DIY Filter towers

[pescador775]

Yeah, just as I suspected. I did a little research on aircraft aluminum. It happened like I thought it would:
http://www.ofm.gov.on.ca/ENGLISH/Publications/communiques/2002/2002-20at1.htm

It's simple, do what I tell you or imitate Bauer. These metals are not very expensive. BTW, Bauer uses 6061-T6 for their big towers. Surely, even a blind squirrel can find some of that stuff. The fact is that 7075 is and has been "used" but I don't approve.
I also said quite clearly:

That is why an alloy like 6061-T6 is used for Scuba cylinders instead of aircraft aluminum which has better properties (for some apps). I know 7075 is used by some folks to build condensators but I am leery of it for home builders.

The man asked a question about building a filter and I answered it. Simple. I dont' judge him for wanting to do it. I just hope I'm not wasting my time.

 

[cool_hardware52]

Yeah, just as I suspected. I did a little research on aircraft aluminum. It happened like I thought it would:
http://www.ofm.gov.on.ca/ENGLISH/Publications/communiques/2002/2002-20at1.htm

It's simple, do what I tell you or imitate Bauer. These metals are not very expensive. BTW, Bauer uses 6061-T6 for their big towers. Surely, even a blind squirrel can find some of that stuff.

The man asked a question about building a filter and I answered it. Simple. I dont' judge him for wanting to do it. I just hope I'm not wasting my time.

Pescador,

I'm not looking for a fight. The tendency for high strenght metals, such as 7075 to fail catastrosphically, instead of first yeilding a bit would make it a poor choice for a pressure vessel. You want toughness, not just high ultimate.

I asked you why because you had earlier suggested that 7075 was an appropriate choice.

6061 is commonly available, and careful selection at a surplus metals dealers might yeild what you need.

I still think DIY pressure vessels are a bad idea.


Tobin

 

[pescador775]

I said:

Why? Really stiff material may display very high tensile but I am concerned the metal could fracture on impact or after many cycles, especially at sub zero temps. That is why an alloy like 6061-T6 is used for Scuba cylinders instead of aircraft aluminum which has better properties (for some apps). I know 7075 is used by some folks to build condensators but I am leery of it for home builders. In any case, heaters should be used at sub zero temps and this may allay concerns. Some may feel differently. An alloy like 2024 is the way to go, IMO.

Later, you said:

The tendency for high strenght metals, such as 7075 to fail catastrosphically, instead of first yeilding a bit would make it a poor choice for a pressure vessel. You want toughness, not just high ultimate.

If you want to avoid a fight, stop copying my statements , altering them a little, and then representing them as your own. Stop trying to quote out of context in such a way as to make me look like an idiot. Stop misrepresenting my position. Your negative opinions are noted, and redundant since your agenda, including the rhetorical questions,was not well concealed.

 

[cool_hardware52]

If you want to avoid a fight, stop copying my statements , altering them a little, and then representing them as your own. Stop trying to quote out of context in such a way as to make me look like an idiot. Stop misrepresenting my position. Your negative opinions are noted, and redundant since your agenda, including the rhetorical questions,was not well concealed.

Well I guess I've been exposed. How cleaver are you to decern my poorly concealed agenda of trying to keep people from getting hurt, and or wasting time and money.

(Secretly I want to retire early by selling filter towers to the DIY crowd, damn now I need a new plan)

Rhetorical questions provoke debate, or further discussion. I damn well know why brittle materials are a poor choice for a pressure vessel, and I suspected you did too. Does the OP know this? Are other readers of this thread aware of this? Did it kill you to expand on this subject?

Some alloys like 6061 T6 are relatively stretchy and 7075 T6 is relatively hard and rigid, but with very high tensile. Either can be used but something in between might be better.

The bolding is mine

First you suggest an aluminum alloy that's expensive, rare, hard to find and proven to be unsafe, then you correct yourself later. If you knew 7075 was unsafe why even mention it? If you are offended by having somebody point this out I'd suggest not making such statements in public.

As I have stated repeatedly IMO DIY pressure vessels are a bad idea, encouraging the fabrication of such is a bad idea.

Adaptation of professionally designed pressure vessel seems fairly safe, and a much better path for the DIY's.

I'm all in favor of DIY, one of the reasons I have the shop and resources I do is because I'm a frequent DIY, but I hate to see somebody injured or killed by a homebuilt Tower.

Tobin

 

[pescador775]

Magneto, I did a quick calc of 6061 T6 aluminum pipe, 2 inch (internal diameter), schedule 80. The maximum allowable stress occurs at 7000 psi. This will drop some when internally threaded since the effective wall thickness will be reduced and this issue will have to be looked at carefully. Do the calc if you want but go farther than that and see what the industry says about threaded pipe. In the USA, a six foot section of this pipe sells for 65 dollars. In addition, you would have to buy the aluminum round bar for the end caps. If you buy the pipe from a reputable company they will certify as to product ID. You will need support from a machine shop to manufacture the end caps and other work, and you will need to support them with detailed drawings. The overall expense would probably be as much as a good used filter bought locally. Remember, you need LONG internal threaded section for an aluminum canister.

So, that may not be an option. There is a reason that filter cans are expensive. However, you could still check into the availability of stainless pipe or tube. Same issues, verify the metal, do the calcs . 304 stainless is hard to thread but less threads are required. For a 2.5 inch diameter can you would need about 1.0 inch length of fine thread, internal for stainless pipe or external for stainless tube. You may even be able to find something locally to copy. Then, provided you could locate the materials, you would begin to understand what is required. You started this thread knowing squat. Now, you know a little more. Keep studying and Good luck.

 

[Hoosier]

my experience is that it is cheaper to buy right than to make a filter canister. Labor is high. .

I was also thinking about the same project about the additional filter stack. To buy the canister chamber and parts are much easier, safer and better way if you don't have any good source in your area. Based on my research, even,if you don't plan to use the repackable design, there is not much price saving between DIY and getting the pre-assembled one.

Sure, I agree this is DIY forum. So, in this case, you had better get the right parts and simply aseemble it in a right order.....

 

[cool_hardware52]

Magneto, I did a quick calc of 6061 T6 aluminum pipe, 2 inch (internal diameter), schedule 80.

Pipe is nominally sized by the ID, with schedule 40 generally used, i.e. "2 inch Pipe" would have a nominal 2" ID for the schedule 40 type. The schedule 80 type of "2 inch" will be the same OD, bu the ID will be smaller. "2 Inch" sch 80 will be ~ 1.94 ID.
My guess is that it could be hard to find 2 inch schedule 80 6061 Pipe with a 2.0 ID

Tubing is usually sized by the OD, with the decimal wall thickness called out.

Remember, you need LONG internal threaded section for an aluminum canister.

This is true, low tensile materials require a longer lenght of engaged thread to withstand a given load, but it's not quite that simple. The effective lenght of engagement will be impacted by the fit of the thread (thread class) and the ductility of the material. Consider a machine screw screwed into a threaded plate, in other words a "through hole" As the fastener is progressively tightened the greatest unit stress will be just under the head, and if tightened sufficently the threads of either the fastener, or the plate will first yeild just under the head. When this happens the load will transfered to the next "deeper" threads, and so on. This will continue until the either the fastener breaks, or the threads fail in either the plate or the machine screw.
The key point is the entire lenght of threads are not equally loaded at the same time. A very conservative safety margin should be applied.


Thread depth vs engaged lenght is worth considering also. Finer threads offer less load per unit of engaged lenght, but also reduce the wall thickness of the tube less. It can be worthwhile to consider both when selecting a thread lead. Better yet leave it to the pro's.

Tobin

 

[pescador775]

Rhetorical questions provoke debate, or further discussion. I damn well know why brittle materials are a poor choice for a pressure vessel, and I suspected you did too. Does the OP know this? Are other readers of this thread aware of this? Did it kill you to expand on this subject?

Here's an idea. Lawrence Factor brags on their 7075 aluminum canisters. Why don't you call them to complain? Truth is, the Germans would not use this metal alloy because they employ actual engineers to design their stuff. These dinky outfits in the US, cottage industries mostly, who make filters are staffed by guys like you who would not have known about these metallugical concerns except for comments from me, or from some other engineer. As far as my comments: I said 7075 "can" be used, I did not say "should" be used. I went on to explain why. Your response was another "why?" You claim that you already knew the answer. That's pure bull. The apparent reason you didn't expand on this subject personally is that you genuinely did not have a clue. Fumbling questions were all you could muster.

 

[cool_hardware52]

Here's an idea. Lawrence Factor brags on their 7075 aluminum canisters. Why don't you call them to complain? Truth is, the Germans would not use this metal alloy because they employ actual engineers to design their stuff. These dinky outfits in the US, cottage industries mostly, who make filters are staffed by guys like you who would not have known about these metallugical concerns except for comments from me, or from some other engineer. As far as my comments: I said 7075 "can" be used, I did not say "should" be used. I went on to explain why. Your response was another "why?" You claim that you already knew the answer. That's pure bull. The apparent reason you didn't expand on this subject personally is that you genuinely did not have a clue. Fumbling questions were all you could muster.

Foiled again oh great one. I guess I couldn't find my ***** with both hands without your help, daily I will thank my maker for your help.

I'm not worthy, I'm not worthy. I'm not worthy, I'm not worthy........

What is apparent is you are perfectly willing to encourage people to engage in potentailly dangerous activities, and without hesitation resort to personal attacks when your errors are pointed out.

Are you saying that only a PHD in Mechanical enginnering would know that brittle materials fail catastrophically, and more ductile materials typically do not?

That a lesson I managed to grasp years ago.

What possible motive could I have other than trying to prevent somebody getting hurt? Again, DIY pressure vessels are a bad idea, potential energy needs to be respected.


Tobin

 

[rjack321]

Olly, I think you should ignore the bickering here.

By the time all the machining you're looking at is done, maybe the shipping on a chamber such as this wouldn't be a bad deal...

http://www.scubacompressor.com/shop...d/152?osCsid=45e01401822260888af8245dc83723bf

A proven product. 6061 Aluminum.

If you continue on with a DIY approach, I suggest thicker pipe than schedule 40. Not based on any metalurgical science, the incremental cost of schedule 80 or even schedule 160 just won't be that much and you'd have a higher safety factor (= allowance for minor errors). I'd also go with stainless, 316 is often used although not so much for pressure vessels since its difficult to machine.

I have a smaller version of the chamber above and I'm very happy for the price (and peace of mind).