Introduction to Closed Cycle Refrigeration (CCR) Technology
Closed-circuit rebreathers (CCR) have revolutionized technical diving, offering significant advantages over traditional Open Circuit Scuba. The basic principle of CCR is exhaled gas recirculationUnlike open-circuit systems, where exhaled gas is expelled into the water (forming bubbles), a rebreather removes carbon dioxide (CO2) with the help of a special absorbent (soda lime) and then replenishes the oxygen (O2) level, creating an optimal breathing mixture. This process allows for longer underwater time, lower gas consumption and significantly reduces decompression time.
JJ-CCR philosophy and mechanical design
JJ-CCR is created with the philosophy of simple, robust and minimalist design, which makes it a reliable tool in difficult and cold environments, such as wrecks in the Baltic Sea, attests instructor Valters PreimanisThe device is based on durable aluminum housing and stainless steel stand, which serves as a rigid frame for all components, including cylinder mounts (usually two small O2 and diluent This design provides good stability both on land and underwater.
One of the most recognizable JJ-CCR features are placed over the shoulder (back-mounted) counterlungsThis position provides low breathing resistance (Work of Breathing, WOB), because the counterlungs follow the contours of the diver's shoulders, making breathing smooth and comfortable regardless of the diving position.
Electronically controlled PO_2 control (ECCR)
JJ-CCR is electronically controlled closed-loop rebreather (ECCR), which ensures accurate maintenance of the oxygen partial pressure ($PO_2$) in the breathing loop. The system electronics use three independent oxygen sensors (usually galvanic-chemical) $PO_2$ for level measurement.
- Oxygen Supply: The main maintenance mechanism of $PO_2$ is solenoid valve, which is controlled by a computer. It periodically injects pure oxygen when the $PO_2$ level drops below the set value (Set Point).
- Optimized Gas Usage: Unlike open-circuit diving, where $PO_2$ with a fixed nitrox mix continuously increases with depth (creating a high N2/He load during decompression stops), a rebreather maintains an optimal $PO_2$ level at all times (e.g. 1.2 – 1.4 Bar/ATA in depth and 0.7 – 0.9 Bar/ATA This allows for maximum use of oxygen and minimizes the intake of inert gases (nitrogen and helium), which significantly shortens decompression time.
Electronic Redundancy and Safety
Safety is a key consideration in CCR diving, and the JJ-CCR has several safety systems built into it:
- Redundant Power Supply: The device uses independent batteries for the main controller, Head-Up Display (HUD) and solenoid valve.
- HUD (Head-Up Display): In addition to the main controller, the HUD provides a visual, colored indication of the $PO_2$ status in the diver's field of view (green = OK, yellow/red = problem), which is critical for quick response.
- ADV (Automatic Diluent Valve): The automatic diluent valve compensates for gas loss in the loop (e.g. during ascent or after manual exhalation through the mouthpiece), ensuring that the tidal volume remains adequate.
- Manual Control: It should be emphasized that the JJ-CCR, like any ECCR, requires the diver to be trained to manually operate the systemThe diver should always be prepared to manually administer O2 or Diluent if the electronics fail.
Technical advantages and applications
The JJ-CCR is especially popular in technical diving – wrecks, caves, and deep expeditions.
- Depth and Time: The ability to maintain optimal $PO_2$ allows for much deeper and longer dives than with open cycle without exceeding toxicity (CNS O2) limits.
- Logistics: The rebreather uses only the oxygen needed for metabolism and minimal diluent gas. This significantly reduces the amount of gas required compared to open cycle, making expedition logistics easier.
- Acoustic Silence: The absence of bubbles makes diving silent, which is a significant advantage for underwater photography, filming, and close contact with marine animals.
On oxygen toxicity (CNS O2) in the context of CCR
“JJ-CCR radically changes the oxygen toxicity (CNS O2) control. In open-circuit diving with a fixed nitrox mixture, the diver has no control over $PO_2$ – it continuously and passively increases with depth, thus increasing the risk of toxicity with each meter of depth. In contrast, when working with JJ-CCR, the diver inhales the gas with constant, set $PO_2$ level (Constant $PO_2$), which the electronics maintain regardless of depth. In practice, this means that when setting Set Point to, for example, 1.3 Bar/ATA, we obtain constant increase in the CNS toxicity “clock” throughout the dive, which greatly facilitates risk calculations.
However, it is this constant $PO_2$ value throughout the dive profile, especially during long decompression stages with high $PO_2$ (e.g. 1.4 Bar/ATA), that requires the diver to follow very closely. for the cumulative CNS time limit and often change $PO_2$ Set Point to a lower value during decompression (e.g. to 0.9 Bar/ATA) in order to effectively manage the total exposure time and not exceed safety standards. This is the main advantage and at the same time the liability of CCR.”
