DIY SPEC Boot

[rsingler]

Yes, I have pressure relief on the chamber, but you're right. The whole thing is a little dodgy. Good idea about the IP gauge on a pony setup. If I do, though, I won't see increasing IP with depth, but constant IP if the thing works properly, right? The submerged IP gauge is now just seeing differential, rather than absolute IP when at depth.
So if the boot in the groove does partially block the ambient pressure, my submerged IP gauge will show declining intermediate pressure, which may accompany increased WOB.

I'll let y'all know.

Rob

 

[Couv]

Yes, I have pressure relief on the chamber, but you're right. The whole thing is a little dodgy. Good idea about the IP gauge on a pony setup. If I do, though, I won't see increasing IP with depth, but constant IP if the thing works properly, right? The submerged IP gauge is now just seeing differential, rather than absolute IP when at depth.
So if the boot in the groove does partially block the ambient pressure, my submerged IP gauge will show declining intermediate pressure, which may accompany increased WOB.

I'll let y'all know.

Rob

Correct. You will still be measuring pressure above ambient.

The work of breathing may not be noticeable with a balanced second stage though, so a classic downstream second stage (ScubaPro 109/ R190/ AIR 2 ) would probably be required to "feel" the difference.

 

[rsingler]

Here's the test rig: a 19CF pony with a MK10 and tight fitting boot, using a Dacor Pacer Aero as my unbalanced 2nd stage.
The gauge is a Chinese POS that I calibrated by bending stuff with the case off. The case fits so sloppily that there's no need to drill a hole. Water will pour into this thing!

Was a fun test comparing with the D-350 as I turned off the tank valve and took mini-breaths from the air in the hoses. The D350 cracked at -1.4" as the IP dropped to 60, but as expected, the unbalanced Dacor was off the scale on the magnehelic. Heck! Maybe having a scuba regulator (vs. the one in a welding shop) is a waste of time! With an industrial regulator putting out 135 PSI and no environmental sensing, plus a D-350 breathing OK at 60 PSI, I could dive to 130 feet and still not reach 60 PSI differential IP after subtracting sea pressure at my second stage. We could put Scubapro out of business! Joe the Mechanic Scuba Company! First Stage Regulators $29.95!

This boot is the small thin inner tube from my first trial SPEC boot. It clings against the holes and does the best job of sealing. There's a little grease under the inner tube to help the seal, but I didn't notice the inner tube sucking hard into the holes as the piston came off the seat when I turned off the tank. I didn't fill this environmental chamber with grease. I figured that with a perfectly full chamber and zero bubbles, this type of boot should be able to keep up with the minimal movement of the piston with breathing, and we'd see no change. But that same boot, after a dozen tank cycles will have oozed out some grease, and then sucked in some air when the tank is turned off while it sits there. So the worst case for a few bubbles is "one big bubble" with an empty environmental chamber.

If the boot seals tightly, we'll see what sea pressure does to the boot and the IP. If the boot doesn't seal, then doing it this way will give us what we'd expect: water and grease in the chamber; a fair barrier of grease to the piston O-rings, but a good place for salt to sit and corrode.
We'll see what happens at depth in a couple of weeks.

By the way, looking at pics of an Atomic M1 environmental seal, I think the dimensions are pretty close. I'm going to try to obtain one of their boots from my LDS and see how that works. Glad to see Atomic still subscribing to a sealed piston design, but I'll take my $70 MK10 anyway.

 

[rsingler]

UPDATE on the DIY SPEC Boot

Well, I'm ten dives into this SPEC boot now.
Everything's going great! Per my previous post, I added a little Tribolube after three dives, but I've left it alone since then. Down to 100 feet on a wreck dive at 50 degrees without a problem.

That said, I also tested the plain inner tube fitted snugly around the holes on an otherwise wasted low-vis day in Monterey. As posted previously, I put a separate Mk10 tuned to an IP of ~126 on a pony bottle with a downstream unbalanced Pacer, a center-balanced D-series, and took it with me as my "sidemount spare gas."
It proved why scuba regulators are designed the way they are, and why Peter Wolfinger's Regulator Savvy is the theoretical Bible. By the time I reached 33 ft, my cheap Chinese IP gauge (which flooded immediately and was a great way to measure what happened on descent) had already dropped to around 115 psi. It wasn't a drop of exactly 14.7 psi, so the inner tube was evidently flexing a little. As I took it lower (not breathing on it yet, by the way), it went down another 12psi by the time I reached 65 feet. I took a suck from the Pacer at an IP of 102 psi or so, and although I thought I could tell it was stiffer breathing, it might have just been my imagination. The D-series reg didn't notice the difference with that IP. I left it on the bottom and came back in a half hour to bring it to the surface. IP had increased to ~110.
And when I took the reg apart after the dive, it was obvious why the IP increased over 30 min of sitting there: there were a few drops of sea water in the environmental chamber, though not much. So, the inner tube only flexed into the holes enough to give me a few psi worth of depth change. The IP should have stayed constant at 126, but instead, the drop matched the increase in pressure at depth almost completely. A very stiff roof over those holes, despite the thin and seemingly flexible bicycle inner tube. Then, it rose as the boot leaked sea water into the chamber over 30 min.

Conclusion? Having a poorly-flexible, zero-volume "SPEC boot" covering the environmental holes is not safe. IP drops with depth as expected from the physics, and it doesn't keep the reg clean inside either. In fact, the salt water I found would now be trapped inside until you take it apart, as the bicycle tire is pretty tight around the holes.

On the other hand, the flexible roof large tire boot that I did the wreck dive with gives with each breath, as well as flexing visibly when turning the reg on and off. As you can see from the pics, it leaks a little bit of Tribolube, but after ten dives and only 0.5 cc added, I'm happy.

Someone else asked about using the Atomic boot. Here's the deal:
3mm difference in the outside diameter of the environmental chamber. The ring is 1mm smaller diameter than the Atomic chamber OD. So, when fitted on the Mk10, the Atomic boot doesn't like that much diameter difference (compared to the 1mm of diam change with an Atomic reg):
As you can see, the roof is almost completely collapsed when mounted on a SP Mk10. More important, the firm sidewalls of the boot pull away from the groove a bit (not easily visible in the photo) so it will not perform the same function reliably. If the boot on the Atomic looks collapsed almost the same to you, it's because I just fitted it on an empty reg, and there is no grease behind it.

So if you want to seal a Mk10, a reasonably easy solution right now seems to be a 29" balloon tire inner tube with a designed tube diameter of around 2.1" zip-tied on one side of the groove after filling the chamber with your grease of choice. In a couple of years, I'll take my Mk10 apart and let you know what's inside the chamber. But I'm confident that my ol' Mk10 will make it as long as Atomic's 2yrs/300 dives service interval. Bad on Scubapro for discontinuing the SPEC boot.

As for just sealing your environmental chamber holes with an inner tube - unsafe! Thus endeth the sermon.

 

[beanojones]

Completely silly question, but I am curious if there is a reason for a 29" inner tube versus the more common 26" inner tube?

Also way to take one for the team!

How much was the IP gauge? I wish some dive geek company would make a cheap IP guage that fit directly on a LP hose. I would gladly burn a few gauges to see what different regs did at depth.

FWIW the other way to find out something interesting is to use a dry diaphragm first stage like the APeks with an unbalanced reg. Around 80' the reg starts to trickle, and by the time you hit 130 or more its a pretty good bubbler. Balanced second stages hide lots of first stage flaws.

 

[rsingler]

Completely silly question, but I am curious if there is a reason for a 29" inner tube versus the more common 26" inner tube?

Also way to take one for the team!

How much was the IP gauge? I wish some dive geek company would make a cheap IP guage that fit directly on a LP hose. I would gladly burn a few gauges to see what different regs did at depth.

FWIW the other way to find out something interesting is to use a dry diaphragm first stage like the APeks with an unbalanced reg. Around 80' the reg starts to trickle, and by the time you hit 130 or more its a pretty good bubbler. Balanced second stages hide lots of first stage flaws.

You'll need to go back to couv's post from March 6th and follow the arduous course of this thread from there, but basically it has to do with the need to create a "chamber" outside the holes in the groove of the environmental chamber. A 26" inner tube fits too tightly, whereas a 2.1" tube for a 29" balloon tire is large enough not to drop into the groove. Now you have a flexible roof that can move with the piston deep inside.

As for the IP gauge, get a $9 0-250 gauge from the Auto/Pneumatic Tools section of Home Depot or Lowes. Add a 1/4" NPT coupling to it to make a female 1/4" NPT connection, and add a BCD adaptor from Northeast Scuba Supply, or Trident, or any of a number of parts places for another $6 plus shipping. For $18, you have yourself an IP gauge.
Here's one attached to a BCD hose.

Your comment about free flow at depth with the Apeks diaphragm and an unbalanced 2nd is a good demonstration of the unbalanced 2nd's susceptibility to increasing IP. Although theoretically the increasing IP should be counterbalanced by the increasing seawater pressure with depth, an unbalanced second that's tuned very light can indeed start to freeflow. In the Apeks case, it's a function of overbalancing and an attempt to improve breathability at depth with "thick" air. Some folks call it a diaphragm design flaw, but either way, it's interesting fluid physics. A balanced second can accommodate that better in many cases. I tend to think of it as making use of that overbalancing, rather than hiding a design flaw.
But it sounds like you're a piston guy, like me. I use my Apeks, but I prefer my pistons. This whole thread was based on my desire to have my Mk10 more resistant to freezing (and silt/sand).

 

[beanojones]

Actually Dive Gear Express sells a cheaper premade IP gauge:

Regulator Accessories - Dive Gear Express

(The reason I was asking about the 29" versus 26" tire is that the enormous volume downhill tires come in 26" in size all the way to 4".) I have to say, this whole thing makes me want to try this even on a MK2 as well, though there might be a different tire diam.

 

[rsingler]

Actually Dive Gear Express sells a cheaper premade IP gauge:

Regulator Accessories - Dive Gear Express

(The reason I was asking about the 29" versus 26" tire is that the enormous volume downhill tires come in 26" in size all the way to 4".) I have to say, this whole thing makes me want to try this even on a MK2 as well, though there might be a different tire diam.

Ah! Now I understand your question. Well, the answer for me was 2.1-2.3" tube, whatever that means. Basically you want something just barely under the OD of your housing. The 29" tube was all I could find at my local WalMart that met the need. My bike shop had hi-quality stuff, I'm sure, but I was too cheap to buy theirs and then cut it up into loops. The WalMart tube had the advantage (for us, if not for biking) of being relatively thin, and thus flexible.

I would be a little concerned with the Mk2, because the key piece of this is the room for the roof to flex. The Mk10 and the Atomic both have a deep groove where the SPEC boot fit. The stiff side walls of the boot formed the "room", and the flexible "roof" of the original SPEC boot (or the inner tube in our case) let this outer "chamber" move with the piston. Total volume change is 0.25-0.5cc when you first pressurize the regulator, and less than 0.1cc with breathing. If you have bubbles in your grease, of course, then the boot will need to have enough volume to supply more grease to make up for the ~75% loss in bubble volume inside the chamber at 99 feet. I don't see a groove on my newest Mk2 housing that overlies the environmental holes,
so I don't think there's any volume that can be created with an inner tube.
As we saw with the tight inner tube on the Mk10 on the pony, the inner tube doesn't flex much at all, and so won't transmit the increasing sea water pressure.

Earlier in the thread, we had a brief discussion about whether a reservoir is necessary. To recap: if the reg is perfectly filled with grease without bubbles, then the inner tube over the holes will transmit sea water pressure to the piston, and probably give enough to be safe, BUT ON THE FIRST DIVE ONLY. The reason is that when you pressurize, some grease squirts out of a tight closure as the piston rises and seats. There's not much further movement during the dive, so the inner tube MIGHT be adequate.
But when you depressurize, that volume has to be replaced. Since the tight inner tube can't go deep enough into the environmental holes, then air is going to seep in over the day/week/month between dives. Next dive you have bubbles inside the chamber, and you see what I found when I dived with the pony - IP drops like a rock. I don't think you can do it on a Mk2 or any reg that doesn't have a place for the reservoir of grease under the inner tube to sit. Sorry!

Re: the IP gauge, you're right! The DiveGearExpress one is nice and compact, and inexpensive - but also moderately sealed inside its cover. Seemed too nice to get wet inside - I have one too!
My (more expensive) homebrew used a Chinese P.O.S. $8 gauge whose case was so loose that water flooded it easily, allowing it to to measure differential IP at depth (which should stay the same as your 1st stage compensates). After the dive, I just pulled the cover off and rinsed and blow dried it before it rusted.

 

[Couv]

Have you hooked up the underwater IP gauge to a different/unmodified regulator (while underwater?)

 

[rsingler]

Have you hooked up the underwater IP gauge to a different/unmodified regulator (while underwater?)

Yep. IP stayed solid (+/- breathing fluctuations as I sucked on the reg) all the way down to 60. The 1st stage kept up with the increasing depth and maintained my relative IP without a twitch. Didn't go deeper, bc I was worried that the cheap valve mechanism (the soldered part) would fall apart and I'd be venting all my LP gas in 90 sec. Guess I could've thrown in my in-line shut-off valve before I dove it, but I forgot.

[I presume you didn't REALLY mean "did I hook it up while underwater" ]
I just bounce-dived on a good reg.