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Flanges and Fittings - Del-Seal™ CF Flanges


Del-Seal™ conflat (CF) flanges are classified as genderless flanges, since the seal geometries on both mating flanges are identical. They are available in both rotatable and nonrotatable geometries with clearance or threaded bolt holes, and for standard tube sizes from .250 to 14.0 inches in diameter. 

The reliable sealing performance of MDC’s Del-Seal™ CF flanges is a result of a unique seal design and geometry which “captures” a metal gasket material. When a flat OFE copper gasket is pressed between the conical sealing edges of two Del-Seal™ CF flanges, a lateral cold flow of the gasket material occurs. This cold flow is limited by a vertical flange wall or capture groove that is concentric to the sealing knife edge. Further material flow away from the seal area is severely limited and high interface pressures are developed. These pressures cause gasket material to fill minor surface imperfections and produce a highly reliable seal. At high temperatures, the “capturing” geometry maintains high pressures despite softening of the gaskets. Del-Seal™ CF flanges can be baked to 450°C and cooled to -200°C and are suitable for vacuum service levels of 1x10-13 Torr. They are ideally suited for the rigorous demands of ultrahigh vacuum environments and capable of maintaining seal integrity through high temperature excursions. Del-Seal™ CF flanges are 100% compatible with the equivalent Varian Conflat® metal seal flanges.

Del-Seal™  CF Flanges
Del-Seal™ CF metal seal flange pair

MDC discourages resealing a Del-Seal™ CF flange with a previously used metal gasket and strongly recommends the installation of a new metal gasket every time a flange is fastened. When flange fasteners are tightened to their specified sealing torques a gap will remain between the mating flanges, this is normal and desirable. Tightening the flanges metal-to-metal is not necessary to achieve a UHV hermetic seal.

OFE copper, which stands for “Oxygen Free Electronic or Electrolytic grade Copper”, is the metal gasket material of choice for most UHV sealing applications. For special applications which preclude the use of pure copper, various metal gasket materials including nickel, aluminum and silver plated copper are also available.

MDC can also provide specialized elastomer gaskets made of DuPont Dow Elastomers Viton® material. These can be used within existing UHV systems fitted with MDC Del- Seal™ CF flanges and allow frequent and repeated assembly and disassembly. These elastomer gaskets have rectangular cross sections and fit within the standard knife edge seal geometry of a Del-Seal™ CF metal seal flange. Note that the use of elastomer gasket seals in metal seal flanges will reduce the system’s minimum and maximum temperatures and its vacuum ratings to -20°C, 150°C and 1x10-8 Torr, respectively. The torque required to make a leak tight seal with an elastomer gasket will be reduced to 7-10 lb-ft.

  • Del-Seal™ CF Metal-Seal Flange
  • Conflat compatable
  • Genderless mating
  • Rotatable and non-Rotatable
  • Tapped or clearance bolt holes
  • Wire seal flanges used for tubes larger than 14 inches diameter
  • Double sided flanges
  • Reducing flanges
  • Hybrid adapters interconnect dissimilar flange systems
Flanges 304ss
Gaskets OFE Copper or Viton® elastomer
Bolts 300ss and silver plated
Alternate material 18-8 SS bolts are supplied
Bolt head type Hexagonal, socket or 12-point head
Nut Type Hexagonal or two hole plate nuts
Bolt Size Fractional Size Torque
.160-32 UNC 8-32 7 lb-ft
.250-28 UNF 1/4-28 12 lb-ft
.312-24 UNF 5/16-24  15 lb-ft
.375-24 UNF 3/8-24 26 lb-ft
.500-20 UNF 1/2-20 33 lb-ft
.625-18 UNF 5/8-18  95 lb-ft
Elastomer seal,all sizes 7-10 lb-ft
Vacuum Range
Del-Seal™ CF or Wire Seal 1x10-13 Torr
Elastomer seal 1x10-8 Torr
Temperature Range
Del-Seal™ CF or Wire Seal -200°C to 450°C
Elastomer seal -20°C to 150°C
Intermittent: 200°C

Mated Cross Section

Intermediate hardware may be required for joining components. These have been omitted for clarity

Double Sided CF Flanges

Del-Seal™ CF Double sided flanges are designed to be inserted between two flanges of the same size. This provides a simple method for adding thermocouple gauge tubes or up-to-air valves to a system with virtually no change in conductance and pumping speed.

All Del-Seal™ CF Double Sided Flanges are made of 304ss material. Each assembly requires two gaskets and longer length bolts. MDC Does not recommend stacking more than one double sided flange in a single assembly.

Zero Length Reducers

Zero length reducers are used for a change in size of flanges within the Del-Seal™ CF family. "Zero Length" means the total thickness of a unit is the thickness of one flange only. Non-zero-length reducers may have straight or conical sections between flanges. Hybrid adapters are used for a change in method of sealing, such as Del-Seal™ CF to ISO and are found in Hybrid Adapters Section.

Double Sided CF Flanges
For product listing, features and specifications click on links below
1-1/3 inch
2-1/8 inch
2-3/4 inch
2-3/4 inch tapped
2-3/4 inch NPT
3-3/8 to 6-3/4 inch
8 to 16-1/2 inch
Zero Length Reducers
For product listing, features and specifications click on links below
Zero Length Reducers

 Related Topics
 Del-Seal™ CF Flange Installation
 Del-Seal™ CF Flange Parts Identification
 Wire Seal Flanges Introduction
 Del-Seal™ CF Fittings Introduction