Info Technical Discussion | HOTDIVE Diving Equipment Development

[kdlv]

Seriously who cares about your stupid equipement? I would never ever buy anything from a company so useless it cannot correct an infected website even when it has been pointed out to them.

Which website are you referring to?
I see nothing wrong with HOTDIVE SCUBA

 

[Mobulai]

The original Hotdive . CN , all I get is that it’s down for a while now anyway

Which website are you referring to?
I see nothing wrong with HOTDIVE SCUBA

 

[HotDive(Hide In Ocean)]

Seriously who cares about your stupid equipement? I would never ever buy anything from a company so useless it cannot correct an infected website even when it has been pointed out to them.

I’ve already explained this to you before, and we are trying our best to improve. If you still don’t like it, feel free to disregard it. I may not fully understand where your anger is coming from, and perhaps life has been bringing you too many troubles lately.
keep smiling, life is going to better!

 

[Tanks A Lot]

I appreciate you sharing information here; it is rare for a company to put themselves out there like this. I would love to get feedback on the following points:

​

1. Oxygen Service​

You use stainless steel extensively in your regulator line-up. I understand the appeal of a more corrosion-resistant material, but I see several critical points that should be addressed, as stainless steel has significantly inferior thermal properties compared with C36000 brass.

• Iron(III) oxide has a standard molar enthalpy of around –1100 kJ/mol, while copper (the main component of brass) has only about –150 kJ/mol. This is especially concerning with respect to particle impacts and high-oxygen usage.
• A similar picture emerges when considering heat of combustion. Brass generates approximately Δh of around 2.9 kJ/g, whereas steels produce well above 7.5 kJ/g; at least twice the amount. This means that if a small portion of material were to ignite, stainless steel is far more likely to sustain a fire and be part of the kindling reaction, whereas brass could possibly extinguish it naturally.
• Brass also has significantly higher thermal conductivity; around four times that of stainless steel. In oxygen service, this helps to spread local hotspots, such as those from adiabatic heating, reducing the risk of ignition.

​

2. Cold Water Performance​

As noted above, brass is a far better thermal conductor. This aids in heat (or more accurately, cold) dissipation after the orifice edge. Similar piston designs made from brass have been shown to comply with EN 250 cold-water requirements. How does the S1 perform under cold conditions? The use of stainless steel would suggest that it may not pass the cold-water auxiliary test.

3. Galvanic Corrosion​

316L stainless steel is high in the galvanic series, well above brass and chromium. Hoses are almost universally made from free-machining brass (C36000) or similar alloys. This introduces an inherent problem in the design: a “big cathode, small anode” effect, where the mass of the first stage is vastly larger than that of the hose end.
Are you mitigating this risk somehow? If not, and it is truly not an issue, I would be interested to understand why. The underlying physics and chemistry are straightforward, and I have seen similar setups in oxygen units where this caused major problems. The standard electrode potentials of brass, chromium, and 316L stainless steel differ significantly, making galvanic corrosion a likely possibility.

​

4. Filter​

From the pictures, it appears that you use flat polymer filters. I have nothing against polymer filters in principle, as I understand they help reduce cost. However, I assume you are not using these polymer filters in your oxygen units, as they would be utterly out of place. Are you using sintered bronze filters, as is standard in the diving and medical oxygen industry, or stainless steel mesh filters? If stainless steel mesh is being used, how are you mitigating what I see as a very high risk of oxygen fire within the filter? Literature repeatedly shows that stainless steel mesh is incompatible with oxygen service.¹

I am not a fan of disc filters; would it not be possible to use a conical design, even without incurring the cost of a sintered bronze filter? The small surface area of a disc filter is inferior to a conical shape for safety and flow distribution. Flat discs clog up much quicker than their conical siblings.

---

Again, thank you for giving us the opportunity to ask questions about some of these design choices, I always enjoy getting an engineers perspective.

¹ ASTM - Flammability and Sensitivity of Materials in Oxygen-Enriched Atmospheres, 10th Volume (2003), among many others.

 

[chrisch]

I’ve already explained this to you before, and we are trying our best to improve. If you still don’t like it, feel free to disregard it. I may not fully understand where your anger is coming from, and perhaps life has been bringing you too many troubles lately.
keep smiling, life is going to better!

I am not angry - I am laughing at you. You really think you stand a chance as a business when you can't run a website?

Best of luck with the kit - you will need it.

 

[HotDive(Hide In Ocean)]

I appreciate you sharing information here; it is rare for a company to put themselves out there like this. I would love to get feedback on the following points:

​

1. Oxygen Service​

You use stainless steel extensively in your regulator line-up. I understand the appeal of a more corrosion-resistant material, but I see several critical points that should be addressed, as stainless steel has significantly inferior thermal properties compared with C36000 brass.

• Iron(III) oxide has a standard molar enthalpy of around –1100 kJ/mol, while copper (the main component of brass) has only about –150 kJ/mol. This is especially concerning with respect to particle impacts and high-oxygen usage.
• A similar picture emerges when considering heat of combustion. Brass generates approximately Δh of around 2.9 kJ/g, whereas steels produce well above 7.5 kJ/g; at least twice the amount. This means that if a small portion of material were to ignite, stainless steel is far more likely to sustain a fire and be part of the kindling reaction, whereas brass could possibly extinguish it naturally.
• Brass also has significantly higher thermal conductivity; around four times that of stainless steel. In oxygen service, this helps to spread local hotspots, such as those from adiabatic heating, reducing the risk of ignition.

​

2. Cold Water Performance​

As noted above, brass is a far better thermal conductor. This aids in heat (or more accurately, cold) dissipation after the orifice edge. Similar piston designs made from brass have been shown to comply with EN 250 cold-water requirements. How does the S1 perform under cold conditions? The use of stainless steel would suggest that it may not pass the cold-water auxiliary test.

3. Galvanic Corrosion​

316L stainless steel is high in the galvanic series, well above brass and chromium. Hoses are almost universally made from free-machining brass (C36000) or similar alloys. This introduces an inherent problem in the design: a “big cathode, small anode” effect, where the mass of the first stage is vastly larger than that of the hose end.
Are you mitigating this risk somehow? If not, and it is truly not an issue, I would be interested to understand why. The underlying physics and chemistry are straightforward, and I have seen similar setups in oxygen units where this caused major problems. The standard electrode potentials of brass, chromium, and 316L stainless steel differ significantly, making galvanic corrosion a likely possibility.

​

4. Filter​

From the pictures, it appears that you use flat polymer filters. I have nothing against polymer filters in principle, as I understand they help reduce cost. However, I assume you are not using these polymer filters in your oxygen units, as they would be utterly out of place. Are you using sintered bronze filters, as is standard in the diving and medical oxygen industry, or stainless steel mesh filters? If stainless steel mesh is being used, how are you mitigating what I see as a very high risk of oxygen fire within the filter? Literature repeatedly shows that stainless steel mesh is incompatible with oxygen service.¹

I am not a fan of disc filters; would it not be possible to use a conical design, even without incurring the cost of a sintered bronze filter? The small surface area of a disc filter is inferior to a conical shape for safety and flow distribution. Flat discs clog up much quicker than their conical siblings.

---

Again, thank you for giving us the opportunity to ask questions about some of these design choices, I always enjoy getting an engineers perspective.

¹ ASTM - Flammability and Sensitivity of Materials in Oxygen-Enriched Atmospheres, 10th Volume (2003), among many others.

Thank you for your interest in our products and for raising such engaging questions. Your questions are highly professional, and I will address them one by one.

 

[HotDive(Hide In Ocean)]

1. Oxygen Service​

You use stainless steel extensively in your regulator line-up. I understand the appeal of a more corrosion-resistant material, but I see several critical points that should be addressed, as stainless steel has significantly inferior thermal properties compared with C36000 brass.

• Iron(III) oxide has a standard molar enthalpy of around –1100 kJ/mol, while copper (the main component of brass) has only about –150 kJ/mol. This is especially concerning with respect to particle impacts and high-oxygen usage.
• A similar picture emerges when considering heat of combustion. Brass generates approximately Δh of around 2.9 kJ/g, whereas steels produce well above 7.5 kJ/g; at least twice the amount. This means that if a small portion of material were to ignite, stainless steel is far more likely to sustain a fire and be part of the kindling reaction, whereas brass could possibly extinguish it naturally.
• Brass also has significantly higher thermal conductivity; around four times that of stainless steel. In oxygen service, this helps to spread local hotspots, such as those from adiabatic heating, reducing the risk of ignition.

You are absolutely correct. Brass does indeed possess some inherent advantages in oxygen service, particularly its higher thermal conductivity and lower heat of combustion, which help dissipate heat and reduce the risk of ignition. Therefore, brass has long been considered a safe and reliable choice for many oxygen applications.
However, 316L stainless steel, when properly cleaned and maintained, is also widely recognized as suitable for oxygen environments. The key point is that stainless steel requires a sufficiently strong ignition source to sustain combustion. We employ numerous processes to mitigate these risks. Through proper design and strict oxygen cleaning procedures, 316L stainless steel components can operate safely even in high-oxygen environments.

I have summarized the potential risks of stainless steel regulators in high-purity oxygen service and our effective mitigation methods:

1. Ignition & Combustion Risk
Sources of Risk:

• Particle Impact Ignition: Under high pressure, particles (such as metal chips or dust) carried by the oxygen flow can generate heat upon impacting internal surfaces, potentially initiating ignition.
• Ignition from Surface Contaminants: Organic residues or combustible materials such as leftover oils, cutting fluids, and metal particles from machining are excellent ignition sources in high-pressure oxygen environments.

Our Solutions:
We implement a comprehensive cleaning process to ensure all components meet strict oxygen service standards:

• Degreasing & Decontamination: Thorough removal of all hydrocarbon residues using ultrasonic cleaning and specialized solvents.
• Pickling & Passivation: Acid solutions (e.g., nitric acid) remove surface oxides and embedded metal particles, followed by passivation to form a dense, chemically stable chromium oxide protective layer.
• Alkaline Cleaning: Hot alkaline solutions effectively remove organic contaminants and fingerprints.
• Hydro-Polishing / Flow Polishing: High-precision polishing of internal flow paths to achieve a surface roughness of Ra < 0.2 μm, significantly reducing flow resistance, eliminating particle retention points, and fundamentally decreasing frictional heating and adiabatic compression risks.

2. Material Degradation
Sources of Risk:

• Metal Oxidation: 316L stainless steel, with its excellent chromium oxide passivation layer, exhibits outstanding stability in ambient high-oxygen environments, without the dezincification or stress corrosion cracking seen in brass.
• Non-Metallic Material Aging & Combustion: Standard seal materials (e.g., NBR, EPDM) are incompatible with high-concentration oxygen, accelerating aging and easily becoming fuel.

Our Solutions:

• Corrosion Resistance Validation: Our stainless steel regulators have passed 1512-hour neutral salt spray testing (ASTM B117), demonstrating extreme corrosion resistance far exceeding conventional industrial standards, reaching marine-grade performance.
• Oxygen-Compatible Seals: FKM/Viton® O-rings are used. The high bond energy of the C-F bond (485 kJ/mol) provides excellent thermal stability and oxidation resistance, making it the industry-standard choice for high-pressure oxygen service.
• Lubrication: We use CHRISTO-LUBE® MCG111, a fully fluorinated grease thickened with PTFE, capable of operating under extreme temperatures with excellent oxygen compatibility. It is highly compatible with metals, plastics, and elastomers. This medium-consistency fluorinated lubricant is particularly suitable for valves and regulator components. CHRISTO-LUBE® MCG111 meets MIL-PRF-27617G Types I, II, and III, and is NSF H-1 registered, meaning it can be used in or around food processing equipment. NSN: 9150-01-441-9016. MCG111 silicone grease has extremely low vapor pressure and excellent thermal stability, preventing decomposition or combustion in high-pressure oxygen environments. It is mainly used on regulator O-rings, valve stems, and threads to reduce friction and avoid mechanical ignition.
• Currently, we only use FKM/Viton® seals and MCG111 silicone grease on certain specific models.

3. Contamination from Gas Supply
Sources of Risk:

• Contaminated gas (water, oil, particulates, CO/CO₂) is a primary external factor leading to regulator blockage, corrosion, or even chemical explosions. Even the cleanest regulator cannot handle continuous input of contaminants.

Our Solutions:

• System Design Philosophy: We adhere to the principle that “a clean gas supply is the first prerequisite for safety.” Oxygen-compatible regulator design can only be effective under clean gas supply conditions.
• Gas Handling & Monitoring:
  We recommend using high-quality filters (combining coalescing filters, activated carbon, molecular sieves, etc.) between the gas source and regulator to remove oil mist, moisture, and particulates. The gas used in our regulator tests undergoes compression (with built-in compressor filtration) + condensation + separate filtration.
• Importance of Clean Gas Supply: Only with pure gas can the high-oxygen compatibility design of the regulator truly function.

Mature Applications Across Industries:

• Medical Oxygen Systems — 316L components are widely used in hospital central oxygen pipelines, ventilators, and anesthesia machines in direct contact with medical oxygen.
• Aerospace & NASA Applications — 316L stainless steel is explicitly approved for oxygen systems when proper cleaning standards are met (e.g., ASTM G93, NASA-STD-6001).
• Hyperbaric Oxygen Chambers — Valves and fittings in medical and diving oxygen chambers are often made of 316L stainless steel.
• Food & Pharmaceutical Production — In oxygen-enriched cleaning and sterilization processes, 316L stainless steel pipes and valves are widely adopted for their corrosion resistance and cleanliness.

These examples demonstrate that while brass remains an excellent choice, under appropriate conditions and proper engineering practices, 316L stainless steel is also a proven and reliable material for oxygen applications.

I will take some videos or photos in the production workshop during my spare time and keep sharing them with you. I hope you will find them interesting.

 

[HotDive(Hide In Ocean)]

2. Cold Water Performance​

As noted above, brass is a far better thermal conductor. This aids in heat (or more accurately, cold) dissipation after the orifice edge. Similar piston designs made from brass have been shown to comply with EN 250 cold-water requirements. How does the S1 perform under cold conditions? The use of stainless steel would suggest that it may not pass the cold-water auxiliary test.

Thank you for raising this question about cold-water performance. The Hotdive S1 is not designed as a cold-water regulator. It is an unbalanced piston model, primarily developed for warm and moderate water environments. Under these conditions, it provides excellent stability, with a simple structure, strong reliability, and very low maintenance requirements, which is why it has become very popular among dive centres and training schools.

For diving in cold waters or even under ice, we recommend our S3. The S3 features a balanced diaphragm design, constructed from SUS316 stainless steel, and incorporates environmental sealing and thermal conductivity optimisation to enhance cold-water performance. It was specifically developed for low-temperature diving scenarios. I will post a detailed introduction about S3 later. Regarding the concern of whether stainless steel can pass cold-water auxiliary testing, I have a strong answer: we have customer feedback reporting successful dives with the S3 in the Arctic Circle, at water temperatures as low as -2°C.

 

[HotDive(Hide In Ocean)]

3. Galvanic Corrosion​

316L stainless steel is high in the galvanic series, well above brass and chromium. Hoses are almost universally made from free-machining brass (C36000) or similar alloys. This introduces an inherent problem in the design: a “big cathode, small anode” effect, where the mass of the first stage is vastly larger than that of the hose end.
Are you mitigating this risk somehow? If not, and it is truly not an issue, I would be interested to understand why. The underlying physics and chemistry are straightforward, and I have seen similar setups in oxygen units where this caused major problems. The standard electrode potentials of brass, chromium, and 316L stainless steel differ significantly, making galvanic corrosion a likely possibility.

You are correct on this point. From an electrochemical perspective, 316L stainless steel indeed ranks higher than brass in the galvanic series, which theoretically could pose a “large cathode/small anode” galvanic corrosion risk when used in conjunction with brass. My primary recommendation is for our customers to pair stainless steel regulators with hoses that have stainless steel fittings. Using brass fittings generally does not cause significant issues either.

This is because the external surfaces of brass components are usually chrome-plated, and under normal conditions, brass does not come into direct contact with stainless steel regulators. If “brass—stainless steel regulator” direct contact does occur, it indicates that the chrome plating has been corroded or worn off, exposing the base material. In this case, the root cause of corrosion is not the presence of stainless steel, but rather plating failure. Moreover, once brass is directly exposed to seawater, it is already subject to corrosion.
In contrast, 316L stainless steel has a natural passive film (chromium oxide layer) that can regenerate even if the surface is scratched, without relying on plating. This makes it more durable in diving environments.
From a galvanic corrosion perspective, the electrochemical potentials of 316L stainless steel and chrome are close, so there is almost no significant potential difference between them. The real difference lies between brass and stainless steel, but if the chrome plating on the brass remains intact, such contact is almost nonexistent under normal use. Therefore, the key is to regularly inspect and maintain the plating on brass components to prevent potential galvanic corrosion.

In other words, if a brass fitting and a stainless steel regulator do come into direct contact, it is already a sign of plating failure, not a “new problem caused by the stainless steel material.”

 

[HotDive(Hide In Ocean)]

I have compiled answers regarding these issues: Oxygen Service, Cold Water Performance, Galvanic Corrosion, and Filter. Please review them, and new questions are welcome.