Girovac · Vacuum fluid selection & supply
Diffusion pump fluids are working fluids for diffusion and vapour booster pumps. Their vapour jets transfer momentum to gas molecules, helping move gas towards the backing pump. Girovac’s range includes hydrocarbon, silicone and polyphenyl ether fluids selected for the pump design and required process performance.
Hydrocarbon, silicone and polyphenyl ether fluids
Convoil 20 and Apiezon AP201 are hydrocarbon entries. CVC 4, CVC 4 Ultra and CVC 5 are silicone fluids, while Santovac 5 is a polyphenyl ether. Their chemistry and operating characteristics differ, so changing fluid requires a check against the pump specification.
Diffusion and vapour booster fluid range
Viscosity is shown in centistokes (cSt) with its measurement temperature. The brochure identifies AP201 for Edwards 30B5 and 18B4 vapour booster pumps; confirm the specification for your exact equipment.
| Product | Fluid type | Application / description | Viscosity (cSt; temperature stated) | Brochure pack sizes |
|---|---|---|---|---|
| Convoil 20 | Hydrocarbon | Diffusion and vapour booster pump fluid. | 58 at 40°C | 5 L; 20 L; 208 L |
| Apiezon AP201 | Hydrocarbon | Vapour booster pump fluid; the brochure identifies Edwards 30B5 and 18B4 applications. | 22 at 40°C | 4 L; 20 L |
| CVC 4 | Silicone | Tetramethyltetraphenyltrisiloxane diffusion pump fluid. | 40 at 25°C | 500 cc to 20 kg |
| CVC 4 Ultra | Silicone | Higher-purity tetraphenyltetramethyltrisiloxane fluid. | 37 at 25°C | Confirm required quantity |
| CVC 5 | Silicone | Pentaphenyltrimethyltrisiloxane fluid for demanding high-vacuum applications. | 175 at 25°C | On request |
| Santovac 5 | Polyphenyl ether | Specialist diffusion pump fluid for high- and ultra-high-vacuum systems. | 370 at 40°C | 100 cc; 500 cc |
On smaller screens, swipe or scroll the table horizontally to see every column.
The catalogue tables are reference information from Girovac’s Vacuum Pump Fluids & Greases brochure. Listed pack sizes are enquiry options, not a live stock feed. Confirm current availability, the latest technical data sheet (TDS), safety data sheet (SDS) and equipment approval before ordering.
What determines the right diffusion pump fluid?
- Pump and heater design. The fluid must suit the specified boiler conditions and the manufacturer’s operating procedure.
- Process cleanliness. Consider contamination sensitivity and backstreaming control, including any baffle or cold trap specified for the system.
- Pressure requirements. Compare like-for-like test conditions. A trapped pressure figure should not be compared directly with an untrapped figure.
- Service history. Identify the existing fluid, contamination and the approved cleaning or changeover procedure before filling.
Reference pressure is not guaranteed system pressure
The final pressure depends on the complete system, including leaks, gas load, cleanliness, backing performance and trapping. Fluid data helps selection but does not promise the pressure your installation will achieve.
Support for the complete vacuum system
A diffusion pump relies on suitable backing-pump performance. Girovac can help source mechanical backing-pump oils, investigate spare parts and discuss servicing requirements.
Questions about diffusion pump fluids
Is diffusion pump fluid the same as rotary vane pump oil?
No. Diffusion fluid is a vapour-jet working fluid, while mechanical pump oil lubricates and seals the relevant pump mechanism. Use the fluid specified for each pump.
Can I replace silicone diffusion fluid with a hydrocarbon fluid?
Do not assume interchangeability. Check the pump manufacturer’s approval, heater and boiler requirements, process compatibility and cleaning procedure before changing chemistry.
What does a trapped ultimate-pressure figure mean?
It describes a result obtained with a trap under the stated test conditions. It is not directly comparable with an untrapped result and is not a guarantee for an installed system.
Which details should I send for a diffusion-fluid quote?
Send the pump make and model, existing fluid, heater or operating specification if known, process requirements, trap or baffle arrangement and required quantity.
Get the right grade for your equipment
Send Girovac the pump make and model, current fluid or grease, operating conditions, process gases and required quantity. A nameplate photograph helps us identify the equipment. We’ll confirm suitability, pack size and delivery when quoting.
Girovac Ltd · Unit 2, Douglas Bader Close, Folgate Road, North Walsham, Norfolk NR28 0TZ, UK.
Reference information
Prepared from Girovac’s Vacuum Pump Fluids & Greases technical reference brochure, section 02 (page 4). Updated September 2026. Contact Girovac for the current product TDS, SDS and application checks.
Manufacturer references: Apiezon vapour booster pump oils.