Psst..... a little counterlung tip......

Genesis

A little brainstorming and playing around with various fabrics led me to attempt something that others apparently haven't thought of.

We know about the MSR bags, right? Nice counterlung fabric, have a nice threaded port, the lids can be easily modified on a lathe to have the center cut out, and with a bit of work you can fashion a T-piece from HDPE on a lathe and heat-weld it (I've shown that on the K1's page) In fact, the KISS classic uses these as counterlungs.

Well, for OTS lung units this leaves you with a "not quite optimal" counterlung shape. Specifically, its too wide and bunches up uncomfortably on your shoulder. It does work well though; I've been diving it on the K1.

Now the "common logic" is that you need an RF welder to get urethane-coated cordura to bond correctly.

Wrong.

Try this experiment. It will cost you one MSR bag. Make it a 10L one just in case it works as you hope it does

Draw the outline you want on it.

Take an ordinary clothes iron and set it to LINEN, dry heat.

Allow to reach temperature.

IRON heavily and with lots of pressure to establish your NEW seam, covering the entire old seam area up to your seam line.

ALLOW TO COOL FULLY.

Presto.

$40 counterlungs, here you are. Attempt to pull apart your seam once it has fully cooled. Not happening, eh?

Fill bag with water, screw on lid, throw on ground. Note that the seam holds.

Now trim to eliminate the excess seam area; leave 3/4" or so all around for strength.

This appears to be just as strong as the original RF-welded seam.

Now you can make OTS lungs of the appropriate shape out of the 10L MSR bags.

How come nobody's tried this one before?

Or - if you have - you're not sharing with people? That's not nice

Take my basic design for HDPE T-pieces and this tip for counterlungs, and you've got the lung + hose + T-piece problems solved. Add mouthpiece and what's left is your scrubber can and oxygen management system (whether electronic or manual)

One rebreather, coming up, and no $600 counterlungs either. Try $40 each for the MSR bags.

I know its common to mark up rebreather stuff by 10x, but now you can raise the appropriate digit to those prices if you're homebuilding.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

Style

I been playing with that idea for my upcoming homebuilt Rebreather, but I was thinking about asking a friend who is working at a clothing shop where the weld plastic bags together to ensure the customers havent put other stuff into bags that the staff have put together as sales bags.

They have a machine thats is mede for this, although that will give you a much smaller welding seam.

You didnt have any problem with the plast melting and got stuck on your iron?

Mark Chase

Not untill his wife finds the iron

ATB

Mark Chase

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Kevin Juergensen 16/11/08
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Genesis

Not in the least.

Guys, think this one through. It took me a while to figure it out - the side you are ironing on is the cordura side; there's no urethane there!

If you know someone with an RF welder, have at it that way. But if not, this absolutely works and the temperature control is good enough to get an excellent bond.

I was surprised; I didn't think the temperature range would work well and/or there'd be insufficient control to get a good seam.

Wrong on both counts; it works great!

The counterlung/T-piece dillema has been one of the biggest bug-a-boos facing me in building the K1, and has been where the largest set of design issues - and redesign issues - has come up.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

cool_hardware52

This is common logic? Really? Urethane is a thermoplastic, at least the type used as film on coated fabrics.

Thermoplastics do not care how they get hot. If you reach the melting point they will weld.

Why do RF welders exist then you might ask. Simple. The "die" in a rf welder does not get hot, atleast not hot enough to directly melt the urethane. In Radio Frequency (RF) welder it is the Hi Frequency AC that causes only the material to get hot. The key benefit is the die does not stick to the material, in fact the die and platten are both effectively cold heat sinks. The other man benefit of RF welders is the process can be controlled, and ican be reliably reproduced.

Inpulse (plastic bag) sealers work by rapidly heating from ambient to above the melting point of the plastic, and then cooling to well below the melting point. With a little PTFE film between the heating element and the work piece this works OK. The problem arises if you want a something other than a straight line. Complex shapes fitted with heaters and covered with PTFE film, and then subjected to many heat cool cycles would be hard to fabricate.

RF dies OTOH are relatively simple big brass "cookie cutters" The shapes possible are endless.

Your "Iron On" cl's should work fine, if you make good welds.

Good luck,

Tobin

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Genesis

Yep. The surprise was that I was able to get to the critical temperature in a controlled fashion via this method.

I didn't think it would work well (or at all.)

It did.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

Skipbreather

Something like this?
Harbor Freight Tools - Quality Tools at the Lowest Prices

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"Entropy RULES! Enjoy the interim."

Yankee Rebel

great work!!


weve been playing with this idea for awhile now. originally it started out as heat seal nylon codura available from most fabric suppliers online. we have been unable to obtain any "food grade" ratings yet though from anyone. i emailed MSR a few times in an attempt to purchase some bulk material from them, and they totally cockblocked me. their materials are supposedly a proprietary secret, and they dont sell bulk material, they dont disclose their supplier, and if i wanted any.. id have to buy the bags.
the best bit of info ive been able to obtain so far was from one fabric supplier.. to paraphrase from memory..
the law says that it is up to the end user/mfg to determine if the nylon cordura is "food grade" or not.
they couldnt tell me.
the MSR "reweld" lungs have been reserved as a last resort for us so far. the cost being the prohibitive factor.. can get bulk material ALOT cheaper than one MSR Lung will cost. one outfit will even give you "free" plans to make your own drybag! id have to put google to work to come up with that supplier again.. my memory sucks and i had a "problem" with my puter that cost me ALL my bookmarks and alotta good stuff.
hope this is helpful to you.
Yankee Rebel

Genesis

Seattle fabrics has a wide assortment of "heat seal" cordura.

However, no info on how safe their material is with regards to "food grade".

BTW, the MSR bag does look a bit pricey, but remember - you get the half the T-piece fitting WITH THE BAG. This helps quite a bit on the cost basis. If you're not going to do it this way, what are you going to use for fittings?

Being able to take the 10L bag and make the correct shape for C/Ls out of it easily makes it a no-brainer.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

Genesis

BTW, here are some pictures showing the construction steps.

First, we have the base MSR 10L bag. I have removed the "handle" from the port - this is necessary; you can't leave it on or you'll NEVER get the backing plate for the valves through the hole!

We draw the outline of what we want on the 10L bag in preparation for modification.



Next, we use an ordinary clothes iron, set to linen, dry, (maximum heat) and very slowly iron along the seam lines we have drawn. It requires about 2-3 minutes for each seam to insure that the seal is solid. The Nylon won't melt - the key is to insure the urethane DOES. Heavy pressure is required. Do this on an ironing board; you want a backing surface that is heat resistant but which does not sink heat, as its imperative that the back side get hot or the weld will be no good (ask me how I know!)

Allow the bag to cool completely (10 minutes or so) after the first seal is pressed before you disturb it, then do the other one. Wait for the second to cool completely before you disturb it, then check BOTH seals by attempting to pull them apart with fairly heavy force. IF YOU CAN DO SO you didn't use enough heat or enough time - go back and do it again.

Now draw a 1/2" boundary on the sealed area so as to have a 1/2" seal. Include a tab on each side halfway down so you can attach a means of securing the lung to the harness at the halfway point. Round the corners on the tabs so as to prevent a "hard point" where the lung can tear - the material is incredibly tough - you will need a VERY SHARP pair of scissors to make the cuts - but still, the idea is for these to LAST. The grommets at the top and bottom are the primary attachments; I use bolt snaps cave-line tied to the shoulder holes on my plate for the top, and 1" webbing with triglide adjustments on my crotch strap for the bottom attachment, again with a bolt snap on the end. Quick, easy, inexpensive and it works.

You wind up with this after you've cut the lung to size:



Now locate and cut the hole for your manual add valve (if inhale side) or manual add and OPV/water dump (if exhale). Press the backing nuts through the T-piece port (this is why you need to remove the "handle" - you won't be able to do that unless you have) along with the valve ports and plastic washer. Install the valves.

You wind up with this (with the original "cap" back on, being pressure tested to insure it does not leak)



Total cost for the lung, $39.95 for the bag plus about 30 minutes of your time. All the other pieces remain the same.

The T-pieces I fashioned for use with these bags are on the K1 thread. They are easily made on a lathe and drill press out of HDPE rectangular stock, HDPE pipe, a small piece of thin sheet for the divider and a heat gun to weld the components; it looks like this:



Simple, inexpensive and elegant. A pair of lungs and fittings can be made, assuming you have the lathe and drill press to make the T-pieces, for about $100. To this you must add the valves (manual add and dump)

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket