If you only remember one thing from this comparison, remember this: the vacuum pump is rarely the bottleneck in resin degassing. Almost any oil-filled rotary vane pump that pulls a steady 29 to 30 inHg will degas epoxy fine. What actually limits your results is the chamber and the hose seal — and most hobby setups leak long before the pump’s ultimate vacuum spec becomes relevant. So buy on CFM-to-chamber-volume fit, not on the headline micron number. The comparison table below lays out all five pumps by stage, CFM, and best chamber size so you can match the pump to your bench instead of chasing specs you’ll never use.
The short version: a 3 CFM single-stage pump like the Robinair 15310 is plenty for a 1 to 2 gallon chamber and is the value pick. Step up to a 3.5 CFM single-stage (XtremepowerUS or VEVOR) if you run a 3 gallon chamber. Choose a 5 CFM two-stage (Kozyvacu TA500 or Robinair 15500) only if you run a 5 gallon chamber, work at altitude, or degas thin, volatile-rich resins where the deeper vacuum genuinely helps.
How vacuum degassing actually works
Vacuum degassing removes air that’s already mixed into your resin before you pour. When you drop chamber pressure to roughly 29 to 30 inHg of gauge vacuum (about -1 bar), trapped bubbles expand, rise, and burst at the surface. The magic moment is when the resin “boils” — that frothing, volcanic rise you see through the lid. That isn’t heat boiling; it’s dissolved gas escaping as the pressure drops below the gas’s vapor pressure, and it strips dissolved air almost instantly. The accepted best practice is to pull vacuum until the resin just begins to boil, hold briefly, then break vacuum.
This is also why cup fill level matters so much. Resin can expand 2 to 6 times its original volume under vacuum. If you fill a mixing cup more than about one-third full, it will climb the walls and overflow into your chamber — a mess that can foul the lid seal and even reach the pump line. Use a tall, narrow container and leave plenty of headroom.
Understanding the boil also explains the single-stage versus two-stage debate, which is mostly overblown for hobby work.
Single-stage vs two-stage: 75 micron vs 25-40 micron
A single-stage rotary vane pump reaches about 75 micron ultimate vacuum. A two-stage pump runs the gas through two compression stages and reaches roughly 25 to 40 micron. On paper, the two-stage looks dramatically better. In practice, that advantage is usually wasted.
Here’s the catch: ultimate vacuum is what the pump can pull against a perfectly sealed, leak-free system. Most hobby chambers and hoses leak. A typical acrylic-lid chamber with rubber gasket and a length of vacuum hose will top out somewhere around 700 to 800 micron — an order of magnitude worse than even the single-stage pump’s 75 micron ceiling. When your chamber leaks at 700 micron, it makes no difference whether the pump is theoretically capable of 75 micron or 35 micron; the leak sets the floor. You’re paying for stages you cannot use.
So when does two-stage genuinely matter? Three cases: you work at altitude (where atmospheric pressure is already lower and every inHg counts), you run a large 5 gallon chamber that benefits from a deeper, faster pull, or you degas thin, low-viscosity, volatile-rich resins where the deeper vacuum can actually push the resin past its boiling threshold to strip more dissolved gas. For everyone else doing coasters, jewelry, and silicone molds in a small chamber, single-stage is the honest answer.
CFM vs micron: match CFM to chamber gallons
CFM (cubic feet per minute of free air displacement) is the spec people most often get wrong. CFM controls how fast the pump evacuates the chamber, not how deep a vacuum it reaches. More CFM means you hit working vacuum sooner; it does not get you a lower ultimate vacuum.
That makes CFM a chamber-volume question. A 3 CFM single-stage pump pulls a 1 gallon chamber down to 30 inHg in about 45 seconds — snappy. The same pump on a 5 gallon chamber takes proportionally longer and the smaller motor works harder. As a rough fit guide: 3 CFM for 1 to 2 gallon chambers, 3.5 CFM for 3 gallon chambers, and 5 CFM for 5 gallon chambers or for high-throughput shops running back-to-back cycles. If you only ever degas small molds, do not overbuy CFM — you’ll pay more and gain nothing but a slightly faster pull-down you don’t need. (For sizing the chamber itself, see our vacuum chamber comparison.)
With the theory settled, here’s how the five pumps stack up.
Reading the comparison table
The comparison table above sorts the field by stage and CFM. The three single-stage pumps (Robinair 15310, XtremepowerUS 3.5 CFM, VEVOR 3.5 CFM) all sit in the $55 to $80 band and cover 1 to 5 gallon chambers depending on CFM. The two two-stage pumps (Kozyvacu TA500 and Robinair 15500) jump to $90 to $230 and are built for 5 gallon and heavy continuous use. Note how the spec table reveals the real story: motor HP and oil capacity vary more meaningfully than ultimate vacuum, because those drive how the pump holds up under repeated degas cycles.
Robinair 15310 (3 CFM single-stage) — the reliable value pick
This is the one we’d hand most resin crafters. The Robinair 15310 is an HVAC-grade pump with a 1/4 HP motor, a generous 8.5 oz oil reservoir, and a finned aluminum housing that stays cool through back-to-back cycles. Its 75 micron ultimate vacuum is far past what any leaky hobby chamber needs, and 3 CFM pulls a 1 to 2 gallon chamber to about 30 inHg in roughly 45 seconds. Parts and oil are easy to source, which matters for a tool you’ll keep for years. The trade-offs are honest: single-stage tops out at 75 micron, it slows on a 5 gallon chamber, and it costs a bit more than generic imports at similar real-world performance. No chamber or hose is included.
XtremepowerUS & VEVOR 3.5 CFM single-stage — the budget step-up
Both 3.5 CFM single-stage pumps sit at the bottom of the price range and add 0.5 CFM over the Robinair, which evacuates a 3 gallon chamber noticeably faster. The XtremepowerUS uses a 1/4 HP, 1400 RPM motor and is often bundled with oil; the VEVOR runs a smaller 1/5 HP motor but lists a tighter ~40 micron spec and a 4-pole copper motor with a T-shaped heat sink rated for 2+ hours of continuous run. The VEVOR’s real advantage is that it’s frequently sold as a complete kit with a 3 or 5 gallon stainless chamber, lid, hose, and oil — often the cheapest path to a ready-to-degas setup. Watch the caveats: both are lower-HP than premium pumps, the VEVOR’s 40 micron listing is optimistic for a single-stage (your chamber leak rate will dominate anyway), and house-brand support and oil sourcing are weaker than Robinair. On some VEVOR kits the acrylic lid can craze over time versus tempered glass.
Kozyvacu TA500 (5 CFM two-stage) — the large-chamber / altitude pick
If you genuinely run a 5 gallon chamber, work at altitude, or degas thin volatile-rich resins, the Kozyvacu TA500 is the sensible two-stage. Its 5 CFM evacuates a big chamber fast and absorbs the 2 to 6x resin expansion without bogging, and its 1/2 HP motor — the strongest in this group — stays composed under continuous load. Users report a real-world 25 to 37 micron, deep enough to actually boil thin resins and strip more dissolved gas. The honest downsides: it costs roughly double a 3 CFM single-stage for benefits most hobby chambers can’t use, it’s heavier on the bench, and its deeper micron rating is moot if your chamber and hoses only hold ~700 to 800 micron. It’s overkill for occasional small-mold work.
Robinair 15500 (5 CFM two-stage) — the HVAC-grade durability pick
The Robinair 15500 is the buy-it-for-life option. It pairs 5 CFM with a verified 35 micron factory rating, a thermally protected 1/3 HP motor, and a 7.5 oz reservoir built for long service life. For a busy shop running daily degas cycles, its durability and parts support are the best of the group. But at $170 to $230 it’s by far the priciest pump here, the two-stage depth is wasted on a leaky hobby chamber, it’s the heaviest and least portable unit, and no chamber or hose is included. Buy it only if frequent professional use justifies the premium.
Vacuum pump vs pressure pot: which method for your project
A common mistake is assuming a vacuum pump and a pressure pot do the same job. They don’t. A vacuum chamber removes bubbles from mixed resin before you pour — ideal for degassing silicone molds, casting resin, and stabilizing porous wood. A pressure pot, run at 40 to 60 PSI, doesn’t remove bubbles; it shrinks any remaining bubbles so small they vanish while the resin cures, which is what produces truly glass-clear castings and deep pours. Many pros do both: vacuum-degas first, then cure under pressure. If your goal is flawless clear castings, prioritize a pressure pot; if it’s pre-pour degassing and wood stabilizing, a vacuum pump is the tool. We break the decision down fully in pressure pot vs vacuum chamber.
Setup and maintenance
Always use the manufacturer’s vacuum-pump oil, not motor oil — vacuum oil has a low vapor pressure so it doesn’t contaminate the vacuum. Check the sight glass before every session and change the oil after heavy use or whenever it looks milky (a sign moisture got in). Pair the pump with a vacuum chamber rated for full vacuum, seal the lid gasket and all hose fittings carefully, and keep hose runs short to minimize leak points. Remember the one-third fill rule on your mixing cup to absorb the 2 to 6x expansion.
A short safety note: epoxy and resin release fumes, and the boiling action under vacuum can drive off volatiles faster. Work in a ventilated space and wear an organic-vapor respirator, especially for repeated or large pours — see our resin respirator guide. If you intend to make food-contact pieces, confirm the resin itself is rated food-safe; the pump and chamber don’t change a resin’s food-safe status.
Troubleshooting
Pump won’t reach full vacuum. Nine times out of ten this is a leak, not the pump. Check the lid gasket seats flat, that hose fittings are tight, and that the chamber valve fully closes. Low or contaminated oil also caps the achievable vacuum — top up or change it. Only after ruling those out should you suspect worn pump vanes.
Resin overflows in the chamber. You filled the cup too high. Resin expands 2 to 6x under vacuum; use a taller, narrower cup filled no more than one-third, and break vacuum the moment the froth nears the rim.
Persistent bubbles after degassing. Either you broke vacuum before the resin fully boiled and settled, or the resin is too thick (high viscosity) to release gas in the time available. Warm the resin slightly to lower viscosity, give it a longer hold once it boils, and consider finishing under pressure for any deep or thick pour.
Verdict
Match the pump to your chamber, not to a micron number on a box. For most resin crafters running a 1 to 2 gallon chamber, the Robinair 15310 (3 CFM single-stage) is the reliable value pick. If you run a 3 gallon chamber, a 3.5 CFM single-stage like the XtremepowerUS or the kit-friendly VEVOR adds useful speed for little money. Reserve a 5 CFM two-stage — the Kozyvacu TA500 for value, the Robinair 15500 for buy-it-for-life durability — for genuine 5 gallon chambers, altitude work, or thin volatile-rich resins. Don’t overpay for two-stage depth your leaky hobby chamber can’t hold. For the full kit picture, start with our resin equipment buyers guide.