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Four unbalanced first stages for single-tank recreational diving and dedicated argon inflation systems. The Diana series — chrome and Duratek black — provides a reliable DIN unbalanced design for standard diving. The Argon and Argon + OPV first stages are purpose-built for drysuit argon circuits, where a lightweight dedicated inflation system is used separately from the main breathing supply.
Unbalanced First Stage Design
An unbalanced first stage delivers intermediate pressure that varies with cylinder fill level. As cylinder pressure drops, so does the delivered IP — by a small but measurable margin. In practical terms, this means the diver experiences marginally increased breathing effort as the tank empties. For recreational diving on full cylinders with short bottom times, this variation is minor enough to be functionally irrelevant. For technical diving with extended bottom times and cylinders run well below half fill, balanced designs are preferred.
The Diana series — 1.St 1010 Diana bright chrome and 1.St 1010 Diana Dur. BK — is the recreational unbalanced option. It is straightforward to service, has fewer internal components than balanced diaphragm designs, and provides reliable performance for its intended application.
The Argon First Stage
The 1.St Argon and 1.St Argon + OPV are not general-purpose regulators. They are single-function first stages designed exclusively for drysuit argon inflation circuits. Argon has approximately 67% lower thermal conductivity than air, making it significantly better as an insulating gas inside a drysuit at depth. An argon system uses a small dedicated cylinder (1–3l) carried separately from breathing cylinders, with its own first stage, LP hose, and drysuit inlet connection.
The OPV (over-pressure valve) variant adds an automatic vent that prevents over-pressurisation of the small argon cylinder. On a sealed argon cylinder left in a warm car or storage area, trapped gas can expand; the OPV allows safe venting. The Argon first stage is not rated for breathing gas — it must not be used as a primary or backup breathing source.
What to Look For
- Diana for recreational single-tank: The Diana is a practical choice for divers who do not require balanced performance — open water recreational divers on standard air or nitrox fills with relatively short bottom times. It is DIN, available in chrome and Duratek black, and uses standard service components.
- Argon vs. Argon + OPV: If you transport your argon cylinder assembled and pressurised, the OPV variant is the safer option. If you always depressurise the cylinder before transport, either variant is appropriate. The OPV provides an automatic safety mechanism but adds a small amount of weight and an additional component that can require servicing.
- Argon cylinder size: A 2l argon cylinder at 200 bar provides 400l of gas — enough for most cold water technical dives. Confirm the argon first stage DIN rating matches your cylinder valve specification.
- Dedicated hose for argon system: The argon circuit requires a separate LP hose running from the argon first stage to the drysuit inlet. This is a distinct hose from the breathing circuit hoses and should be clearly identified (typically with a bungee or colour-coded tie) to prevent confusion.
- Service simplicity: Unbalanced piston first stages like the Diana have fewer internal parts than diaphragm balanced designs and are straightforward to service. Service kits for Diana are available in the Replacement Parts category.
Maintenance and Care
Rinse Diana first stages in fresh water after every dive with the DIN cap installed. Annual service is recommended for regulators in regular use. For argon systems, the Argon first stage should be serviced on the same schedule as breathing regulators despite lower cycle counts — static storage under pressure still stresses o-rings and seals over time. The OPV on the Argon + OPV variant should be checked during service to confirm it opens and reseats correctly at the design pressure. Argon first stages must be cleaned with oxygen-compatible lubricant if there is any possibility they will contact high-fraction oxygen, but this is not a standard argon system requirement.
FAQ
Can I use an unbalanced first stage for technical diving?
Technically possible but not recommended for demanding profiles. Unbalanced first stages deliver increasing breathing effort as tank pressure falls. For recreational dives where cylinders are not run below 50 bar, this is acceptable. For technical diving — twin tanks, sidemount, or extended range dives where cylinders are run to lower pressures or where consistent breathing effort throughout the dive matters — balanced first stages are the appropriate choice.
Why use argon instead of air in a drysuit?
Argon has significantly lower thermal conductivity than air — approximately one-third as much heat transfer per unit of time. At depth, the drysuit inflation gas becomes the primary insulation medium rather than the undergarment alone. Inflating with argon rather than air substantially reduces heat loss through the suit, which matters for cold water technical dives with long bottom times. The additional complexity and weight of a separate argon cylinder and first stage is considered worthwhile for extended cold water dives below 10°C.
What is the OPV on the Argon + OPV first stage?
OPV stands for over-pressure valve. On the Argon + OPV first stage, it is an automatic safety valve that vents gas if the pressure in the cylinder exceeds a set threshold. This protects the small argon cylinder and connected hose from over-pressurisation during storage or transport in warm conditions. The standard Argon first stage without OPV is functionally equivalent for diving purposes; the OPV adds a safety feature relevant to storage and transport scenarios.
Is the Diana available in INT (yoke) connection?
The Diana is listed in DIN configuration. Some Sopras Tek first stages support INT adapters; check the product detail page for available connection options. DIN is generally preferred for technical and European recreational diving. If INT connection is required, an adapter can convert a DIN first stage to accept yoke-mounted valves.
How large an argon cylinder does the Argon first stage work with?
The Argon first stage is compatible with standard small DIN cylinders used in argon systems, typically 0.4l to 3l capacity. The most common configuration is a 2l cylinder at 200 bar providing approximately 400 litres of argon — sufficient for most cold water technical dives. Cylinder size selection should account for dive duration, suit inflation frequency, and depth. Larger cylinders add weight and bulk; most experienced technical divers settle on 1–2l as an appropriate balance.