearing material and grade.

Do not automatically apply the PV limit of one material to another.

6. Ignoring Temperature

A PV calculation that ignores temperature can give an incomplete picture, particularly for dry-running applications where frictional heat may be significant.

7. Ignoring Motion Type

Rotary, oscillating, and reciprocating applications can have different wear and thermal behavior.

A single simplified PV calculation may not fully describe a complex motion profile.

8. Treating PV as the Only Selection Criterion

PV is an important engineering parameter, but it is not a complete bearing-selection method.

PV ≠ complete bearing selection.

Bearing PV Calculation Checklist

Use the following checklist when reviewing a sliding bearing application:

This checklist can also be used as a starting point when preparing an engineering inquiry or bearing RFQ.

When Should You Ask a Bearing Manufacturer?

Manufacturer input is particularly useful when the application involves conditions that are difficult to evaluate using a basic PV calculation alone.

Consider an engineering review when you have:

• PV close to the published application limit

• High load combined with low speed

• High-frequency reciprocating motion

• Unusual or elevated operating temperature

• Water or chemical exposure

• Tight or highly controlled clearance requirements

• Custom bearing dimensions

• A new OEM design

• A demanding service-life requirement

For an engineering evaluation, useful application information typically includes:

• Shaft diameter

• Bearing dimensions

• Load

• Speed

• Motion type

• Operating temperature

• Shaft material and surface condition

• Lubrication conditions

• Environmental conditions

• Expected operating life

Have a specific bearing application? Send us the shaft diameter, bearing dimensions, load, speed, motion type, operating temperature, shaft condition, and environment. Our engineers can help evaluate the appropriate bearing material and design for the application.

For a broader view of bearing selection, see our PTFE Composite Bearing Selection Guide.

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 used to evaluate the combined severity of load and sliding motion in a bearing application.

How do you calculate bearing PV?

For a typical cylindrical radial plain bearing:

1. Calculate projected area: A = D × L

2. Calculate bearing pressure: P = F / A

3. Calculate sliding velocity for rotary motion: V = πDn / 60

4. Calculate PV: PV = P × V

The result should then be compared with manufacturer-specific technical data and the actual operating conditions.

What is a good PV value for a sliding bearing?

There is no single PV value that is universally “good” for every sliding bearing.

The allowable PV depends on the specific bearing material and grade, temperature, shaft condition, clearance, motion type, lubrication, environment, and other application conditions.

Always refer to current manufacturer data for the specific bearing being evaluated.

Does a higher PV rating mean a better bearing?

Not necessarily.

A higher published PV capability may be useful for a particular application, but bearing suitability depends on more than PV. Load, temperature, shaft condition, clearance, motion, environment, lubrication, and required service life must also be considered.

The appropriate bearing is the one whose characteristics match the application requirements.

What is the difference between PV and bearing load capacity?

Bearing load capacity and PV describe different aspects of a bearing application.

Load capacity primarily relates to how much load a bearing can support under specified conditions, while PV combines pressure and sliding velocity to indicate the severity of a sliding application.

A bearing may satisfy a specified pressure or load requirement while still exceeding its recommended PV condition at higher sliding speed.

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

Some manufacturers specify separate short-term or peak PV limits. These values are application- and material-specific and should not be assumed unless confirmed by the manufacturer.

Do not assume that exceeding a published continuous PV value is acceptable without application-specific confirmation.

Does PV apply to oscillating and reciprocating bearings?

Yes. PV can be an important parameter for oscillating and reciprocating applications, but the velocity calculation and interpretation must reflect the actual motion.

A simplified average velocity may be useful for an initial estimate, while peak velocity, acceleration, frequency, stroke, angular travel, dwell periods, and load variation may need to be considered for a detailed engineering evaluation.

Conclusion

Calculating bearing PV value is straightforward, but using PV correctly requires more than applying a single formula.

For a typical cylindrical radial sliding bearing, the basic process is:

1. Determine the operating load

2. Calculate the projected bearing area

3. Determine bearing pressure

4. Calculate sliding velocity

5. Calculate PV

6. Compare the result with current, material-specific manufacturer data

7. Check temperature, shaft condition, clearance, motion, lubrication, and environment

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

A reliable bearing selection process combines the calculated PV with the actual operating conditions and the technical data for the specific bearing grade. When the application involves high loads, unusual motion, elevated temperature, demanding environments, or tight service-life requirements, an application-specific engineering review can provide a more reliable basis for selection.

Need help evaluating a sliding bearing application? Send us your shaft diameter, bearing dimensions, load, speed, motion type, operating temperature, shaft condition, and environment. Our engineers can help assess the appropriate bearing material and design.

Request Engineering Evaluation | Send Your RFQ

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