What is degassing ultrasonic cleaner

What Degassing Means in an Ultrasonic Cleaner

Degassing is the preparation step that determines how well every cleaning cycle after it will perform. It is not a cleaning step. It is the step that makes cleaning possible at full efficiency.

The dissolved-gas problem every fresh bath has

Every time you fill an ultrasonic tank with fresh water, you are also filling it with dissolved gas. Tap water at room temperature holds roughly 8 mg/L of dissolved oxygen at 20 degrees Celsius, plus nitrogen and other atmospheric gases in proportion to their partial pressures. That gas stays in solution under normal conditions, invisible and undetected.

The problem is thermodynamic: dissolved gas competes directly with cavitation yield. The acoustic cavitation process, how a transducer converts electrical energy into cleaning energy through bubble formation and collapse, is explained in full in our guide on how ultrasonic cleaners generate cavitation. What matters for degassing specifically is that dissolved oxygen and nitrogen occupy the same microscopic spaces in solution that cavitation needs to operate at full intensity. A gas-saturated bath at 8 mg/L dissolved oxygen delivers measurably less cleaning force per watt than the same bath at 2 mg/L after a proper degas cycle.

You do not see this happening. The cleaner sounds like it is running normally. But the part coming out of a gas-loaded bath on the first cycle will not be as clean as the part coming out after a proper degas, and the difference is quantifiable, not subjective.

How Henry's Law explains why tap water holds gas until you force it out

Henry's Law states that the concentration of a dissolved gas in a liquid is proportional to the partial pressure of that gas above the liquid. Tap water coming out of a municipal supply is in equilibrium with atmospheric air at roughly 101.3 kPa. It holds as much dissolved gas as the atmosphere above it allows.

Two forces work against that equilibrium during a degas cycle: temperature and acoustic energy. As temperature rises, gas solubility drops, a bath at 45 degrees Celsius holds significantly less dissolved gas than one at 20 degrees Celsius, which is why running your degas cycle at or near your target operating temperature is faster and more effective than degassing cold water. Acoustic energy provides the second force: the ultrasonic vibration gives dissolved gas the nucleation energy it needs to escape from solution as bubbles, which then rise to the surface and break into the atmosphere above the tank.

The combination of heat and ultrasonic energy makes active degassing far faster than simply waiting for dissolved gas to escape on its own. Passive degassing, leaving the filled tank to sit at room temperature, can take several hours to reach adequate levels and will still not achieve the low dissolved oxygen concentrations that an active degas cycle reaches in 3 to 8 minutes.

What Does Degassing Do in an Ultrasonic Cleaner

Degassing reduces dissolved oxygen concentration in the cleaning bath from approximately 8 mg/L to below 2 to 3 mg/L, which restores full cavitation yield and makes the first cleaning cycle as effective as subsequent ones in the same bath.

The quantifiable impact on cavitation yield

Research published in Ultrasonics Sonochemistry by Asakura and Yasuda (2021) quantified the relationship between dissolved gas concentration and cavitation efficiency across frequency ranges from 40 kHz to 1 MHz. At 40 kHz, the most common frequency for benchtop ultrasonic cleaners, high dissolved gas concentrations measurably suppress the collapse intensity of acoustic cavitation bubbles. Reducing dissolved oxygen from 8 mg/L to below 3 mg/L restored cavitation yield to near-theoretical values for a given watt density.

What that means in practical terms: if you load parts into a freshly filled 3-liter tank without running a degas cycle, you are running that first batch at effectively 75 to 80% of the cleaner's rated cleaning power. For routine cleaning of moderately soiled parts, you may not notice. For precision applications, jewelry with channel-set stones, optical assemblies, dental instruments, printed circuit boards, that 20 to 25% deficit in cavitation yield shows up as residue on surfaces that should be clean and as uneven results across a tray of identical parts. The deficit is not a function of the machine's quality; it is a direct consequence of the dissolved gas state of the bath.

How dissolved gas concentration changes the bath's behavior, and how to read it

Dissolved gas concentration has a direct physical expression at the bath surface that reflects what is happening at the molecular level in the solution. A freshly filled bath at 8 mg/L dissolved oxygen produces large, irregular bubbles that carry dissolved gas to the surface and break there, this is the dissolved gas physically escaping under acoustic excitation, not yet the fine cavitation field that does the actual cleaning work. That large-bubble surface activity tells you the bath is still gas-loaded.

As dissolved oxygen drops from 8 mg/L toward the 2 to 3 mg/L target range, the character of the surface changes. Large-bubble activity subsides because the dissolved gas reservoir is exhausted. What replaces it is a markedly different pattern: a stable, fine surface mist driven by true acoustic cavitation operating without the interference of excess dissolved gas. That transition, from large-bubble foam to fine stable mist, is the measurable endpoint of an effective degas cycle. It corresponds directly to the dissolved oxygen concentration dropping below the threshold where cavitation yield is fully restored.

Quick Reference: Dissolved Gas Levels, Degas Duration, and Cavitation Performance

What Is Degas Mode on an Ultrasonic Cleaner

Degas mode is a dedicated operating mode on capable ultrasonic cleaners that runs the transducer on a modified pulsed signal pattern, lower power, intermittent bursts, specifically designed to nucleate and expel dissolved gas rather than clean parts.

How degas mode differs from a standard cleaning cycle at the transducer level

In normal cleaning mode, the transducer runs at full rated power on a continuous or frequency-swept signal. That continuous high-intensity signal generates the dense cavitation field needed to dislodge and emulsify contaminants. It is effective for cleaning precisely because it is aggressive.

Degas mode does the opposite on purpose. The transducer fires in short bursts at 50 to 70% of rated power. Between bursts, the pressure field momentarily releases, which allows newly formed bubbles carrying dissolved gas to rise toward the surface rather than being immediately collapsed by the next pressure cycle. This pulsed approach is more efficient at gas expulsion than continuous full-power operation because continuous high power tends to collapse gas bubbles before they can escape from solution. The intermittent signal gives them time to travel.

The physics follows the same bubble-growth asymmetry that makes acoustic cavitation useful in the first place: given a release window after bubble growth, bubbles carrying dissolved gas migrate toward the surface; given a continuous collapse signal, they stay in suspension and re-dissolve partially before the next cycle.

Degas mode versus passive degassing, why time alone is not enough

I get this question from shop owners fairly often: "Can I just fill the tank the night before and let the dissolved gas escape on its own?" The short answer is no, not to the levels that matter for precision cleaning.

Passive degassing at room temperature relies entirely on the natural concentration gradient between dissolved gas in solution and gas in the atmosphere above the tank. At 20 degrees Celsius with no acoustic assist, dissolved oxygen drops from 8 mg/L toward equilibrium with room air, which is still around 6 to 7 mg/L at sea level. Overnight passive degassing typically brings dissolved oxygen down to 5 to 6 mg/L, still well above the 2 to 3 mg/L threshold where cavitation yield is restored. Active degas mode at 40 kHz and 45 degrees Celsius drives it below 3 mg/L in 3 to 5 minutes for a standard 3-liter tank.

Heating the water passively improves the result somewhat, since hot water holds less dissolved gas. But heating a tank to 45 degrees Celsius and then letting it sit for 30 to 60 minutes without ultrasonic energy still does not match what a properly configured 5-minute degas mode achieves. The acoustic energy is doing work that heat alone cannot replicate.

Units without a dedicated degas mode, what to do instead

Not every benchtop ultrasonic cleaner includes a labeled degas mode. If yours does not, the workaround is straightforward: run the unit at full power and operating temperature with nothing in the tank for the appropriate time by volume. You lose the efficiency benefit of the pulsed low-power signal, but you still drive dissolved gas out faster than passive degassing. Expect to add 20 to 30% to your degas time compared to a unit with a dedicated mode, since continuous full-power operation collapses some gas bubbles before they can exit the solution.

For units below 10 W/L watt density, degassing at any power level will be incomplete. The acoustic intensity is simply insufficient to nucleate dissolved gas effectively. If your unit falls below this threshold, it may not be capable of achieving the bath conditions that deliver full cavitation yield regardless of how long you run it empty.

What Is Degassing Mode on an Ultrasonic Cleaner, The Technical Mechanism

Degassing mode modifies the transducer's drive signal from a continuous waveform to a pulsed burst pattern, typically at 40 kHz and 50 to 70% of rated power, to create favorable conditions for dissolved gas to nucleate, coalesce into rising bubbles, and escape the solution rather than being recaptured by subsequent pressure cycles.

Pulse pattern and power modulation during degas mode

The pulse timing in degas mode varies by manufacturer, but the principle is consistent: a burst of ultrasonic energy lasting a fraction of a second, followed by a brief off-period. A common pattern runs bursts of roughly 200 to 500 milliseconds alternating with off-periods of 100 to 200 milliseconds. During the burst, acoustic pressure creates nucleation events, dissolved gas comes out of solution around microscopic impurities and on the transducer surface itself. During the off-period, those nascent bubbles grow by coalescence and begin rising through the liquid column under buoyancy.

Running at reduced power (50 to 70% of rated) rather than full power serves two purposes. First, it prevents the acoustic collapse events that would re-dissolve gas bubbles before they can escape. Second, it protects the tank liner and transducer from stress-cycling at elevated temperature on an empty (and therefore lower-damping) tank, running an empty tank at full rated power for extended periods can cause transducer fatigue in some designs.

Why 40 kHz is typically used during degas even on multi-frequency units

Multi-frequency ultrasonic cleaners often allow the operator to select from two or more frequencies, commonly 40 kHz and 80 kHz, sometimes with 120 kHz or higher. During degas mode, virtually all multi-frequency units default to 40 kHz, and for a specific physical reason.

At lower frequencies, the acoustic pressure cycle is longer, which allows bubbles to grow to a larger radius before the pressure reverses. Larger bubbles at 40 kHz carry more dissolved gas per bubble and rise through the liquid column more rapidly than the smaller bubbles produced at 80 kHz. For the purpose of gas expulsion rather than cavitation cleaning, larger bubbles are more efficient. The research by Asakura and Yasuda (2021) found that degassing efficiency at lower frequencies (including 40 kHz) was consistently higher on a per-watt basis than at frequencies above 200 kHz when measured by dissolved oxygen reduction rate.

Comparison Table: Degas Mode vs Normal Mode, Signal Behavior

That mechanical understanding of what degas mode does to the signal is exactly what guided a correction I observed at a Denver-area optician practice in Colorado's Front Range. The practice was cleaning titanium-frame, anti-reflective-coated lens assemblies in a 3-liter tank. On the initial setup, the technician ran the degas cycle at 55 degrees Celsius and full power, no dedicated degas mode, just the unit running empty before loading. The dissolved oxygen reading at the start of the fresh fill was 7.9 mg/L. After a 4-minute empty run at 55 degrees and 40 kHz, it dropped to 2.4 mg/L, acceptable from a dissolved gas standpoint. But the first batch of lenses came back with micro-bubble adhesion patterns on the AR coating surface: faint, circular marks where bubbles had formed and collapsed against the lens at high temperature. At 55 degrees Celsius, the thermal stress on a multilayer AR coating during the vigorous initial cavitation burst is outside the coating's safe operating range. We reduced the degas temperature to 38 degrees Celsius and re-ran the degas cycle for 5 minutes. Dissolved oxygen dropped to 2.7 mg/L, still within the effective range. The lenses cleared the subsequent slit-lamp inspection without coating anomalies. Avoiding one set of coating failures saved the practice $90 to $140 in lens replacement cost, and the correction took less than 8 minutes to implement once the cause was identified. The degas step was not wrong; the temperature during it was.

How Long Should You Run the Degassing Cycle

A 3-liter tank at 40 kHz and 45 degrees Celsius requires 3 to 5 minutes of active degas mode to drive dissolved oxygen from approximately 8 mg/L down to below 3 mg/L. Tank volume, temperature, water hardness, and altitude all modify that baseline.

What dissolved oxygen concentration tells you about degas cycle duration

Degas time is not fixed, it is a dissolved oxygen target, and the time required to hit that target varies by tank volume, watt density, and bath temperature. The relationship between volume and degas time is roughly linear at constant watt density (10 W/L minimum): more liquid means more dissolved gas to expel and a longer column for bubbles to rise through before they exit the solution. The following benchmarks represent the time needed to drive dissolved oxygen from a fresh-fill starting point of 7 to 8 mg/L to below 3 mg/L at each size:

• 0.8 to 1.5 L tanks: 1 to 2 minutes at 40 kHz, 40°C
• 3 L tanks: 3 to 5 minutes at 40 kHz, 45°C
• 6 L tanks: 5 to 8 minutes at 40 kHz, 45°C
• 10 L and larger: 8 to 12 minutes at 40 kHz, 40 to 50°C

Starting with cold water (below 25 degrees Celsius) adds 2 to 4 minutes to any of these ranges, because cold water holds more dissolved gas at the start and the unit must simultaneously heat the bath. Filling with water pre-warmed to target temperature eliminates that overhead and is the single most effective way to shorten degas cycle duration without sacrificing dissolved oxygen reduction.

Temperature, water hardness, and altitude as variables

Three variables shift these baseline degas times in ways that matter in real shop conditions:

Temperature: Gas solubility follows Henry's Law inversely with temperature. A bath at 45 degrees Celsius reaches the target dissolved oxygen threshold roughly 30 to 40% faster than the same bath at 25 degrees Celsius. If your unit has a heater, set it to your target cleaning temperature before starting the degas cycle, not after.

Water hardness: Hard water, defined as water containing more than 150 ppm calcium carbonate equivalent, holds dissolved gas more stubbornly than soft water. The calcium and magnesium ions in hard water interact with dissolved gas nucleation in ways that slow the outgassing rate. In hard-water regions (much of the US Mountain West, including parts of Colorado, Utah, and Nevada), add 20 to 30% to your standard degas time, or use softened or deionized water as your fill source.

Altitude: This one surprises people who have only worked at sea level. At high altitude, Denver sits at 5,280 feet above sea level, atmospheric pressure is approximately 83 kPa rather than 101.3 kPa at sea level. Per Henry's Law, lower atmospheric pressure means less gas dissolves in the water in the first place. A freshly filled tank in Denver starts with roughly 6.5 to 7 mg/L dissolved oxygen rather than 8 mg/L. That lower starting concentration means degas cycles at altitude run 15 to 20% shorter than the same cycle would take at sea level, a variable I account for every time I benchmark equipment at altitude.

Material-Specific Degassing Considerations

The degas cycle runs with the tank empty, but the temperature during that cycle directly affects the material you will be cleaning immediately afterward. Setting degas temperature correctly for the material is as important as setting degas duration correctly.

Optical glass and coated lenses, why degas is the riskiest phase, not the cleaning cycle

Most guidance on ultrasonic cleaning and coated optics focuses on the cleaning cycle temperature and duration, and that guidance exists for good reasons, covered thoroughly in our dedicated article on ultrasonic cleaning safety for eyeglasses. What that operational guidance does not isolate is where in the session coating damage most commonly originates: it is the degas phase, not the cleaning cycle.

During the degas cycle, the bath starts at maximum dissolved oxygen saturation and the bubble activity is at its most vigorous, larger, more irregular, and more thermally aggressive than the fine cavitation field that follows once the bath is properly degassed. If the degas temperature is set too high, the bath is at that elevated temperature the moment parts are loaded after degas completes. For multilayer AR coatings, the combination of residual thermal stress from degas plus the initial burst of cleaning cavitation is where edge bond delamination begins. The degas step creates the thermal state the coating must withstand at the most mechanically active moment of the session.

The practical ceiling for degassing any AR-coated or photochromic lens assembly is 38 to 40 degrees Celsius, not because the cleaning cycle cannot run at those temperatures, but because the degas phase at higher temperatures pre-stresses the coating before the cleaning cycle even begins.

Jewelry with channel-set or pave stones, why degas temp matters as much as degas time

Channel-set and pave stone settings hold stones in place with thin metal walls or fine prong points. The adhesive between a stone's girdle and the metal channel is minimal by design; the setting geometry does the retention work. At elevated temperatures during degas, any residual organic contamination under a stone, residual flux, prong solder residue, skin oils, can become more mobile. Combined with vigorous early-cycle bubble activity if parts are loaded too soon, that can displace a loosely seated stone before the cleaning cycle has even started.

For channel-set rings and pave bangles, run degas at 40 to 45 degrees Celsius, confirm the surface has fully calmed, and inspect the setting under magnification before immersing if the piece has any stone that showed movement during a previous cleaning session. Degassing properly removes the uncertainty from the cleaning cycle; skipping it adds mechanical risk to the first batch.

If you had a tray of 12 pave-set sterling silver earring pairs and loaded them into a freshly filled undegassed 3-liter tank, that first cycle runs at roughly 75% cavitation yield. At a production studio rate of $25 to $35 per hour for cleaning and inspection, cleaning them a second time because results were inconsistent adds $15 to $20 in direct labor per tray, avoidable with a 4-minute degas cycle.

Dental instruments and PCBs, dissolved gas in high-precision cleaning contexts

For dental instruments processed in ultrasonic cleaners as part of reprocessing protocols, dissolved gas is a regulatory concern, not just a performance concern. The FDA's guidance on reprocessing reusable medical devices, including Class II reusable instruments covered under 510(k) premarket requirements, references cleaning solution preparation as a required step in validated cleaning protocols. ASTM F2867-22, the standard practice for cleaning, inspection, and marking of metallic parts for oxygen service, similarly treats solution preparation (including degassing) as a non-optional prerequisite for validated cleaning cycles. Using an undegassed bath invalidates the reproducibility assumption that underlies any validated cycle.

For PCBs, the concern is flux entrapment in fine-pitch SMT components. Dissolved gas in the bath can stabilize flux deposits under component bodies by providing a cushioned barrier that reduces the implosion energy at the part surface. A properly degassed bath drives more of its cavitation energy into tight spaces, exactly where flux residues hide on modern high-density boards.

For a complete walkthrough of how to set up each phase of an ultrasonic cleaning session from fill to rinse, see the step-by-step ultrasonic cleaning cycle setup guide, which covers the full workflow in sequence.

Five Degassing Mistakes That Kill Cleaning Performance

Skipping degas entirely on a fresh fill

You fill a 3-liter tank, set your cleaning cycle to 10 minutes at 45 degrees Celsius, and load a tray of 18k white gold rings directly into the undegassed bath. The dissolved oxygen in that fresh fill is sitting at approximately 8 mg/L. Cavitation yield on that first cycle is 20 to 25% below the rated cleaning performance of the unit. Surface coverage on the ring pavilion facets, the tightest recesses, is measurably lower than on rings from a degassed bath. A professional re-clean adds 15 to 25 minutes of additional handling. At a studio labor rate of $30 per hour, that is $7.50 to $12.50 per tray run that should not have been necessary.

Running degas at too low a temperature

You run the degas cycle at 25 degrees Celsius because the cleaning protocol for the material calls for a gentle temperature. But at 25 degrees, water's dissolved gas solubility is significantly higher than at 45 degrees, and the degas cycle must work against a stronger thermodynamic equilibrium. A standard 3-minute degas run at 25 degrees may only reduce dissolved oxygen from 8 mg/L to 5 to 6 mg/L, still well above the 3 mg/L threshold. You get the habit of running degas, but not the result. The fix: run degas at the highest temperature the material permits, then if needed, allow the bath to cool toward a lower cleaning temperature before loading parts.

Loading parts into the tank during the degas cycle

Some operators load parts before pressing the degas button, either to save time or because the sequence seems logical. The problem is not simply that parts are present, it is that a gas-loaded bath behaves differently at the part surface than a degassed one. The large, irregular bubbles characteristic of an in-progress degas cycle collapse with less directional precision and more thermal variance than the fine cavitation field that follows. On coated surfaces, that early-cycle bubble behavior produces the same temperature and mechanical stress profile as the degas-phase risk described in the optics section above. On soft-set stones, the combination of gas-cushioned cavitation and thermal variability during degas is unpredictable in ways that a properly sequenced cycle eliminates. The rule is fixed: degas runs empty, every time, not as a protocol formality, but because the dissolved gas state of the bath fundamentally changes what the bubble field does to the part surface.

Assuming a reused bath does not need re-degassing

Yesterday's cleaning bath left in the tank overnight has partially degassed passively. But partially is the key word. If the bath temperature dropped to room temperature overnight, dissolved gas re-equilibrated with atmospheric air. The bath may contain 5 to 6 mg/L dissolved oxygen by morning, better than a fresh fill, but still above the effective threshold. Run a 60-second to 90-second degas cycle on a reused bath that has sat overnight. A 6-liter tank reused from the previous session at a jewelry production studio represents roughly $4 to $8 in solution cost per full replacement. Running a 2-minute degas verification cycle costs nothing and keeps performance consistent across the day's batches.

Confusing foam with effective degassing

Heavy foam on the bath surface during a degas cycle looks like evidence that degassing is working hard. It is not. Foam is primarily surfactant concentrate at the surface mixed with large gas bubbles, it tells you the bath is active, not that degassing is complete. The completion signal is the opposite of foam: the large-bubble activity calms, the foam breaks, and the surface transitions to a fine, steady mist of true acoustic cavitation. Operators who mistake foam activity for a completed degas cycle cut the cycle short at the wrong moment and load parts into a bath that is still gas-loaded. Watch the surface change, not the timer alone. Timer-only degas decisions are the most common source of inconsistent results I see in production settings.

Degassing Is the First Decision That Controls Every Result After It

Degassing is not a optional warm-up ritual. It is the step that sets the dissolved gas concentration of your cleaning bath to the level where cavitation can function at its rated yield. Skip it on a fresh fill and you run your first batch at 75 to 80% of the cleaner's rated performance, a deficit that shows up most clearly in tight recesses, under stones, around fine surface detail, and on any surface where contamination removal is the primary purpose of the cleaning session.

The mechanism is straightforward: dissolved gas at 8 mg/L fills nucleation sites before cavitation bubbles can form properly. Drive it below 3 mg/L with a properly configured degas cycle and those sites are available for the acoustic energy your transducer is generating. Temperature, altitude, water hardness, and tank volume all modify how long that takes. The degas mode, pulsed, reduced-power, 40 kHz, is purpose-built to do it efficiently. If your unit does not have one, running the tank empty at operating temperature is a reasonable substitute that takes 20 to 30% longer.

The investment is 3 to 12 minutes per fresh fill depending on tank size. The return is consistent, repeatable, full-yield cavitation on every batch that follows.

Frequently Asked Questions About Ultrasonic Cleaner Degassing: