The decades of expertise behind Mares and rEvo rebreathers have combined to create a unique semi-closed rebreather (SCR) like no other, the Mares Horizon SCR. Priding itself on innovation and safety, with sleek good looks to match, the Mares Horizon SCR rebreather has a unique design and scrubber system. Read on to find out more about the cutting-edge technology that is taking semi-closed rebreather diving to new levels.
Rebreathers allow you to breathe your air repeatedly. Put simply, the air you exhale enters a rebreather system that absorbs the CO2 you have breathed out and replaces the O2 you have used during your last breath.
Rebreathers have several sought-after advantages over open-circuit scuba apparatus, including a lack of bubbles and extended dive times. These advantages give you more time to explore the underwater world and allow you to get closer to marine life than ever before.
The Mares Horizon SCR does not need dedicated cylinders and can be used with standard nitrox cylinders. It provides warm, moist breathing gas and the lightweight system is perfect for traveling.
Mares and rEvo have left no stone unturned when they designed this fantastic system - the ergonomic design of the Mares Horizon even improves your trim, position and comfort in the water.
There are two key components of any scrubber system used in a semi-closed rebreather:
Together, they make up a scrubber system, which completes one important function: to remove carbon dioxide (CO2) from the exhaled gas as quickly and with as little friction as possible.
To achieve this function, the distance the gas travels through the semi-closed rebreather scrubber system needs to be just the right length. If the distance is too short, the contact time of the gas with the chemicals in the scrubber material is too brief. The CO2 will skip the material, which undoes the benefits of the scrubber material. If the scrubber system is too long, the work of breathing becomes difficult and limits performance.
Rebreather scrubbers contain granules that remove CO2 from your exhaled air. The type and size of scrubber granules are very important and affects:
It is critical to stay well within the manufacturer’s prescribed scrubber time. If the scrubber material has a large granule size, there is less surface area in contact with the carbon dioxide. A smaller granule size means a better active surface area but a higher breathing resistance. This need for precision is why we should use only manufacturer tested and approved products as a scrubber absorbent.
The gas plenum, or scrubber canister, is the housing of the scrubber material. This area should be warm, dry, and shelter the scrubber from impact. Most semi-closed rebreathers have their sensors and electronics located here. There are a variety of scrubber canister designs to choose from, including:
The axial canister is the most common design of scrubber canister. It consists of a tube filled with granules made of a variety of components, commonly calcium hydroxide, water, and a small amount of caustic sodium hydroxide.
The gas enters from the bottom of the canister and exits from the top, so the scrubber material saturates from the bottom upwards. This distance is the furthest the gas can travel. If we keep a good reserve distance from the end of the tunnel, it is a safe system design that makes it less expensive and easier to prepare. The Mares Horizon uses an axial scrubber system.
In a scrubber system with a radial design, the gas enters from the side through a mesh or sieve. The gas then travels through the scrubber material until it reaches the center tunnel, where it then travels upwards. The surface area of the scrubber material is much larger, making the work of breathing easier, and it uses all of the scrubber material more effectively.
The Mares Horizon uses a unique dual scrubber canister configuration. Two canisters are mounted in an axial, in a serial configuration to improve streamlining and reduce the size of the unit. Each canister holds approximately one kilogram of scrubber material, also called “absorbent” or “sorb”.
The two canisters are connected by a channel in the main case cover. The scrubber material that is closest to the point where gas flows into the scrubber canister is saturated first. The scrubber material in the far end of the scrubber canister should never become saturated because you will always change the scrubber material before it becomes completely saturated.
The scrubber system used in the Mares Horizon is only effective if the correct procedure for changing scrubber material is used. Each scrubber canister is labelled to avoid mistakes.
Start with two canisters that are filled with fresh scrubber material and follow these instructions:
During the refill and replacement phase of the cycle, half of the total scrubber material is discarded. Since you always discard the half from the top canister, where CO2 saturation begins, the scrubber material that is most saturated (or the material closest to the incoming gas) is always discarded first.
By placing the unused scrubber material in the lower cavity, we ensure that any CO2 that is not absorbed by the older material is captured by the fresh material in the second canister.
When compared to a single-canister system that completely replaces the scrubber material each time, this process increases the use of the scrubber material by about 50% without affecting safety.
The Mares Horizon TOP Marker
Confusing which scrubber canister contains fresh scrubber material is a potentially dangerous mistake. To help avoid this error, the Mares Horizon includes a “TOP marker”. This marker is a small indicator that is installed on the top of the canister in the upper cavity over the exhale lung.
To prevent any mistakes, you should follow this procedure exactly:
Experience a new horizon – SSI SCR DIVING.
Dive into the world of rebreather diving with the SSI SCR Diving program. In this entry-level rebreather program, you will learn all you need to dive safely with the Mares Horizon rebreather up to 30 meters deep. It is the perfect introduction to rebreather diving, and you can start this certification online today.