Why do you think you need so much drawdown? You probably need more contact time in a tank that can be flushed out. Yes, it is easy to get more contact time and more drawdown by having a larger tank provided you have the room for it.
Again, as I mentioned before, tune your system by matching draw to supply to not cycle as much.
The composite hydro-pneumatic tank I mentioned is serviceable whereas most bladder tanks are a throw-away. You really should not use a bladder tank anyway as the air you inject has no properly designed place to be vented off. You shouldn't let the air collect in the top of your media tank.
I assumed I needed more drawdown because of how my pump cycles when I am watering the lawn in the summer with an impulse sprinkler.
It seems to work fine at all other times. That is why I have always been interested in the prospect of using a CSV.
Earlier this week when I had a well guy, fairly familiar with my system, come over to determine what was wrong with my pressure tank. I also mentioned the lawn watering issue. He stated that the best thing to do was to replace my existing (12 gallon drawdown at 40/60) P tank with a larger capacity tank like the 251 or 255 (with drawdowns of 18.2 and 23.8 at 40/60) and that he would install a 50/70 pressure switch instead of the 40/60 I now have. He did not know anything about a CSV. Nor did he address the issue of the air injector even though I pointed that out to him. He just stated that a larger P tank would benefit my well pump by cycling less often and that my conditioning equipment would also benefit from the higher PSI I'd get from a 50/70 P switch.
I realize that my system would probably benefit from a properly sized retention tank and that it would be much easier to maintain if it could be flushed out by having a drain at the bottom. I'm all for this. Its just that my old system (which I installed in 2003) had incorporated a UT-80 with a compressor, a 8" x 48" "off-air tank" (that's what the guy who sold it to me called it) and a pH neutralizer. So, when I changed my system over to using an air injector as the oxidizer, the installer who sold me on adding a softener to aid in filtering the iron, determined that the 8x48 with an AVC would suffice and remain in-line after the P tank as a retention/contact tank, and that the UT-80 would not be necessary?, or would have to go because of space requirements for the new softener and brine tank? (I don't recall why the UT-80 was not re-used as the contact tank)
I will definitely take your advice and "tune your system by matching draw to supply to not cycle as much", once I determine which replacement components to specify.
So, I guess if I want to water a certain portion of my lawn efficiently and effectively, as a prerequisite for my determining my system componentry, then I should choose a certain sprinkler head and manufacturer which states the required GPM usage, so that I can make an informed decision.
Thanks for pointing out that the hydro-pneumatic tank is serviceable. I'm just not sure I want to deal with the additional maintenance which may be required because of the numerous parts associated with using that type of tank in my system.
As per your statement : "You really should not use a bladder tank anyway as the air you inject has no properly designed place to be vented off. You shouldn't let the air collect in the top of your media tank."
I neglected to tell you that there is an ACV? (pressure relief valve?) on the top of my existing "off air" tank. I just don't know if it works. I will be taking that tank apart to see what is in it, when I shut down the system to replace the P tank. Hopefully it has at least worked to vent/release accumulated air, even if it hasn't worked as a proper contact tank.
I really appreciate all your knowledge and input.
I just wish I was smarter so that I could comprehend it all quickly and put it all to the best use in a short period of time.
It takes me forever to "get it".