• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer

Linear Motion Tips

Covering Linear Motion Systems, Components and Linear Motion Resources

  • New
    • Editor’s blog
    • Industry news
    • Motion Casebook
    • Video
  • Applications
  • Slides + guides
    • Ball + roller guides
    • Track roller (cam + wheel) guides
    • Crossed-roller slides
    • Linear bearings
    • Plastic + composite guides
  • Drives
    • Ball + lead + roller screws
    • Belt + chain drives for linear
    • Rack + pinion sets
  • Actuators
    • Ball + leadscrew driven
    • Belt + chain driven
    • Linear motors
    • Mini + piezo + voice coil
    • Rack + pinion driven
    • Rigid-chain actuators
  • Encoders + sensors (linear) + I/O
  • Stages + gantries
  • Suppliers

What is a PV rating?

November 4, 2016 By Danielle Collins 2 Comments

When discussing bearing life, what comes to mind for most engineers is the standard L10 bearing life equation. But this equation was developed for bearings with rolling balls. (A similar equation exists for bearings that use rollers rather than balls.) For plain bearings, which have no rolling elements, determining the suitability of the bearing for a particular application requires an examination of technical and environmental factors, coupled with empirical testing and the experience of the manufacturer.

Of the factors to be considered, the most important are the pressure imposed on the bearing (P) and the bearing’s velocity (V). These are combined to develop a PV rating, which represents the highest combination of load and speed under which the bearing can operate properly.


Pressure is determined by dividing the maximum load (force) on the bearing by the supporting area of the bearing. 

PV rating
Image credit: Polygon Company

PV rating

Where:

P = pressure (N/mm2 or lb/in2)

F = load on bearing (N or lb)

A = area (mm2 or in2)

For a round bearing riding on a shaft, the supporting area is simply the length of the bearing times its inner diameter.

PV rating

Where:

l = bearing length (mm or in)

d = bearing inner diameter (mm or in)


One of the critical performance characteristics of a plain bearing is its ability to dissipate heat. Heat affects a bearing in two ways. First, it can degrade lubrication or the lubricating properties of the bearing. But more importantly, heat can change the clearances between the bearing and its housing or between the bearing and shaft. The result is increased friction, greater wear and reduced bearing life.

A bearing’s PV rating is related to heating caused by friction in the bearing, and takes into account multiple factors that contribute to the system’s ability to transfer heat away from the bearing, including:

  • thermal conductivity of the bearing and the shaft (or rail)
  • difference between the maximum bearing temperature and the ambient temperature
  • thickness of the bearing
  • coefficient of friction between the bearing and the shaft

While the bearing’s maximum PV value is a key criteria, and often the starting point, for choosing a linear bearing, it’s important to note that the PV rating isn’t the only indicator of a bearing’s suitability for an application. The individual pressure and velocity values should also be kept within the maximum allowable limits, noting that some bearings perform well in high-load/low-speed applications, while others perform better in high-speed/low-load conditions. And environmental factors are a major consideration when choosing the best bearing and shaft materials for an application.


Is it a “plane” bearing or “plain” bearing? The terms are often used interchangeably, but the American Bearing Manufacturers Association uses the term “plain” bearing. 


Feature image credit: igus

You may also like:

  • plain bearing
    A guide to plain bearing materials in linear motion applications

  • A glossary of linear guide terminology
  • boxway
    What are the differences between plain and rolling linear guides?

  • Bearing load capacity explained

  • What You Need to Know about the 2:1 Ratio

Filed Under: FAQs + basics, Plastic + composite guides, Slides + guides (all)

Reader Interactions

Leave a Reply

You must be logged in to post a comment.

Primary Sidebar

DESIGN GUIDE LIBRARY

“motion
Subscribe Today

RSS Featured White Papers

  • Evaluating actuators for washdown in food & beverage applications
  • Identifying Best-Value Linear Motion Technologies
  • Introduction to accuracy and repeatability in linear motion systems

RSS Motion Control Tips

  • Schneider Electric launches Universal Automation Discovery Packs to foster industrial innovation
  • Encoders from SIKO support Industrial Ethernet
  • Draw-wire encoders from SIKO measure position, speed and inclination
  • Incremental encoders configurable via NFC (near-field communication)
  • Low-cost motion control offered with CLICK PLUS PLCs from AutomationDirect

Footer

Linear Motion Tips

Design World Network

Design World Online
The Robot Report
Coupling Tips
Motion Control Tips
Bearing Tips
Fastener Engineering

Linear Motion Tips

Subscribe to our newsletter
Advertise with us
Contact us
About us

Follow us on TwitterAdd us on FacebookAdd us on LinkedInAdd us on YouTubeAdd us on Instagram

Copyright © 2022 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy