Sleeve bearings and hydraulic bearings are two common types of bearings used in various machines and equipment. In this article, I will share the differences between them in detail
The key difference between sleeve bearings and hydraulic bearings:
Sleeve bearings are simple and cost-effective, but have limited load capacity and require periodic lubrication. Hydraulic bearings, on the other hand, use pressurized fluid to support the load and provide frictionless rotation but are more complex and expensive.
Let us check the differences between Sleeve Bearing and Hydraulic Bearing in detail:
Differences Between Sleeve Bearings and Hydraulic Bearings
Sleeve bearing can be partially regarded as journal bearing because Journals (shafts) pass through them. Sleeve bearings exist in two types; the solid and the split type. The solid type looks like a section of tubing or pipe.
The split type as the name sounds, is split length-wise down to the center of the pipe, it is the common type of sleeve bearing in use. A standard sleeve bearing usually exists in a size range between less than ½” internal diameter to more than 4½” Internal Diameter. They can also be made for nearly any sized shaft.
Variations in materials used for the fabrication of sleeve bearings are subject to their application. The shell (casing) of the bearing is made up of cast iron, bronze or aluminum. Sleeve bearings with shells of cast iron are usually made of linings called “Babbitt” which is an alloy of porous metals made of a thin coating around the shell. They can absorb and retain lubricating oil. The lubricant filled between the blade shaft and sleeves acts as a drag reducer.
Hydraulic bearings have larger oil storage space than the sleeve bearing and have a unique oil supply circuit loop type in which oil is supplied and returned to the tank. In this type, an externally pressurized fluid is forced between two elements that are in relative motion.
The pressurized fluid forms a wedge between the moving parts and keeps them apart. The fluid layer may be very thin but as long as there is no direct contact, there will not be any wear. The fluid is circulated by means of a pump. The exit orifice diameter may be adjustable to ensure the fluid is always under pressure at all shaft speeds and loads. Thus, precise gap control is possible.
2. Durability/Bearing life
The lifespan of a bearing is said to be the number of revolutions per hour at some given constant speed that the bearing runs before the first evidence of fatigue development in the material.
The bearing life of a Sleeve bearing is relatively shorter than that of a hydraulic bearing.
This is because the Sleeve bearing creates an increased load on the driver during the startup of the machine. This is because the shaft is driving directly on the bearing.
A higher horsepower will be required and the shaft journal and is more likely to be damaged. On the other hand, the hydraulic bearing is more durable due to less contact with the shaft because the shaft runs in an oil field.
3. Availability and Cost
Hydraulic bearing is more expensive compared to sleeve bearings. Due to high production costs. This results in low availability.
During operation, the sleeve bearing makes loud noise due to its contact with the shaft, unlike the hydraulic bearing which has little or no contact.
It is much easier to maintain or change a sleeve bearing than a hydraulic bearing. Changing the hydraulic bearing seems to be a herculean task, due to its weight, size and complex design, whereas a sleeve bearing can be replaced in a short time. This is why it is regarded as an example of “an off-the-shelf bearing replacement”.
A hydraulic bearing has a larger amount of oil storage than a sleeve bearing. Hydraulic bearings, therefore, require and consume more lubrication fluid than sleeve bearings.
Hydraulic bearings are used in machines that work at extreme speeds and loads. Also, their longer life span in tough conditions makes it run for a longer time. Sleeve bearings are used for lighter machines because they provide more precise speed control than hydraulic bearings.
Sleeve bearing has a simple design which makes it easier for maintenance, servicing and replacement, hydraulic bearings usually have a complex design and requires extra care and experience to work on it.
9. Storage, size and weight
Hydraulic bearings are considerably heavier and larger than sleeve bearings. But, sleeve bearings require more axial space.
Also, they do not deteriorate during storage therefore, they do not require much care during storage unlike Hydraulic bearings which are expensive, they should be handled and stored with great care.
Hydraulic Bearing Vs Sleeve Bearing [Comparison Summary]
|Bearing Type||Sleeve Bearings||Hydraulic Bearings|
|Working Principle||Grease or Oil based fluids||Lower-density applications such as fans|
|Application||High-Density applications such as cranes||Lesser noise lasts longer compared to sleeve bearing. It’s a better choice since the hydraulic bearings are designed to emit little or no heat.|
|In Fan Design||Simple but easy gets uneven as lubricant evaporates which causes a high wear rate and low service life. The sleeve bearing a negligible about if heat therefore, it’s Less suitable for heavy duty fan designs.||Lifespan ranges from 20,000 to 30,000 revolutions per hour with proper maintenance|
|Noise||Usually quieter when new (20 to 30dB) gets louder with age and usage (30 to 70dB)||Minimal or no noise between 5 to 10dB (Usually quieter in high speeds)|
|Durability||Simple but easy gets uneven as lubricant evaporates which causes a high wear rate and low service life. The sleeve bearing a negligible about if heat therefore, it’s Less suitable for heavy-duty fan designs.||It can last forever with proper maintenance and lubrication.|
|Cost||Low cost, cost varies based on sizes, can be gotten as low as $9.99; not worth maintaining||It is more expensive due to its performance and lifespan. Price range from $49.99 and above.|
|Assembly||They support heavy loads at high speed that require less radial space for installation||It’s more difficult to assemble, disassemble or replace do to its complex design.|
|Operating Conditions||It can perform properly only in normal temperatures ranging from 14℉ to + 140℉||It can perform properly in harsh environments and temperatures ranging from -4℉ to +176℉|
|Application||Covers lesser storage space, does not require much care during storage. Occupies more axial space.||They are used for extremely heavy loads and high speed.|
|Storage||Covers lesser storage space, do not require much care during storage. Occupies more axial space.||Covers larger storage space and, it must be stored properly.|
|Weight||Lighter in weight||Heavier in weight|
Hydraulic bearings should be utilized in heavy-duty or high-speed applications because they provide more reliable, smoother action. Also, Hydraulic bearings are not as susceptible to variation. This is because they usually have unique designs unlike a sleeve bearing. The viscosity of hydraulic bearings does not alter significantly with variations in temperature, pressure, or altitude.
A sleeve bearing is less expensive to operate and is simple to replace or maintain. A hydraulic bearing might not be the best choice if you want to boost durability.
The fact that they rely on oil to keep them lubricated means that they often do not last as long as a sleeve bearing. The bearings will suffer rapid and permanent damage if the oil supply is cut off. Another is that because the hydraulic bearing depends on an external source of incompressible fluid, there is a chance of leakage while employing it.
Nonetheless, it has been demonstrated that some designs have a low enough leak rate to prevent serious issues and damages. Also, Sleeve bearings are suitable for off-the-shelf replacement because they are readily available and are best for emergency and temporary use and replacements.