Question on counter lungs

[cool_hardware52]

The CL's that I am replacing were welded. The first set gave way on the second dive. The replacement pair have given away twice, the seal just comes apart. I don't have near this kind of trouble with drysuit parts that I do, so the glue I know beats the seam I don't trust anymore.
About those monkey signs, there is a gorilla back east that is writing a book....

deepblueh2o,


RF welding urethane is part art and part science. Joint strenght is dependent on several factors, including the age of the urethane, the welding machine parameters, the temperature of the both the material and welding dies.

If you have cl's that pull apart at the seams, you have defective product. If a seam pulls apart through the seam, i.e. the two material halves are intact, but the seam "unsticks" it's likely that not enough rf power, time or pressure was used, or old material.

If the part fails next to the seam, i.e one piece tears off the other leaving two layers at the seam, it may be too much power, pressure, time.

Destructive testing is key with every part run, i.e. weld a few and then test.

When you consider the range of goods that rely on good rf welds in urethane, like IV bags, scuba BC's, even the gell inserts used in some auto seats, it's pretty clear that the process can be highly reliable, your results with your CL's indicates something is wrong.

Glue would be my last resort. I do know of a case where a "well known" CCRB builder made a glue repair to a unit under test by the US navy. The officer who dived the rig next reported a head ache he attributed to the glue and terminated the test, effectively removing the company from consideration. Point being if a CCRB maker could not furnish a glue that would both seal and not off gas nasties what do you plan to use?


Regards,



Tobin George

 

[iain/hsm]

The CL's that I am replacing were welded. The first set gave way on the second dive. The replacement pair have given away twice, the seal just comes apart. I don't have near this kind of trouble with drysuit parts that I do, so the glue I know beats the seam I don't trust anymore....

I am not surprised you dont trust them but something doesn't quite add up. A radio frequency (RF) weld on a 200 denier packcloth nylon would requre a pretty thick 12 to 14 oz urethane coating to start with to make a good weld, anything much less and the seam will rip apart. These bags you have been buying sounds like not enough coating on the nylon. Standard 200 denier uses only about 7 oz of coating.

The RF weld width is also very important say 1/8 wide minimum for a waterproof seam, going to 3/16 wide for a industrial application, to 1/4 wide for mil spec. For a breathing bag use 3/16 wide weld. The welder needs a metal pattern frame and a large enough plattern area then its a calculation of weld width times weld length, as the "weld" is basically done in one hit. The other problem may be the welding machine is too small in size. A weld of say 200 inches long and 3/16 wide is 40 square inches, The 200 Den x 14oz coated material would need about 10kW minimum with some heavy duty pressure on the electrode to "seal" the bag. At a guess these bags were made on a standard PVC Welder at 4Kw. A properly designed breathing bag will not split at the seam.
Other test are:
moisture vapour transmission
Breaking Strength
Elongation at Break
Tearing Strength
Adhesion
Resistance to Aromatic fluids, salt water,
Accelerated weathering
Punchure resistance and seam strength

Ok maybe not the sort of thing you want to make as a one off, but I hope the info helps you,

 

[cool_hardware52]

I am not surprised you dont trust them but something doesn't quite add up. A radio frequency (RF) weld on a 200 denier packcloth nylon would requre a pretty thick 12 to 14 oz urethane coating to start with to make a good weld, anything much less and the seam will rip apart. These bags you have been buying sounds like not enough coating on the nylon. Standard 200 denier uses only about 7 oz of coating.

The RF weld width is also very important say 1/8 wide minimum for a waterproof seam, going to 3/16 wide for a industrial application, to 1/4 wide for mil spec. For a breathing bag use 3/16 wide weld. The welder needs a metal pattern frame and a large enough plattern area then its a calculation of weld width times weld length, as the "weld" is basically done in one hit. The other problem may be the welding machine is too small in size. A weld of say 200 inches long and 3/16 wide is 40 square inches, The 200 Den x 14oz coated material would need about 10kW minimum with some heavy duty pressure on the electrode to "seal" the bag. At a guess these bags were made on a standard PVC Welder at 4Kw. A properly designed breathing bag will not split at the seam.
Other test are:
moisture vapour transmission
Breaking Strength
Elongation at Break
Tearing Strength
Adhesion
Resistance to Aromatic fluids, salt water,
Accelerated weathering
Punchure resistance and seam strength

Ok maybe not the sort of thing you want to make as a one off, but I hope the info helps you,

Little here for me to disagree with. I'm not sure from Deeps posts if his current CL are coated nylon, or are inner urethane with nylon sewn outer.

If laminated stock I'd be as suspicious as you about the thickness of the urethane, and the power used to weld. Urethane requires ~ 40-50% more power than vinyl.

Tobin

 

[Diver Mike]

I have the mountian sports (camel bladders) in my KISS rebreather. I bought these from Gordon at KISS in the basic kit.

They now have around 35 dives and are yet to have any issues what so ever.

 

[deepblueh2o]

The previous CL's that came apart were original equipment, dreager ray CL's. The 200 deneir is the material that I am using for replacement CL's. In all cases the seam seperated. If all else fails.... that's why we carry bailout. Will let you know.