Hydrostatic bearings use fluid or gas to support loads, with an externally pressurized source forming a barrier film between the outer shell and the shaft. They offer superior performance, precision, and longevity compared to conventional bearings, with minimal friction, noise, and vibration. They are cheaper to maintain and have a particularly long service life, with one example running continuously since 1912.
A hydrostatic bearing is a mechanical device that uses nothing but 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 bearing’s outer shell and the shaft it supports. The rotational speed of the shaft therefore maintains a high pressure in the surrounding fluid which supports the shaft with minimal friction. Hydrostatic bearings are used in applications where high workloads, speeds and accuracy requirements require bearings with long life, low noise and minimal vibration. A hydrostatic bearing offers far superior performance in these areas and is much more cost effective than conventional ball or roller bearings.
The device works by pumping a fluid under pressure into the space between the device or machine shaft and the bearing outer shell. Fluid enters the bearing through a restrictive opening and is held in the bearing cavity by seals. If some of the fluid were to escape, the gap between the shaft and the casing would decrease, causing an increase in pressure in the fluid. This increase in pressure forces the surfaces back, which makes the fluid bearing largely self-adjusting and allows for very precise control of tolerances.
Compared with ball or roller bearings, hydrostatic bearings are very simple in design, manufacture and operation. Conventional bearings require precision machining of balls or rollers and the inner and outer shells in which they ride. This is obviously expensive and time consuming, especially when taking into account the limited life of these bearings. Ball and roller bearings also generate significant amounts of noise and vibration making them undesirable for high precision use. A hydrostatic bearing operates 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 a particularly long service life. A good example of this longevity is the hydrostatic bearing set installed at the Holtwood Hydroelectric Plant in Pennsylvania. These bearings were installed in 1912 and have run continuously ever since with no parts replaced. Manufacturers calculate that the bearings would have a maintenance-free lifespan of approximately 1,300 years. These bearings support total loads in the order of 205 tons and are an excellent example of the efficiency and long life of the hydrostatic bearing.
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