Spec Boot For Mk-15

[Couv]

I just had a little Cabernet therapy to clear out some of the cobwebs. Good guy Rsingler put a lot of effort into a very similar experiment a few years ago. See this thread for some great information. DIY SPEC Boot

 

[lowviz]

couv, you must be psychic.

I just today got the MK10 boot (courtesy of uncfnp, Thank you), logged on, and was just about to ask what the 0.082-0.089 hole was for.

Now I know. I have to change Tigger's procedure a bit so that I can add a removable pin. The part has to be pullable.

Question: Entertaining all views on keeping or losing the hole. I'll keep the hole unless someone reassures me that it is unnecessary.

 

[redacted]

It seems to me that it would be easier to add a hole if you need it than to close one off. A hole is just another route for water to enter and eventually cause a problem. I guess the boot needs to be able to expand and contain between 0.1 and 0.2 cubic inches of packing material.

I think I am convinced that sealed diaphragms are the answer to cold water. Or a completely different approach, like maybe something on a Mk 7 chassis converting the Honker section into a sealed ambient chamber. (That might not be that difficult, but it sure would be ugly.)

 

[lowviz]

It seems to me that it would be easier to add a hole if you need it than to close one off. ...//...

Good input!

I'm now planning on a knockout hole of the same size in the same location. Thick core with the edge of the circle thinned out. You want a hole? Punch out the slug.

 

[halocline]

The lesson from rsingler's old thread is that there needs to be a layer of grease outside the ambient chamber holes to work correctly. This allows the boot to flex in and out enough to keep the IP stable. If you just put a rubber band right on top of the holes to seal them, there's not enough area for flexion; the rubber band gets drawn into the holes and can't transfer the pressure as accurately.

This is why the MK10 spec has the groove, and the boot has those ridges which keeps the boot off the surface of the groove and creates space for a layer of grease between the boot and the groove, outside of the ambient chamber itself.

So this means simply covering up the holes on the MK5 won't work. That said, I've packed a few MK5s without any boot and due to the very small ambient chamber holes, it works fine. A little grease comes out after each pressurization, but not much.

 

[lowviz]

Time for a decision.

It will cost me several hundred dollars for a proper analysis of the boot material. I'd love to know, but might be foolishly wasting my money on this academic question.

Should I just start making the mold and finding a similar urethane that will hold up to silicone grease and oil?

 

[halocline]

I'm pretty sure anything close to the original in terms of stiffness will work fine. Don't forget those ridges along the edges on the inside of the boot and make sure the material you use is stiff enough so that those ridges don't collapse. Of course, these are just guesses. It wouldn't surprise me if Bryan at vintagedoublehose.com would be interested in selling a few of these as long as they work well.

I'm pretty sure the hole is there to allow excess grease to escape without distorting the boot. If you really pack the chamber well, making sure there are no voids inside, quite a bit of excess grease will escape when you put the reg together and pressurize it for the first time. I'd leave the hole in place.

 

[Couv]

As we already know that whatever material the original boots were made from is not very dependable, the only advantage to knowing what material type is to avoid using it again. If you've found an inexpensive method of producing a replacement my vote would be to press on.

FWIW one of the methods of determining rubber type materials such as o-rings is to use a device which is basically a small weigh (like a bee-bee) in a straw. After dropping the weight onto a set of known materials mark the straw with the bounce height of the weight. Then test the unknown material against the samples.

Edit: A picture is worth more than a thousand of my words.
O-Ring Identifier

 

[lowviz]

I'm pretty sure anything close to the original in terms of stiffness will work fine. Don't forget those ridges along the edges on the inside of the boot and make sure the material you use is stiff enough so that those ridges don't collapse. ...

No worries there, Tigger's method preserves an unbelievable amount of detail. I just need to pick the correct material for the boot.

... It wouldn't surprise me if Bryan at vintagedoublehose.com would be interested in selling a few of these as long as they work well.

I'll send him a mold if it works...

As we already know that whatever material the original boots were made from is not very dependable, the only advantage to knowing what material type is to avoid using it again. ...

Thanks, I'm now convinced that it is not worth spending upwards to three hundred dollars to find out that it is synthetic rubber.

FWIW one of the methods of determining rubber type materials such as o-rings is to use a device which is basically a small weight (like a bee-bee) in a straw. After dropping the weight onto a set of known materials mark the straw with the bounce height of the weight. Then test the unknown material against the samples.

I'll try that for comparison when I get some things to try.

 

[raftingtigger]

The lesson from rsingler's old thread is that there needs to be a layer of grease outside the ambient chamber holes to work correctly. This allows the boot to flex in and out enough to keep the IP stable. If you just put a rubber band right on top of the holes to seal them, there's not enough area for flexion; the rubber band gets drawn into the holes and can't transfer the pressure as accurately.

This is why the MK10 spec has the groove, and the boot has those ridges which keeps the boot off the surface of the groove and creates space for a layer of grease between the boot and the groove, outside of the ambient chamber itself.

So this means simply covering up the holes on the MK5 won't work. That said, I've packed a few MK5s without any boot and due to the very small ambient chamber holes, it works fine. A little grease comes out after each pressurization, but not much.

I'm working on molding a boot similar to the Mk10 for the Mk5. I agree with the info above. The only issue I see is keeping the boot from slipping on the regulator body.

I know you aren't supposed to put silicone grease on silicone o-rings, etc. as the silicone grease absorbs into the solid silicone. How bad it this really? Would it make that much difference in a boot where the tolerances are large? I.E. Swelling of the material might even be an advantage.