DIY Filter towers

[Magnet6x6]

has any body been succesful at building their own filter towers?

 

[pescador775]

It can be done. A friend is a machinist who built several from 7075 aluminum and other guy used 2026 alu. They variously used pipe or round stock. This is not something I can discuss in detail over the internet due to the complexity of the subject. Whatever alloy is used must be traceable and verifiable. Otherwise, the wrong alloy or heat treatment can fail (boom). Some guys take a 3000 psi hydraulic accumulator, stainless, the type used in aircraft, and stuff with chemicals, etc. Works.

 

[Magnet6x6]

It can be done. A friend is a machinist who built several from 7075 aluminum and other guy used 2026 alu. They variously used pipe or round stock. This is not something I can discuss in detail over the internet due to the complexity of the subject. Whatever alloy is used must be traceable and verifiable. Otherwise, the wrong alloy or heat treatment can fail (boom). Some guys take a 3000 psi hydraulic accumulator, stainless, the type used in aircraft, and stuff with chemicals, etc. Works.

Would be possible to see some photos of what they built?

I'm nervous about using aluminium and was thhinking about SS. However what would really help is to see photos of what people have built and hearing what changes they'd make in version 2.

 

[pescador775]

Sorry, I would have to demount the items from my compressors to display internals, and besides, it doesn't sound like you are serious.There are web sources for designs. BTW, you haven't mentioned what type of "filter" you are interested in. Is this a coalescing device or a chemical filter, or something else? Aluminum pipe is easiest to machine and perfectly safe if the material and heat treatment are correct. Alloys 6061-T6 and 7075 are easiest to find but are different in properties. Make sure the end caps are good and deep with at least 1 1/2 inches of thread on a 2 1/2 inch dia canister/3000 psi WP. Use Barlow's equation to calculate wall thickness. The calculator below will get you started. You can look up the tensile strength (psi) of whatever alloy you decide to employ. Easiest for a final filter is aircraft surplus hydraulic accumulator. Almost no work involved except to find the end fittings (McMaster Carr in the US).
http://www.corrosionmaterials.com/Tools/calculators/BurstingCalculator.asp

 

[oxyhacker]

There are some pictures of homemade stacks in the gallery section of the airspeedpress.com website - should be a link below.

Aluminum is tricky stuff to work with, so I would highly recommend adapting a suitable HP vessel which is known to be up to the job (like the accumulators mentioned) or SS seamless pipe rated for the pressure. The thing about aluminum is that even if you get the big things like wall thickness and threading right, the little details, like a improper radius or a slightly too deep cut can form a stress riser can get you. There have been a number of recalls of commercial aluminum filter stacks over the years due the them bursting due to fatigue as they aged. Smaller is safer than bigger, both because smaller diameter housings can handle more pressure, and because there's less energy contained should they let go.

SS is also better because you can put the media directly inside without a cartridge which would be required with alu since some of the filter media will corrode it.

 

[Magnet6x6]

There are some pictures of homemade stacks in the gallery section of the airspeedpress.com website - should be a link below.

Aluminum is tricky stuff to work with, so I would highly recommend adapting a suitable HP vessel which is known to be up to the job (like the accumulators mentioned) or SS seamless pipe rated for the pressure. The thing about aluminum is that even if you get the big things like wall thickness and threading right, the little details, like a improper radius or a slightly too deep cut can form a stress riser can get you. There have been a number of recalls of commercial aluminum filter stacks over the years due the them bursting due to fatigue as they aged. Smaller is safer than bigger, both because smaller diameter housings can handle more pressure, and because there's less energy contained should they let go.

SS is also better because you can put the media directly inside without a cartridge which would be required with alu since some of the filter media will corrode it.

Thanks Oxyhacker, I appreciate the constructive response.

I've spent a fair bit of time searching and I saw the gallery photos. The accumulator idea is excellent and some one was kind enough to send their photos. It's a very elegant solution but I'm unlikely to find any where I am, although I am looking hard.

I'd read some thing from an earlier post that you didn't advise the use of aluminium, that leaves me with the option of building one from scratch in SS. I'm not an engineer so I'd feel a lot more comfortable following or adapting some one elses proven and tested design rather than working out side of my limited field of experience. I should add that I have there no problem getting machining done other that the fact that I have to pay for it

So far I have the following information;
seamless SS sched 80 pipe
450 bar minimum rating (I only pump to 200bar)
ID 3.2cm - 3.8cm recommended
(I'd prefer 76mm but understand there are safety issues. Is 82cm x 3.8cm the same as 41cm x 7.6cm? )

What I can't get straight in my mind is how to cap it. I had visions of threading the ID and the OD (as per Bauer), getting plugs made, (with some sort of O ring seal), that would screw into the ID and a collar with a part of the center removed that would screw down over the top as additional security. Gas in and out would be through fittings tapped into the top and bottom.

Any advice would be appreciated

 

[Magnet6x6]

Sorry, I would have to demount the items from my compressors to display internals, and besides, it doesn't sound like you are serious.There are web sources for designs. BTW, you haven't mentioned what type of "filter" you are interested in. Is this a coalescing device or a chemical filter, or something else? Aluminum pipe is easiest to machine and perfectly safe if the material and heat treatment are correct. Alloys 6061-T6 and 7075 are easiest to find but are different in properties. Make sure the end caps are good and deep with at least 1 1/2 inches of thread on a 2 1/2 inch dia canister/3000 psi WP. Use Barlow's equation to calculate wall thickness. The calculator below will get you started. You can look up the tensile strength (psi) of whatever alloy you decide to employ. Easiest for a final filter is aircraft surplus hydraulic accumulator. Almost no work involved except to find the end fittings (McMaster Carr in the US).
http://www.corrosionmaterials.com/Tools/calculators/BurstingCalculator.asp

Actually I'm very serious and despite hours of searching I've only been able to find a very limited amount of information. If you know of the availability of plans I'd appreciate a link.

My most pressing need is for chemical filters but if you have information on coalecorsers I'd appreciate that as well.

I'd previously heard that aluminium wasn't a good medium in less than expert hands so I was leaning away from using it. Am I right in assuming the cap specifications you suggested would suffice for SS?

I'd love to use accumulators but they're all but impossible to find here and I suspect international shipping would be prohibitive.

Thanks for the calculator link, it'll be very useful.

 

[pescador775]

I don't know why anyone would be so cautious about aluminum, unless they expect to make some mistakes and think that a harder substance like stainless would cover their azz. Stainless is hard to work with and its characteristics with respect to cycle life are harder to verify. It changes also when worked. However, stainless is corrosion resistant and more resistant to some types of abuse like high temps. As far as aluminum, Bauer cites a cycle life of 68,000 for their heavy duty PO. For most purposes, cycle life of aluminum alloy is a non issue, yet, it keeps resurfacing in various places, from various people. It is irrelevant whether the tube is threaded ID or OD. Generally, the DIY type does not have ability to do internal thread and find an external cap easier to deal with. Basically, the search out a piece of commercial pipe with cap. It looks like a pipe bomb but will work OK. Aluminum devices are softer and need longer thread count. Two inches is not too much for aluminum and 1 1/2 inches for stainless. The more the better. The coalescer is a simple device. Obtain a micronic cylinder or disc and engineer it into the can. These sintered metal or ceramic elements appear in various civilian applications from air generators (bait tank) to fuel filters. Place it above a small chamber or hang it from the top. If you place it directly in the air stream, tiny particles from the compressor will clog it up. The small chamber or plenum is needed to prevent this. Also, inside this plenum can be placed a coil of spun metal ribbon or plastic ribbon (abrasive pad) which increases the surface area. Basically, this is a plumbing project which involves high pressures. Therefore, some details are more important than others. These relate to the high pressure aspects. A filter is nothing more than some chemicals stuffed in a sock inside a high pressure can. If you are worried about corrosion from the chemicals stuff the media in a plastic tube. However, then you encounter the problem of ensuring that air flow is directed only through the tube. This means an O ring seal going into the top. So, the bottom and top should be internally threaded and rather deep. This makes sense because deep theads are advisable anyway. Plus, there can be an unthreaded portion or extension with the O ring. Moreover, since the top and bottom plugs are deep, there is room to drill or otherwise form passages and cavities. For example, the bottom can be hollowed out for the plenum and a sintered disc can be inserted in a snug fit over top the plenum. This forms a hollow bottom "cap" with a sintered hat. Inside the hollow is a coil of ribbon. Air flow can be directed into the bottom or side of the cap. For safety, the bottom can be drilled and tapped and a blow out plug inserted.

 

[cool_hardware52]

I don't know why anyone would be so cautious about aluminum, unless they expect to make some mistakes and think that a harder substance like stainless would cover their azz. Stainless is hard to work with and its characteristics with respect to cycle life are harder to verify. It changes also when worked. However, stainless is corrosion resistant and more resistant to some types of abuse like high temps.

I agree that Aluminum can be safely used for pressure vessels, but one must be careful. There exists a wide variety of Aluminum alloys and tempers, some more appropriate than others.

Regarding threading; Highly stressed parts need to be carefully threaded. Cut threads, in particular 60 degree threads cut with a sharply pointed tool, can fail. Even with a proper radiused root tool improper feeds, speeds, chatter, etc can lead to a "torn" not smoothly cut surface. Becareful.


SS can be difficult to work, the tendency to work harden, and the poor thermal conductivity can be very challenging. Rigid set ups, correct feeds, Depth of cut, and careful selection of insert type are key.

I own a well equipped machine shop, and I've have to think a long time about building my own towers.


Tobin

 

[pescador775]

Tobin, my experience is that it is cheaper to buy right than to make a filter canister. Labor is high. That is true at least as concerns the more complex, integrated coalescer/filters. However, simple filters can be made from relatively cheap, used items. If someone is concerned about the cost of paying $25 for an accumulator and shipping a four pound package from the USA it may also be premature to consider making one from scratch. However, finding a piece of stainless pipe with caps may be easier in the middle east than finding virgin materials and building from scratch. One thing, there are plenty of heat treatable steels which would be more reliable or easier to work than stainless. The catch is finding someone to heat treat the item. Also, don't try to chrome plate the steel. Hydrogen embrittlement could be a problem (boom).