Type 28SC John crane
Type 28SC John crane

Features mechanical seal type 28sc

  • California Residents: PROPOSITION 65 WARNING
  • Unbalanced primary ring and a very short design length.
  • The design of the secondary O-ring enables reliability in a vacuum environment — a circumstance common in Plan 02 containment chamber designs.
  • Non-contacting operation ensures like-new seal faces until primary seal leakage is encountered, where the 28SC operates as a full face contacting containment seal.

Recommended Applications type 28sc

  • Process pumps
  • Other rotating equipment

About Mechanical seal type 28sc

The 28SC is a gas-lubricated, non-contacting secondary containment seal, which is applied as a component of a multiple seal cartridge. Secondary containment seals are intended to contain primary seal leakage in the event of a primary seal failure. Patented bi-directional seal face pattern provides non-contacting operation, preserving the seal faces until the seal is required to seal primary seal leakage.

Design Features mechanical seal type 28sc

  • Balanced design allows higher gas pressure operation
  • Non-contacting seal — near zero wear or maintenance, no need for liquid face lubrication, low power usage, high vapor recovery system or flare pressure tolerance
  • Unidirectional and bidirectional mating rings
  • Compact short axial length
  • Simplified dual containment using Plan 72/76
  • Spiral groove pattern on mating ring pumps a small amount of inert buffer gas from the outside diameter towards the ungrooved portion of the mating ring. This compressed gas cushion separates the primary seal face and mating ring and creates a non-contacting seal
  • Contains process liquid in the event of primary seal failure and handles up to 580 psi(g)/40 bar(g) in contacting mode
  • Can operate in a vacuum as outside mounted single seal
  • Can operate as a single seal in a blower, fan and turbine with safe, clean and dry gas

Material mechanical seal type 28sc

  • Primary ring: Antimony impregnated carbon (9048)
  • Mating ring: Tungsten carbide (9205)
  • O-rings: Fluoroelastomer (9549)
  • Springs: Hastelloy C-276 (0690) 316
  • Retainer: 316 stainless steel (0550)
  • Set screws: 316 stainless steel (0550)
  • Thrust ring: 316 stainless steel (0550)
  • Snap ring: 316 stainless steel (0550)

Operating range mechanical seal type 28sc

Temperature Limits

32°F to 400°F/0°C to 205°C


Pressure Limits

Dry: 45 psi(g)/3 bar(g)


Wet: 600 psi(g)/40 bar(g)


Speed Limits


Product Description type 28sc

The type 28SCB is a compact dry running non-contacting gas seal designed for secondary containment.

Secondary containment seals perform in response to primary seal leakage or failure and represent a less complex alternative to a dual unpressurized (tandem) seals using a Plan 52 lubrication system.

Normal leakage from the primary seal is small and measured in ppm. The use of a containment seal gland and buffer gas injection moves vaporous leakage to a flare system. The 28SCB is typically applied with a Plan 72/76 secondary seal support system. When called upon to seal gross primary seal leakage, 28SCB closes down to run as a contacting wet seal directing leakage to a flare system or drain.