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Hydraulic Bearing Is Used to Reduce the Friction in Fluids.
Hydraulic bearing prevents wear and tear, damage, to the fluids and there is no sliding friction. Two main types of hydraulic bearings are used for different purposes.

Hydraulic Bearing

Hydraulic bearings are a bearing in which the load is supported by a thin layer of swiftly moving liquid and gas (usually oil). A maximum amount of pressure is applied to the liquid or gas between the bearing surfaces. Hydraulic bearings allow fluids to have lower friction, wear, and vibration levels compared to many other bearings. This is because there is no contact between the moving parts of the hydraulic bearings; hence there is no sliding friction. Therefore, correct operation is necessary to ensure some hydraulic bearings have near-zero wear. Hydraulic bearings are often referred to as fluid bearings. There are mainly two broad categories of hydraulic bearings: hydrodynamic bearings and hydrostatic bearings.

Hydrostatic bearings mainly function by applying pressure on the fluid bearing using a pressure pump. The fluid used is usually oil, water, or air. On the other hand, hydrodynamic bearings heavily depend on the high speed of the journal to fill up the wedge with pressurized fluid. This process is also cost-effective as it reduces costs. Hydraulic bearings have widely used applications in the basic rotating machinery industry. Some industries include:

  • Engineering,
  • Manufacturing,
  • Automotive, etc.

Furthermore, the manufacturers of hydraulic bearings keep a great check and balance on the superior quality standards by following a series of processes, monitoring every quality parameter to ensure the client receives an excellent product.


Manufacturing hydraulic bearings is a technical process that goes through several steps. Here we shall discuss the steps involved in the manufacturing and assembling hydraulic bearings.

Hydraulic Bearing Manufacturing
Hydraulic Bearing Design

Hydraulic Bearing Design

The hydraulic bearings typically consist of a body, rod, and seal. In terms of dimensional aspects, shape, position tolerances, surface roughness etc., all hydraulic elements and sealing components have distinct requirements. In case the tolerance of the hydraulic bearing is non-satisfactory, for example, the bearing’s inner diameter, the piston’s (if attached) outer diameter, seal furrow depth, width, and extent of the seal ring hole or burrs, or chrome plating as a result of processing issues, if it is falling off, the corresponding seal will be crushed, deformed, or not be compressed. The seal’s function will be disrupted while the hydraulic bearing’s normal operation cannot be guaranteed. Hence, we need to take preventative measures to avoid such difficulties initially. During the designing process of the hydraulic bearing, consider the geometric accuracy of every single component and opt for the right seal. Similarly, each element’s upper and lower tolerances must be matched during manufacturing. Leakage of the hydraulic components is also a serious matter; hence effective techniques must be applied to reduce the leakages.

Selecting the Correct Steel Material

The three most frequently used materials in hydraulic bearings are:

  • #20 steel: It has the lowest hardness. It is generally used for low-pressure hydraulic bearings and cylinders
  • #45 steel: usually used in high-pressure areas, with a price less than half of Cr40. Usually, lower quality products use #45 steel in the body.
  • Cr40 steel: The higher price indicates it is a much superior quality product than #45 steel, also used in high-pressure areas. In heat treatment, the major role of Cr is to enhance the hardenability of steel, which in turn improves its mechanical attributes, such as hardness, strength, toughness etc.

Moving on, we have two sorts of raw materials used in hydraulic bearings or cylinders:

  • Pipe Material: the pipe material is purchased only through quenching and tempering treatment. The pipe material is used if long-stroke cylinders are manufactured (in the case of hydraulic cylinders). It is extremely complicated to employ the machining process to the deeper part of the solid steel material.
  • Solid Steel Rod Material: in the opposite case for short stroke hydraulic bearings and cylinders, the solid steel rod material is suitable.
Selecting the Correct Steel Material
Hydraulic Bearing production

Cutting and Drilling

The length of the hydraulic bearing is determined according to the design, after which the cutting takes place with a sawing machine. The drilling process is also based on the plan.

Heat Treatment

The right amount of heat treatment (which includes quenching and tempering materials) is necessary for ensuring the quality standards and mechanical properties such as strength, hardness, and durability of the hydraulic bearings.

Hydraulic Bearing Heat Treatment
Hydraulic Bearing Machining Process

Machining Process

  • Turning: The chuck is combined with the middle tip, one clamp and one tip at a time while ensuring the centre frame holds the bearing to ensure the closeness of the machine allowance and the bearing.
  • Boring: This is the key process of machining the hydraulic bearing’s body (or hydraulic cylinder). The boring process forms a bore in the bearing or cylinder to develop a stable structure by the boring tool, the iron-bearing, and the bearing seat. After this, the boring device is utilised to finish the procedure. The hydraulic cylinder or the hydraulic bearing is fixed by placing it in the holder of the boring machine, adjusting the height of the tooltips, and tightening the bolts. Then the finishing of the inner hole boring is completed independently. Additionally, in the process of Rolling, the tolerance inside the holes of the bearing can get to the required accuracy while reducing the errors.

Coting, Polishing, & Painting

  • Hard chrome coating or blackening surface treatment on the hydraulic bearing is used.
  • For painting, the electrostatic spray is used on the outer surface of the body of the hydraulic bearing. The outside surface must be covered to avoid surface damage.
  • The inner cylinder/bearing surface is polished once the spraying process is over.
  • Dirt and particles must be cleaned to avoid friction between the sealing and the inner surface of the hydraulic bearings. An air compressor should be used to clean up the whole space.
Hydraulic Bearing


Assemble all the components of the hydraulic bearing or hydraulic cylinder.


  • Appearance inspection: ensure whether the physical objects such as the paint colour, the spray’s uniformity, colour difference, notable dust, blistering, whether the surface is rusty, if there are any marks or indentations, whether the surface is smooth or flat, all are checked and matched with the design drawings.
  • Dimensional inspection: Using multiple measurement tools, we can check the proportions, length, width, diameters, etc., of the hydraulic bearings and make sure whether the dimensional tolerances are according to the requirements of the drawings.
  • Test Methods:
    • Starting pressure test
    • Pressure resistance test
    • Endurance test
    • Leak test
Hydraulic Bearing Testing
Hydraulic Bearing

Hydraulic Bearing

Categories of Hydraulic Bearing
Categories of Hydraulic Bearing

Hydraulic bearings are divided into 2 categories; first is hydrostatic bearings and the other one is hydrodynamic bearings.  Each depend on a thin film of oil/air to generate clearance between the stationary and moving objects. The appearances of these two types of hydraulic bearings may seem similar on the outside. However, this bearing and hydrodynamic bearings have distinct operations from standard bearings. Plain bearings are cheaper. They have a decent and simple structure. The shaft links with the bearing surface when the process starts. Hence some sort of lubrication is needed to reduce the friction that is being caused. Opposite to this scenario, hydraulic bearings (fluid film), i.e., hydrostatic and hydrodynamic bearings, are much more expensive and complex in design. Common applications for these bearings require high stiffness and precise movements, such as machine tool spindles and slides.

Hydrostatic Bearing
Hydrostatic Bearing

Hydrostatic bearings are a specific type of hydraulic bearings that work on the primary goal of separating sliding surfaces using pressurised fluid, such as air, oil etc. The working proceeds as the separating film are initiated into contact by external pressure. Regardless of the speed or geometry, satisfactory lubrication can be provided independently. A hydrostatic bearing can be divided into the pad (the hydrostatic bearing) and the hydraulic circle. The bearing pad consists of a recess groove that ensures enough area to lift the bearing load. In the case of multi-recess pad types, several grooves are used. The hydraulic circuit must be strong enough to endure the pressures generated during the lifting phase.

Hydrostatic bearings are beneficial as lubrication prevents contact between the sliding surfaces. These surfaces are completely separated by a thick lubricating film. The friction levels are generally very low, while little or no wear is present. Additionally, the fluid film results in greater stiffness and vibration damping.


  • Supports very large loads
  • Longer life span with less or no wear on surfaces
  • Lubricant viscosity or film thickness does not define load
  • Large magnitudes of stiffness and damping coefficients are provided
  • Suitable for exact positioning and control


  • Greater installation and maintenance costs as more ancillary equipment is required.
  • Performance deteriorates due to fluid contamination; hence, fluid filtration equipment is required.
  • Due to pumping losses, high power is consumed.
  • In hybrid mode operation, there is a potential to induce hydrodynamic instability.
Hydrodynamic Bearing
Hydrodynamic Bearing

In this type of hydraulic bearing, the bearing motion generates the gap dynamically. Hydrodynamic bearings are used in applications that involve rotary motion. Some external pressure may be required a primary or secondary bearing to stay away from excess friction when the rotation starts. Hydrodynamic bearings are also designed for thrust (or radial) loads.

A hydrodynamic bearing is generally a low-clearance assembly that depends on a film of oil (sometimes air), generating space as the spindle is rotating. The journal bearing is the primary and most basic hydrodynamic bearing, which has a cylindrical bore with normally two axial grooves for lubrication. This bearing encompasses a high load capacity. The design is simple and compact, bi-rotational, and manufactured with ease. Numerous tests have proved that the pivoted-shoe concept applied to the journal design has been effective. There are multiple benefits to this; they are cheaper, smaller, need low maintenance, and are long-lasting.

Machines that use hydrodynamic bearings should be careful not to withstand high loads initially. The industries and applications which utilize hydrodynamic bearings are as follows:

  • Cooling pumps
  • Electric motors
  • Steam turbines
  • Rock crushers.

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Hydraulic Bearing

Specifications Of Hydraulic Bearings

Hydraulic bearings Lubrication
For the safe operation of hydraulic bearings, a suitable lubricant must be present always. The lubricant must be cooled down to filter out the heat produced by the oil shear. Similarly, it must be sufficiently warm to flow freely.
Hydraulic Bearing Accuracy
The accuracy of the hydraulic bearings depends upon the accuracy of the components. The hydraulic linear motion bearings have been created with meter accuracy.
Hydraulic Bearing Speed Limits
Speed Limits
During the motion of the bearing, hydraulic bearings only have viscous friction combined with a fluid film layer being trimmed. If the lands are extensively wide, they can encounter hydrodynamic effects in high-speed conditions. As a result, heat is generated. The DN number shows the bearing diameter in mm (D) and the top speed in rpm (N). the maximum speed is approximately 1,000,000 DN.
Hydraulic Bearing Size and Weight
Size and Weight
The bearings are small in size and hence, take up very little space. However, the size and weight of the pump, oil distribution system etc., are excluded.
Hydraulic Bearing Stiffness and Damping.
Stiffness and Damping
Usually, rolling or sliding contact bearings, preloaded against each other, have a loss of contact problems. In contrast, the hydraulic bearings do not face this issue. Hydraulic bearings easily fit into the Newton per nanometre range of stiffness.

How Do I Measure a Hydraulic Bearing?

Start by measuring the hydraulic bearing pin-to-pin length from one end to another. Also, measure the diameter of the bearing, the bore in the case of a cylinder, and the outer diameter of the barrel. Vernier callipers are widely used for measurements of diameters.

Do Hydraulic Bearings Increase Friction?

No, they don’t. The moving parts of the hydraulic bearings have no contact, so there is no friction. This allows fluid to flow freely without any wear, vibration, and least amount of friction.

Which Type of Hydraulic Bearing Will Best Tit Me?

To understand this, you should know your industry and the machinery you are using. For instance, if your machinery requires a heavy load to be supported at the start, it is preferable to use hydrostatic bearings. Hydrodynamic bearings should be considered if your machine is based on significant rotary motions.

What Oil Should Be Used in Hydraulic Bearings?

The majority of the time, the manufacturer recommended oil is used. Commonly systems use hydraulic oils such as AW32 (light viscosity) or AW46 (medium viscosity). Avoid using cheap oils as they can overheat the system.

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