DIY Filter towers

[cool_hardware52]

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).

Pescador,

I'd be very careful about using pipe with screw on caps. The WP for pipe falls off fast as the diameter increases. Pipe threads scare me :11:

Hydrogen embrittlement can be a problem with Chromed steels, hi carbon heat treated steels in particular. You can reduce / eliminate embrittlement by baking after plating, but that's another expense, and many platers wait too long to bake.

One of my favorite materials is 4130N 90ksi min. Fairly easy to machine, easy to weld (please don't weld any pressure vessels) and often no need to heat treat.

Tobin

 

[Magnet6x6]

Pescador,

I'd be very careful about using pipe with screw on caps. The WP for pipe falls off fast as the diameter increases. Pipe threads scare me :11:
Tobin

How would you recomend sealing the tubes?

 

[pescador775]

We're not talking about water pipe and not tapered pipe threads. Nothing against pipe thread but it is a pain to deal with. Do some research magneto. You can find stainless HP pipe (tubing?) like that used in nuclear power plants and chemical plants. You make the seals by fabricating billets which are grooved for O rings. The billet fits inside the cap. It can be held in place with a sealant, a screw, or allowed to float. The billet can be through drilled and tapped. If the floating billet is trapped inside the can, a bolt can be inserted to facilitate removal.

 

[pescador775]

I was not able to edit the above message before Scubaboard, big joke that it is, crashed again. I'm taking a rest from this frustration. Meanwhile, disregard the above. Below is the correct versionl.

We're not talking about water pipe and not tapered pipe threads. Nothing against pipe thread but it is a pain to deal with. Do some research magneto. You can find stainless HP pipe (tubing?) like that used in nuclear power plants and chemical plants. You make the seals by fabricating billets which are grooved for O rings. The billet fits inside the cap. It can be held in place with a a screw, or allowed to float. Problem is I can't figure out how to do it with a thin steel cap. The billet is in the shape of a washer about 3/16 inch thick. The washer is hat shaped so it seals against the inner surface of the cap and the inside of the pipe. Possibly you could adopt the Bauer solution and bore out the cap leaving a ring. Then, you could fabricate a core from brass or aluminum. This core would have an annular O ring and be drilled and tapped for a small pipe thread, 1/8 npt or whatever. The core would be cylindrical except for a shoulder to hold against the lip of the tube and keep the core from slipping into the tube. Screwing down the ring (made from cap) would secure the core into the tube. Bauer's old condensator cans were built like this. With a thick aluminum tube it would be possible to make this shoulder small enough that the cap would not jam on it when threading onto the tube.

 

[oxyhacker]

Re aluminum, yes it can be used safely, but if Bauer and Mako and several others cannot make aluminum stacks that don't fatigue and occasionally let go (or at least stress crack), or have to be severely limited in cycles, what chance does a DIYer have? Remember they don't only design the things and hope they've though of everything, , but also test the design extensively before putting it into production. A DIYer doesn't have this luxury an basically gives it his best shot and then keeps his fingers crossed.

If alu is to be used, I think a Bauer style setup where an O-ringed plug goes into the tube and is held on by an externally threaded collar is preferrable to the a stepped plug that fits inside and is retained by internal threading - less reduction of the tube diameter, less steps to act as stress risers and external threading is always easier than internal for the amateur.

SS is hard to work, yes. So the secret is a design that requires the least workng possible. Cross bolted O-ring sealed plugs are probably the easiest way, though you have to keep the diameter fairly small to avoid overloading the bolts, though plugs retained by a collar can also be done with a minimum of machining. You wouldn't want to do this with alu, since the cross bolts would likely overstess it.

(Those Groban accumulators are starting to look pretty good even with postage)

 

[pescador775]

Threads, external or internal, both reduce the thickness of the tube and this has to be figured into the calculation using Barlow's. This is not rocket science. Aluminum tubes have amazing cycle life, thousands of cycles. Select an alloy tube which has good ductility and medium hardness. 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. However, for medium pressure (3000), the hydraulic accumulators are dirt cheap. Remember, it will not be possible to determine the total cycles to which a used tube has been subjected. Even so, I haven't heard of any problems. As far as the aluminum condensators which exploded, there were a couple and estimated to have sustained 80,000 cycles according to an Aussie govt report. I certainly agree that with aluminum tubes, internal thread with threaded plugs make the neatest installation. The ideal size for a small compressor is 2 3/4 inches OD.

 

[pescador775]

Here is a quick reference for aluminum alloys. Possible application for 2024 T6 or 6061 T6. Figuring out what stainless steel to use could be tricky. However, common austenitic steels like 304 are used for high pressure tubing. It's just that the steel should be fairly soft (Rockwell hardness) in order to ensure good ductility. Large diameter, commercial High pressure tube should have this property but some professional advice would be desirable.
http://www.aerospacemetals.com/aluminum.html#technical

 

[cool_hardware52]

Aluminum tubes have amazing cycle life, thousands of cycles. Select an alloy tube which has good ductility and medium hardness.

Why?


Tobin

 

[pescador775]

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.

Are you making a condensator, also? Why the ??

 

[cool_hardware52]

Really stiff material may display very high tensile but fracture after many cycles, especially at low 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).

Are you sure? My guess is the workability of 6061, in particular the cold forming / forging properties of 6061 make it an attractive choice. The lower cost plays a part too.

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.

You suggest that either 6061 or 7075 is appropriate. Their properties are very different.

I agree that aluminum can be used for towers or water seperators. I have towers I suspect were cast and then machined. I also have a cast seperator, all have performed fine to date.

As a practical matter how does one source cheaply and locally aluminum with a known pedigree? I live in Los Angeles, and even here with my not insubstantial scrounging skills, I'd be hard pressed to find a short lenght of surplus aluminum tube with certs.

I can of course order whatever I need from a variety of suppliers, but I venture that if I needed 3 ft of 3" od 7075 heavy walled tube the cost would exceed what one might pay for a real tower. Now all I have to do is machine it.

I could always dig through the mountain of tubes to be found at any number of surplus houses and pay ~$3-4 /lb, but do I have sufficient confidence in that tube to build a potential bomb out of it?

What is being discussed in this thread scares me. DIY pressure vessel seems like a very bad idea. What next? DIY tanks?


Tobin