Edwards supplies a range of fluids of different vapour pressures and physical properties. From this range, you can choose the optimum fluid for your applications. In general, the more volatile fluids are used with vapour booster pumps and for vapour diffusion pumps used on industrial processes (for example, decorative coating and vacuum furnaces) where high gas loads are encountered and high critical backing pressure is advantageous. The less volatile fluids are used for processes or experiments requiring more exacting high vacuum conditions. The least volatile fluids are used for clean or ultra high vacuum applications (mass spectrometry, electron probe apparatus, surface studies, and so forth). Fluid selection depends also on the particular physical and chemical characteristics of the fluids (apart from vapour pressure). Edwards has a long history of co-operation with various fluid manufacturers in the development of new pumping fluids and is well placed to advise in cases of uncertainty.
Vacuum achievable at 20 °C
Vapour pressure at 20 °C
Vapour pressure at 100 °C
Vapour pressure at 150 °C
Boiling temperature at 1.3 mbar (average)
Molecular weight (average)
Viscosity cSt at 20 °C
Viscosity cSt at 100 °C
Viscosity cSt at 150 °C
AP201 Vapour booster pump fluid
Apiezon® AP201 is a hydrocarbon fluid prepared by molecular distillation and protected against oxidation by a thermally stable additive of matched vapour pressure. It has an auto ignition temperature of 305 °C. It exhibits a fair degree of resistance to chemical degradation (so that high throughputs of air and water vapour can be pumped without damage to the fluid) and it can withstand limited accidental admission of atmospheric air at operating temperature. The fluid has low viscosity which permits easy filling and draining. It does not attack synthetic rubbers used for seals and gaskets in vacuum systems. It is non-irritant, non-toxic and environmentally non-polluting.
Edwards L9 diffusion pump fluid
Edwards L9 fluid has been developed for use in Diffstak and diffusion pumps. It is a naphthalene based synthetic material which is ideal for use in applications where silicones (which form insulating films) cannot be tolerated. L9 fluid is rugged, has a very good vacuum performance and gives an ultimate pressure of typically 5x10⁻⁹ mbar (at 20 °C). In addition, the fluid is chemically stable and is resistant to acids, alkalis, halogens and oxides of nitrogen. It does not react with common engineering metals or elastomers. It is immiscible to the common solvents alcohol, acetone and trichlorotrifluoroethane. The toxicity level of L9 is very low.
Safety note: When changing to this fluid the pump should be cleaned using a proprietary fluid. The pump should then be rinsed in acetone and dried prior to re-charging.