IDA-72 Gas Plenum

IDA-72 Breathing Plenum and Switching-Block

At the top of the rig is what is likely the most interesting component of the system, the breathing plenum. On the left we see the piston-actuated device that converts the rig to an open-circuit device. The grey cylinder is a heat exchanger, fed by hot-water by the fitting at its extreme right, and exhausting through the short hose that will later be connected to the water-jacket of the divers breathing hoses. The demand valve is in the center of the photograph.

The automatic demand valve is very high performance, as it must also be able to function as a high-volume demand breathing regulator when the rig is selected to "Demand" mode. As the rig was designed for depths in excess of 1000 feet, the flow-rates of these components is quite high. In fact, this is the only Russian rebreather that I have examined that has unique components, not a standard component as used in all other Russian rebreathers. All other Russian rebreathers use one type of add valve. This one is the only different variety.

Before getting into the workings of the plenum, let's look at the belt-block in more detail. Essentially, the middle hose feeds umbilical-gas to the block. No internal gas is available to this system. The flip-valve on the left simply supplies a calibrated free-flow of gas into the plenum, as a manual bypass mode or loop-flush mode. The other valve switches the rig to a demand-only mode, and terminates recirculating (rebreather) mode. These valve-levers are designed exactly like an aircraft locking-switch, in that they must be lifted before being selected.

Here's the back of the valve. The casting of the actual valve body is visible, and one can see how the gas flow path is designed.

The counterlung has been removed to expose the mode-select valve assembly. The port on the left is the exhale port feeding the scrubber (through an internal hose in the counterlung), and the one facing up is the inhale port from the counterlung itself. Feeding directly into the inhale side of the system is the flush-line, controlled by the belt-block. The clean gas from the counterlung is fed into the heat-exchanger where it is heated with hot water before being breathed by the diver.

Here's what makes the demand system work: The plate that is visible through the port is in its "relaxed" position, and allows gas to be sucked from the counterlung into the heat-exchanger and then to the diver. When the flip-lever on the belt-block is switched to the "Demand" mode, the feed-line at the top of this picture is pressurized, driving the piston-actuated plate down, and sealing the heat-exchanger off from the counterlung. When the diver then breathes, the only gas that is supplied to him is fed by the demand regulator sitting on top of the heat-exchanger. When the diver exhales, he exhales into a dead-ended counterlung, and his breath is dumped overboard through the exhaust valve. This is a VERY clever system and should be studied carefully.

Here is the entire plenum again: Study the gas flow and you'll realize how well designed it is. The pneumatic system that splits the loop when desired is a feature that should be considered for incorporation into new designs, as the ability to simply flip a lever and have access to open circuit gas is extremely nice.

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	At the top of the rig is what is likely the most interesting component of the system, the breathing plenum. On the left we see the piston-actuated device that converts the rig to an open-circuit device. The grey cylinder is a heat exchanger, fed by hot-water by the fitting at its extreme right, and exhausting through the short hose that will later be connected to the water-jacket of the divers breathing hoses. The demand valve is in the center of the photograph.
	The automatic demand valve is very high performance, as it must also be able to function as a high-volume demand breathing regulator when the rig is selected to "Demand" mode. As the rig was designed for depths in excess of 1000 feet, the flow-rates of these components is quite high. In fact, this is the only Russian rebreather that I have examined that has unique components, not a standard component as used in all other Russian rebreathers. All other Russian rebreathers use one type of add valve. This one is the only different variety.
	Before getting into the workings of the plenum, let's look at the belt-block in more detail. Essentially, the middle hose feeds umbilical-gas to the block. No internal gas is available to this system. The flip-valve on the left simply supplies a calibrated free-flow of gas into the plenum, as a manual bypass mode or loop-flush mode. The other valve switches the rig to a demand-only mode, and terminates recirculating (rebreather) mode. These valve-levers are designed exactly like an aircraft locking-switch, in that they must be lifted before being selected.
	Here's the back of the valve. The casting of the actual valve body is visible, and one can see how the gas flow path is designed.
	The counterlung has been removed to expose the mode-select valve assembly. The port on the left is the exhale port feeding the scrubber (through an internal hose in the counterlung), and the one facing up is the inhale port from the counterlung itself. Feeding directly into the inhale side of the system is the flush-line, controlled by the belt-block. The clean gas from the counterlung is fed into the heat-exchanger where it is heated with hot water before being breathed by the diver.
	Here's what makes the demand system work: The plate that is visible through the port is in its "relaxed" position, and allows gas to be sucked from the counterlung into the heat-exchanger and then to the diver. When the flip-lever on the belt-block is switched to the "Demand" mode, the feed-line at the top of this picture is pressurized, driving the piston-actuated plate down, and sealing the heat-exchanger off from the counterlung. When the diver then breathes, the only gas that is supplied to him is fed by the demand regulator sitting on top of the heat-exchanger. When the diver exhales, he exhales into a dead-ended counterlung, and his breath is dumped overboard through the exhaust valve. This is a VERY clever system and should be studied carefully.
	Here is the entire plenum again: Study the gas flow and you'll realize how well designed it is. The pneumatic system that splits the loop when desired is a feature that should be considered for incorporation into new designs, as the ability to simply flip a lever and have access to open circuit gas is extremely nice.