In the Turbomachinery industry there are a variety of seals used to prevent a machine's process gas from leaking into the atmosphere or keep oil from going into the process gas. These types of scenarios can lead to efficiency loss or severe damage to a machine. As temperatures and pressures vary, the choice of a seal will change to meet the specific need and create a suitable seal. To meet these needs, there are a lot of different materials used such as: rubber or graphite. The first choice for a design engineer when sealing is necessary is the Oring.
The different types of seals are listed below:
-Orings: elastomers that are stretched and compressed to create the seal. Can be used in static and dynamic applications, as well as axial or radial sealing configurations.
-Gaskets: fills the irregularities between two mating surfaces while compressed (e.g. Flanges on pipes) in order to prevent leakage.
-Spring Energized Teflon (PTFE) Seals: These seals consist of a spring energized "U-shaped" jacket with different profiles and make use of different spring types and materials. They are used when normal elastomer orings cannot meet the temperatures (e.g. cryogenic temps in the Expander side of a Turboexpander), friction requirements, or chemical resistance of an application. These seals can meet temperature ranges from -328°F to 500°F or -200°C to 260°C.
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| Labyrinth Seal Example |
-Labyrinth Seals: used for low pressure gas applications and where low leakage could be tolerated. They have the main advantage of being low cost. These seals are non-contact and use multiple "teeth" in order to create a difficult path for the process gas to overcome. Typically these laby seals use little to no friction with very small clearances and will sometimes wear into a mating babbitted bore after a machine is first started up. The main disadvantage with this type of seal is that it can be destabilizing at high pressures.
-Floating Carbon Ring Seals: One of the most commonly used shaft seals for the rotor assembly of an integrally geared compressor. Makes use of floating carbon rings with a very tight clearance. These type of seal has a reasonable cost and also lower leakage rates than labyrinth seals. The main disadvantage is the wear that occurs on the carbon rings over time and the risk of these rings locking up due to high pressure and leading to destabilization.
Floating Carbon Ring Seal Exploded View
-Dry Gas Seals: The most expensive and complex seal available. Can have various configurations in order to have redundancy to aid in the event of a failure. This however, will require the shaft to grow axially to account for the larger seal configuration. The main disadvantage with this seal is cost and the rotordynamics challenge due to the larger shaft.
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