From Dry Gas Seals Handbook

Centrifugal compressors in process gas service require shaft sealing to prevent the process gas from traveling down the shaft and escaping the compressor case into the atmosphere. Multistage, beam-style compressors (with impellers located between two bearings) require two seals, one at each end of the shaft (fig. 1-1). Single-stage, -overhung style compressors (with a single impeller located outboard of the bearings) require a single shaft seal, directly behind the impeller.


Figure 1-1: Cross section of a centrifugal compressor

Radial Seals

Early shaft seals were simple labyrinth seals, which oftentimes required complicated eductor/ejector systems to deal with substantial gas leakage through the seals. The next generation of compressor shaft seals was oil film floating ring seals (fig. 1-2). There are two sealing surfaces in a typical floating ring oil seal, the inside diameter of the seal rings and the mating surfaces between the seal rings and the seal housings. Oil is injected into the seal at a pressure slightly higher than the process gas (sealing) pressure. This high-pressure oil forms a seal against the process, and also serves to cool the seal components. Thousands of floating ring oil seals remain in operation today.


Figure 1-2: Floating ring oil fi lm seal

Mechanical Contact Seals

Both labyrinth and oil film floating ring seals are radial seals, sealing the radial space created between a rotating shaft and a stationary seal. This limited the level of sealing that could be obtained, because the parts had to operate at a clearance large enough to avoid...

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Products & Services
Labyrinth Seals and Clearance Seals
Labyrinth seals and clearance seals are minimum-leakage seals that protect machine elements from contamination through a noncontact method. They operate on the principle of positive clearance and do not rub on shafts or housing. 
Dynamic Seals
Dynamic seals include oil seals, hydraulic and pneumatic seals, exclusion seals, labyrinth seals, bearing isolators, and piston rings. They create a barrier between moving and stationary surfaces in applications such as rotating shafts and pistons rings.  This is a general search form; more detailed search forms are available.
Oil Seals and Grease Seals
Oil seals and grease seals have a flexible lip that rubs against a shaft or housing to prevent the leakage or ingress of fluids and dirt.
Bearing Isolators
Bearing isolators are dynamic seals designed to protect bearings from outside contaminants.  They are comprised of a rotor (rotating) and stator (stationary) member.
Hydraulic Seals and Pneumatic Seals
Hydraulic seals and pneumatic seals include piston seals, rod seals, U-cups, vee, cup, and flange packings.

Topics of Interest

Overview Dry gas seals are gas-lubricated, mechanical, noncontacting, end-face seals, consisting of a mating (rotating) ring and a primary (stationary) ring. The principal rotating components consist...

Overview Thousands of centrifugal compressors were manufactured before the advent of dry gas sealing technology. Most of these compressors are equipped with oil film seals (fig. 6-1). Figure 6-1:...

Dry gas seals are available in a variety of configurations, including single, tandem, tandem with intermediate labyrinth, triple, and double opposed. Triple gas seals were used in the past when tandem...

Overview Using dry gas seals in a centrifugal compressor requires a support system designed to supply sealing gas to the seal as the working fluid for the running gap. These gas seal support systems...

Overview As discussed in chapter 3, a barrier seal is an integral component of the dry gas seal assembly, installed outboard of the dry gas seal (see chapter 3 figures). The barrier seal, sometimes...