SPEC Boots for MK10 and MK15 primary regs

[Angelo Farina]

Nope.

The very best option is to send either @couv or @rsingler your finished boot for professional analysis. The exact size very likely depends on the elastomer that you choose...

Of course I will send the samples to you, @couv and @rsingler ...
The silicon rubber molded parts will cost almost nothing, hence that's no problem. The mold will take instead some effort and cost, so before giving the drawing of the parts for the mold to my technician in the workshop I want to be sure of the measurements.
the silicon part will come out exactly of the same size, as I have ordered liquid silicon with platinum reagent, which has no retraction while solidifying.
Here the first attempt for the mold drawing:

 

[lowviz]

Problem is, we don't have any way of knowing which size is best for each elastomer. Thus my request to Couv to give Tigger a range of sizes to print. I'll choose a range of elastomers and run each through the range of molds. Back to the reg gurus to assess.

We all have skills, let each of us do what we do best. No guessing, pass the problem on to one who is better suited...

 

[rsingler]

When comparing with the Atomic boot (obviously of different dimensions), my first impression of your AutoCAD plan is that the walls are too low for the Mk10. Hence the volume under the roof of the chamber might be too small for the depressurization mode. The volume looks large enough for breath to breath, but not for gas off.

DIY SPEC Boot

 

[Couv]

here the dimensions in mm:
View attachment 571612
View attachment 571617

Can you verify that these dimensions are OK for a MK10?

Hi @Angelo Farina et. al,

I'm holding a MK10 with a SPEC cutout and at least one of our measurements differs. Your groove width dimension 11.75mm is different than the unit I'm holding with a width of 11.2mm Therefore if we subtract the ambient hole figure of 5mm then divide by 2 the seal width on each side of the ambient holes you show as 3.38mm should be 3.1mm if I'm measuring correctly.

The i.d. of the seal needs to be small enough to tightly fit the o.d. of the groove. As we are designing a seal, I test fitted a few o-rings to get an idea of a firm seal. The best fit I could find was a -024 which has an (un-stretched) i.d. of 1.114 inches (28.30mm) I think this issue is significant as just measuring the o.d. of the groove will result in a seal that is not tight enough.

I'll have to leave the material selection to you guys, but remember if this seal is will be coming into contact with silicone grease, it cannot be made of silicone as the seal will absorb the oil and distend.

BTW I think Angelo is every bit as capable to evaluate the boots as I am-but I gladly volunteer to be a test subject and proud owner of a few of the finished product.

 

[lowviz]

I also agree with @rsingler that the seal should have a bulbous shape like the MK15 boot rather than a flat rubber band shape of the MK10

Can you, rsingler, and Tigger come up with something (hard polymer forms)? She comes and goes, haven't heard much from her lately...

 

[rsingler]

I'll do a little measuring tonite and make a suggestion. Depending upon your duro, the sidewall thickness might be less than initially suggested, with a thinner sidewall having the advantage of increasing the chamber volume. The Atomic seal, for example, uses a C-shaped sidewall. That gives it a broad footprint adjacent to the ambient holes, but larger internal volume. I don't know if that will complicate molding, however.

 

[lowviz]

I don't know if that will complicate molding, however.

I don't think so. If Tig needs a hand with the math, I'm here...

 

[Angelo Farina]

Hi @Angelo Farina et. al,

I'm holding a MK10 with a SPEC cutout and at least one of our measurements differs. Your groove width dimension 11.75mm is different than the unit I'm holding with a width of 11.2mm Therefore if we subtract the ambient hole figure of 5mm then divide by 2 the seal width on each side of the ambient holes you show as 3.38mm should be 3.1mm if I'm measuring correctly.

The i.d. of the seal needs to be small enough to tightly fit the o.d. of the groove. As we are designing a seal, I test fitted a few o-rings to get an idea of a firm seal. The best fit I could find was a -024 which has an (un-stretched) i.d. of 1.114 inches (28.30mm) I think this issue is significant as just measuring the o.d. of the groove will result in a seal that is not tight enough.

I'll have to leave the material selection to you guys, but remember if this seal is will be coming into contact with silicone grease, it cannot be made of silicone as the seal will absorb the oil and distend.

BTW I think Angelo is every bit as capable to evaluate the boots as I am-but I gladly volunteer to be a test subject and proud owner of a few of the finished product.

I measured my own MK10, and the measures i found are much more close to the drawing of the SPEC I have than yours.
here the photos showing my measurements:

However I agree with you that the boot should be slightly slimmer than the regulator's body, so it will be slightly stretched when mounted and will be more stable.
I will revise my drawing accordingly, reducing the inner diameter by a couple of mm (actually it was 31.00 mm).
Your estimate of an optimal I.D of 28.33 mm is a bit too small in my opinion. This is not a toroidal O-ring, which can stretch freely, this is a cylindrical shell.
As rubber has a Poisson coefficient nearly 0.5, if you stretch the cylinder radially it will squeeze axially (and this is a good reason for leaving the height of the cylinder at 11.75mm instead off 11.50mm).
As inside the groove the diameter of the reg's body is 30.4mm, I think that the boot should have an internal diameter of something as 29.00 mm. I will post the new drawings when ready...

 

[Angelo Farina]

I'll have to leave the material selection to you guys, but remember if this seal is will be coming into contact with silicone grease, it cannot be made of silicone as the seal will absorb the oil and distend.

This sounds quite odd to me. Isn't the diaphragm of regulators usually made of silicon rubber? And isn't in contact with silicon grease, which packs the space between the diaphragm and the external seal?

 

[Couv]

OK, well I stand corrected then.