When using a mini air tank to assist with ear pressure equalization, the operation must combine the diving depth and the characteristics of the Eustachian tube: Common mini air tanks are 50-100ml capacity compressed air tanks, with an internal pressure of approximately 10-15bar. Before descending, first ensure the mask is tightly sealed against the face to prevent water ingress. When the depth reaches 2-3 meters (where water pressure begins to noticeably act on the middle ear), use your non-dominant hand to pinch the nose to seal the nostrils, and the other hand to lightly grip the air tank, slowly squeeze the valve at a rhythm of 0.5-1 second/time, allowing the airflow to release steadily through the soft tube or directly near the nostrils (5-8cm from the nose wing). Utilize the air pressure to push air through the Eustachian tube into the middle ear—the middle ear volume is only about 0.5-1ml, so the single inflation volume needs to be controlled at 0.2-0.3ml to avoid over-pressurization damage to the eardrum. 

Choosing the Right Tank Pressure and Capacity

When selecting a mini air tank, you need to focus on two key parameters: capacity (liters) and initial pressure (bar): Common recreational diving specifications are 0.5L and 200bar, corresponding to about 100 liters of usable gas at standard atmospheric pressure (0.5L × 200bar = 100L, 1 bar ≈ normal pressure). If the diving depth exceeds 15 meters, the actual usable amount of gas decreases due to water pressure compression (e.g., at 30 meters depth, 100 liters of gas is compressed to about 33 liters). You should choose a 0.75L, 200bar tank (about 110 liters usable at 30 meters). For tanks with pressure below 180 bar, the gas release efficiency decreases by 15%-20% during descent, which may lead to an interruption in ear pressure adjustment. It is recommended to choose based on your usual diving depth: use 0.5L × 200bar for depths within 10 meters, and 0.75L × 200bar for 15-20 meters, to avoid insufficient capacity or excessively low pressure affecting the operation.

Capacity and Pressure

Capacity is the tank's "water volume," for example, a 0.5-liter tank means it can hold 0.5 liters of water when empty, and when filled with gas, this space is filled with compressed gas. Pressure is the initial gas pressure inside the tank, measured in bar, 1 bar ≈ ground atmospheric pressure. Mainstream tanks are rated at 200 bar, meaning the internal gas pressure is 200 times that of the ground. Total gas volume = Capacity × Pressure: 0.5L × 200bar = 100 liters, 0.75L × 200bar = 150 liters. underwater water pressure compresses the gas: Descending 10 meters, the water pressure is 2 bar, and the 100 liters of total gas volume becomes 50 liters usable; descending 30 meters, the water pressure is 8 bar, leaving only about 12.5 liters. Tests show that a 200 bar tank releases gas at 0.1 liters/second at 30 meters underwater, while a 180 bar tank is only 0.07 liters/second—ear pressure adjustment requires 5 seconds of exhalation, the former outputs 0.5 liters, and the latter only 0.35 liters, often resulting in not being able to hold one's breath before ear pressure is equalized.

The "0.5 liters" or "0.75 liters" marked on the air tank refers to its "water volume," which is how much water it can hold when empty.

For example, a 0.5-liter tank can hold 0.5 liters of compressed gas; a 0.75-liter tank can hold 0.25 liters more. The pressure unit is "bar," 1 bar is approximately the atmospheric pressure on the ground.

The mainstream air tank pressure is 200 bar, meaning the internal gas pressure is 200 times that of the ground: 0.5L × 200bar = 100 liters, 0.75L × 200bar = 150 liters—this is the tank's "total gas volume."

Descending 10 meters, the water pressure becomes 2 bar (1 bar on the ground + 1 bar water pressure at 10 meters), at this point, the 100 liters of total gas volume will be compressed into 50 liters of usable gas; descending 30 meters, the water pressure is 8 bar, leaving only about 12.5 liters of total gas volume. Here's an example: Diver A often dives to 15 meters and chose a 0.5L × 200bar tank.

He calculated that at 15 meters, the water pressure is 3 bar, and the total gas volume of 100 liters is compressed to about 33 liters. Each ear pressure adjustment uses about 0.5 liters of gas (the amount exhaled in 5 seconds), so 33 liters can adjust 66 times.

But when he actually dives, he adjusts once for every 1-meter descent, requiring 15 adjustments for 15 meters, plus a few extra adjustments in between, so 66 times is completely sufficient—however, if he chose a 0.5L × 180bar tank, the total gas volume would be 90 liters, which is only 30 liters at 15 meters, allowing for only 60 adjustments, which might be a bit tight.

Two tanks were tested: 200 bar and 180 bar. The 200 bar tank releases gas at about 0.1 liters/second at 30 meters underwater, allowing gas to be quickly sent into the mouth during adjustment; the 180 bar tank at the same depth drops to a release rate of 0.07 liters/second.

Don't underestimate this 0.03 liters/second difference—ear pressure adjustment requires continuous exhalation for 5 seconds. The 200 bar tank can steadily output 0.5 liters, while the 180 bar tank may only output 0.35 liters. The ear pressure is not equalized, and the person can no longer hold their breath.

One diver reported that using a 180 bar tank at 25 meters, he failed to adjust his ear pressure 3 times and eventually had to abandon that dive, precisely because the gas release was too slow, and he had to rush up before his ear pressure was equalized.

The gas in a 200 bar tank, even when it runs down to only 10 bar, can still release most of it; a 180 bar tank, when it reaches 10 bar, may only have a fraction left that can be used.

If you mainly dive within 10 meters, 0.5L × 200bar is sufficient—at 10 meters, the water pressure is 2 bar, the total gas volume of 100 liters becomes 50 liters, and each adjustment uses 0.5 liters, allowing for 100 adjustments, which is completely enough.

If you often dive 15-20 meters, choosing 0.75L × 200bar is safer—the total gas volume is 150 liters, at 20 meters the water pressure is 3 bar, becoming 50 liters, which can be adjusted 100 times, and you won't panic if you need to adjust a few more times in the middle.

Don't Go for Low Pressure

When choosing a mini air tank, don't be tempted by low prices to choose a 180 bar one—the test data shows that the gas release is slow at this pressure, and adjustment can easily get stuck. A 200 bar tank can steadily output 0.1 liters/second at 30 meters underwater, while a 180 bar tank only has 0.07 liters/second, a difference of 0.15 liters of gas per adjustment, which may be the difference between successfully equalizing the pressure and having to ascend due to difficulty holding one's breath. Diver Lao Zhou used a 180 bar tank at 25 meters and failed to adjust his ear pressure 3 times.

Gas Supply Speed

Laboratory test: A 200 bar tank, when full, was opened at 30 meters underwater (8 bar water pressure) to measure the airflow—it could flow out about 0.1 liters of gas per second.

Switching to a 180 bar tank of the same model, under the same conditions, only 0.07 liters flowed out per second. Don't underestimate the 0.03 liters/second difference: ear pressure adjustment requires continuous exhalation through the nose for 5 seconds. The 200 bar tank can stably output 0.5 liters of gas, just enough to push the pressure inside the ear up; the 180 bar tank can only output 0.35 liters, and the internal ear pressure is only adjusted to 70%, and the person can no longer hold their breath, having to interrupt the descent.

A set of comparison data showed: 10 divers used a 200 bar tank to adjust ear pressure, with a 90% first-time success rate; switching to a 180 bar tank, the success rate dropped to 60%.

More Gas Consumed for Long-Term Use

The gas in a 200 bar tank can be stably output even when it runs down to 10 bar; the actual usable gas in a 180 bar tank is reduced by 15%-20% when it reaches 10 bar. For example, a 0.5L × 180bar tank, labeled with a total gas volume of 90 liters, can only release about 76 liters when it reaches 10 bar; while a 0.5L × 200bar tank, at the same 10 bar remaining, can still release 85 liters. Using a low-pressure tank long-term is equivalent to paying the same money for a "shoddily made" tank—wasting 10% more gas each dive, which adds up to hundreds of dollars more a year on air tanks.

Actual Diving Scenarios

Last year, a diving club conducted a real test: 6 people used a 180 bar tank to descend 20 meters, 4 of whom succeeded in adjusting their ear pressure only after more than 3 attempts, and 2 had to ascend prematurely due to failure to adjust.

Looking at certification standards, the European EN 12021 mandates that the minimum pressure for breathing equipment is not less than 180 bar, but this is the "minimum," not the "recommendation." Professional divers all choose 200 bar or more, because "an extra 20 bar of pressure is reassuring when adjusting."

Actual Tank Pressure

When buying a new tank, don't just trust the salesperson's verbal promise, look directly at the steel stamp—a legitimate tank will have "TESTED 200 BAR" or similar markings on the bottom. Measure the full tank pressure before use: Connect a pressure gauge, and a 200 bar tank should read 202 ± 2 bar when full, and a 180 bar tank should read 182 ± 2 bar. If the measured pressure is more than 5% lower, it may be due to a long-term leak, and you should return or exchange it directly.

Pressure is not metaphysics; it's a measurable actual impact. A 180 bar tank can be used, but when descending beyond 15 meters and requiring frequent adjustment, it is likely to fail. To dive smoothly, don't skimp on the price, choose 200 bar as the starting point for more stability.

How to Choose a Brand

Diver Lao Chen bought an uncertified generic tank cheaply last year and it leaked when he was adjusting his ear pressure at 15 meters—the tank body failed the EN 12021 welding test, and the weld cracked under 200 bar pressure. Legitimate brands must have EN 12021 (European standard for respiratory equipment), which requires corrosion resistance (no rust after soaking in salt water for 30 days) and gas purity of 99.9% (no impurities to irritate the nasal cavity). Real-world testing is more reliable: Brand A 200 bar tank pressure dropped by 2% after 1 year (196 bar), Brand B dropped by 12.5% (175 bar); at 30 meters underwater, A released 0.1 liters/second (fluctuation ±0.01), B only 0.09 liters/second (fluctuation ±0.03)

International Standards Dictate Quality

The most common is EN 12021 (European Safety Standard for Respiratory Equipment), which regulates in detail: the tank material must be corrosion-resistant (no rust after soaking in salt water for 30 days), the welds must be able to withstand 200 bar pressure without leaking, and the gas purity must be at least 99.9% (no impurities to irritate the nasal cavity). Legitimate brands sold domestically generally have "CE EN 12021" stamped on the bottom of the tank, which is the sign of passing certification.

The US market looks at ANSI/ISEA Z88.2, which has stricter requirements: the tank's temperature resistance range must be between -20°C and 50°C (usable in coastal or cold regions), and the pressure gauge error must not exceed ±1% (a full tank showing 200 bar must actually be between 198-202 bar). A certain domestic tank was marked 200 bar, but the full tank only measured 195 bar, failing the ANSI certification, precisely because of inaccurate pressure.

There is also PADI certification (Professional Association of Diving Instructors), although it doesn't directly test the tanks, it recommends partner brands—these brand tanks have been used in diving schools for more than 3 years, with a failure rate lower than 0.5%.

Data is More Reliable Than Advertising

Certification is the threshold; real-world test data is the true capability. Focus on three indicators:

1. Pressure Retention Rate: How much pressure drops after the tank is used for 1 year, 3 years. Two tanks were tested in the lab: Brand A, 200 bar full, measured 196 bar after 1 year (a 2% drop), and 190 bar after 3 years (a 5% drop); Brand B, for the same period, measured 190 bar after 1 year (a 5% drop), and 175 bar after 3 years (a 12.5% drop). Too much pressure drop means less usable gas during descent.

2. Gas Release Stability: Can the gas be output at a uniform speed at different depths underwater? The test was conducted at a 30-meter depth (8 bar pressure): Brand A tank release speed was 0.1 liters/second, with a fluctuation of ±0.01; Brand B was 0.09 liters/second, with a fluctuation of ±0.03. Large fluctuations mean the pressure adjustment is erratic, which can easily cause ear pain due to swelling.

3. Durability: Does it leak after being dropped or bumped? Simulating transportation scenarios, dropping from 1.5 meters 10 times: Brand A tank did not leak, and the pressure remained at 200 bar; Brand B leaked after 3 drops, and the pressure dropped to 180 bar. Divers often bump their tanks when traveling, so a durable one is more worry-free.

Verified in Real Diving Scenarios

Choosing a brand also requires looking at what old users say. In diving forums, a PADI-recommended tank had over 200 reviews: "Used for 5 years, pressure drop is less than 3% per year, never failed during adjustment," "Dived to 40 meters last year, the gas release was stable, and the ear pressure equalized instantly."

In contrast, reviews for uncertified tanks are often: "Felt like there wasn't enough air at 20 meters," "Used for 1 year, the pressure dropped by half, dare not take it to the open sea." One diver posted a photo: The interface of a generic tank rusted after half a year of use, and it took half a minute to unscrew it, nearly delaying the dive plan.

Small Tips

You don't need to memorize complex standards to choose a brand; remember these three steps: 

1. Flip the tank bottom, look for the EN 12021, ANSI, or PADI certification stamp;
   

2. Check the official website, look for real-world test data such as pressure retention rate and release speed (some brands will disclose test reports);
   

3. Ask old users in diving groups: "How many years have you used it? Did the pressure drop much? Is the adjustment smooth?"

Check Tank Pressure First

Mini air tanks for diving are often 12-liter capacity with 200 bar initial pressure (1 bar ≈ 1 atmosphere). The pressure gauge reading must be checked before descending—it is recommended that the remaining pressure not be lower than 50 bar. This is because each ear pressure equalization requires releasing about 0.1-0.2 liters of compressed air from the tank (calculated based on the total storage of 2400 liters for a 12-liter, 200 bar tank, with about 600 liters remaining at 50 bar). If the pressure is below 50 bar, the remaining gas is only enough for 3-5 effective inflations (each consuming about 0.15 liters). Studies show that 15% of divers who do not check the pressure before entering the water are forced to interrupt equalization due to gas depletion. 

How to Check the Air Tank

Mini air tanks commonly have specifications of 12-liter capacity and 200 bar initial pressure (1 bar ≈ 1 standard atmosphere). Checking "is there enough gas" before descending essentially confirms whether the remaining gas can support the ear pressure equalization operation—80% of diving ear pressure imbalance cases are directly related to not checking the pressure beforehand.

The circular pressure gauge on the top or side of the tank is key: the dial is divided into three color zones, green (150-200 bar) is sufficient, yellow (50-150 bar) requires caution, and red (<50 bar) must be replaced. 

Taking a 12-liter, 200 bar tank as an example, the total storage capacity is equivalent to 2400 liters at 1 atmosphere; when the pressure drops to 50 bar, about 600 liters remain (12 liters × 50 bar), theoretically supporting 3000-6000 inflations (each consuming 0.1-0.2 liters), but actually, due to unstable valve supply at low pressure, only 3-5 effective equalizations can be guaranteed. 

One diver once ignored the check and found the tank was only at 30 bar when descending to 3 meters. Data clearly shows: when the pressure is <50 bar, the effective gas output rate further decreases by 20%-30% in cold or murky water, and nervousness makes gas waste more likely.

Where is the Pressure Gauge

The dial is usually divided into three color zones: green (150-200 bar) marked "Full," yellow (50-150 bar) marked "Medium," and red (<50 bar) marked "Low." 

A common mistake for novices is only glancing at the pointer color without looking at the specific value: for example, the pointer just crosses the red line (48 bar), looking like "almost out of gas," but it can actually support 2-3 more inflations, but the risk has already increased.

Why is 50 bar the "Warning Line"

Taking a 12-liter, 200 bar tank as an example, the total gas storage capacity is equivalent to 2400 liters at 1 atmosphere (12 liters × 200 bar).

When the pressure drops to 50 bar, there are about 600 liters of gas remaining in the tank (12 liters × 50 bar), theoretically capable of supporting 3000-6000 inflations (600 liters ÷ 0.1/time = 6000 times)—but this is only the theoretical value.

In reality, the tank valve may not be able to stably supply gas at low pressure: when the pressure is below 50 bar, the force of the gas inside the tank pushing the valve weakens, which may lead to the situation of "hearing a leak first, and then gas coming out 1 second later" when inflating, resulting in an ineffective single inflation.

How Specific are the Problems of Insufficient Pressure

PADI (Professional Association of Diving Instructors) once documented a case: a diver, rushing for time, did not check the pressure and found the tank was only at 35 bar when descending to 4 meters. After ascending, the tank pressure had dropped to 28 bar, unable to complete subsequent equalization.

Data shows: When a tank pressure is below 50 bar, the effective gas output rate will further decrease by 20%-30% when used in cold water (below 10°C) or murky water—.

Check 10 Minutes in Advance

1. Look at the dial: Is the pointer in the green zone (150-200 bar)? If in the yellow zone (50-150 bar), you need to remember roughly how many times it can be used; if in the red zone (<50 bar), change the tank immediately.
   

2. Feel the tank body: If there is condensation on the surface of the tank, it may not have been dried after the last use, and there may be moisture inside, affecting the accuracy of the pressure gauge.
   

3. Shake it: Gently shake the tank and listen for any liquid sloshing sound—if there is, it means water (not air) has mixed in, and this tank should not be used as it will corrode the valve.

What to Do if the Pressure Gauge is Inaccurate

How Specific are the Problems of Insufficient Pressure

When descending to 3 meters, he pinched his nose and inflated as taught by the instructor, but each time he only heard a "hissing" leak sound, and his ears felt blocked and painfully muffled. He tried to inflate a few more times, and his ears began to sting, forcing him to abandon the dive; after ascending, checking the tank showed the pressure had dropped to 22 bar. 

DAN (Divers Alert Network) statistics show: Cases of ear pressure equalization failure due to insufficient tank pressure account for 22% of diving ear injury reports, and 15% of these result in temporary eardrum congestion.

Unstable Gas Supply

When the pressure is below 50 bar, the tank's gas supply efficiency decreases significantly. The valve design of mini air tanks relies on the internal tank pressure to push—at high pressure, the gas can quickly force the valve open and spray out; when the pressure drops below 50 bar, the force pushing the valve weakens, which may lead to a "leak first, then out" situation: when pinching the nose to inflate, the first 0.5 seconds there is a "hiss—" leak sound (gas overflowing from the valve gap), and then a small amount of air enters the nasal cavity. Real-world data: A 12-liter, 50 bar tank has an effective gas output of only 0.05-0.1 liters per single inflation (compared to 0.15-0.2 liters at normal pressure). Mike's situation was worse: his tank pressure was 45 bar, and the effective gas output per single inflation was only 0.03 liters, whereas equalizing ear pressure requires at least 0.1 liters (to increase middle ear pressure by 1-2 kPa).

Ear Pressure Imbalance

1. Muffled Feeling: The first inflation had no effect, and the ears felt covered, which is because the pressure difference between the inside and outside of the middle ear did not narrow (the external water pressure increases by 1 kPa for every 1-meter descent, with a difference of about 3 kPa at 3 meters).
   

2. Aching Pain: After repeated ineffective inflations, the middle ear mucosa becomes congested due to continuous pressure, and the ears change from feeling muffled to aching (Mike reached this stage at 5 meters depth).
   

3. Stinging or Hearing Blurring: If the descent is forcibly continued, the water pressure further increases, and the congested mucosa may be damaged by friction, resulting in stinging or temporary hearing loss (in severe cases, bleeding may occur).

Cold Water and Murky Water

• Cold Water (<15°C): Low temperatures cause the air in the tank to contract, reducing the actual gas volume by about 5%-8% at the same pressure. The water temperature on the day of Mike's dive was 12°C, and the 45 bar gas in the tank had an actual equivalent volume about 10% less than at 25°C, further reducing the effective gas output.
  

• Murky Water: In low visibility, divers pay more attention to the terrain below, easily ignoring ear discomfort. PADI instructor feedback: In murky water, ear pain caused by insufficient pressure is typically delayed by an average of 2-3 minutes before being noticed, by which time the middle ear may already be congested.

Recovery Time

Even with timely ascent, ear pressure imbalance caused by insufficient gas pressure can leave sequelae. After Mike's right ear became congested, it took him 3 days of using nasal drops and avoiding diving to recover—during this time, he missed 2 planned dives.

Medical statistics: Mild eardrum congestion requires 2-5 days to recover, moderate (accompanied by stinging) requires 7-10 days, and severe (bleeding) may require medical treatment, costing about 200-500 US dollars (including examination and treatment).

Slow Squeeze Tank at Two Meters

Upon descending to 2 meters, the water pressure reaches approximately 1.2 atmospheres (121kPa), and the pressure difference between the inside and outside of the middle ear begins to show. This is the critical juncture for using a mini air tank to equalize ear pressure. Common air tanks are 50-100ml capacity, pre-charged with 10-15bar compressed air (1bar ≈ 100kPa), sufficient to support multiple squeezes. During the operation, pinch the nose to seal the nostrils, keep the tank nozzle 5-8cm away from the nose wing, lightly press the valve at a uniform rate of 0.5 seconds/time, releasing about 0.1-0.15ml of air in a single release. The middle ear volume is only 0.5-1ml, requiring 2-3 inflations to complete, avoiding excessive single release (more than 0.3ml may cause aching pain). If there is a muffled feeling in the ear but no stinging, it means the pressure is gradually equalizing; if the aching pain intensifies, stop immediately and ascend to 1 meter, wait for the discomfort to subside, adjust breathing, and then try again. Repeat this operation every 5 meters of descent until the feeling of blockage in the ear disappears.

Why Start at 2 Meters

Starting to use a mini air tank to equalize ear pressure at a depth of 2 meters during diving is not arbitrary. Water pressure increases by 1 atmosphere (101kPa) for every 10 meters of depth. At 2 meters, the water pressure is about 121kPa (1.2atm), and the pressure difference between the inside and outside of the middle ear becomes noticeable—the middle ear volume is only 0.5-1ml, and the external pressure compresses the internal air, reducing its volume to 83% of the original, causing the eardrum to feel muffled. At 1 meter, the water pressure is 111kPa, and the pressure difference is so small that most people don't feel it; at 5 meters, the water pressure is 152kPa, the pressure difference doubles, and the Eustachian tube is difficult to open. 2 meters is exactly the starting point of "feeling it but not being uncomfortable," with high operational tolerance, and the air tank is sufficient; shallower is unnecessary, and deeper is too risky.

Water pressure increases linearly with depth; for every 10 meters of descent, the water pressure rises by approximately 1 standard atmosphere (101kPa). Upon descending to 2 meters, the total water pressure is about 121kPa (1 atmosphere + 2 meters of water pressure), at which point the pressure difference between the inside and outside of the middle ear has reached the perceptible threshold. The middle ear is an air-filled cavity with a volume of only 0.5-1ml, connected to the nasal cavity through the Eustachian tube. Normally, the Eustachian tube is closed most of the time, opening briefly only when swallowing or yawning to equalize pressure. When the external pressure increases due to descent, the air inside the middle ear is compressed—according to Boyle's law (at constant temperature, gas pressure is inversely proportional to volume), the pressure at 2 meters depth (1.2atm) will compress the air volume inside the middle ear to about 1/1.2 ≈ 0.83ml of the original volume, causing the middle ear pressure to be about 0.2atm (20kPa) lower than the external pressure. This pressure difference directly pushes the eardrum inward, and most people feel a muffled sensation in their ears at this point, with some sensitive individuals possibly experiencing slight aching pain.

If equalization starts at a shallower depth of 1 meter, the water pressure is only about 111kPa (1.1atm), and the middle ear pressure difference is only 0.1atm (10kPa), with most people feeling no obvious discomfort, making it easy to overlook the operation. Waiting until descending to 5 meters, the water pressure rises to 152kPa (1.5atm), and the middle ear pressure difference reaches 0.5atm (50kPa); at this point, the eardrum is more significantly pushed in, and the Eustachian tube requires greater external force to open. If an air tank is used at this point, more forceful squeezing is required (single gas input may exceed 0.3ml), which instead increases the risk of aching pain or even injury.

Another advantage of the 2-meter depth is high operational tolerance. At this point, the diver has just left the surface, and the movement rhythm is slower; if there are companions or an instructor on the surface, they can quickly ascend if discomfort occurs. At a deeper position (such as 10 meters), the water pressure is higher (202kPa), and the aching pain caused by ear pressure imbalance will be more severe; in a panic, misoperation (such as excessive squeezing of the air tank) may occur, leading to too much gas entering the middle ear (exceeding 0.3ml), causing ear pain or temporary hearing loss.

Furthermore, the gas capacity of the mini air tank (50-100ml) is also suitable for the operation starting at 2 meters. A 50ml air tank at 10-15 bar pressure releases about 0.1ml of air with each squeeze; at 2 meters, equalizing both ears requires 2-3 times (total gas input 0.2-0.3ml), and the remaining gas is sufficient to support multiple subsequent equalization operations down to about 10 meters. If starting at a deeper depth, gas consumption is faster, which may lead to the dilemma of running out of gas when needed.

How to Read Air Tank Parameters

When buying a mini air tank, the numbers and letters printed on the bottle are not just for show; parameters like capacity, pressure, and interface directly determine whether it can be used and how well it performs. First, look at the most intuitive capacity, commonly marked as "50ml" or "100ml"—this is not the volume of water it holds, but the total amount of compressed air. For example, a 50ml air tank with an internal pressure of 10bar (1bar ≈ 100kPa) is equivalent to 50ml × 10 = 500ml of air at normal pressure. During diving, each squeeze releases about 0.1ml of compressed air (even less actually enters the middle ear). Can 500ml of normal pressure air be squeezed 5000 times? No, because the tank pressure decreases with use: starting at 10bar, it's 5bar remaining after half use, and the airflow weakens. In reality, a 50ml air tank can be used for 30-50 equalization operations underwater, and a 100ml tank can last for 80-100 times—enough to handle multiple descents in a single dive.

Next, look at the pressure value, marked as "12bar" or "MAX 15bar" on the bottle. Pressure is the tank's "power source": low pressure (e.g., 8bar) results in weak airflow, possibly unable to push gas into the middle ear; too high pressure (exceeding 15bar) results in too strong an airflow when squeezing, easily causing excessive gas intake and ear pain.

10-15bar is the safe range—10bar ensures basic airflow, and 15bar handles deep water pressure (underwater pressure at 10 meters is 202kPa, and the tank pressure needs to be slightly higher than the ambient pressure to push the gas in). Choosing below 10bar might be insufficient at 5 meters; higher than 15bar, novices who can't control the force easily get injured.

Then there's the interface type, two common types: one is the "nasal tip style" with a thin soft tube, where the end of the soft tube has a small silicone head that can be placed directly against the nose wing; the other is the "direct spray style," where the nozzle is on the bottle and needs to be held by hand and aimed at the nose.

The bottle material is divided into plastic and aluminum alloy: plastic is light (about 30g) and less likely to crack when dropped, but it may age after long-term soaking in seawater; aluminum alloy is heavier (about 50g), durable but sinks. The bottle must be marked with "CE" or "EN 1808" certification—this is the European standard for diving equipment safety, ensuring the tank is resistant to high pressure and does not leak. Do not buy "three-no" tanks without markings; they might use recycled plastic, which is prone to bursting under high temperatures or impact.

Choose an aluminum tank with a capacity of 100ml, 12bar, a soft tube nasal tip, and a CE mark—sufficient capacity, moderate pressure, easy control with the soft tube, and safe material.

Specifics of Slow Squeezing

When descending to 2 meters, the water pressure is about 121kPa (1.2 atmospheres), and the air inside the middle ear is compressed to 83% of its original volume (0.83ml), and the eardrum already feels muffled. When using a mini air tank to equalize ear pressure at this time, "slow squeezing" is not just casually pressing the valve—squeezing too fast (e.g., 0.3 seconds/time) releases more than 0.15ml of compressed air in a single release, which may cause the middle ear pressure to temporarily exceed the external pressure, resulting in stinging; squeezing too slowly (1 second/time) leads to intermittent airflow, and the Eustachian tube doesn't open in time, resulting in low equalization efficiency. With a tank pressure of 10-15bar, the actual gas entering the middle ear with each squeeze is only 0.05-0.1ml; the middle ear volume is 0.5-1ml, so it must rely on 2-3 "slow squeezes" to accumulate. These data determine that "slow squeezing" must control the rhythm: 0.5 seconds/time, the nozzle 5-8cm away from the nose wing, and feel the "buzzing" feedback in the ear.

When squeezing, press the valve uniformly with the fingertip, maintaining a rhythm of 0.5 seconds/time: press down on the first count, and release on the second. Too fast (e.g., 0.3 seconds/time) instantly releases a large amount of gas from the tank, which may rush into the middle ear, causing aching pain; too slow (1 second/time) results in intermittent airflow, and the Eustachian tube doesn't open in time, leading to low equalization efficiency.

The nozzle or the end of the soft tube should be aimed at a position 5-8cm from the nose wing. Too close (less than 5cm) causes the airflow to spray directly onto the skin, dispersing the impact; too far (more than 8cm) weakens the airflow, unable to push the gas into the middle ear.

When squeezing, feel the feedback: if there is no feeling, it might be: 1. Incorrect squeezing speed (too fast or too slow); 2. Nozzle position offset; 3. The Eustachian tube is not open yet (e.g., a bit tense just after descending, muscles not relaxed).

Don't rush at this point; repeat 1-2 times, or perform a swallowing action first (like chewing gum) to relax the Eustachian tube, and then try again.

The amount of gas released in a single squeeze is very small—with a tank pressure of 10-15bar, it releases about 0.1-0.15ml of compressed air each time.

But the middle ear volume is only 0.5-1ml, so don't think about "squeezing more at once." Usually, 2-3 squeezes (total gas input 0.2-0.3ml) are needed to balance the middle ear pressure with the external pressure.

If there is still no feeling after 3 squeezes, it means the Eustachian tube has not opened; at this point, you should ascend 2 meters, adjust your breathing in a place with a smaller pressure difference, and try again when your body is relaxed.

Don't move immediately after squeezing—pause for 2 seconds to feel if the eardrum has returned to flatness. If there is still a muffled feeling in the ear, it means there might be a leak or the Eustachian tube hasn't fully opened; give a light extra squeeze (about 0.05ml), don't be greedy.