The most common failures in the first stage will result in a free flow. And these would be a massive freeflow due to icing in the ambient pressure chamber, a slight freeflow due to a failed HP seat or in the case of a balanced piston first stage, pinching of the piston stem o-ring that in severe cases can cause an excesively high IP and cause a mild to moderate freeflow. All the other common failures are minor and result in small leaks when a static or dynoamic o-ring begins to fail and starts leaking small amounts of air.
One of the interesting failures that can occur is a fire in the first stage caused by high 02 nitrox mixes and incompatible lubricants and o-rings. This will normally just char the o-rings and cause them to leak. The bad news is that depending on what the 0-rings are made of the burnt gases can be very toxic. The not so bad news is that the fire is most likely to occur when you turn on the air (especially if you turn it on very quickly without the purge on the second stage depressed) rather than during the dive when you are breathing off it.
One of the few first stage failures that will not allow continued airflow would be a broken mainspring but that is extremely unlikely unless it was very poorly serviced and excessively shimmed to get sufficient intermediate pressure. Mainsprings are extremely durable and unless they are compressed more than 2/3rds of their travel they will normally last the life of the regulator
On a down stream second stage, a lever failure, or more likely but still very rare, the nyloc nut on the end of the poppet coming off, will result in a loss of the ability to flow air from that second stage, but then you should have an octo that will still work.
The other common failures in a second stage is a pin hole or tear in the diaphragm or an exhaust valve failure that allows water into the reg. This can vary from a mildly annoying mist to a flood of gag and choke proportions. Less common is a cracked housing that can occur if you drop your tank or weightbelt on your nifty lightweight composite second stage. (This was not an issue with the older chrome plated brass second stage housings.) The results are much the same as a leaky diaphragm and can be cured by switching to the octopus.
One of the very common failures in the second stage is a crack or hole in the mouthpiece that will cause the reg to breath very wet. It's a good item to pull on and check periodically to ensure it is in good shape and that there are no cracks hiding in the nooks and crannies.
Calling any of the fist stage failures "common" is a bit of misnomer as they tend to be very simple and reliable designs. If you have it properly serviced at the required intervals, you will probably never experience a first stage mechanical failure.
One of the interesting failures that can occur is a fire in the first stage caused by high 02 nitrox mixes and incompatible lubricants and o-rings. This will normally just char the o-rings and cause them to leak. The bad news is that depending on what the 0-rings are made of the burnt gases can be very toxic. The not so bad news is that the fire is most likely to occur when you turn on the air (especially if you turn it on very quickly without the purge on the second stage depressed) rather than during the dive when you are breathing off it.
One of the few first stage failures that will not allow continued airflow would be a broken mainspring but that is extremely unlikely unless it was very poorly serviced and excessively shimmed to get sufficient intermediate pressure. Mainsprings are extremely durable and unless they are compressed more than 2/3rds of their travel they will normally last the life of the regulator
On a down stream second stage, a lever failure, or more likely but still very rare, the nyloc nut on the end of the poppet coming off, will result in a loss of the ability to flow air from that second stage, but then you should have an octo that will still work.
The other common failures in a second stage is a pin hole or tear in the diaphragm or an exhaust valve failure that allows water into the reg. This can vary from a mildly annoying mist to a flood of gag and choke proportions. Less common is a cracked housing that can occur if you drop your tank or weightbelt on your nifty lightweight composite second stage. (This was not an issue with the older chrome plated brass second stage housings.) The results are much the same as a leaky diaphragm and can be cured by switching to the octopus.
One of the very common failures in the second stage is a crack or hole in the mouthpiece that will cause the reg to breath very wet. It's a good item to pull on and check periodically to ensure it is in good shape and that there are no cracks hiding in the nooks and crannies.
Calling any of the fist stage failures "common" is a bit of misnomer as they tend to be very simple and reliable designs. If you have it properly serviced at the required intervals, you will probably never experience a first stage mechanical failure.
