There are two primary types of recreational closed-circuit rebreather: electronically controlled CCRs, commonly referred to as an eCCR, and mechanical CCR or mCCR. The greatest difference between mCCR’s and their electronic counterparts is that they do no rely on complex electronic systems such as oxygen injection valve’s or solenoid’s to add oxygen to the breathing loop. Instead, they use simpler mechanical components that are less susceptible to failure in a wet environment.
Many divers feel that an mCCR provides a greater margin of safety. If any one of a number of electronic components of an eCCR fail—including the oxygen sensors, the CPU governing the solenoid, or the solenoid itself—the system may not continue to deliver a safe level of oxygen to the diver. To help overcome this shortcoming, most eCCRs also have modes of operation that will allow the diver to operate the unit manually should the electronics fail. These systems are not always the most intuitive, however, and too often, eCCR divers succumb to the temptation of complacency, and are not prepared to handle manual overrides when the electronics fail. And based on real-world experience, failure is not a matter of if, but when.
mCCRs, due to their relative simplicity as compared to eCCRs, have far less dependency on on-board electrical components. The oxygen sensors embedded in these units—usually three, but sometimes more—are used to report on oxygen levels rather than control them. Additional electronic components can be as simple as a basic PPO2 display that is wired to the sensors to show real-time PPO2 levels. Instead of a solenoid, oxygen addition uses “leak technology,” meaning it flows at a measured rate through either a variable-flow or mass-flow valve whenever the oxygen supply valve is opened.
In 1998, KISS Rebreathers became the first company to incorporate a mass-flow addition system that also included a Manual Add Valve (MAV) into a recreational rebreather.
From that start, KISS Rebreathers still retains one of the highest safety records of any commercially built closed-circuit rebreather for recreational/technical diving use. eCCR divers who dive their rebreather’s manually must pay constant attention to oxygen addition, as the diver adding oxygen is the only way the gas will flow into the system. Not so with KISS mCCR’s as oxygen is added first by the mechanics of the mass-flow system with the diver only needing to augment oxygen levels manually as/when needed.
The advantage of using a small orifice in a mass flow valve introduces fresh oxygen at a constant, low rate of flow that closely matches the diver’s own metabolic rate, eliminating the large spikes in PPO2 that are more likely to occur with exclusively manual addition systems.
All KISS mCCR units use MAV Technology.