DIY SPEC Boot

[rsingler]

Any reason not to try a proper width slice of an inner tube (with or without pinholes) to create a SPEC boot for a MK10 that I want to protect from heavy silt in coldish (45-50 deg) water by filling the environmental chamber with Tribolube? Yes, expensive, but wanted to try filling the chamber and wanted to try to minimize the mess. Pinholes necessary? Or will the water pressure equalize around the edges of the tubing?

Rob Singler

 

[Couv]

I just use the grease with no boot installed. I think Halocline and Six2Life have experimented with a DIY boot. Perhaps a bump to this thread http://www.scubaboard.com/forums/repairing-your-own-gear/445595-mk10-spec-boot-vs-trim-boot.html with your findings would be of value. I am certainly interested.

 

[halocline]

There's a type of tribolube that is designed for this, I think it's model 66. It's thicker than the 71, and cheaper. I've used it in my MK10s for packing the chamber. I might have the numbers mixed up....sorry! Just use the cheaper one.

I have been warned by an expert that packing the MK10 chamber is a bit tricky; it's harder to reach all the nooks and crannies to make sure that the chamber is completely filled than it is with the MK5. That said, I used the syringe package and from what I can tell, I didn't leave any air pockets. There was quite a bit of excess grease exiting the ambient chamber holes as I assembled the body.

I don't know how the inner tube will work. It might be fine; of course you'll have to make sure it's not loose, it needs to fit snugly in the recess. I wouldn't bother with putting any pinholes in it, maybe one. The first time you pressurize it, get ready for some grease shooting out. Try to pressurize slowly if you can.

In an ideal world the only flexing of the rubber boot would be with piston movement; obviously not very much. The grease itself is not compressible, I assume, so it's simply a transfer of pressure. The inner tube itself will compress; that's probably not such a good thing as I guess it would at least theoretically absorb some of the pressure change with depth increase. The stock boot is pretty stiff rubber.

I'd say it's worth a shot. You might want to have an alternate air supply on the first deep dive, and then disassemble the reg after to see if there's been any water intrusion into the chamber. Unfortunately that probably means re-packing, but at least you'd know how it worked.

Another option is silicone grease which is much stiffer. If you're using higher percentages of O2 that would be considered risky. One thing to consider, though, is that the chamber grease never comes into contact with the breathing gas unless you have an o-ring failure.

 

[rsingler]

You're right about the numbers, it's Tribolube 66 and 71. But they're both $210/lb from Aerospace Lubricants. Yes, I'll fill with the thicker (66, I think).

Anyone else want to weigh in on this "compressibility of rubber" thing? I think this is a legitimate concern, hence my thought about the pinholes.
I don't know what the instructions were for the old hard SPEC boot, but I figured the water leaked in around the edges when the boot was rotated to cover the ambient holes. Piston movement, even with a perfectly filled chamber, is still going to result in a little to-and-fro of goop right at the ambient holes.

With an inner tube, I am concerned that the soft rubber would make a semi-perfect seal without a pinhole, and therefore the elasticity of the rubber would decrease the transmission of ambient pressure into the environmental chamber by whatever amount of resistance it created as the rubber bulged into the hole. Therefore, the contribution to the piston would be ambient pressure minus all the little resistances imposed by the inner tube. I figure that's why the SPEC boot was hard and a little loose. It ensured water passage around the back, but still created a little barrier to decrease the mess.

I'm still in favor of pinholes, but I think I should remove the boot after every dive to allow any water to trickle out. I never saw the SPEC boot instructions, but I'll bet they said to rotate the boot so the holes lined up with the ambient chamber holes after every dive.

After I create this thing, I'll put it into my pressure chamber with some food coloring in the wet basket and run it down to 150 feet. We'll see how much water I can find inside the boot after. I'll try to post pictures.

 

[halocline]

I never saw the SPEC boot instructions, but I'll bet they said to rotate the boot so the holes lined up with the ambient chamber holes after every dive.

My SPEC boots don't have holes in them, although I think there are some that do. Those, I believe, are simply trim boots.

 

[rsingler]

Hmmm. How removable are they? I'd hate to think of even a little sea water sitting there for long periods after a dive. The filling process can't keep ALL the water out.

 

[halocline]

They're definitely not designed to be removed without taking the regulator apart. They fit in such a way that grease comes out of the ambient chamber holes and sits underneath the boot but still on the exterior of the reg underneath the boot. So, the idea is that all surfaces underneath the boot are coated with grease. That's supposed to water off of everything; from what I can tell so far, it's working great. But, it's coincidentally worked out that I've never used those two regs for salt water other than sections of salt water in the mexican cenotes.

The ambient chamber expands the most when the reg is depressurized, presumably happening after it's out of the water, so it's not like you're pulling water in. When my regs are dry, the boot sits a little concave in the groove. When pressurized, it expands out a bit. Does that make sense?

There is a single small drain hole (maybe 1mm) in each boot that grease squirts out the first time you pressurize it, and if you have a big free flow a little more comes out. You can clearly see the grease is completely filling up the space under the boot. That's one thing about the inner tube that might not be great...with the stock boots there are small ridges along the edges that basically create some space under the boot for grease to accumulate. It's a pretty thick layer, and I suspect that keeps water intrusion down IF you get all the airspaces out when packing.

Edit; thinking about it, if you're using air, use silicone. It's thicker and could last a lot longer. I've bought a few MK5s with silicone in the chamber presumably from 10+ years ago, maybe quite a bit longer, and the chambers looked brand new.

 

[Couv]

There's something about these boots that just don't understand me. What purpose does the boot serve if it has holes in it? Admittedly, I don't recall ever having seen one. The MK 10s with the spec groove I've owned had the boots previously removed so I'm probably overlooking something. I had imagined the boots were thin/flexible enough to allow ambient pressure to act on the grease which would in turn transmit ambient pressure to the piston.

 

[halocline]

There's something about these boots that just don't understand me. What purpose does the boot serve if it has holes in it? Admittedly, I don't recall ever having seen one. The MK 10s with the spec groove I've owned had the boots previously removed so I'm probably overlooking something. I had imagined the boots were thin/flexible enough to allow ambient pressure to act on the grease which would in turn transmit ambient pressure to the piston.

It doesn't have holes in it, except the one tiny drain hole for excess grease. It is flexible enough to transmit pressure. It doesn't have to move much.

 

[Couv]

It doesn't have holes in it, except the one tiny drain hole for excess grease. It is flexible enough to transmit pressure. It doesn't have to move much.

Thanks Halo, that makes sense. That being the case, I don't see why a piece of bike inner tube trimmed to fit the groove wouldn't work just fine.