The first stage is based on the well-respected DS4.
It is, of course, environmentally sealed and has had a lot of thought put into maximising the surface area available for heat exchange to prevent icing, consequently avoiding those exciting freeflows that can make inland UK diving so much fun in the winter.
An over-moulded end-cap also helps to prevent freeflows, and adds some protection against impact damage for your beautiful new valve set.
The XL4 second-stage exhaust T and Comfobite mouthpiece.
An over-balanced diaphragm design allows the intermediate pressure in the hose between first and second stages to increase more quickly than ambient pressure on descent, and is claimed to improve performance at depth.
The first stage has four medium-pressure ports and a single high-pressure port for a contents gauge or sender to mate with your gas-integrated computer.
You might like to know that the first stage isn’t much larger than a gas-pressure sender unit. In fact, the whole kit and caboodle is neat and small and just yummy.
The new XL4 second stage is compact and lightweight to prevent jaw fatigue on long dives, and comes complete with the legendary Comfobite mouthpiece.
This features a bridge across the upper palate intended to make it easier to hold the second stage in your mouth without having to bite down on it.
Actually, Comfobite mouthpieces might not be legendary, but they ought to be. I’ve always used them, regardless of the make of reg I’ve used, and they work extremely well.
I’ve never bitten through a mouthpiece and never had to clamp my teeth down to feel that the second stage I was using was held securely in place.
The XL4 mouthpieces are retained with a reusable clip to make field replacement simple and easy.
To be fair, the octopus second stage doesn’t have a Comfobite, but then you’ll be handing that one to a less-discerning diver than yourself if the worst comes to the worst, and in a situation like that the receiving diver will be in no position to be picky over mouthpieces, and just needs to be grateful to have gas to breathe.
The second stages can be configured for left- or right-hand hoses. Each also features a +/- venturi control, pretty much standard equipment these days, and Apeks uses braided hose for better coldwater performance and lighter weight.