Amtrol lists an 88 gal pressure tank with acceptance volume as 46 gal. They also list 119 gal tank with acceptance volume of 46 gal. The cost difference is around $300. I don't understand why acceptance volumes are the same but the tank volumes are different. Can someone explain this? Tks
Tank acceptance Volume
- Thread starter tedn332
- Start date
Users who are viewing this thread
Neither one of those is correct. They like to over estimate the "acceptance volume", as a sales feature. It depends on the air charge and pressure switch setting as to how much water a tank will accept. With the correct air charge and a 40/60 switch, an 86 gallon tank holds 23.03 gallons while a 119 gallon size tank holds 31.86.
Now if you go up to a 50/70 pressure switch setting the 86 gallon tank holds 20.31, and the 119 gallon tank holds 28.10 gallons.
If you go down to a 20/40 pressure switch setting an 86 holds 31.44, while the 119 holds 43.51 gallons.
Either way your water doesn't come from the tank, it comes from the pump. The only reason to increase the size of a pressure tank is to reduce the number of on/off cycles, so the pump doesn't get destroyed prematurely. There are better ways to stop the cycling, then you don't need a large and expensive tank.
Here is a picture of a pump system with an 80 gallon pressure tank (white tank in corner) that feeds a city with over 100,000 people and has three 200HP pumps.
Now if you go up to a 50/70 pressure switch setting the 86 gallon tank holds 20.31, and the 119 gallon tank holds 28.10 gallons.
If you go down to a 20/40 pressure switch setting an 86 holds 31.44, while the 119 holds 43.51 gallons.
Either way your water doesn't come from the tank, it comes from the pump. The only reason to increase the size of a pressure tank is to reduce the number of on/off cycles, so the pump doesn't get destroyed prematurely. There are better ways to stop the cycling, then you don't need a large and expensive tank.
Here is a picture of a pump system with an 80 gallon pressure tank (white tank in corner) that feeds a city with over 100,000 people and has three 200HP pumps.
Sponsor
Paid Advertisement
I have wondered about the difference between "acceptance" vs drawdown too. They sound so similar, but they must mean something different. (like alkalinity vs pH, although I mostly understand that one now) WX-252 and WX-302 offer a more even contrast. Both list the same drawdowns, but the acceptance factor is very different. I have read that for the same drawdown, the wider tank would tend to last longer because its diaphragm is not raising as much. I don't know where you would find numbers.
When thinking about drawdown, note that there should normally be a little water remaining by the time that the new water arrives, except under the very highest rate of draw.
https://www.rcworst.com/Shared/content/mfr/amtrol_well_x_trol/docs/wellxtrolsizing.pdf
When thinking about drawdown, note that there should normally be a little water remaining by the time that the new water arrives, except under the very highest rate of draw.
https://www.rcworst.com/Shared/content/mfr/amtrol_well_x_trol/docs/wellxtrolsizing.pdf
LLigetfa
DIYer, not in the trades
As was already mentioned, drawdown is calculated with typical pressure switch settings that have a 20 PSI delta. Of course anyone can fiddle with the settings and change the delta so AFAIK the tank acceptance volume is the amount of water that can stretch the bladder to its maximum. It really has no practical value unless you use the tank in uncommon ways.
That's interesting and helpful. That would seem to imply that a high acceptance tank might be suitable for a wider pressure range, or have more margin when used with a normal pressure range. That might go along with the thought that for a given nominal size, the wider tank tends to last longer.
LLigetfa
DIYer, not in the trades
I really should stop using the term "bladder" since there is a big difference between a bladder and a diaphragm. Bladders fall into two categories in that they either hold water or hold air so the effect on them varies as to stretching or squeezing.
A diaphragm generally should just roll back and forth between being turned inside out and outside in, kind of like turning a sock inside out. Under normal use it should not stretch unless it is designed to stretch. On diaphragm tanks, you can usually see at what height the diaphragm is located by a bump or indentation and that gives some indication of its range of up/down travel as they are usually below the middle.
A diaphragm generally should just roll back and forth between being turned inside out and outside in, kind of like turning a sock inside out. Under normal use it should not stretch unless it is designed to stretch. On diaphragm tanks, you can usually see at what height the diaphragm is located by a bump or indentation and that gives some indication of its range of up/down travel as they are usually below the middle.
Similar threads
