The short answer
The 15500, 15600 and 15800 are two-stage vacuum pumps with listed free-air displacement of 5, 6 and 8 CFM respectively. The 15600 has a 15-micron factory rating; the 15500 and 15800 are rated at 35 microns. Compare displacement and vacuum rating separately, then check the setup and electrical requirements.
Compare the three vacuum pumps
CFM describes free-air displacement. A factory micron rating describes a different part of pump performance, so a larger CFM number does not automatically mean a lower factory vacuum rating. The figures below are manufacturer-listed specifications for the standard models.
| Specification | 15500 | 15600 | 15800 |
|---|---|---|---|
| Free-air displacement | 5 CFM | 6 CFM | 8 CFM |
| Factory micron rating | 35 microns | 15 microns | 35 microns |
| Stages | 2 | 2 | 2 |
| Motor | 1/3 hp | 1/3 hp | 1 hp |
| Electrical rating | 115 V / 60 Hz | 115 V / 60 Hz | 115 V / 60 Hz |
| Oil capacity | 7.5 oz / 220 ml | 15 oz / 445 ml | 18.6 oz / 550 ml |
A factory rating is not a promise that an installed system will reach that pressure in a set time. Measure the system and use its prescribed evacuation and verification procedure.
15500
Robinair 15500 VacuMaster 5 CFM Two-Stage Vacuum Pump
View specifications and current price →
15600
Robinair 15600 6 CFM Two-Stage Vacuum Pump
View specifications and current price →
15800
Robinair 15800 VacuMaster 8 CFM Two-Stage Vacuum Pump
View specifications and current price →15500: the 5 CFM option
Compare the 15500 when a 5 CFM pump matches your required setup. Its lower listed oil capacity differs from the larger models. Check the supplied intake fittings and your hose arrangement before purchase.
15600: 6 CFM with isolation and gas ballast
The 15600 combines its 6 CFM displacement with a lower listed factory micron rating. Robinair also lists an Iso-Valve for isolation and a gas ballast. These controls are useful comparison points when deciding how the pump fits your routine.
15800: the 8 CFM option
The 15800 has the highest free-air displacement and largest motor in this comparison. Its 35-micron factory rating is the same as the 15500, so select it for the required setup rather than assuming it is best in every measure.
A practical selection checklist
- Confirm application compatibility. Check the model's permitted refrigerants and systems. Do not assume suitability for flammable refrigerants, ammonia or other applications from the CFM figure.
- Check the complete flow path. Pump capacity is only part of the setup. Review hose and connection requirements in the equipment instructions.
- Check electrical supply. These are the listed standard 115 V, 60 Hz versions. Match the actual model and nameplate to the supply available at your work location.
- Plan oil maintenance. Use the specified vacuum-pump oil and the manufacturer's service procedure. Oil capacity is a maintenance specification, not a performance ranking.
- Compare total purchase needs. Include suitable hoses and vacuum measurement equipment in the assessment and check what the order includes.
For an existing workshop, write down the limitation you are trying to address before upgrading. More displacement, a different control arrangement and a different factory vacuum rating are separate reasons to compare equipment. Avoid buying solely from the largest number in the table.
View the full vacuum pump and gauge selection.
Common vacuum-pump questions
Is the 15800 always better than the 15600?
No. The 15800 has higher listed displacement, while the 15600 has a lower factory micron rating and different controls. Choose the specifications that match your service setup.
Does 8 CFM guarantee a particular evacuation time?
No. The listed displacement alone does not establish the time needed for a complete installed system. Follow the system procedure and verify the result with appropriate measurement.
Can these pumps replace a refrigerant recovery machine?
No. Recovery and evacuation are different functions. Recover refrigerant with suitable equipment before evacuation.
Should I use the factory micron rating as my system acceptance target?
Use the acceptance criteria and test procedure specified for the system being serviced. A pump factory rating is not itself a complete system test.
Specifications and scope
Prepared from Robinair 15500, 15600 and 15800 product specification tables, checked September 26, 2026. This is a buying comparison, not a hands-on test or operating procedure. Confirm the exact model and follow its operating manual. Current prices and availability appear on the product pages; see our delivery information and store warranty for purchase terms.
