IDA-59
Its a Russian military submarine escape rebreather. Originally designed for submarine escape upto a depth of 300m. But also rated to 90m for 'light work'! I've adapted it for civilian use. This unit required all its old cylinders (o2 and trimix diluent tank), plus its gas pneumatics basically stripped out and binned. There are examples out there where the owners have made use of its constant mass flow feed on the o2 regulator, but its a down right faff. Much simpler to make use of a kiss valve.
o2 is fed via the kiss valve into the counterlung (worn around your neck), as is diluent via its inbuilt ADV. The ADV sits at the back of the counterlung at the back of your neck. Breathes 'ok'. I upgraded the DSV with a Drager Ray, but have since switched back to a Russian IDA-71 DSV. The angle of the hose ports sit well. PPo2 monitoring was added via a P port directly into the counterlung close to where diluent is injected to keep moisture on the cells to a minimum, and high up. The 'stock' DSV is really well made, but work of breathing is poor. They were really only designed for submarine escape in an upwards direction.