With decades of proven use in other induistries, Externally Pressurized Porous (EPP) gas bearing technology is used as the basis for New-Seal® sealing technology.
The two types of gas bearings include aerodynamic bearings and aerostatic bearings. Many large pumps and turbines have rotors which are supported on hydrodynamic oil bearings. For hydrodynamic and aerodynamic bearings, a wedge of fluid (or gas) must build up as the rotor spins before lift-off occurs. Dry Gas Seals in compressors operate with aerodynamic seal behavior. Other turbomachinery (especially that with light loads) operate using foil-type aerodynamic bearings. With all hydrodynamic or aerodynamic bearings, relative motion is necessary between the rotor and the bearing surfaces in order to produce lift-off. Until that occurs, there will be friction during the start-up motion, and hence, wear will occur. This is not the case with aerostatic bearings where, even at zero rpm, a gap is generated between the bearing faces and the rotor (hence no wear occurs).
For aerostatic bearings to work, a source of externally pressurized gas must be present. This pressurized flow is introduced through precision orifices, steps, or in the case of New-SealTM....through porous media. Knowledge in the concept of restriction and compensation is key to the understanding of how New-Seal® technology functions.
Externally Pressurized Porous (EPP) gas seal technology requires less space than most conventional seals, and can be provided in familiar mounting geometries, making retrofitting relatively easy. EPP seals can be used on:
New-Seal® externally-pressurized gas seals are aerostatic seals (as opposed to a conventional aerodynamic seal, as in the case of a dry gas seal). The “gap” area for a New-SealTM seal, as shown in the figure on the right above, is orders of magnitude greater than that for an aerodynamic seal…this provides for superior sealing capability. New-SealTM seals allow flow through the area shown on the right (above); A New-SealTM seal does not have flow across the face of the seal, whereas an aerodynamic seal does have flow across the face.
To further explain the function of the above seal, external pressure is injected into the inner and outer seal housings. Either a single supply or two separate gases may be employed for each face. The input gas flow is directed to plenum regions, and then migrates through the Porous Media, and into the gap between the Porous Media face and the runner. Some flow will exit to atmosphere, and some will be vented. The “gap” pressure between the Porous Media face and the runner (assuming a 50% pressure drop, or "efficiency") would be half of the input pressure. As long as this gap pressure is higher than the sealed cavity pressure, there will be zero leakage across the gap. The above seal will flow a total of about 0.5 SCFM, for both faces (assuming a 4-inch shaft). The "efficiency", as shown in the graph below, is very sensitive to the size of the gap (flow through the gap is proportional to the gap3). New-Seal's small gaps, high gap pressures, and low flows are superior to conventional seals.
Source for certain information shown on this page: Pumps and Systems Magazine, "Using Gas Bearing Technology for Non-Contact Shaft Sealing" by Drew Devitt, April 2017
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