Undersea personal filter naked with cartridge

On a Red Sea liveaboard or a Mediterranean cave-diving trip, you rarely know the full maintenance history of the compressor used to fill your cylinders. Oil vapour, moisture and odour contamination are invisible under pressure — and the consequences of contaminated breathing gas in overhead environments are severe. The UNDERSEA 6300 fits between fill hose and cylinder valve, acting as a last line of defence before compressed air enters your tank. Precision-machined from HE30 aerospace aluminium alloy and hard-anodised blue, this British-made inline filter has been the choice of travelling technical divers since UNDERSEA pioneered high-pressure accessories in Southampton in 1970.

Technical specifications

• Manufacturer reference: 6300
• Body material: HE30 aluminium alloy, blue hard-anodised
• Maximum service pressure: 414 bar
• Proof pressure: 850 bar
• Dimensions (excluding fittings): 250 × 55 mm diameter
• Maximum recommended flow rate: 283 L/min (16.8 m³/h)
• Cartridge autonomy: approximately 50 fills of 12-litre cylinders on correctly pre-filtered air
• Standard connections: G1/4 female both ends — bare version, no adapters included
• Filter cartridge supplied: molecular sieve + activated carbon (~85 cm³ filter media)
• Non-return valve (NRV): not included — strongly recommended for nitrox fills to prevent oxygen backflow
• Pure oxygen service: prohibited (adiabatic compression risk of activated carbon auto-ignition)
• Modular design: inlet and outlet fittings replaceable with DIN 200, DIN 300 or M26 thread standards

Recommended uses

Key strengths

• HE30 hard-anodised aluminium body: aerospace alloy delivering strength-to-weight ratio and salt-water corrosion resistance
• 850 bar proof pressure, more than twice the maximum service rating: structural safety margin well beyond industrial standards for high-pressure breathing air
• Dual-media cartridge (molecular sieve + activated carbon): simultaneous removal of water vapour, hydrocarbon vapours, oil traces and organic contaminants
• Bare modular design: choose only the connections you need — no wasted spend on adapters already in your kit
• 283 L/min rated flow: matches high-capacity compressors up to 16 m³/h without restricting fill speed
• UNDERSEA pedigree since 1970: replacement cartridge (ref. 0520) permanently available; UNDERSEA products are stocked and supported by specialist technical diving retailers across Europe and the US

Product information

Note on service pressure: UNDERSEA commercial documentation cites 300 bar for the G1/4 BSP fittings supplied as standard. The filter body maximum service pressure, confirmed by authorised distributors, is 414 bar with a proof pressure of 850 bar. For cylinders filled above 300 bar, replacing the G1/4 fittings with rated DIN 300 high-pressure connections is recommended.

For compressed breathing air quality guidelines applicable to UK recreational and technical diving: refer to BSAC (British Sub-Aqua Club) technical guidance.

Official documentation