AKA-60 Operation

The AKA-60, or "Orca" is a semiclosed circuit rebreather operating on the constant mass flow principle. This principle of operation is identical to that used by the more commonly seen Draeger Atlantis/Dolphin/Ray series, and to the less commonly seen Draeger FGT-1D and FGG-III rebreathers. In fact, the AKA-60 is most nearly the similar to the FGT-1D, which shares the same basic layout in many respects. It appears to be a good choice for sporting use, with some slight modifications that are appropriate for increased safety and comfort.

As far as I'm concerned, the very first order of business is to install a PP02 meter of some sort. In order to make this easy, I used a Draeger Oxygauge. You can see in this photo the port that I have installed to accept the Oxygauge, and the plug that is installed when the Oxygauge is removed. The installation of this port takes just a few minutes, and the procedure is well detailed on my page "How to Install an Oxygauge". If you prefer to make your own PP02 sensing unit, you may do so, or you may decide to add one of the commercially available PP02 sensing decompression computers. In any case, you will need to add a PP02 meter of some sort.

I positioned the port for the Oxygauge just under the inhalation connector on the counterlung. This position allows the sensor to be in a clear stream of inhalation gas, and not off in a corner of the counterlung that may be poorly ventilated. Here you can see the inhalation hose on the rig, and also you can actually see the port that it connects to, if you peer through the inner diameter of the Oxygauge port. This is a nice installation.

The Oxygauge directly reads PP02 in BAR, which is close enough to ATM that it's academic. The unit features audible alarms for high and low PP02. Annoyingly enough, the high PP02 alarm is preset to whine at 1.2 PP02, but with a little-known function accessed by removing the back and intermittently shorting a pair of contacts with wetted fingers, the alarm may be raised to as high at 1.6 PP02. This is more reasonable.

Here's one last view of the port position.

The next problem is filling the rig with gas. I had a filler fitting available from another Russian system, and I made up a filler using a 6mm Swagelok compression fitting that was attached to the tube of the fitting, and then in turn had a 1/4 inch pipe thread on the other side. This was in turn connected to the filler whip. I believe, but am not certain, that this fitting is a BSP fitting, of undetermined size, which would make it a standard European gas connection. This is something I am researching now.

The cylinders can be filled one of two ways: In-situ, by removing the bottom filler port, or by removing the cylinders from the rig. Here I've connected to one of the bottles directly. One thought that comes to mind is to fill the cylinders independently, with two gas mixes. This would allow one to be used for descent and decompression, and a second, leaner mix to be used as bottom gas. Closing one valve and opening the opposite one is all that would be required to switch gas mixtures.

In this photo, I'm filling the two cylinders directly through the High Pressure port.

For those with a more technical bent, this port is a direct High Pressure inlet to the rig. Even with the valves turned off, the CMF regulator and orifice is fed when this port is pressurized. I plan to attach a high-pressure line (braided stainless steel) to this port to allow the use of offboard bottom gas, for longer duration diving and for gas-switching. If you don't understand what I am talking about, don't try it. For those who say "YEAH!" you have the ability to carry THREE gas types, one in each bottle and another offboard. Hmmm....... Don't ask me how or why.

Of course, to dive SCC rigs you MUST flow the rig to see what it's doing. You can disconnect the feed-line to the counterlung and attach a flowmeter to the rig with a bit of rubber tubing stretched over the fitting. I was lucky enough to have one of the correct fittings so I made up this little test-rig, using a Dywer flowmeter. It attaches to the fitting on the CMF regulator after disconnection of the feed-line to the counterlung.

Here I've removed the fitting and attached the flowmeter. You can see the disconnected line laying just below the flowmeter fitting.

With air, (NOT the correct gas, which should be obvious), the flow was 12 LPM. This will obviously change with gas supply pressure and gas type. I have no clue as to if they use a sonic flow orifice or not, but I will be conducting experiments to learn. I will also be disassembling the CMF regulator as well, in order to determine if we may be able to interchange different orifice selections to optimize the rig for different gas types and depths of operation.

For a "Quick Check" of orifice flow, I set the rig up to time the inflation rate of the counterlung. I screwed on a blanking plug to the exhale side of the rig and attached the DSV and hose to the inhale side. Opening the DSV, I breathed, collapsing the counterlung and then relying on the one-way valves to vent the gas to the atmosphere (since the exhaust hose was not connected). I closed the DSV before removing it from my mouth, and the bag, as shown, is fully collapsed with a vacuum inside.

Next, I turned on the gas and times the time to when the exhaust valve began venting gas. This reliably took 30 seconds, so this will be my "Quick Check" before jumping into the water. You can see the plugged exhaust hose fitting (into the rig) in this photo.

To see what the supply pressure to the orifice is, I used another of the same fittings I used for the flowmeter to make up a test-gauge to measure the output pressure. The regulator is a simple diaphragm model which makes it easy to adjust the output pressure.

The regulator is a diaphragm type, identical to all other Russian diving first stages. Based on my knowledge of those, they are usually set at 140 to 160 PSI. To adjust the pressure, the cap is removed and the diaphragm spring retainer is screwed in. This is an easy job, but I simply ran out of time. The next update will answer the question of how adjusting the pressure affects the flow, and will define if the orifice uses sonic flow for constant mass supply. That is my assumption, but I'll wait until I have proof to state it as fact.

There is a second supply line running to the counterlung, which I correctly guessed runs the 'whistle' for low supply pressure. I attached the flowmeter and with the rig open, there was no flow through the line. With the line disconnected, the low-pressure whistle was not working either, thus confirming my guess as to this lines purpose. The 'Whistle' is a high-pitched 'eeeeeeee' sound that begins when the pressure in the cylinders reaches about 30 BAR. It's not loud, nor is it distracting, but it is audible. It's a good feature.

Lastly, I learned that the DSV, hoses, and Oxygauge may be stowed in the area of the counterlung for transport, if you fully collapse the counterlung and are careful about coiling the hoses. This makes the rig a compact and portable unit.

I hope that you have enjoyed this. Dealing with a new rig without any technical data is always interesting, and I'm sure we'll be learning about these rigs for a while to come. But this day on the bench has answered a lot of questions. If you have one of these rigs and have any comments, please forward them. If you are interested in diving one of these, let me know and I'm sure it can be arranged.

	As far as I'm concerned, the very first order of business is to install a PP02 meter of some sort. In order to make this easy, I used a Draeger Oxygauge. You can see in this photo the port that I have installed to accept the Oxygauge, and the plug that is installed when the Oxygauge is removed. The installation of this port takes just a few minutes, and the procedure is well detailed on my page "How to Install an Oxygauge". If you prefer to make your own PP02 sensing unit, you may do so, or you may decide to add one of the commercially available PP02 sensing decompression computers. In any case, you will need to add a PP02 meter of some sort.
	I positioned the port for the Oxygauge just under the inhalation connector on the counterlung. This position allows the sensor to be in a clear stream of inhalation gas, and not off in a corner of the counterlung that may be poorly ventilated. Here you can see the inhalation hose on the rig, and also you can actually see the port that it connects to, if you peer through the inner diameter of the Oxygauge port. This is a nice installation.
	The Oxygauge directly reads PP02 in BAR, which is close enough to ATM that it's academic. The unit features audible alarms for high and low PP02. Annoyingly enough, the high PP02 alarm is preset to whine at 1.2 PP02, but with a little-known function accessed by removing the back and intermittently shorting a pair of contacts with wetted fingers, the alarm may be raised to as high at 1.6 PP02. This is more reasonable.
	Here's one last view of the port position.
	The next problem is filling the rig with gas. I had a filler fitting available from another Russian system, and I made up a filler using a 6mm Swagelok compression fitting that was attached to the tube of the fitting, and then in turn had a 1/4 inch pipe thread on the other side. This was in turn connected to the filler whip. I believe, but am not certain, that this fitting is a BSP fitting, of undetermined size, which would make it a standard European gas connection. This is something I am researching now.
	The cylinders can be filled one of two ways: In-situ, by removing the bottom filler port, or by removing the cylinders from the rig. Here I've connected to one of the bottles directly. One thought that comes to mind is to fill the cylinders independently, with two gas mixes. This would allow one to be used for descent and decompression, and a second, leaner mix to be used as bottom gas. Closing one valve and opening the opposite one is all that would be required to switch gas mixtures.
	In this photo, I'm filling the two cylinders directly through the High Pressure port. For those with a more technical bent, this port is a direct High Pressure inlet to the rig. Even with the valves turned off, the CMF regulator and orifice is fed when this port is pressurized. I plan to attach a high-pressure line (braided stainless steel) to this port to allow the use of offboard bottom gas, for longer duration diving and for gas-switching. If you don't understand what I am talking about, don't try it. For those who say "YEAH!" you have the ability to carry THREE gas types, one in each bottle and another offboard. Hmmm....... Don't ask me how or why.
	Of course, to dive SCC rigs you MUST flow the rig to see what it's doing. You can disconnect the feed-line to the counterlung and attach a flowmeter to the rig with a bit of rubber tubing stretched over the fitting. I was lucky enough to have one of the correct fittings so I made up this little test-rig, using a Dywer flowmeter. It attaches to the fitting on the CMF regulator after disconnection of the feed-line to the counterlung.
	Here I've removed the fitting and attached the flowmeter. You can see the disconnected line laying just below the flowmeter fitting.
	With air, (NOT the correct gas, which should be obvious), the flow was 12 LPM. This will obviously change with gas supply pressure and gas type. I have no clue as to if they use a sonic flow orifice or not, but I will be conducting experiments to learn. I will also be disassembling the CMF regulator as well, in order to determine if we may be able to interchange different orifice selections to optimize the rig for different gas types and depths of operation.
	For a "Quick Check" of orifice flow, I set the rig up to time the inflation rate of the counterlung. I screwed on a blanking plug to the exhale side of the rig and attached the DSV and hose to the inhale side. Opening the DSV, I breathed, collapsing the counterlung and then relying on the one-way valves to vent the gas to the atmosphere (since the exhaust hose was not connected). I closed the DSV before removing it from my mouth, and the bag, as shown, is fully collapsed with a vacuum inside.
	Next, I turned on the gas and times the time to when the exhaust valve began venting gas. This reliably took 30 seconds, so this will be my "Quick Check" before jumping into the water. You can see the plugged exhaust hose fitting (into the rig) in this photo.
	To see what the supply pressure to the orifice is, I used another of the same fittings I used for the flowmeter to make up a test-gauge to measure the output pressure. The regulator is a simple diaphragm model which makes it easy to adjust the output pressure.
	The regulator is a diaphragm type, identical to all other Russian diving first stages. Based on my knowledge of those, they are usually set at 140 to 160 PSI. To adjust the pressure, the cap is removed and the diaphragm spring retainer is screwed in. This is an easy job, but I simply ran out of time. The next update will answer the question of how adjusting the pressure affects the flow, and will define if the orifice uses sonic flow for constant mass supply. That is my assumption, but I'll wait until I have proof to state it as fact.
	There is a second supply line running to the counterlung, which I correctly guessed runs the 'whistle' for low supply pressure. I attached the flowmeter and with the rig open, there was no flow through the line. With the line disconnected, the low-pressure whistle was not working either, thus confirming my guess as to this lines purpose. The 'Whistle' is a high-pitched 'eeeeeeee' sound that begins when the pressure in the cylinders reaches about 30 BAR. It's not loud, nor is it distracting, but it is audible. It's a good feature.
	Lastly, I learned that the DSV, hoses, and Oxygauge may be stowed in the area of the counterlung for transport, if you fully collapse the counterlung and are careful about coiling the hoses. This makes the rig a compact and portable unit.