Best rebreather (CCR) for technical deep diving

Introduction – Why Your CCR Matters at 100 m+

When the helium bill climbs higher than the flight to your dive site, the last thing you want to doubt is your life support system. Choosing (and configuring) the right closed circuit rebreather (CCR) can make the difference between a textbook dive and a bailout scramble. In this guide we’ll walk through proven Liberty CCR setups for dives beyond 60 m / 200 ft, lay out the engineering that keeps them running, and share field feedback from the explorers who trust them at depth.

Who This Guide Is For

• Advanced recreational divers transitioning to their first CCR course or Mod 1 trimix training.
• Experienced trimix divers extending bottom times beyond recreational limits.
• Cave divers negotiating variable depth passages where diluent consumption spikes.
• Technical instructors spec ing student units for advanced courses.
• Expedition leaders planning multi hour decompression schedules.
• Whether you’re comparing units for your very first Mod 1 class or selecting a redundant stack for a 200 m project, this guide will help you choose—and configure—the right Liberty platform.

New to Technical Diving? Read This First

Before we plunge into deep end configurations, nail these fundamentals:
1. Training before hardware – Agencies like TDI, IANTD, BSAC or RAID insist on an air diluent CCR course (Mod 1) before any helium or cave curriculum. A solid foundation needs to be laid before tackling the hard stuff.
2. Entry level Liberty package – The standard Liberty Backmount with 2 × 3 L cylinders, single HUD, and 2 Liberty handsets meets every agency’s starter spec while lightening the rig for skill drills.
3. Service & mentoring network – New CCR divers lean on instructor and dealer support. Divesoft’s certified service hubs in 28 countries slash downtime the first time you flood a handset seal.

Keep these points in mind as you dive into the advanced chapters below; the engineering that keeps Liberty alive at 300 m also rewards your first 40 m deco dive.

What Makes Deep‑Rated CCR Setups Different?

Top Liberty CCR Setups for Deep Technical Diving

1. Liberty Backmount – The Expedition Workhorse

Ideal For: Trimix divers on multi stage open water descents, liveaboard operations.

Core Specs:

• 2.5 or 3.3 kg radial scrubbers
• Dual electronics
• Integrated BOV
• Why It Excels: Familiar twin set trim, easy cylinder switchover, and a backplate that matches standard DIR harness spacing.

2. Liberty Heavy – All in One Backmount

Ideal For: Divers who prefer a single back mounted system with integrated diluent and bailout, particularly in DIR/GUE style setups.

Core Specs:

• Electronics & scrubber architecture identical to Liberty Backmount)
• Cylinder accommodation: twin 7 L or twin 3 L steels plus 3 L oxygen centre mounted

• Integrated Liberty Heavy backplate & wing (25 kg lift) for familiar twin set trim

GUE Configuration – 2 × 7 L diluent + 3 L O₂

Pros: All gases on the back; uncluttered chest D rings for stage handling; single gas switch discipline.
Cons: Truly deep dives (>150 m) still call for extra off board stages; large diluent volume makes mix changes costly; loop diluent use depletes bailout reserve.

Lightweight Configuration – 2 × 3 L diluent

• Drops ~5 kg from rig weight yet keeps Heavy’s rigid chassis; ideal for travel or training dives ≤100 m.

Versatility & Ergonomics

• Cam bands accept varied cylinder diameters without shims.
• Backplate geometry mirrors standard DIR harness so divers keep muscle memory in the water.

3. Liberty Sidemount – The Tight Passage Specialist or as a secondary rebreather

Ideal For: Cave explorers, wreck penetrations, divers who prefer side mount cylinder distribution.

Core Specs:

• 2l oxygen & diluent cylinders
• Requires experience with multi-stage sidemount bailout
• Ideal as a bailout rebreather to backmount or second sidemount unit
• Why It Excels:

  • Streamlined profile keeps the loop off the floor in silty restrictions
  • Quick clip harness simplifies donning in small inflatables

4. Liberty DUAL (Liberty Backmout + Sidemount or Dual Sidemount)

Ideal For: Record depth attempts, commercial bell standby, filmmakers who simply cannot surface.

Core Specs:

• Two completely independent Liberty heads, loops & scrubbers
• Automatic master/slave handover on PO₂ deviation >0.2 bar for >30 s
• Weight: 34 kg in dive trim (without cylinders)
• Why It Excels:

  • Redundant loop in case of flooding the primary.
  • True two double brains redundancy: each half can drive its own solenoid & HUD.
  • Serves as self contained bail out – just one open circuit stage required for all depths.

Configuration Tips for Depth & Duration

Cylinder Size & Positioning

• 3 L steel diluent + 3 L O₂ covers 120 m descent with 20 min bottom and full CCR bail out margin.

• Push deeper? Clip on 7 L off board diluent.

Work of Breathing & Counterlung Placement

• Front mounted counterlungs (FMCL) sit high on the chest, keeping differential hydrostatic pressure minimal and work of breathing (WOB) as low as 1.8 J/L at 100 m — this is why the original Liberty FML remains the benchmark for deep mix dives.
• Back mounted counterlungs (BMCL) trade a slight WOB increase (~0.3 J/L higher in a 30° head up posture) for uncluttered chest D rings, crucial when you stage multiple bailout cylinders during deep descents.

• Choosing FMCL vs BMCL: If your dive plan involves long penetrations with frequent bailout cylinder handling (typical on 150 m ocean drops), many teams pick BMCL for workspace. For maximal respiratory comfort on fixed rope vertical descents, FMCL wins.

Off Board Diluent Strategy (Critical for Cave Profiles)

• Why it matters: Cave profiles surge through depth changes, forcing the loop to add gas constantly. An off board diluent stage prevents low volume warnings and keeps work of breathing down.
• Standard setup: 7 L aluminium left clip with QC 6 quick connect hose feeding the diluent MAV.
• Alternative (ADV manifold): Fit the Divesoft Off Board Manifold to the Automatic Diluent Valve – plug any off board bottle via QC 6 in seconds and swap or share gas under load.
• Carry a second off board diluent (travel mix) for the shallow exit and as contingency for CO₂ breakthrough bailout.
• Deco marathon? Off board your O₂ too: Plumb a QC 6 hose from the oxygen MAV so you can swap in a fresh high pressure O₂ bottle at the 6 m stop.

  • Connector orientation best practice: “QC 6 on oxygen should be male on the rebreather side, the opposite of diluent, to make misconnections physically impossible,” notes
    Tonda Ptáček, elite Czech cave explorer.

• Drill it: Practise feather drills and hose swaps so every teammate can donate or receive off board gas.

Bail Out CCR: Liberty SM as Redundant Life Support

Using a second Liberty Side Mount unit as bailout instead of stacking open circuit stages slashes drag and helium spend on >80 m dives. Liberty’s dedicated Bail out CCR firmware mirrors sensor status from the primary until activation, then runs fully independent once switched.
Master this only after a specialised course. The world’s first Bail out Rebreather curriculum was written by Jakub Šimánek (author of this article) in 2023 and is now taught under TDI/RAID.

Conclusion – Choosing Your Life Support Partner

Deep technical dives demand hardware that feels boringly reliable when everything else gets exciting. Liberty’s modular platform lets you pick the footprint (SM, Backmount, Heavy, or dual) that meets your risk envelope while keeping sensor voting, redundant electronics, and hot swappable batteries common across the line. Compare your mission profile against the tables above, and you’ll descend knowing your CCR is dialed long before you crack open the helium. Ready to spec your unit? Reach out to a Divesoft or chat with one of our instructors for a demo dive.

Author: Jakub Šimánek