Editing Diffusion pump (section)

===Oil types===
{{See also|Polyphenyl ether#Ultra-high-vacuum fluids}}

The least expensive diffusion pump oils are based on [[hydrocarbon]]s which have been purified by double-distillation. Compared with the other fluids, they have higher vapor pressure, so are usually limited to a pressure of
{{convert|1e-6|Torr|Pa|abbr=on|lk=in}}. They are also the most likely to burn or explode if exposed to oxidizers.

The most common [[silicone oil]]s used in diffusion pumps are [[trisiloxane]]s, which contain the chemical group Si-O-Si-O-Si, to which various [[phenyl group]]s or [[methyl group]]s are attached. These are available as the so-called 702 and 703 blends, which were formerly manufactured by [[Dow Corning]]. These can be further separated into 704 and 705 oils, which are made up of the isomers of  tetraphenyl tetramethyl trisiloxane and pentaphenyl trimethyl trisiloxane respectively.<ref>{{cite book | title=A User's Guide to Vacuum Technology | chapter=Pump Fluids | publisher=John Wiley & Sons, Inc. | location=Hoboken, NJ, USA | date=2004-12-07 | isbn=978-0-471-46716-8 | doi=10.1002/0471467162.ch13 | pages=229–246}}</ref>

For pumping reactive species, usually a [[polyphenyl ether]] based oil is used. These oils are the most chemical and heat resistant type of diffusion pump oil.