solenoid isolator/shutoff

swadiver

as i begin to venture back into cave diving on the Rebreather, i am considering adding a solenoid isolator/shutoff to avoid having to feather the O2 tank valve in the event of a solenoid failing in the open position. i dpv a lot in the caves, so it would be damn near impossible to use my right hand to feather the O2 vlave. in addition, even when swimming and especially when deep, this appears to be quite a task loading exercise.

on the other hand, the optima solenoid is an upstream valve that appears more likely to fail open (let's say for an IP rise in the O2 first stage). Shutoff / isolator valve also adds more potential failure points, and could accidentally be left off/shutoff.

Soooooooooo.... opinions please

PaulTG2

Hello,

Issolation valves have been on my mind quite a bit recently for some reason. Frankly I wonder if they cause more problems than they solve. It seems they are installed to prevent a rare problems but but create more frequent problems because people have leave them off.

I don't read many stories where things free flow or lock open, but I do see quite a few postings caused by having the isolation valve off.

It would make a good poll -- have you had problems because you didn't have one, or did having one cause a problem because it was off.

-p

__________________
Paul's first law states that the safety of an activity is determined by how forgiving of mistakes the activity is.

Paul's second law states that the difference between an adventurer and an explorer is whether the doing or the learning comes first.

Dave Sutton

Really? I'd be interested to see *one*, since a short search failed to produce any examples.
I'm sure someone, someplace has forgotten one but have not found evidence.


And if so, what's the downside? None really, it's pretty binary:

(1) The diver either knows his PP02 at all times and opens it up after detection (and manually adding 02 to correct it, as well)

OR

(2): Is too stupid to do so, dies, and acts as an example to the rest not to dive rebreathers if you don't always know your PP02....

(Yes, that's my version of a joke. If you are offended, you have thin skin. Toughen the **** up!)



+++++++++++++++++++++++++++++++++

Seriously now:

Isolators are just another tool: Proper use can help, improper use can harm. Use wisely.

As far as the technical side of the tool is concerned, using slide isolators is sub-optimal, as you cannot really toutch-drill one to see where it's positioned with gloves on, and visually seeing the position (looking at a buddy, for example) is difficult. Add in the fact that there are two different ones (towards flow to stop, counter-flow to stop) and it's a nightmare. I never use or recommend them. Category: Junk.

A good system can do more than isolate the solenoid. One is shown here. This system can be used as an offboard 02 feed system as well as being used as a solenoid isolator. Look at the system and then consider the matrix:


Offboard = NOT CONNECTED, Isolator Valve = ON, 02 reg = ON: Result is that the rig is in it's basic mode, solenoid and 02 manual add valve fed by onboard 02.

Offboard = NOT CONNECTED, Isolator Valve = OFF, 02 reg = ON: Result is that solenoid is deactivated, but 02 manual add valve still functions.

Offboard = CONNECTED, Isolator Valve = OPEN, 02 reg = OFF: Result is that offboard 02 is fed to the solenoid, and also to the manual add valve via the offboard gas being passed back to the first stage ports of the onboard 02 regulator and then to the hose c0onnecting that regulator to the manual add valve.

Offboard = CONNECTED, Isolator Valve = OFF, 02 reg = OFF: Result is that the solenoid is isolated and that the manual add valve is being fed by offboard 02 thru the same path as in the previous matrix


That's a lot of value for one valve being added to the system....


Note: This system in a mirror image can be used on diluent systems to isolate the ADV while keeping diluent fed to the manual add valve, and to allow offboard diluent to be fed to the rig as well.


This is NOT the identical system as seen in the thread below:

http://www.rebreatherworld.com/rebre...anifold-q.html

But is a kissing-cousin and understanding one of these systems means you also understand the other. Study the other system as well to get a full picture of what magic can be done with a simple hose and valve.



The photo example system was built for an Inspiration, and is for sale, the individual who bespoke it having never completed his part of the job, IE: actually paying for it. If anyone wants it, let me know.


Dave

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Attached Images

o2isolate.jpg (213.3 KB, 300 views)

Hanssing

Nice crimps on those hoses Dave - did you make them your-self?

Or are you still doing "Ötheker"-crimps or wasitsname?

Nicolai - Still way more into the combination of the two systems - ie. three hosed gasblock :-)

__________________
Woohooo - I can change my rEvo!
Its going to be bitchin' tricked out piece of gear

diverreb

My shut off is easy to get to and operate in warm water.... It's a bit more difficult to get to and operate with cold water gloves on and in a dry suit, but it's doable.

The M & J valves are stiff and it would be very difficult to have it accidently slide off.

As far as it not being on predive.... Just another item on your checklist. You should be able to get to it to turn it on if for some reason it isn't when you get into the water.... If you can't, don't use one!

With an O2ptima, if you are doing your pre dive breathing it will be fairly obvious that something is wrong as the the solenoid will not fire if the shut off is in the off position.

Warning: If you are a failure point fanatic do not read further....

I use an M & J Omni-swivel between a short hose from the O2 Reg then I have the shut off in line so that the off position is a pull back. The ball on the Omni-swivel helps as a leverage point to shut it down, if necessary.

The Pivot swivel on the reg keeps the hoses from being unduly stressed with sharp bends.

The Omni-swivel has a captured O-Ring.

My position regarding failure points is that if you properly inspect, maintain and lubricate the parts on a regular basis you greatly reduce the chance of a failure.

Worst case is you may have to bail in a rare case of failure.

In addition to this I also carry a 6 CF bottle of O2 which can be popped on the the manual add valve via a BC hose in the event of a total failure of the O2 side. ( Loss of gas, reg failure, etc.)

Richie

Attached Images

IMG_0835.JPG (113.9 KB, 286 views)

ScubaDadMiami

I have been using the Optima since before this was a standard option. Like Richie says, it is just another option. If it is off (like Richie says, it will not turn off by accident without some real doing on your part), you will notice that the solenoid is dry firing. You can do a manual gas addition, check the shut off, open it, and you are done. Like Dave said, if you aren't watching your PO2, you will have a bad result in the rare instance that the valve gets shut off during the dive.

The valve is in a position that makes it so that I don't worrry about it getting shut off by accident.

__________________
Howard Packer
IANTD CCR Instructor
Miami Beach, Florida
CCRDiveTraining.com

Dave Sutton

Let's see, let's compare the 'factory solution' to the LDSOH solution.

The factory one features:

More Failure Points, and of a lower reliability seal (O-Rings V/S 1/8 NPT tapered threads with sealing tape)

No 'at arms length' visual identification of a closed valve or visually intuitive understanding if the valve is open or closed

No offboard gas injection point (which is a 1/8 NPT port that can be sealed with a non O-Ring sealed plug to disable in event it is not desired)

More Expensive.


Yeah... I'll buy one right away! ... on second thought.... .


For the other question: I'm using Oetkers to prototype lengths, for rapid-fix, and for my own stuff. For customer quality stuff I have custom hoses made. AFAIK I'm the only one using the BULLETPROOF 1/8 pipe thread (no O-Ring) in critical points on the systems I build. Reduce O-Rings and reduce failure points. Simple things work best.



I count 12 O-Rings on Ritchie's solution including what's in the swivels and inline shutoff, v/s, uh.... TWO on mine, one at each end of the complete system. The rest are tapered thread with no O-Rings needed to seal. Go figure out which system offers better utility and reliability. Takes nothing way from the alternate system, which is what you get it you try to plug and play from the parts catalogs. Bespoke stuff is always better than off the shelf mass-maket generica: Choose wisely where your life depends on the outcome.

Or in the immortal words of someone:

"Good Enough Aint Always Good Enough"



Dave

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Hanssing

Well, you're not the only one thinking like that (see: http://www.rebreatherworld.com/home-...or-diving.html )- Though I have yet to do it, but I will only use NPT and reduce use of O-rings to where needed for sviwel and 1st-stages.

You allready know I turned down you original design due to the 90dgr LP oring-fitting . I'll have three ports on top, and a safe NPT plug on the side, where drilled (or the check-valve on the side).

My focus for such a system is robustness first - functionality second. No compromises with thread-reducers, converters etc (unless prototype-testing), if an O-ring or fitting can be avoided through another part, then that part get bought. But as a engineer I tend to go a bit overboard on theese matters .....

Wich reminds me - I owe you a McMaster-list. I will take some time untill I through testing my BOV.

Nicolai

I feel kinda schizophrenic with theese discussions on different threads and emails concerning the same topic - hehe. Must tell myself off now, or is it mySelf?

__________________
Woohooo - I can change my rEvo!
Its going to be bitchin' tricked out piece of gear

AM

Nicolai

Taking a break from fettling and just had some more ideas about further configuration options on the gas switching elements we've been discussing. I agree it's getting kinda difficult to keep track of the various threads on this!

I agree that the reduction of o-rings is a definite positive. But I'm just not sure if it warrants all the extra time re-solutioning everything. If an o-ring goes within the gas connection architecture, there are still mitigations to re-routing gases, the system just becomes a bit less redundant.

But isn't this specifically engineering a different solution and altering the check valve location just to reduce o-rings further? OK I can see the benefit if you want to be ultra-anal but at the end of the day other failures can still occur which impact gas config paths.

Ah I see....ok, but you can't engineer out every single o-ring!

On the point in another thread (can't recall which one) about 2 hose vs 3 hose implementation, I agree that 3x hose is much better. Also, the extra feed to the wing means more redundancy options in terms of isolating/switching which gas paths feed BOV/Wing/Drysuit/Loop. Without referring to specific accidents, there is evidence that creating a single point of failure in the form of feeding all inflation points from one gas path is responsible for at least one accident.

As for flow stop versus ball valve comparison made by another commentator (in another thread) there is no question in my view that the ball valve is infinitely better. I have never like inline shut-offs (and hate them on ADVs), it is just more intuitive to look at/feel by hand, the ball valve and know instantly which position it's in, not to mention harder for it to be switched off/on inadvertently during a dive. This is a major advantage in poor vis if you're cross connecting stuff/re-routing gas paths or in a hurry. It's just so much better all round. How often do you see an inline shut-off versus a ball valve on a gas path in applications other than diving?

Regards

AnneMarie

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Dave Sutton

Using pipe threads actually makes it easier, not more difficult. And since they can seal well within perhaps a full 360 degrees of rotation as they are threaded together, making hoses lay correctly is far easier. Using O-Ring seals at each end of the supply hoses would mean that "however the thing lays is the way it is" as opposed to being able to rotate the pipe thread hose attachment point a little this way and a little that way until it's all laying nicely.


I am going to re-think this though as I am now looking at the CIS Lunar Mark-5P on the bench and seeing how they used Swagelok fittings and high pressure plastic tubes to run lines. Small diameter outer diameter for the same inner diameter and very durable, and rotatable. Thinking... always.


Dave

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