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The RGU-FM oxygen rebreather is an East German system designed as a semi-disposable rig for use by armored fighting vehicle crews for setting tow-bridles, etc., on vehicles stranded in shallow water. It was designed for diving use, but I do not believe that it was designed or manufactured for intentional diving in open water. These rigs have become fairly widely distributed, due to their low cost. They feature a constant mass-flow of oxygen into the loop, and a disposable scrubber. Several people have made refillable scrubbers for these, and it is possible to make one refillable scrubber from two disposable ones. Without any further discussion, let's get down to business:

Here's the rig in its bag, all strapped and set. The bag has wooden toggles to hold the flaps down. Not very high-tech. A foreboding of things to come.

Opening up the bag we find a real-life diving mask, a bottle of anti-fog, and the rig. The mask is held in a metal-partitioned area of the bag to prevent it from being broken in transit.

The mask is of the cheapest quality, and the rig is not a lot better. The large bottle of defog is a nice touch though. I wonder if the East Germans ever heard of spit? Or even more technical, if they ever realized that pure 02 rigs never allow the divers mask to fog, due to no C02 in the gas?

Excuse me, Sir: Did you want a shut-off DSV? Sorry. We'll offer you this nice rubber bung-plug to keep the water and bugs out of your counterlung, though. We'll even give you a string so you won't lose it! I should not make fun of the DSV, as it does have nice stainless-steel sprung one-way valves, of typical Warsaw Pact design. This is an effective system, especially when the quality of your rubber one-way valves are suspect.

Looking at the front of the rig, we see a removable rubber plug. This covers a filling-port for the cylinder so the bottle may be filled in the rig. Sadly the fitting is not one that I had here in the shop, so I'm not able to fill it using that method.

Interestingly, the bottle has the same outlet fitting as the cylinder on my US spec LAR-V! The LAR-V filling adapter on the lower left fits it perfectly. This also means that LAR-V owners may want to get one of these rigs as a source for a spare 02 bottle. The size is a bit smaller, but they would fit just fine.

With the rig opened, you can see the basic layout. Green button on the regulator is the manual addition valve. Counterlung is an around-the-neck type. The stud at the center has the thumb-nut on it that attaches the lid, and a second nut that holds the bottle/scrubber bracket into the rig. No tools are needed to service the rig.

The counterlung is a simple design of modest size. The only component of interest is the exhaust valve. This uses the typical stainless-steel spring and flat-plate system as used on all other Eastern Bloc diving gear. This is actually a good system. Here I've removed the cover to expose the valve.

The regulator is sort of clever: The nut at the top of the photo is the cylinder connection. The green button is the manual add valve. The red-painted object is an overpressure relief valve. The clear aquarium-type tubing runs from the regulator to the breathing-hose manifold and carries a small trickle of 02 at about 0.9 liters per minute to the rig. This is just slightly less than the divers metabolic use rate, and keeps the system running a little while longer between manual additions of 02 than would be the case with a straight manual-add rig. There is no automatic addition regulator provided.

This is the breathing-hose manifold. I have unscrewed it from the top of the scrubber and turned it so we can see inside. The inhale and counterlung hoses are on the left, the exhale and 02 injection hoses are on the right. You can see the 02 injection "aquarium tubing" clearly here, I am holding the fitting that screws onto the regulator at the bottom of the rig.

A better view of the inside of the manifold reveals it's flow-path. The exhale gas runs to the center of the block, and then into the center of the scrubber. Clean gas from the scrubber flows into the annular space on the periphery of the manifold. To that area are connected the inhale hose, the counterlung hose, and the 02 injection line. Using this system only one hose needs to run to the counterlung.

The scrubbers are throw-away units and come in these cardboard boxes. I got two, plus one used one that was cut in half to show the flow-path. The material is a standard C02 absorbent, not the nasty binary scrubber stuff used in some Russian rigs.

Looking at the top of the scrubber, you can see the annular exhaust from the media surrounding the central gas-tube that brings dirty gas into the scrubber.

This is a used scrubber that has been cut in half to show the internal gas-path. The tube in the center brings dirty gas to the bottom of the cannister, and then the gas flows back up through the media, exiting from the coaxial slots back at the top.

This is the rig with the half of the cut scrubber reinstalled. The scrubbers are tapered, and it's a fairly easy job to make two of the disposable scrubbers into one rechargeable one. The taper of the cartridge allows one to make a 'telescoping' assembly to connect two halves to each other. That's my next step, after which I'll have a dive report available.

Well, that's it for this little rig. What do I think about it? It's hard to say. It's certainly the most cheaply constructed rig I've ever examined, and I'm not at all convinced that it would stand up to repeated use unless carefully handled. While Russian equipment has a reputation for rugged durability, the East Germans seem to have a lock on cheaply made equipment of indifferent quality. It's hard to believe that the folks that made this and the folks at Draeger ever came from the same country! With all of that said, the rig is available for a fairly low cost, and may be fun to play with if you don't have anything else with which to compare it. If you want a first-time pure 02 rig just to jump into the pool with, this would do the trick. For any serious use, I'd opt for something a bit more robust. But it's cheap enough that you could get one, hike to that mountain lake, dive it, and then toss it in the trash-can at the end of the trail.

Here's a thought: For experimenters, the 02 dose-unit with manual bypass and the cylinder alone are worth the cost. Add that to any pure 02 rig, fill the original rigs 02 bottle with air, add a PP02 meter, and you'd have a neat little CCR. The dose-unit would add 02 a slightly less than metabolized rate, and a little push of the manual add every now and then would keep you straight. The original bottle in the newly modified rig would become a diluent source. Hmmm....... Naah, I wouldn't do that, would I? You never know! Stay tuned and see "Dr. Frankensteins' Projekt" arise when rigs are torn asunder and recombined in the Diveshop of Horrors.

	Here's the rig in its bag, all strapped and set. The bag has wooden toggles to hold the flaps down. Not very high-tech. A foreboding of things to come.
	Opening up the bag we find a real-life diving mask, a bottle of anti-fog, and the rig. The mask is held in a metal-partitioned area of the bag to prevent it from being broken in transit.
	The mask is of the cheapest quality, and the rig is not a lot better. The large bottle of defog is a nice touch though. I wonder if the East Germans ever heard of spit? Or even more technical, if they ever realized that pure 02 rigs never allow the divers mask to fog, due to no C02 in the gas?
	Excuse me, Sir: Did you want a shut-off DSV? Sorry. We'll offer you this nice rubber bung-plug to keep the water and bugs out of your counterlung, though. We'll even give you a string so you won't lose it! I should not make fun of the DSV, as it does have nice stainless-steel sprung one-way valves, of typical Warsaw Pact design. This is an effective system, especially when the quality of your rubber one-way valves are suspect.
	Looking at the front of the rig, we see a removable rubber plug. This covers a filling-port for the cylinder so the bottle may be filled in the rig. Sadly the fitting is not one that I had here in the shop, so I'm not able to fill it using that method.
	Interestingly, the bottle has the same outlet fitting as the cylinder on my US spec LAR-V! The LAR-V filling adapter on the lower left fits it perfectly. This also means that LAR-V owners may want to get one of these rigs as a source for a spare 02 bottle. The size is a bit smaller, but they would fit just fine.
	With the rig opened, you can see the basic layout. Green button on the regulator is the manual addition valve. Counterlung is an around-the-neck type. The stud at the center has the thumb-nut on it that attaches the lid, and a second nut that holds the bottle/scrubber bracket into the rig. No tools are needed to service the rig.
	The counterlung is a simple design of modest size. The only component of interest is the exhaust valve. This uses the typical stainless-steel spring and flat-plate system as used on all other Eastern Bloc diving gear. This is actually a good system. Here I've removed the cover to expose the valve.
	The regulator is sort of clever: The nut at the top of the photo is the cylinder connection. The green button is the manual add valve. The red-painted object is an overpressure relief valve. The clear aquarium-type tubing runs from the regulator to the breathing-hose manifold and carries a small trickle of 02 at about 0.9 liters per minute to the rig. This is just slightly less than the divers metabolic use rate, and keeps the system running a little while longer between manual additions of 02 than would be the case with a straight manual-add rig. There is no automatic addition regulator provided.
	This is the breathing-hose manifold. I have unscrewed it from the top of the scrubber and turned it so we can see inside. The inhale and counterlung hoses are on the left, the exhale and 02 injection hoses are on the right. You can see the 02 injection "aquarium tubing" clearly here, I am holding the fitting that screws onto the regulator at the bottom of the rig.
	A better view of the inside of the manifold reveals it's flow-path. The exhale gas runs to the center of the block, and then into the center of the scrubber. Clean gas from the scrubber flows into the annular space on the periphery of the manifold. To that area are connected the inhale hose, the counterlung hose, and the 02 injection line. Using this system only one hose needs to run to the counterlung.
	The scrubbers are throw-away units and come in these cardboard boxes. I got two, plus one used one that was cut in half to show the flow-path. The material is a standard C02 absorbent, not the nasty binary scrubber stuff used in some Russian rigs.
	Looking at the top of the scrubber, you can see the annular exhaust from the media surrounding the central gas-tube that brings dirty gas into the scrubber.
	This is a used scrubber that has been cut in half to show the internal gas-path. The tube in the center brings dirty gas to the bottom of the cannister, and then the gas flows back up through the media, exiting from the coaxial slots back at the top.
	This is the rig with the half of the cut scrubber reinstalled. The scrubbers are tapered, and it's a fairly easy job to make two of the disposable scrubbers into one rechargeable one. The taper of the cartridge allows one to make a 'telescoping' assembly to connect two halves to each other. That's my next step, after which I'll have a dive report available.