Mineral tanks usually have a max working pressure rating of 125 psi. Exceed that and they will eventually "breath" alright, by splitting open. Plumbing codes call for no more than 80 psi or you have to install a pressure regulator valve.
Less pressure than that max will not make the tank increase in height or diameter by more than a couple thousands of an inch maybe. Otherwise millions of pieces of water treatment equipment that have been hard plumbed over the last 70 years would have sprung leaks, and they haven't.
And Falcon flexible SS lines will not grow in diameter or length in any measurable way either.
Sigh... are we really going to do this again? Is it a mandate that you express your opinion based on a lack of real world experience,
rather than field work, manufacturers warranties/requirements, and actual lab testing?
Please see the note below, from Pentair regarding mineral tanks.
NOTE: Flexible connectors must be installed between hard piping and tank openings. These pressure vessels are rated for an internal
negative pressure of 5ý HG (17 Pa) vacuum below atmospheric. If negative pressure could ever exceed 5ý Hg (17 Pa), an adequate
vacuum breaker must also be properly installed. Failure to install flex connection properly, or improper installation of a vacuum breaker
when required, may void the warranty.
The reason for the flexible connectors is primarily due to the fact that mineral tanks will vary in size, as does every other pressure vessl ever manufactued since the beginning of time, as pressure increases or decreases. Try this and tell me where I am wrong. Take a 10x54 and rapidly pressurise it and depressurise it from 0-80 psi, and tell me that the diameter and height do not change. It is very minimal, but when you do it to the extreme as I just mentioned, you can and will see the tank grow and shrink. It is also measurable. unless the tank is some special tank that has the amazing ability to not be affected by pressure changes, then it will grow and shrink as pressure varies. I feel like I am teaching 6th grade science. It is also part of our mineral tank qualifications and testing protocols. Tanks are designed to handle these slight changes in height and width for many years without fail. The tank threads are what will usually fail if some flexibility is not designed into the system. Ever wonnder why all of the new residential valves now include flexible connections? Clack and Fleck have both engineered considerable flex into their connections to accomodate the systems "breathing" The bypass, meter, pipe connectors all have some flexibility built into them. Commercially, warranty requirements dictate that flexible connectors be used.
I do not mind being corrected, and when I am wrong I consider it a learning experience. I would suggest you either do your research, do some commercial/industrial field work for 15 years, or maybe... trust the guys who have far more experience than you do and consider their advice. If you would like, I can go to my test bench and get you the reading for the height change between 0 psi and 100 PSI, and lets see if it a couple thousanths.
I had our testers re-run the 10x54 test to see what the actual growth was, they are doing a full cycle test but so far they have given me the low pressure numbers.
0-50 PSI, .0775" height gain
0-70 PSI, .135" height gain
Wow, looks a little more than a couple thousandths to me. Unless my math is wrong, I would say that we are seeing a growth of over 1/8". This is not insignificant and it does exist.
I am not sure how else to answer you. According to our test facility, a USA made structural tank has significant variances in height accoring to the pressure. I did not ask them to do the diameter, but it will also change with pressure.
We also distribute some less expensive, and lighter weight tanks, I can guess that these may have an even wider variance from 0 PSI to 80 PSI.
In regards to why millions of pieces of equipment havent sprung leaks... most softeners that are installed have some flexibility in the plumbing, the pipe connectors, etc.
I prefer hard plumbing softeners for aesthetic reasons, but flexible connectors are the correct way to install them.
Check out this link to Falcon stainless, they basically repeat what I say regarding warranty on water softeners and flexible connectors.
http://www.falconstainless.com/mega-flow_SUPER_Water_Flex.html