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What is a Hydrostatic Bearing?

By Paul Scott
Updated May 17, 2024
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A hydrostatic bearing is a mechanical device that uses nothing more than a thin film of fluid or gas to support its load. Also known as a fluid bearing, a hydrostatic bearing uses an externally pressurized source of air, oil, or water to form a barrier film between the outer casing of the bearing and the shaft it supports. The rotational speed of the shaft then maintains a high pressure in the surrounding fluid which supports the shaft with very little friction. Hydrostatic bearings are used in applications where high working loads, speeds, and precision requirements demand bearings with a long service life, low noise, and minimal vibration. A hydrostatic bearing delivers far superior performance in these areas and is far more cost effective than conventional ball or roller bearings.

The device works by having a fluid pumped under pressure into the space between the device or machine shaft and the outer casing of the bearing. The fluid enters the bearing through a restrictive opening and is kept in the bearing cavity by seals. If some of the fluid should escape, the gap between the shaft and the casing will decrease, causing the pressure in the fluid to increase. This increase in pressure forces the surfaces apart again which makes the fluid bearing largely self regulating and allows for very fine tolerance control.

When compared to ball or roller bearings, hydrostatic bearings are very simple in design, manufacture, and operation. Conventional bearings require the precision machining of balls or rollers and the inner and outer casings they run in. This is obviously expensive and time consuming especially when the limited lifespan of these bearings is taken into account. Ball and roller bearings also generate considerable amounts of noise and vibration which make them undesirable for high precision use. A hydrostatic bearing runs with very little friction and vibration and generates almost no noise. This makes it ideal for high precision applications such as disk drives.

Hydrostatic bearings are also cheaper to maintain and have particularly long service lives. A good example of this longevity is the hydrostatic bearing set installed in the Holtwood hydroelectric plant in Pennsylvania. These bearings were installed in 1912 and have run continuously ever since with no parts being replaced. The manufacturers calculate that the bearings would have a maintenance free life span of approximately 1,300 years. These bearings carry total loads in the region of 205 tons and are an excellent example of the efficiency and long service life of the hydrostatic bearing.

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