The Cis-Lunar Rebreather

I first began my interest in rebreathers during a technical diving trip aboard the Nautilus Explorer, where I met several divers who remain friends and dive buddies to this day. I was diving a set of twin 112cf cylinders and a pair of deco cylinders, doing excursions down to the 300 fsw and complaining about the weight of all the gear necessary to do this level of dives. (I have compression fractures in my back from a car running into me about 8 years ago) Alan Studley was one of the divers I met on this trip and as I drooled over his Drager Dolphin (knowing nothing about RB’s at this time, or the differences between them), he was drooling over a KISS RB that was being used by Greg Grant, marveling at its simplicity and ease of maintenance. (there was a considerable amount of drooling going on during this dive trip) After I returned home I began an exhaustive search on the web about rebreathers and how they work. One of the articles I came across was the one written by Rich Pyle entitled “A beginners guide to Rebreathers” and was as such introduced to the Cis-lunar RB, invented by Bill Stone. For those of you who have read Richie’s article, you know how complicated he makes the unit sound, and to the RB initiate, it was daunting. Several years later, I find myself staring at a Cis in person, for the first time. Rarer than hen’s teeth, with supposedly the majority in the hands of the military and the balance in the hands of the true aficionado (only the true believer would cough up 15-20K for one piece of dive gear) and these not showing up on the market very often, a Cis-lunar is quite the rare sight on a dive boat.

The Cis-Lunar is an electronically controlled, closed circuit rebreather that uses over the shoulder counterlungs, it has a radial scrubber and is the only rebreather to have a hydrophobic membrane completely protecting the scrubber from water ingress thereby allowing the use of Lithium Hydroxide scrubber material as well as IN WATER scrubber changes. How cool is that? This is truly an expedition level rebreather that can be fully recovered from a flood during a dive, yes, like without leaving the water. It has gas options that other rebreathers can only dream of, onboard, off board and an amazingly versatile gas block that allows the diver to divert on or off board diluent, or oxygen, to his RB, bailout mouthpiece, or long hose for buddy OC bailout. The possibilities are almost endless, you could literally live underwater for days on this unit, if sufficiently supplied. The electronics are as fail-safe as any electronics package could be, immersed in salt water. There are mechanical injections for diluent and oxygen and a passive display of individual cell outputs, allowing complete manual operation in the event of computer failure. The design and manufacturing of this unit is extremely well thought out and it is truly a shame that they are no longer being produced.

Nick Jewson was kind enough to allow me to take a few pics of his Cis and pick his brain for a couple hours one afternoon during the event Zero Gravity, at Sunset House, Georgetown, Grand Cayman B.W.I. His Cis-lunar is Serial number 004, and one of the first released to the general public and Nick has owned it since it was new. The military units were not numbered in the same series as the civilian units, but as far as I know, are built the same.

Notice the date of manufacture and the serial number.

The unit standing up, over the shoulder counterlungs just in front of the BC wing. The blue hose (all the Cis gas hoses are color coded) feeds the ADV automatic diluent (add) valve.

Closer shot of the ADV, it works via a stem that protrudes into the exhale CL and when the CL bottoms out the stem gets pressed and gas added. This is the method the current generation of the Meg uses. Other RB’s use a negative pressure diaphragm and valve similar to a second stage reg, this is nice and compact.

The DSV (dive surface valve) from the back side, this knob is opposite the mouthpiece, a quarter turn of the knob closes the loop and allows the diver to inhale from the second stage open circuit regulator on the bottom. Also notice the HUD (heads up display) with the cable running into my hand. It might seem that the breathing hoses are quite small, but if you look into them they are very smooth, the corrugations are an armor wrap that prevents the hose from being crushed and do not show up on the inside diameter. The LP hose feeding the OC regulator comes from the gas block, more on that later.

The HUD. Three LED’s, marked D, O and S. The D is dive, or deco, it is your ascent rate warning, red flashing if you are ascending too fast, it also turns red at your deco ceiling and flashes if you are above your deco ceiling. Green means normal. The next LED is oxygen, green is PPO2 near setpoint, orange is slightly too high or low, red flashing is much too high or low. The last LED is system health, green is systems normal, red means there is a problem and checking the handset will give more information. In this case there is no high pressure gas turned on, so the light is red.

The back side of the handset, a passive display of the output of the three galvanic oxygen cells, by sliding the lever on the right side the voltage from the cells is shunted to this led display that gives the dive PPo2 readings without any processing. A nice bit of sanity. Red bad, green good!

Lots of information on the dive screen, but nicely organized. Your PO2 setpoint top left, deco mode (open circuit or closed circuit) diluent gas below that, depth and deco ceiling, stop times and TTS (total time to surface) dive time and bar graphs for scrubber stack time (What a nice feature that is, but don’t forget to reset the timer when you refill the scrubber), HP oxygen and diluent pressure and ascent rate. Top right are your three sensors PPO2, the current status of the CPU’s in the system (there are three independent processors), max depth, OTU’s (oxygen tolerance units) and your CNS % (Central Nervous System toxicity, another method of measuring your oxygen tolerance) and then your remaining NDT (no decompression time). The computer has a built in decompression dive program, but its always best to carry a backup computer too. The computer is menu driven and has many options accessible to the diver. There is also a predive check menu. The computer is locked out by a PIN and it can remember deco info on 3 divers at once, allowing hot swapping of the RB during long expeditions. The handset has two batteries, one for the system memory and another for the LED backup display. The central processor has 2 C cells and one D cell.

A pre dive checklist is printed on the side of the handset.

Top of the unit shows the buddy LED’s. Left LED is green for OK, red for high PPO2 and flashing red for low PPO2. The second light duplicates the system LED on the HUD. The black plug is a data port.

This is almost too cool for words, here is the gas block. It hangs down on the divers left chest area and is a wizard of a machining job, the gas paths inside must look like the shift body of an automatic transmission. Diluent is on the divers left (right on the picture) and oxygen is on the divers right. Notice the color coded hose wraps, green O2, blue dil. There are several controls on the block, the large rotary control on the face, the levers on each side at the top, and two more rotatable knobs on the sides below the levers. The levers are manual injection, divers left is diluent injection, and divers right is oxygen, a push inward activates the injection. The rotatable knobs below, on the sides, control where the RBs supply gas comes from. With the point of the knob rotated up, the RB is supplied with onboard gas from the cylinders in the unit, this is the same whether it the diluent or oxygen side. With the knob rotated 90deg so the point is out away from the diver, the gas supply is turned off and with the knob turned another 90 degrees to pointing down, the RB is being supplied from off board gas. These knobs have a safety tap that must be pushed for them to rotate. There is a nipple with a quick disconnect on the diluent side, that is partially visible in this pic. The large knob on the front is normally aligned up and down, this will send diluent to the OC regs, both the long hose and the DSV bailout and keep oxygen supplied to the solenoid. If the diver pulls out the knob and rotates it 45 degrees counterclockwise, this will turn off the oxygen feed to the electronic injection solenoid, in the case of the solenoid sticking open. This 45 degree position will still allow manual oxygen injection. Diluent is still fed to the OC regs. The knob can be turned to a 90 degree position, but there is a safety lever that must be released and in the 90 deg position the OC regs receive pure oxygen from on or off board oxygen, depending on what supply is chosen by the rotatable knob on the side. It all sounds kinda complicated but in essence, quite simple and extremely versatile.

Another view of the gas block. Notice the safety tabs on the rotatable knobs on the sides, as well as the safety tab on the big knob. Oxygen is set to on board, diluent is set to off board and the large rotary knob is set to deliver O2 to the OC regs, this is probably not the best way to start a dive though. The pigtail hanging down is a connector for offboard diluent, there is a port for an offboard oxygen too but the pigtail is not attached.

This pic shows where the sensor pod slides in, notice the three small nipples pointing at you in the pic. These nozzles line up with the face of the oxygen sensors and when you manually add diluent with the injection lever on the gas block, this is where it come out, gently blowing a puff of diluent onto the face of the sensors. This does two things, one, gives you a sanity check on your sensor health, by doing the math you can see which sensors are reading correctly (diluent oxygen fraction X depth in ATA should match your PPO2 of the diluent gas), two, it clears moisture that may be beaded up on the hydrophobic membrane that is the face of your oxygen sensors. In the event of a full loop flood, after it is cleared this will bring your sensors back on line. The yellow material just below the nozzles is a common sponge, there to absorb any moisture loose around the sensors and it also helps prevent moisture from dripping onto the sensor faces when the diver goes inverted.

The face of the sensor pod.

The easily removable sensor pod, and 3 Teledyne R-17 oxygen sensors. Nice to be able to quickly remove it to bring it into a temperature and humidity controlled environment between dives. The white cylinder is a gel pack that equalizes the ambient pressure to the back sides of the oxygen sensors without allowing any moisture to come in as well. O rings keep water out and gas in. A slick bit of engineering.

The sensor pod being slipped into place. The hole the o ring is visible through, indexes with the button on the pod, when the two align the button snaps out and locks the pod into place, no tools required.

Here is the sponge and its holder, sliding in below the sensor pod, yup, its just a common household sponge you can buy anywhere. Its holder snaps in with the same button-hole indexing system.

The back side of the unit minus the cover, notice the red nylon loop to pull the sponge holder out. The metal casting at the top front of the unit is the central processor, solenoid and battery housing. The extra weight up top helps trim too.

The bottom of the scrubber housing, the cutout in the shell is designed to allow scrubber changes under water. The diver switches to OC, a tender flips the latches and pulls on the red nylon loop.

Then the tender pulls the scrubber canister out, and slides a new one in and replaces the cover. The diver then purges the loop with diluent, by pressing on the ADV, remember the scrubber is protected by a hydrophobic membrane, taps the dil injection lever on the gas block which clears the water off of the sensor faces and switches back to the loop. Kids, don’t try this at home!!

The Cis-lunar uses Poseidon regulators. The scrubber is good for up to 6 hours of diving and holds 2.4 kilo’s of scrubber material.

I am hoping to get a copy of the manual for this unit and I can add more to this article about the operation and menu options etc. Its hard to know what questions to ask when you get your hands on a unit like this, so I know that my information here is not nearly as complete as I would like it to be, but if I get more info, I will add it in.

Thanks again to Nick Jewson, for spending his time educating me about this venerable, but still highly competent, piece of dive gear. I must say that I was very impressed with this unit and it is worth every penny one might have to pay to own it. I understand that servicing and some parts are still available through Kevin Jurgensen. The Cis-lunar scrubber canister will fit in a Meg rebreather, manufactured by ISC.

Ron Micjan

4 OCT 2005