Shrimp And Smooth Bore Hoses For An Sf2

[tbone1004]

@The Chairman thought about just going to button gauges for the two onboard bottles? What benefit do you have by checking them during the dive?

@JohnnyC for the dil flush you'd just inhale from loop until it bottoms out, open the bov and exhale. Inhale from bov, close bov, and exhale into the loop. Lather, rinse, repeat until flushed. Standard cave-style dil flush, though probably a bit more annoying than having some sort of mav on there since you have to open and close the bov several times.
Dewatering would suck and I'm not familiar enough with the shrimp to know how you'd pressurize the loop to blow the water out.

Pete, have you thought about keeping the dilmav as a convenient plug-in point for the QC6 and then have that go out to the BOV? Since you're still using the onboard 3l for dilout it may get a little clunky vs. just using your offboard for dilout

 

[The Chairman]

@JohnnyC for the dil flush you'd just inhale from loop until it bottoms out, open the bov and exhale. Inhale from bov, close bov, and exhale into the loop.

I like the idea that we share how we would do this. The SF2 is incredibly easy to dil flush. Butt down, head up and smile. The water pressure will collapse the counter lung until the ADV fires and completely flushes the unit. You don't need a MAV to do this and I've never felt a need for one with dil flushes.

For de-watering, I would try a different approach. Do a barrel roll. Go head up, butt down. Switch to OC, nail the O2 MAV until I hear the fart from the OPV on the bottom. Switch back to CC and smile, doing a complete dill flush. FWIW, this was the brainchild of an instructor I had a discussion with. I'll be trying it @ 20ft a few times to be sure it's "doable" by me before I head deeper. I might head over to Troy Springs today when it warms up.

Again, feel free to share how you would do this.

@The Chairman thought about just going to button gauges for the two onboard bottles?

I have heard of this and it just doesn't give me the warm fuzzies. How do I quickly determine where a leak is? If I hear a leak behind me, I crank off both tanks and look at which SPG is dropping. That's easy and I have not figured out how I would make the same determination without gauges. It's not like they are in the way or are flopping about. That's why figuring out how to bungee my O2 SPG to my O2 MAV made sense to me. I might even add a small clip to really keep it in control. I hate, hate, hate danglies.

 

[tbone1004]

@The Chairman not sure I'd dewater with O2. Bit risky IMO.
Not sure which dil mav you had/have, but if you're having a QC6 offboard plugin point, the delrin ones give a good enough plugin point that isn't much bigger than a normal 2:1 manifold block.

On the SPG's, just listen after shutoff. Shut off O2, inject into the loop to purge the line and listen. If it stops, it's the O2. If not, do the same with the dil side and done. Less bulk and less risk of leaks

 

[The Chairman]

not sure I'd dewater with O2. Bit risky IMO.

Not risky if you're off loop during the process. I could even plug in dil to the Q6 on the O2MAV to make it "safer" or to preserve O2. I have set both O2 and Dil regs to a 130psi IP while my offboard regs are set to 145psi IPs. The gas will only flow from the reg with the higher IP.

A dil flush on an SF2 is nigh on to instantaneous and it's quite effective. The ADV might be almost all I need and keep me to min loop volume. I might have to add some through the Shrimp, but I don't know. I think I'll be OK, but if not, the Dil MAV will be added PDQ. I won't know until I dive it.

 

[JohnnyC]

I know how I would do it, I was curious how Pete was going to go about it, seeing if he came up with some other way I hadn't considered.

The "breathe down the loop" method is a less-than-ideal solution as you are passing possibly compromised gas through your lungs, what you're trying to avoid by doing a dil flush, especially if you're over minimum loop and can't bottom out the lungs with one breath. Dil flush is in anger to re-establish a viable loop. Breathing the compromised loop is contrary to that, especially when you REALLY need to get fresh, known gas in the loop. It's certainly a viable method if you're not dealing with a compromised loop and just want to exchange the gas. A better option would just be a full bailout IMO. At shallower depths something like a giant O2 spike is less of a problem than at serious depth. An O2 boom in Eagle's Nest will pretty quickly jack your PO2 up like a bottle rocket and be pissing out so much gas that you'd fill your CL enough that you couldn't bottom it out. Your only option would be a full bail.

The head down vent method is probably the best non-MAV method of doing it, the only problem is that's only viable if you can get head down enough. Fine in open water or large passage, not always possible in a tight passage with a tight ADV. In that instance, full bail out, deal with it when you can. As an aside, units with a head mounted ADV require the diver to turn turtle and the hydrostatic pressure blows the loop for you. It's a cool trick, provided you can flip on your back.

As for de-watering, the BOV and blow is probably the best viable method without a MAV. It shouldn't be too hard to bottom out the CL and trip the OPV just with gas added from the BOV. I would not jam the O2 MAV.

Personally, after exploring all the options with my own unit to try and get rid of my dil MAV, I elected to keep it, just ditch the factory hoses and completely replace them with hoses that fit best with my setup. It took an extra set of hands and a fabric tape measure, but not too painful. A 2" wide piece of industrial hook-and-loop holds it dead flat against my shoulder webbing. It's tiny money for a metric ton on Amazon. My wing inflator is more obtrusive than my dil MAV. The O2 MAV is a little bulkier since I've got one of Chris Kennedy's needle valves on it. Either way, I'd rather have the option to jam a dil MAV than do something wonky to accomplish the same thing, or be forced to bail because I was out of reasonable options.

The stock SF2 MAV's have either QC4's, or lately LP connectors on them for plugging in offboard, not QC6's, at least nothing shipped since 2016ish? I don't know the exact timeline. You could easily replace them though. I don't dive a sidemount unit, but I believe the O2 is the button MAV attached to the body, I think the dil MAV is an additional option. Interestingly enough, with the shutoffs on the unit, you can shutdown onboard gas, and the ADV/MAV's will function from the offboard gas as if it were your onboard. Saves any IP tomfoolery, which introduces its own set of problems.

 

[The Chairman]

Saves any IP tomfoolery, which introduces its own set of problems.

What problems? Most who've not liked the idea simply aren't comfortable maintaining or setting a regulator. 1 bar means that a reg might be 10% harder to breathe, but that's about all I can see as any negative.

 

[tbone1004]

@The Chairman you have to be careful if the first stages aren't identical though. While it does obviously work, if the regulators aren't balanced or compensated equally, you may get into an issue. I.e. if your "low" IP reg is say a DS4, but your "high" IP reg is a MK25, when you start going deep, the DS4 will be playing catchup because it is overcompensating.
Say you have two matching regulators, but one is relatively poorly balanced *having a 1bar swing is not all that uncommon with some regs, especially with big cave fills*, you may be fine at 3600psi, but the low IP could start playing catchup.

Me personally? mine's in a rack and I don't bother with the onboard 3l for dil because I think it is of no real benefit. Unfortunately it gets a little clunky as you would have to get a hose from the onboard 3l to plug into the bottom of the block.

Talk with Ted about his setup, though you may not get very far because he uses the rack.

 

[JohnnyC]

Maybe I'm just lazy. I don't check IP every time I dive, and even if I did, there's potential for issue. IP is a funny thing sometimes, and unless you're checking it religiously, you may not catch a change, or you may have stable lockup when you test it before, but start to get creep midway through your dive (I actually had a real life pissing ADV when the IP, which ostensibly I had actually tested before the dive, crept up and an hour in starting blowing dil into the unit). It would suck to suck down your onboard dil bottle to a vacuum because you thought your lower IP would keep your tank full. Fortunately we were just putzing around doing shakedown stuff in open water. It would have been far more annoying an hour into the cave.

My primary issue with it is that you are not able to actively monitor and control it at any time. That's fine when it's acting by itself, but when you put that into a system where you're relying on the relationship between two IP's that you can't actively monitor, and can't actively control outside a surface environment, you can run into problems that you may not be able to identify. Obviously none of this should really be an issue, but it can certainly be annoying or even stressful.

I had an O2 reg that during preflight started popping the OPV on the bench. Again, had tested fine 15 minutes before. Checked IP again and it held stable, just 2 bar higher!

ETA: This is assuming that it's a failure, not even taking into consideration the issues Tom brought up. In my mind it's just more trouble than it's worth.

 

[The Chairman]

It's mostly a failsafe. I don't plan on having the onboard tank turned on with the offboard connected so the onboard reg is mostly a fancy manifold. I'm fairly fastidious about my regs, trust them implicitly and check them often. I wouldn't dive if any of them had an IP creep. I always have an IP gauge close by and I'm not reluctant to clip it on. I'm surprised that more aren't that concerned.

Say you have two matching regulators, but one is relatively poorly balanced *having a 1bar swing is not all that uncommon with some regs, especially with big cave fills*, you may be fine at 3600psi, but the low IP could start playing catchup.

Citation needed. We would be seeing all sorts of free flows if this were the case. Where do you find stats to support "not all that uncommon"??? I think I'm diving with my IP gauge so see just how much of a variation exixts, but since I replaced the Dil reg, those first stages are all from the same factory.

 

[tbone1004]

@The Chairman no citations, but my MK10's swing about 1bar from ~3800-3900 down to 200, so do my older Poseidons. The MK25's and newer diaphragms are a lot more stable though.

Is it a real issue? It probably isn't, but is it worth the hassle? I'd argue no. If you're using the onboard as a manifold because it's there, and aren't doing trimix stuff where you'd need drysuit inflation, then I'd still consider the MAV block for your QC6 inlet from offboard since it's as good as anything for plugging in