Spec Boot For Mk-15

[lowviz]

Tigger,

I was cautioned that the silicone oil/grease will soften and (over time) weaken a silicone elastomer. So we are back to the same problem, boots that don't hold up over time. D-C had nothing to gain by telling me that, it eliminated their product. I'm supposed to be getting samples of urethanes from one of your supplier's distributors. Haven't arrived yet. I'll not have the boots analyzed, but spend the money on a range of urethanes and send the prototypes to the experts for assessment.

None of this stops you from perfecting a silicone mold for an MK5, though.

 

[raftingtigger]

Tigger,

I was cautioned that the silicone oil/grease will soften and (over time) weaken a silicone elastomer. So we are back to the same problem, boots that don't hold up over time. D-C had nothing to gain by telling me that, it eliminated their product. I'm supposed to be getting samples of urethanes from one of your supplier's distributors. Haven't arrived yet. I'll not have the boots analyzed, but spend the money on a range of urethanes and send the prototypes to the experts for assessment.

None of this stops you from perfecting a silicone mold for an MK5, though.

Thanks, that was the info I was looking for. My plan right now is to make a silicone mold, then mold a silicone boot (simply since I have silicone and not urethane at home). If the boot fits and stays on, I'll pack it with silicone grease and test dive it - as a spare bottle. If that works then I'll get some urethane rubber material and make as many boots as I want.

 

[Couv]

That's a good point Tigger. The boot is not a critical seal and its failure would be of little consequence.

 

[redacted]

Sure, it has little impact on the next week of diving, but it may impact the required frequency of service which can be significant if you are using an expensive synthetic packing. The problem is a poor seal will allow water in and it does not flush out with a post dive soak.

My mk5 enviro instructions recommend service at least annually to replace the packing.

 

[lowviz]

Sure, it has little impact on the next week of diving, but it may impact the required frequency of service which can be significant if you are using an expensive synthetic packing. ...//...

Yeah, as we were told, a silicone boot will be a problem. Found this as confirmation: http://www.cmrubber.com/pdf/elastomer_compatibility_chart.pdf

However, no reason avoid making and testing silicone prototypes until we decide on the final material. Long talk with the experts again today. They are leading me towards Mold Max 30 for the mold. The jury is still out on the urethanes, samples haven't arrived yet. Just for grins, look at the compatibility between urethanes and salt water...

Reg guys/gals: The way I see it, there is one seal between the packing grease and 100% O2 in my safety bottle. Do I REALLY need to use Christo Lube???

 

[redacted]

I suspect the old silicone packing will hold up much better against water. It really is thick. You could always use a bead of Christolube at the head and stem of the piston and silicone for the main filler.

I think the groove is important to provide space for the 0.1+ cu inches of packing material that has to go somewhere when the piston moves from the fully open to the locked up position. I wonder if Herman could mill a groove into a mk5 ambient chamber.

 

[lowviz]

...//... You could always use a bead of Christolube at the head and stem of the piston and silicone for the main filler. ...

Great suggestion.

Straight silicone elastomer is out due to incompatibility with silicone oils and urethane is out due to incompatibility with salt water. Tigger's molds are still hanging in there as they will allow for heat curing.

My latest first choice for the boot material:
https://www.dowcorning.com/content/publishedlit/45-1569-01.pdf This material covers all the requirements but getting it in small volumes might be an issue...

 

[lowviz]

Getting close.

Need experienced input concerning the durometer spec for a promising material: MED50-5338 | Fluorosilicone Liquid Silicone Rubber | NuSil

I've found a two part, no solvent, fluorinated silicone that will definitely hold up to silicone oil. It can be purchased as a two tube kit with a one-year warranted shelf life. You can also get an adapter (cheap) so that you can use the two-tube kit (with mixing head) in a standard caulk gun.

Problem: the durometer rating is 23-40. The fairly wide range indicates that it isn't a controlled property. (BTW, I'm assuming that the durometer spec is a Shore A rating)

23-40 sounds low to me. Experts???

 

[Couv]

I'm no expert, but I would think softer, and more flexible is what is called for.

 

[lowviz]

Yeah, this one is hard to call. Their median specification for this material is for durometer 30. This link might help put 30 into perspective: http://www.paramountind.com/pdfs/paramount_durometer_scale_guide.pdf The compatibility properties are truly fabulous, though.

Close enough. Time to bench test. Since I couldn't find a low-viscosity material that can be poured into a mold, I'm forced to go to liquid injection molding. Unfortunately, this stuff is too viscous to pour into a mold but their tech support confirmed that the pressures aren't all that high. The best part is that I can get it in small quantities.

I'm going to try making one of Tigger's molds but have it pocketed into a closed aluminum cavity so that it can't deform under pressure.