If you are choosing between a single-stage and a two-stage vacuum pump for resin degassing, here is the short answer most retailers will not give you: for the vast majority of resin work, the single-stage is the right buy, and the two-stage is a niche tool — not a quality upgrade. The reason is physics, not marketing. Both pumps will pull your epoxy past its boiling point and pin your gauge at the top of the scale. The two-stage’s extra depth lives in a region your hobby chamber almost certainly cannot reach. Spend the difference on a leak-tight chamber and a decent gauge instead.
This page compares four real pumps across the two stage types: two single-stage units (the Robinair 15310 and a VEVOR 3.5 CFM kit pump) and two two-stage units (the Kozyvacu TA500 for value and the Robinair 15500 for buy-it-for-life durability). The full numbers — stage, CFM, ultimate vacuum, gauge reading, motor, and ideal chamber size — are in the comparison table and the specs below. The sections here explain what those numbers actually mean for your resin.
Bottom line up front: single-stage for most, two-stage for a few
Degassing epoxy is a low-bar vacuum task. You need a continuous 29 to 30 inHg (about -1 bar) of gauge vacuum: enough to make trapped air bubbles expand, rise to the surface, and burst, and enough to push the resin to its boiling point so dissolved gas escapes almost instantly. Every pump in this comparison clears that bar with ease — a single-stage’s 75-micron ultimate vacuum is already far deeper than the threshold where resin boils.
So the question is not “can it degas?” — they all can. The question is whether the two-stage’s deeper ultimate vacuum (roughly 25-40 micron versus 75 micron) translates into better degassed resin in your setup. For most hobbyists, it does not, because the limiting factor is not the pump. It is the chamber.
The micron vs inHg trap: why both pumps read ~29.9 inHg
This is the single most misunderstood point in vacuum degassing, so it is worth being precise. inHg and micron measure the same thing — absolute pressure — at wildly different resolutions. The inHg scale runs from 0 (atmosphere) to about 29.92 (a perfect vacuum at sea level). Microns measure the tiny sliver of pressure that remains near the very bottom of that scale.
Here is the trap: 500 micron already corresponds to roughly 29.90 inHg. A single-stage pump bottoming out at 75 micron and a two-stage bottoming out at 35 micron both sit visually pinned at the top of an analog inHg gauge. The needle has no room left to move. If you watch two setups side by side on standard analog gauges, you will see no difference whatsoever — both read about 29.9 inHg.
To actually resolve the gap between a 75-micron single-stage and a 35-micron two-stage, you need a dedicated micron (digital vacuum) gauge that reads down into the tens of microns. For resin work, that resolution is rarely worth the cost, because — as the next section explains — your chamber gives the depth back as leakage anyway.
How single-stage and two-stage rotary vane pumps actually differ
Both designs are rotary vane pumps. A single-stage pump compresses the evacuated gas once before exhausting it; that single compression stage bottoms out around 75 micron. A two-stage pump runs the gas through two rotary-vane stages in series: the first stage roughs out the bulk of the gas, then hands off to a second stage that pulls the final deep vacuum. The result is a deeper ultimate vacuum, roughly 25-40 micron.
The key insight is where that advantage lives. The two-stage’s extra capability is entirely at the bottom of the range — below about 500 micron. Above that, the two stages perform essentially identically. Since resin degassing only needs a steady 29-30 inHg (well above the 500-micron threshold in micron terms), the two-stage’s design advantage simply does not get exercised by the task. It is a tool built to chase the last few microns, and resin does not ask you to.
The leak ceiling: your chamber tops out at 500-800 micron, not the pump
This is the part that decides the whole question. A pump’s ultimate vacuum is what it can reach against a perfectly sealed, leak-free volume. Your chamber is not that. A typical hobby setup — an acrylic lid, a rubber gasket, a length of hose, a brass fitting or two — leaks, and tops out around 500-800 micron at equilibrium, where the leak rate matches the pump’s pumping speed.
Sit with that number. A leaky chamber at 700 micron is worse than even the single-stage pump’s 75-micron ceiling. The chamber, not the pump, is the binding constraint. In that scenario, the difference between a pump rated at 35 micron and one rated at 75 micron is completely academic — neither one will ever see those numbers, because the chamber bleeds air back in faster than the second stage could ever pull it out. Buying a two-stage to fix bubbly resin when the real problem is a leaking lid is spending money in the wrong place. A better gasket, tighter fittings, and a glass lid will do more than a second pump stage ever could.
Three real cases where two-stage is genuinely worth it
Two-stage pumps are not a scam — they are simply specialized. There are three honest cases where the depth pays off.
1. Altitude. Atmospheric pressure sets the ceiling on attainable vacuum. At sea level it is about 760 Torr; in Denver at roughly 5,280 ft it is only about 630 Torr. You start with less headroom, so the deeper-pulling two-stage helps you reach a usable working vacuum that a single-stage might struggle to hit cleanly.
2. A tightly-sealed metal chamber. If you run a quality stainless or aluminum chamber with good fittings and a proper lid that can actually hold below 500 micron, then the pump’s deeper rating becomes usable. Only when the chamber can get out of the way does the two-stage’s 35-micron capability matter.
3. Thin, volatile-rich resins. For low-viscosity resins loaded with volatiles, pushing further past the boiling threshold strips more dissolved gas. The deeper pull of a two-stage does measurably more here than on thick, slow casting resin.
If you do coasters, jewelry, and silicone molds in a small acrylic chamber at sea level, none of these apply, and single-stage is the honest, money-saving choice.
CFM vs stages: a separate decision driven by chamber gallons
Do not confuse the two specs. Stages control vacuum depth; CFM controls evacuation speed. A 3 CFM single-stage will pull a 1-gallon chamber to about 30 inHg in roughly 45 seconds. On a 5-gallon chamber, that same 3 CFM gets slow, and you will appreciate a 5 CFM unit — but the deeper vacuum still comes from the second stage, not the higher CFM.
So size CFM to your chamber gallons, and choose stage type by the three cases above. A 5 CFM rating is genuinely useful on big chambers because resin expands 2-6x under vacuum and a faster pump absorbs that surge without bogging. That is a speed and headroom argument, independent of whether you need a single or two-stage. For chamber-sizing guidance, our resin equipment buyers guide walks through matching pump CFM to chamber volume.
Reading the comparison table
In the comparison table and specs below, watch four columns. Stage tells you single versus two. CFM tells you speed — match it to your chamber size. Ultimate vacuum is the headline number retailers push, but read it knowing your chamber’s leak rate sets the real floor. Analog gauge reads is the reality check: every pump here shows ~29.9 inHg on a standard gauge, which is precisely why the ultimate-vacuum column rarely matters in practice.
Note one honest caveat on the listings: the VEVOR is listed at ~40 micron, tighter than the typical 75-micron single-stage spec, and the Kozyvacu is listed at ~40-50 micron while users report 25-37 micron. Listed numbers from house brands are optimistic; the factory-verified Robinair ratings (75 micron single, 35 micron two-stage) are the more trustworthy anchors.
Single-stage picks: Robinair 15310 and the VEVOR 3.5 CFM kit
The Robinair 15310 is the buy-it-for-years single-stage. Its 3 CFM, 1/4 HP HVAC-grade motor and 8.5 oz oil reservoir run cool through back-to-back degas cycles, and Robinair parts, vanes, and OEM oil are easy to source. At 75 micron it is already deeper than any leaky hobby chamber will hold. It ships bare — no chamber, hose, or fittings — and 3 CFM is on the slow side for a full 5-gallon chamber.
The VEVOR 3.5 CFM kit pump is the cheapest path to a complete, ready-to-degas setup, frequently bundled with a stainless chamber, lid, hose, and oil. Its 4-pole copper motor is rated for 2+ hours of continuous run. The trade-offs: only a 1/5 HP motor (the weakest here, so it works hard on a full 5-gallon load), an optimistic 40-micron listing, weaker house-brand support, and acrylic lids on some kits that can craze over time versus tempered glass.
Two-stage picks: Kozyvacu TA500 (value) and Robinair 15500 (buy-it-for-life)
If you have a real reason for two-stage, the Kozyvacu TA500 is the value choice: a 5 CFM, 1/2 HP two-stage that reaches a real-world 25-37 micron, evacuates a 5-gallon chamber fast, and absorbs 2-6x resin expansion without bogging. It is heavier with a larger footprint, and its depth is fully wasted on a chamber that only holds 500-800 micron.
The Robinair 15500 is the buy-it-for-life professional unit: 5 CFM, a verified 35-micron factory rating, a thermally protected 1/3 HP motor, and the best long-term vane life and parts support of the group. It is also by far the most expensive here and the heaviest at ~28 lb — hard to justify for hobby resin unless you run daily, high-volume work on a well-sealed chamber.
Setup, oil, gauge choice, and the one-third cup-fill rule
A few practical notes. Use the correct vacuum pump oil and change it when it darkens — contaminated oil costs you ultimate vacuum. For a gauge, an analog inHg gauge is fine for confirming you reached working vacuum; only buy a digital micron gauge if you genuinely need to see below 500 micron (most resin crafters do not). The accepted degassing technique is to pull vacuum until the resin just starts to boil, hold briefly, then break vacuum.
Safety note: resin can expand 2-6x its original volume under vacuum, so never fill a mixing cup more than about one-third full. Overflow into the chamber or up the hose toward the pump is the most common — and most expensive — beginner mistake. Always use a chamber rated for vacuum service and follow your resin manufacturer’s working- and pot-life guidance.
Troubleshooting
If your pump won’t reach full vacuum, the cause is almost always a leak (lid gasket, hose, fittings) or tired oil — not an underpowered pump. Check the seal before blaming the stages. If resin overflows, you overfilled past the one-third line or pulled vacuum too aggressively on a thin, fast-boiling resin; fill less and ease in. If you get persistent bubbles despite a steady 29-30 inHg reading, suspect the chamber is leaking back at 600-800 micron, or that you broke vacuum before all the dissolved gas escaped. None of these are solved by buying a two-stage pump.
Verdict and where to go next
Buy a single-stage pump for the vast majority of resin degassing — its 75-micron ultimate vacuum already pins an analog gauge near 29.9 inHg, and most hobby chambers leak at 500-800 micron, which erases any two-stage advantage. Put the savings toward a leak-tight chamber and a good gauge. Step up to a two-stage only in the three real cases: altitude, a tightly-sealed metal chamber that holds below 500 micron, or thin, volatile-rich resins.
To match pump CFM to your chamber gallons and round out the rest of your degassing setup, see the best resin equipment buyers guide, or browse all of our head-to-head equipment comparisons.