Controlled Gap/Bushing Seals​

Really two pieces in one, Qualiseal’s controlled gap/bushing seals are the best solution when pressure is an issue.

Controlled gap or bushing seals are comprised of a carbon insert that is shrink-fitted into a separate retaining band. This floating circumferential ring assembly grows at a rate similar to that of the shaft when exposed to elevated temperatures.

Under normal operating conditions, the pressure on the air side is higher than the pressure on the oil side. This creates some air leakage through the controlled gap between the carbon ring and shaft. The differential air pressure, along with the spring load, provide the closing force necessary to maintain contact between the carbon and housing secondary sealing face. Meanwhile, the shaft turns freely within the carbon ring.

The seal design also features a unique stabilizer ring with fins which minimize stress on the carbon ring, thereby maintaining roundness of the circumferential ring assembly. Dimensional tolerance of the critical inside diameter of the bushing ring is tightly controlled to minimize leakage variations.

Click here to download a Qualiseal circumferential seal success story.

Ideal For:

  • High-pressure applications
  • Also suitable for sealing low-pressure liquids


  • Minimal leakage in an exceptionally wide temperature range
  • Tolerance to unlimited shaft axial movement
  • Very long life
  • Very low heat generation


  • Rides on a buffer that centers the ring and minimizes seal-to-shaft contact
  • Available in a wide variety of materials suitable to a broad range of applications
  • Often paired with other seals to create sealing systems that meet demanding requirements
  • Diameter sizes up to 12 inches (30.5 cm)

Operating Conditions:

  • Pressures: up to 2,000 PSIA (13,789 kPa)
  • Temperatures: -100° F  (-73°C) to over 2,000°F (1093°C)
  • Shaft rotation speeds over 50,000 FPM (254 m/s)

Design Configurations:

  • Single seal for dual pressure conditions
  • Spring loaded double back-to-back seal
  • Separable designs to facilitate replacement and/or rework of internal components
  • Double tandem seal arrangement for sealing a combination of liquids and gases
  • Multiple labyrinth ring assemblies
  • Housing for mounting directly onto equipment case

Seal Ring Materials:

  • Carbon-steel composites
  • Stainless steel alloy
  • Silicon carbide
  • Bronze

Mating Surfaces/Seal Housing:

  • 300 series stainless steel
  • 400 series stainless steel
  • Alloy steel
  • Aluminum
  • Titanium
  • Brass


  • Aircraft engine main shaft seals
  • Compressors
  • High-speed processing equipment

Industries Served:

  • Aerospace
  • High-speed compressors
  • Military
  • Alternative energy

Contact us to learn more about our Controlled Gap/Bushing Seals.