Pressure Relief valves are the most important part of your chamber
If you buy a chamber with just one PRV and it fails to open there will be a build up of CO2 which is poisonous. Second as I mentioned in my "why chamber burst page", if a single PRV fails to open the chamber will over pressurize.
Many people prefer using chambers that have 2 or 3 PRVs. This redundancy so that there will be no CO2 build up and you will not end up with a burst chamber.
Some companies have the 2 release valves on their smaller chamber but have 3 on their largest chambers.
Most of the gauges are precise within about 5% but they must, by law, produce the specific pressure as approved by the FDA. Basically, the gauges are just a reference of "at pressure and completely decompressed".
Release valves can often cause a problem depending on the location of them, especially if they are side or top loading types. If someone is buying a hyperbaric chamber that has the belts and buckles, most of them are side loading and have the release valves in different positions than top loading or the combo top and side loading types.
The release valves can be near the top or near the feet. This also effects the sound, also with the oxygen concentrator. On most of the non buckle types, the release valves are at where the head is and some are near the top and very pointy. The biggest complaint is when you don't lift it up and the release valves can scratch you. Plastic ones definitely don't hurt as much as the metal ones. Sooner or later the person in it will instinctively have their arm up as a guard so it doesn't come down and hit them.
Know the location of the release valves and by trying both types of chamber types with the different release valve locations, most people have a preference of one type over the other.
Most of the release valves on the more expensive models are metal. Some of the home use models have metal valves now too. The early generation home models had plastic back then.
The cheaper type of chambers usually are the ones with the valve stems that go out first and are usually not metal. Check to see if they are turned down into the floor or or up into the chamber. There is no difference in performance in stainless steal versus plastic ones, its mainly looks and noise issue and the scratching issues with people that are not careful.
Notice: This is a becoming a huge problem. People are asking me questions that make it hard to talk about because it is illegal in the USA to use 1.5 ATA pressure release valves. Many people are buying them from gray market dealers. These illegal replacement valves usually coming out of Canada are only about 10 dollars but the problem is people aren't replacing their compressor with a more powerful one. I have connections with hyperbaric chambers but not these valves so please don't ask me about these valves. If you want a recommendation on a chamber and who to get the best deal from or whatever "legal questions" you have I can help with that. But once you get the chamber, please ask those other questions to a dealer in another country where it is legal.
Pressure Release Valves Questions to ask:
Can you move locations with them?
Are there different grades of PRVs?
What is the DB level? Some are louder than others
How many PRVs are there?
Can I replace the valves without sending in the chamber?
Are they covered in warranty?
Are the regulators tamper-proof or can you adjust them?