Prism Rebreather Teardown

During my recent trip to LaPaz I had the opportunity to check out and actually dive a Prism rebreather, albeit in only 15 feet of water and 1 foot of visibility (due to the intervention of Hurricane Marty).

I wish to thank Luke Inman and Sal Jorgensen at the Cortez Club in LaPaz (www.cortezclub.com) for their assistance and patience while I photographed and picked their brains about the unit. These guys got a hold of these fine rebreathers for their goal of tagging and tracking hammerhead sharks. Check back to my home page for more updates on progress on the Adopt a Shark program.

Here is a shot of the unit and Luke. The RB has dual over the shoulder counter lungs, this makes for a very nice work of breathing and this holds true in most swimming positions.

Unit in place. System comes with the Scubapro air2 for bc inflation and bailout.

The unit looks a bit large but in Luke’s words, I’m a little guy. Unit ready to dive is only 47 lbs, but the size of the counter lungs requires a bit more weight to get negative than, say, my Dolphin. The units specs say it is neutral when ready to dive.

This is really slick, an analog backup that reads all sensors, the state of the internal 9v battery, and the setpoint. The rotary knob at the top is a selector between the different functions.

This is the heads up display and shows nicely through the bottom right side of my mask during the dive. Adjustable for position, It has 3 leds that give info on battery life, ppo2, and alarms. This is nice but no replacement for looking at the primary analog gauge during the dive. The DSV has very robust construction and turning the closure knob could be done with one hand.

This is the main power, on/off switch, here it is strapped to the scubapro bc inflator/bailout. When you first turn on the unit it fires the solenoid and illuminates the LED’s on the HUD. The beauty of this unit is that even if the internal battery dies, you still can fly the thing manually using the o2 inject on the exhale CL and monitoring the PP02 on the analog display.

This is the top of the unit, there is a watertight cover that mounts over this compartment. Inside we see the 9v Duracell battery that will provide power for up to 40 hours of diving. The brass solenoid is on the right, fed by a ss line from the regulator. These connections are outside the breathing loop so that if any connection leaks it wont affect the PP02 in the loop. Breathing hoses thread into the top of the unit. Flow direction: exhale travels out the dsv and to the divers left into the exhale CL which doubles as a water trap and manual oxygen injection point, this CL also can be purged of water by a valve at the bottom, nice addition, beats dismantling and draining them on the deck of the boat like I have to do on my Drager. The flow continues over the divers left shoulder and into a chamber where the electronic oxygen injector is and then into the center of the axial scrubber canister. The injection point being before the scrubber helps to homogenize the mixture before the galvanic oxygen sensors and the inhale CL. The flow continues from the center of the scrubber out to the outer sheathing and back up into the top of the unit where the sensors are at and then out the inhale hose and down to the inhale CL. There is a ADV or automatic diluent addition valve on the right or inhale counter lung. There are three external electrical connections visible here go out to the two displays and the on/off switch.

Better view of the two display connections.

With the watertight caps off you can see the 3 calibration adjustments for the sensors and in the top spot is an adjustment for the setpoint. The unit has a depth sensor that controls whether the setpoint is at .7 or at the divers preset point, it remains at .7 until the diver goes beyond 18fsw. The AP valves folks could learn something here. This entire area is potted so even if the top cover floods the only thing ruined is the battery.

This is looking up into where the scrubber hooks to and shows the 3 galvinic sensors set into rubber rings that cushion them and hold them in place. The center hole is where the divers exhaled gas comes down, after the injection point and into the center of the scrubber canister. The last hole here is the path for the mix to go back to the diver, after the scrubber. The sensors have a 1 year dive life or 2 years in air. The system uses a voting logic to determine when to inject oxygen. I didn’t get a chance to see how well that worked as I dived it on manual in shallow water, but I understand that the system keeps the ppo2 to a close tolerance. This spot on the rb stays quite dry due to the design and placement of the water trap. The small posts you see coming out from the main housing are where the scrubbers external housing bayonet on with a push and short twist.

Look closely and you can see the scrubber pins as above. The system comes with 19cf aluminum cylinders and with about 6 lbs of scrubber you have quite a bit of bottom time at your disposal. The cap for the electronics is in place on this pic, at the top of the scrubber canister. The center of the scrubber sheath is knurled to make it eaiser to twist and lock in place. Nice touch. This housing is also quite durable and Luke says you could drop it off a building. I will take his word for it but it, like everything on this unit is well built. Oxygen is on the divers left side and dil on the divers right, the valves are easy to access and can be left on without using gas, something I have to remember on my Drager or my oxygen runs out between dives.

The bottom of the unit showing the Mark 2 regulators and the very neat plumbing. Cylinders and scrubber are held tight with nylon and Velcro straps.

Putting the scrubber cover in place.

One of the galvanic sensors.

Photo of the specs page of the manual.

So, in a nutshell, the Steam Machines inc. Prism rebreather looks like a great unit, it is fully closed, electronically logic controlled with manual operation, over the shoulder counter lungs, radial scrubber design, integrated BC with weight pouches, comes with everything needed to dive except scrubber material and gas. It uses off the shelf batteries, reliable regulators, is lightweight and simple to set up and use. Looks like I need to save my pennies though because the unit retails for $7800 usd and expect to pay around $1000 usd for training. Check out more details at www.steammachines.com

Thanks again to Luke and Sal of the Cortez Club for all their help, this is a great place to go diving, the shop is obviously rebreather friendly, with a supply of scrubber on hand as well as a great filling station. They offer certifications from PADI ANDI and DSAT and will soon offer certifications on the Prism RB. Luke is a PADI course director and can teach a dizzying range of courses. Look up the Cortez Club on your next south of the border vacation, you wont be sorry.