Nitrogen Fill in Expansion Tank?

alaskawild said:

Hello everyone. I've been watching this forum for a number of years but have finally decided to join and post. I'm semi-retired so I have a little time now! LOL
Anyhow I have a question to toss out and would appreciate any feedback. I'm currently installing a 2000 gallon pressurized storage system (LP tanks) and I'm going to use a 150 gallon LP tank for expansion. I've researched many threads on here about nitrogen filling but I don't really see anyone that has had experience with it. It would be simple enough to do but was wondering if it is even worth considering. I'm very familiar with B&G (non bladder) type expansion tanks as there are still many here in Fairbanks. Of course they only contain air. My question. Does anyone have any feedback to share on nitrogen filling expansion tank?

Click to expand...

That was something Amtrol started years ago, I don't know that they still pre-charge with nitrogen.

The concept with a diaphragm or bladder tank and the nitrogen was that the pre-charge would stay longer, just like nitrogen in your tires.

With a compression style , non-bladder or non-diphram tank I don't see any advantage to nitrogen.

You will need to check the air bubble in a compression tank from time to time, as the fluid heats it will re-absorb some of that air. Install a B&G ATF Airtrol fitting if you can.

http://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2012/07/S10300H.pdf

alaskawild said:

Bob...

Thanks for the info. I was just rolling around in my mind an idea. I was wondering about purging and then pre-charging the non bladder tank with nitrogen and then use a traditional air separator to scrub out the air. So most of the atmosphere in the tank would be nitrogen. Wouldn't work like a traditional airtrol setup. I'm thinking I'm overthinking! LOL . An ATF would be the way to go I'm thinking. Like I said I had to much time on my hand and was trying to recreate the wheel

Thanks!

Click to expand...

Pros and cons for a non- bladder or non-diaphragm tank. They are inexpensive to buy or make

You could put a vented, open type tank in, but it would need to be at the highest point in the system and it does allow O2 into the system. The height of the tank dictates the pressure in the system.

Crunch some numbers if you use a non bladder, pressurized tank, to be sure you have enough space to handle the expansion. It's a good idea to add a site glass to see if it gets waterlogged and needs to be drained and have the air bubble increased.

Most of the heating systems in the UK have open expansion vessels in the attic. Corrosion is a huge issue and as a result treatment chemicals are commonly added. Just like an open system OWF.

Your tank will need to be 75- 80-% larger than a bladder type tank as it does not have a pressurized (captive) air bubble.

Typical diaphragm tanks have an EPDM or Butyl rubber crimped mid range in the tank. These tanks will have a volume capacity and an acceptance capacity. The acceptance will be less as you cannot stretch that bladder to allow the entire tank to fill with water, or fluid. Not for very long anyways.

A bladder, or bag style expansion tank (more expensive) will have about the same acceptance as capacity, as the fluid in inside a bag and it can expand into the entire dimension of the tank.

Here is what the two types of tanks look like, under the hood.

It sounds like your expansion tank might also be above the top of storage. If that's the case you can also run a line from the top of the storage tanks up to the expansion tank to collect any gas that makes it past the separator. This would help guarantee that the expansion tank is the only place in the system that gas can accumulate, in which case it should run for decades without need for maintenance.

Charging the expansion tank with nitrogen sounds like an excellent idea. If you charge it with air it's going to end up as all nitrogen after the oxygen is converted to iron oxides, so why not start with nitrogen and skip the rusting step.

alaskawild said:

Bob...

Thanks again. You are correct. The simplest way to go would be diaphragm route but I'm an old retired boiler guy that likes to tinker. LOL! I'm fairly sure I'm going to go the non-bladder route and convert a 150 gallon horizontal LP tank with the ATF. The size of the tank allows clearance for proper installation. This is still a fairly common setup here and it does work fairly well. I do not want an open system. Too many problems as you stated. Thanks for the great info!

Click to expand...

Check the size, I thing the engineeringhandbook site has a formula for compression tank sizing.

Sizing a bladder tank from the Amtrol site shows a 264 gallon tank. Without a pressurized bladder your tank will need to be even larger.

I thought about doing that for a while, AK. But I have the same water treatment chemicals in my system as Garn uses because I started out vented at the top of my expansion tank (up on the second floor). The chemicals will absorb the oxygen in that original compressed gas charge and it will end up nitrogen and argon. I'll then add some more air to top up and repeat until, as ew describes, it will finally be nitrogen anyway. I have liquid nitrogen around on the farm anyway, but if you don't have that or a tank and regulator for compressed nitrogen already, the purchase or rental price will quickly pay for the treatment chemicals or a good part of a bladder tank.

Hi, just read all of the above. I work for Global Water Solutions UK and we manufacture & distribute Bladder tanks. They are available to order via any plumb centre now .. Hope this helps. PS. our tanks have the longest warranty period & and also they are 'No Maintenance' as they do not lose pressure Good luck with your install