In this blog post, we’ll take a look at the types of spherical spare bearings commonly encountered at a hydraulic cylinder service station and go over a few basic things to keep in mind when installing and removing them.
The purpose of spherical bearings is to allow for slight movement (“flex”) in hydraulic cylinders and to reduce friction when the direction of force applied to the cylinder changes. Bearings are commonly used in both the rod eye and the base eye of the cylinder.
Bearing Damage and Prevention
Regular greasing of the bearings is a critical part of cylinder maintenance. Proper lubrication can significantly extend the service interval between cylinder removals and help prevent wear in the bearing housings. Without lubrication, friction can wear out the bearing housing or the pin to the point where replacement is needed. Grease also helps keep dirt and dust out of the bearing housings.
In addition to wear and seizing, bearings may suffer various degrees of mechanical damage—often caused by external impacts.
Common Types of Spherical Bearings and Materials
In hydraulic cylinder maintenance, the most commonly encountered bearings are standard open bearings (DO) and sealed bearings (2RS). Sealed bearings provide better protection against dirt and are ideal for more demanding environments.
You’ll also frequently come across bearings with a wider inner race, such as the FO and HO types, often nicknamed “bull’s eye” bearings due to their wider, eye-like profile. These allow for a greater range of motion in the cylinder.
Beyond standard materials, bearings are also available in stainless steel, acid-resistant steel, and aluminium bronze. It’s important to choose the bearing type and material based on the specific demands of the operating environment.
Bearing Inspection and Removal
During bearing inspection, the general condition, movement, and clearances are checked. The bearing is examined visually to ensure there are no cracks or other visible damage. The movement should be smooth, and there must be no axial or radial play between the bearing and the housing.
Before removing the bearing, always check how it is locked in place. The most common locking methods are circlips (Seeger rings) or pin locking. In some cases, you may also come across spherical bearings secured with a bolt circle. Circlips are removed using pliers, though they are often tightly seated, so a screwdriver or another tool may be needed to assist.
The bearing is pressed out of the housing using a sleeve of the correct size. Note that the sleeve must not press on the inner race (the rotating eye section of the bearing). If pressure is applied to the inner race, the outer race may expand and grip the housing, making the bearing much harder to remove.
Bearings often have markings that indicate the model and size. If there are no markings, the correct replacement can be identified by measuring the inner and outer diameters, as well as the width.
The joint line on the outer race is the bearing’s weakest point. To improve wear resistance, it’s important to consider the correct orientation during installation. The joint should be positioned at a 90° angle to the direction of the rod. If the joint is aligned with the direction of force, constant stress could cause the outer race to crack along the seam.
The bearing is pressed into the housing using a correctly sized installation tool. When pressing the bearing into place, make sure the force is applied to the outer race to avoid damaging the bearing during installation.
Once the bearing has been pressed into place, it’s secured by installing a circlip (Seger ring) or by staking the edges of the housing with punch marks. When using a circlip, make sure it clicks firmly into its groove. If you’re using punch marks, place them close to the edge so they form a lip that prevents the bearing from coming loose. Usually, at least three marks spaced evenly around the housing are recommended.
Check that the bearing moves smoothly and doesn’t bind. Before putting the cylinder back into service, be sure to grease the bearing. With regular greasing during maintenance, your cylinders will stay in working condition for much longer.
Thanks for reading. If you have any questions about bearings or installation, don’t hesitate to reach out — we’re happy to help.
