I want to have a large capacity air tank for for holding shop air at home. However such a large tank would run me into the thousands if I bought one. I was thinking since PVC drain pipes are rated to 200 psi, maybe I could build my own air tank out of PVC which would cost me hundreds instead of thousands.

My question is: How long will PVC last in a dry environment under high pressure with possible large temperature fluctuations (100-125PSI @ -40c winter +30c summer)? I know it's been used in some cities underground for almost 20 years and are still holding up but that's different from being above ground and exposed to temperature changes. Also, should I be worried about fatigue from pressurization and pressurization? Will that affect the life of the PVC?

Note: I do understand the material weaknesses of PVC, particularly its brittleness, and worse, loss of mechanical properties at low temperatures. I will need to design the air tank system to have blast shields around it in case of failure and vents positioned strategically to quickly exhaust air should a module burst.

Have you considered looking on the used market... burned out compressors can be had for very cheap, free or scrap value even... and the tanks reporposed.

How many gallons of reserve do you need and why?

I'm hoping to get 100 gallons or more.

I'm using a very small weak electric compressor which can't keep up with the use of a blow gun. I was hoping to have this tiny little compressor precharge the entire system like a capacitor and I would draw off it as needed. The compressor will be hooked up to some electronics that lets it run for maybe 5 minutes before being shut off for 20 minutes to let it cool down and preserve it's life (it will take a long time to first precharge the system but after that I can use the system as I need it without having to resort to an expensive compressor).

To be honest, I've seen the state of some old compressors with their tanks and I trust them even less than PVC. When opened up, the air wasn't dried properly and there's massive rust everywhere. Worst yet, there's serious pitting corrosion going on at the bottom of the tank (because the manufacturers didn't clean the grit and garbage out the bottom of the tank before closing it).

As for my PVC tank system, I hope for a 10-15 year lifespan before needing replacement. Dose this sound reasonable?

You can spend about $800.00 (or even less) and get a real air compressor that will keep up with most of what is done with compressed air. See link below:

http://www.sears.com/shc/s/p_10153_12605_00916781000P?vName=Tools&cName=Air+C ompressors+%26+Air+Tools&sName=Air+Compressors&prd No=1&blockNo=1&blockType=G1[/URL]

Where do you live? If its in the USA, Harbor Freight has a 60 gallon upright that can feed roughly 14 cfm forever essentually.

And do it for under $400. It's a 209v single phase... any electrician can wire it into a split phase 220v breaker panel. I have one.

Not perfect for a business... but you clearly aren't a business.

What you describe won't run much for very long before you have to sit and wait for a long time.

Unfortunately I live in Canada and stuff from the States tends to be extremely expensive (mostly because a lot of the stuff in the States is no longer made in the States and thus subjected to fairly heavy duties and taxes, not to mention freight which can easily cost hundreds of dollars).

100 gallons is a lot of air. Most of the time I use compressed air for cleaning up the shop after I'm done (amazingly fast and easy when you can just blow everything into a specially designed corner trap and simply run a vacuum over it and be done).

If I use a metal container, I will need proper air drying equipment to ensure condensation and corrosion will not occur inside the tank. If I use PVC/ABS I don't need to worry about any corrosion period. I use my air for cleaning and don't own any air tools so I don't need dry air.

Anyway, back to the question: How well will PVC/ABS stand up to long term high pressure (100 - 150 psi) use in widely fluctuating temperatures (-40 to +30C) but being shielded from sunlight?

Are you saying that you want to build your own tank? If so, just how do you plan on doing that.

PVC will theoretically last for ever. It is not recommend that PVC be use for compressed air. The reason being that should a rupture occur the PVC will shatter and could send out shrapnel.

As for as condensation in the tank, it's going to occur if moist air is drawn in and compressed. To handle this a drain plug is usually provided and dryers are use on the output lines. You may be able to find some kind of dryer for the input side but I doubt it.

About any tank that will handle the pressure should work as an air tank. A few years ago my neighbor, who was a plumber, told me that they had received a commercial water heater that leaked. Manufacturer replace it but didn't want the faulty one back. We remove the heating element, made a gasket for it.
I sat it in my garage and ran some copper pipe to my shop and connected my 20 gal portable compressor to it.
I now have a 80 gallons of air and my portable compressor is still portable.

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Originally Posted by hkstroud

The reason being that should a rupture occur the PVC will shatter and could send out shrapnel.

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And this is precisely the reason why most jurisdictions have banned air tests for plumbing systems and instead require hydrostatic tests.

All it takes is one small weak spot in the extrusion process (or prolonged exposure to ultraviolet light) and you have a fragmentation grenade just waiting to explode.

Personally, I'd strip the outer shell off a used electric hot water tank and utilize the already tapped fittings (and pressure pop-off) if I were looking for a cheap alternative for storing compressed air.

I apologize, it is actually ABS pipe (a tougher material) but yes, I definably understand the brittle nature of some of the "stronger" plastics, especially at low temperatures (-30C is not uncommon up here, -40C, rare but happens at least once a year).

Building the actual tank itself isn't hard. I will go about doing using a series of U bends straight sections with the entire tube capped at each end. The entire structure will resemble something like a snake going back and forth. One of the ends will be tapped with a 1/4" NPT and fitted with a quick disconnect (the end caps are 1/2" thick so there's enough material there to form an NPT thread). All the joints are cemented together.

The entire construction will be screwed down using metal straps to a large piece of plywood and mounted to a wall with the plywood only side facing outwards and a shield made to cover the rest of the exposed ABS pipe to protect it against possible shards of flying material in the shop.

As for the Material itself, using conservative values, I calculated the failure pressure to be around 600 PSI (which is in line with the rated 200 PSI, giving a reasonable factor of safety of 3).

About the water heater, I had considered it first (seeing as tested failure pressures are around 300-350 PSI) but in the end, they are still made of steel and still prone to corrosion. I wanted to have an absolutely maintenance free system which I could leave in place for a decade and never need to check on it. Corrosion of metal tanks is the biggest factor in my idea to use ABS. (I'm a mechanical engineer and have taken a course in corrosion... corrosion scares me. You can do your PHD thesis on it and still have no way of predicting with 100% accuracy what will happen. A mere scratch or piece of dirt on material submerged in water can cause even 1/4" thick stainless steel to be eaten through in a matter of months. Never mind regular steel! Unfortunately ABS is not a metal and thus we never studied it, hence why I'm asking).

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Originally Posted by faken

I apologize, it is actually ABS pipe (a tougher material) but yes, I definably understand the brittle nature of some of the "stronger" plastics, especially at low temperatures (-30C is not uncommon up here, -40C, rare but happens at least once a year)

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Nearly all commercially available ABS pipe is foam core (cellular core), which has a lower pressure rating than both foam core and solid core PVC pipe.

If corrosion is the only drawback to using a H/W tank, then keep your eyes open for a newer glass lined H/W tank.

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Originally Posted by Widdershins

And this is precisely the reason why most jurisdictions have banned air tests for plumbing systems and instead require hydrostatic tests.

All it takes is one small weak spot in the extrusion process (or prolonged exposure to ultraviolet light) and you have a fragmentation grenade just waiting to explode.

Personally, I'd strip the outer shell off of a used electric hot water tank and utilize the already tapped fittings (and pressure pop-off) if I were looking for a cheap alternative for storing compressed air.

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I understand. A single scratch or casting void in the process can cause a stress concentration and result in failure, however I am using pipe rated to 200 PSI and modern extrusion processes don't lend themselves to voids in material. Either way, the entire assembly will be shielded and designed to break away and move with the force should a rupture occur countering the effects of shrapnel (though if you didn't wear ear plugs while it ruptured, you would likely go deaf, though any pressure vessel failing inside a confined space will likely give the same results).

A used hot water tank is likely more dangerous. Pitting corrosion is the most likely method of failure, not to mention also being the most difficult to detect and prevent. If it has been used for many years already it is likely at the end of its useful life and adding pressure to it is dangerous and unpredictable.

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Originally Posted by faken

I understand.

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T'would appear you are more interested in seeking validation for your own ideas than you are in seeking advice.

Not a big deal, really, just an observation.

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Originally Posted by Widdershins

T'would appear you are more interested in seeking validation for your own ideas than you are in seeking advice.

Not a big deal, really, just an observation.

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I was looking for an answer to how long PVC (now ABS) will last under pressure at a wide varying temperature range and if fatigue from pressure fluctuations would be a factor.

Your answer has nothing to do with the question, you know... not a big deal, really, just an observation...

Faken, I think my deal is this. I don't know what import duties are in Canada, but let's assume it is 100%. That would make a $450 compressor cost $900. I would 100 times rather spend 900 for something that works and is safe than spend hundreds for a collection of pvc pipes to work with a weak compressor with the constant risk of failure. Now, you might just want to be doing this simply for the experience of doing it, on the level of a hobby. That is understandable. But I just can't imagine doing this for some supposed saving of money. I can't see that.

To answer your original question, try this site. It states its pvc is rated to 300# at up to 140 degrees.

Product Specifications: PVC Pipe Schedule 120—Harvel Plastics, Inc.

If you do this, I would definitely do a hydrostatic pressure test first, which simply means to fill it with water and then apply something in excess of your planned working pressure to it. That way, should the pipe fail, it won't be catastrophic as water does not compress in the manner of air.

Your name strikes me as a little strange. I hope "Faken" is not "faking" this post.

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Originally Posted by faken

I was looking for an answer to how long PVC (now ABS) will last under pressure at a wide varying temperature range and if fatigue from pressure fluctuations would be a factor.

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Right -- And pretty much every person who responded cautioned you not to proceed with this project and even stipulated why they were opposed -- Nobody here is going to rubberstamp a project they deem dangerous.

Look at it this way: ABS and PVC have been around for about 40 years, give or take, is vastly cheaper than steel and far easier to mold than steel, yet not one tool manufacturer has ever released an air compressor with an ABS or PVC storage tank.

That should tell you something, Faken.