There are two basic designs for diaphragm first stage regulators, and they are single hose regulators or double hose regulators. The double hose regulator is virtually immune to cold water freeze-up. This is because the double hose regulator houses both stages in air, not water. There's currently is only one double hose regulator being manufactured, the Argonaut Kraken.
Store | Vintage Double Hose
Now, concerning single hose diaphragm regulators, you need to look at a diagram of these regulators. You will see that the large spring is typically exposed to the water, so it is interference with this spring that would l ad to a malfunction. This spring normally pushes the upstream seat open, and it is closed when air pressure pushes up on the diaphragm, and overcomes the spring pressure to close the seat. Now, at the start of the dive, this seat is closed until the diver inhales, causing the interstage pressure to lower, and opens the first stage seat. This causes air to flow, which drops the temperature of the water inside the chamber housing the main spring and diaphragm. As this ice builds up, it interferes with the spring, ultimately not allowing the high pressure air to close the seat. This could cause a high pressure leak, which would result in a very high volume free-flow out the second stage. This can happen in very cold water (around or below 32 degrees F (0 degrees C).
But, it is much more likely for a second stage free-flow in cold water with a diaphragm first stage. I had this happen with a MR-12 II regulator in 38 degree F water.
SeaRat
Store | Vintage Double Hose
Now, concerning single hose diaphragm regulators, you need to look at a diagram of these regulators. You will see that the large spring is typically exposed to the water, so it is interference with this spring that would l ad to a malfunction. This spring normally pushes the upstream seat open, and it is closed when air pressure pushes up on the diaphragm, and overcomes the spring pressure to close the seat. Now, at the start of the dive, this seat is closed until the diver inhales, causing the interstage pressure to lower, and opens the first stage seat. This causes air to flow, which drops the temperature of the water inside the chamber housing the main spring and diaphragm. As this ice builds up, it interferes with the spring, ultimately not allowing the high pressure air to close the seat. This could cause a high pressure leak, which would result in a very high volume free-flow out the second stage. This can happen in very cold water (around or below 32 degrees F (0 degrees C).
But, it is much more likely for a second stage free-flow in cold water with a diaphragm first stage. I had this happen with a MR-12 II regulator in 38 degree F water.
SeaRat
