All our fluids and sealants are tested under formal laboratory conditions. In addition, we have gained considerable on-site experience through our own use of these materials and by maintaining close contact with users who have specific problems. As many cases of suspected equipment under-performance are eventually traced to the use of unsuitable or unsatisfactory fluids and sealants, we are pleased to advise on the correct selection of fluids and sealants for your application.

Mineral-based materials: These materials include rotary pump oils, Diffstak and diffusion pump oils and greases. They are available with or without various additives for different applications.

Silicone-based materials: These materials are used for Diffstak and diffusion pump fluids and greases. They comprise either Tetramethyltetraphenyltrisiloxane or Pentaphenyltrimethyltrisiloxane.

Synthetic-organic compounds: These include various hindered esters, phenyl ethers and napthalene based compounds. They are offered for use in Diffstak and diffusion pumps, but they can also be used as a rotary pump oils in certain unique applications. Edwards can advise on the matching of the fluids to particular applications.

Fluorinated materials (PFPE): These are perfluoropolyethers. Perfluoropolyether is a fully fluorinated material free from other halogens and from hydrogen, and so is of particular value where freedom from hydrocarbons is important. It is inert to most reactive chemicals such as UF 6 , F 2 , O 2 , O 3 , and so on, and it does not polymerise when exposed to electron and most ion bombardment. Perfluoropolyether fluid is available in grades suitable for use in rotary pumps. A low vapour pressure Fomblin® grease (AR555) is available which combines good lubrication properties with superior vacuum properties.

PFPE for semiconductor applications: The major growth in the use of perfluoropolyether (PFPE) compounds has been in applications where hostile process conditions quickly destroy normal hydrocarbon pump oils. This applies particularly in semiconductor processing. The corrosion resistant properties and chemical inertness of PFPE result in greatly increased operation times between oil changes and pump maintenance, and this provides a cost effective solution to many difficult pumping applications. These are the basic properties of PFPE and the advantages for use in vacuum systems:

• Chemically Inert Ideal for pumping aggressive materials, particularly in semiconductor processes.
• High Oxidation ResistanceFluid is not damaged by repeated exposure to air at operating temperatures.
• Non-InflammableNo fire risk.
• High Thermal ResistanceNo residual tar compounds formed by overheating. Eventually reduced to gaseous products.
• Oxygen CompatibleAllows absolutely safe pumping of oxygen (NASA approved for liquid oxygen systems). Maximum recommended operation temperature and pressure for 100% oxygen is 250 °C and 91.4 kg cm-2 and 60 °C, 175.75 kg cm-2.
• Non-polymerisationDoes not polymerise on exposure to energetic particle bombardment (except hydrogen ions). This reduces the impact of backstreamed vapours, and is an important property where polymers cannot be tolerated (for example, in electron microscopes).
• Miscible with most common solvents.
• Allows pumping of solvent even without gas ballast.

Before charging with PFPE, thoroughly clean the pumps to achieve maximum advantage. If you do not have skilled technicians available, we recommend that you return the pumps to a Edwards Service Center to be cleaned and filled. Some models of high vacuum rotary pumps and mechanical booster pumps adapted for use with PFPE are available as standard and can be found in the appropriate sections of this catalogue: these pumps are assembled and tested with PFPE.

Safety notePerfluoropolyether is a fluorinated compound and will give-off toxic vapours if exposed to temperatures above 280 °C. Do not expose PFPE to naked flames and prohibit smoking in work areas.