Switching blocks

diverklondike

Well if you had done a search on some of the previous threads you would have seen that everyone had done a pretty good job at

the topic up...

Dive Safe

Mark

Drmike

sell it to an interested open-minded inter-lectual?


your welcome for the safety advice and for the money Ive just saved you

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Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you

Drmike

personally I can hold my breath for way more than enough time to switch OC regs or plug in a QC. dont need an 'instant' switch valve that I could easily knock or have in the wrong position leading to toxing and death....all to achieve a gas switch that a one armed blind man could achieve in a reasonable time without one.

Gas switch blocks off on-boards? added co failure points, added risk, added clutter, added weight....for what advantage?? I dont see any, other than an incorectly percieved need for 'imediate' availablity of gas. Its like the muppets that added additional o2 and dil add buttoms to their units CLs....as if you nbever had enough time to swap qc hoses

and who uses them?


Almost nobody.


All the OC tech divers in the world seam to get on fine switching gases without need for switchblocks

No wait I do recall one guy who used one...but he toxed and died due to switching it to wrong position so.........

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Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you

Dave Sutton

Uhh..... Mike, you know I love ya, and we usually are like peas and carrots in the way we look at technical things, but:

Different environments drive different requirements, and the prism of your (or my, or anyones) experience often causes us to loose sight of the fact that other places may be different. I know that I make the error of assuming that everyone is diving anchor-line descent, non-drift deco, in cold water with minimum vis, a strong current, and three finger mitts, so sometimes I am incredulous that people think they can do some 'action' in the water when for them, in their environment it is easy. So, I can see that for some people it's hard to believe that is might be simply IMPOSSIBLE to do what seems a simple task elsewhere.

YES, Switch blocks are generally not needed. No argument. I've been able to rig my system to work without them. I play with them and I gently caress them at the dive shows (cannot resist nicely made chrome plated brass hardware), but... I don't own one. Come to think of it, I don't know anyone else who does either.

BUT:

Back to "my" environment, I'm not so sure I could hold my breath reliably long enough to switch a QD while task saturated in a high workload bailout situation on an anchor line deco, in sea-surge conditions, in minimum visibility, in a strong current, in a thick drysuit, with three finger mitts. If I bobble one thing it can go bad very fast. Bottom line is that if I am holding onto the anchor line for my life with one hand, I have one other hand left to do the rest. Having been there and done that.... it can be a task saturation condition that causes one to wonder how it'll all turn out. My solution is neither a switch block OR a QD that needs to be changed, but rather an integrated system that requires neither. The process of thinking it out drove the result. Then again... my rig itself has valves for switching (Mark-15 onboard/offboard Whitey), so one mans 'rig control' might be another mans 'switch block' mounted on a harness, eh?


So:

Best advice to our new correspondant is what Mark Nix suggests: Read the old threads and then make a decision, and then come back and ask a reasoned question if doubts still exist. Yes, the answer will 'probably' be "You can do without", but he'll have come to that point by self realization, and not by receipt of a dogmatic short-answer.

Hope you're well, bet there's no damned ice-storm happening there today!


Dave

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"All animals are equal, but some animals are more equal than others"


Professional Small Boy: Never Successfully Cubicled.

Drmike

Hi Dave, I agree different invironments suit different methods but I think a degree of standardistation is also useful. But to clarify I too dive in many conditions including the one you describe. Ive spent many-many a happy dive hanging for dear life off a violently bouncing anchor chain in bad viz and horendous currents. Not a fun place to be. Ive had my arm ripped out the socket, Ive been hit by the chain, by the boat, even had the chain hit my scooter and pop the end off it! - all very unpleasant I agree.

Hanging on with one hand I soon found was largely impossible given the typical currents and anchor chain bounce so I long ago stopped trying.

Basically the technique I developed would be I would attach a jon line to the anchor chain when still deep and below the depth where anchor chain would be bouncing uncontrolably. It would be an extra long and strong jon line. I attach it deep (when no bounce) but only start using it shallow when the bounce or current gets crazy. It has a Y end with a clip on each end of the y that clips to my 2 chest D rings. With the jon line both hands are free to do whatever needs to be done, Im safer as the anchor chain cant get ripped out my hands suddenly, and my hands are free.

My jon line would have an 'emergency release' clip about half way along - to release Id sometimes (but rarely) in really bad conditions unclip it there and remove the rest (thats stilll attached to anchor line) when we pull up the anchor.

I found when we reallly Must deco off the anchor/down line in raging currents that this method makes deco much safer and far less stressfull, it also negates the need for a switchblock Of course drifting platform deco is preffered but not always possible

__________________
Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you

Dave Sutton

No disagreement, having suffered a dislocated shoulder once on a hang (had a prior injury, so... but in any event it SUCKED), and I have a Jon line on my rigs and use it. 100% of my dives are done under these conditons, so it's just business as usual here. I also engineer for "worst case", as I've found that the following is invariably true:

"Things go well slowly, but they go wrong all at once"

In a real-world bailout from 220 last year, I found myself in exactly the conditions described. All went 'fine' except if 'one more thing' had been tossed on my plate, it would have been one too many. There was no chance at all to deploy the Jon Line, and as far as QD's are concerned there is no way in hell I could have connected anything to anything else. Not to say a switch block would have helped either.. that's exactly all of my gas is available OC without changing a thing except what is in my mouth.


Damned Ice. I hate you for living in the tropics.

Dave

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__________________
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"All animals are equal, but some animals are more equal than others"


Professional Small Boy: Never Successfully Cubicled.

divetheworld

I think you missed the point. I have access to inboard dil for the bov sanity breaths and the O2 on the same regulator for additional deco gas in the case of a full bail.
No one said anything about quick changes except you.

Anyway, for the others who are interested, the M&J block has to be turned 180deg with ball detent positions. The knob has a part that sticks out whn in one position allowing tactile feedback of position. Its very difficult to "accidentally" turn but still requires discipline to check it, like all the other checks you do before entering the water.

If I recall correctly the OR switchblock has a ring pull like a grenade that you must remove before you can switch over. I wasnt convinced on the build quality though.

Sartek Industries, Inc. RSV-1 Redundant Supply Valve
The Sartek is similar to the OR with the security clip. Its more expensive but better made.

Kirby Morgan Manifold Block Assembly - Amron International
KM block is the most expensive and uses one "tank valve" like device and so is not strictly a switchblock but a method of introducing a second supply gas and isolating the other. Used on almost every commie system to bail out when the umbilical of SS is compromised. But nobody uses them nowadays

All of these were made with OC full face masks in mind for changing gas supplies without removing the FFM.

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Dave Sutton

Exactly... something missed by many.

The KM one is the same system as used on their band masks and helmets, and the globe-valve and checkvalve system is bulletproof. Just remember to turn OFF the supply to the checkvalve after opening the supply fed thru globe valve. It's designed to be used by an umbilical fed diver, who upon loss of umbilical gas (fed thru the checkvalve) simply opens the globe valve and ascends. The ones I had in the shop magically had their guts removed, were screwed to the sides of my Mark-15, and are now fed from the backside thru newly drilled and tapped ports and are the offboard 02 and diluent external manifolds... so much for using them as switchblocks... .

The Sartek one (have one in my hand actually...) is a slider-type, well enough made from Delrin, (2) 3/8-24 inputs and (1) 3/8-24 output (or one input available to two outputs, you choose). The removable clip to prevent inadvertant change is, err..... well...... OK I guess..... but I'd never rely on it for life critical 'lockout'. Mine was given to me as an engineering sample at least ten years ago, and although I have played with it for years, it's NEVER actually been diving and is now a paperweight (thus the fact that it's in my hand as I write this).


Group Hug Now....


Dave

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__________________
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"All animals are equal, but some animals are more equal than others"


Professional Small Boy: Never Successfully Cubicled.

silent running

Another alternative to switch blocks or external manifolds is to use a dil 1st stage spare lp port for a whip with a QC that's connected to your BO tank 1st stage with a QC lp whip from the BO reg's spare lp ports. That way you don't have to fiddle with the QCs in an emergency, you only have to turn one valve and shut another. Whichever 1st stage is open is the one driving the gas. This works well for me as my onboard reg is a plain old Mk2 Scubapro while my BO reg is a better breathing Mk17.

And of course, this same setup can work through the O2 side if you are carrying offboard O2.

Drmike

most rbs are using 3L or 2L tanks..
most rbs see less than 200bar O2 starting pressure (no booster = 140bar? max)
at time of bail if you have significant deco the tank pressure isnt likely to be very much. (100bar max typically?)

personally I carry/stage adequate bailout (especially shallow tanks which are the easiest to stage). I just dont rely/consider the variable small volume in my on boards for bail - i see that akin to carry a band-aid into a mine field

i think if people are considering the usefulness of that little 300L of O2 for bail gas then they simply arent carrying enough real bail gas! Just my opinion

I like to keep the 2 systems seperate OC and Rebreather. Blow a hose or o-ring with a linked system on a deep dive and you could lose much of your O2 supplies.

Trust me if your at 6m and you are running low on off board O2 bail gas you can find a way to remove your Rebreather take out the O2 tank and shove a reg on it - I know Ive practiced it

he he a few years ago diving eagles nest with CV he had forgoten to bring the bail O2 so before the dive we dry ran through what we would do if someone bailed. How one diver would assist removal of O2 tank from one of the RBs and shove a reg on it Stupid I agree but in the real world faced with a long drive back and missed diving day.... we went ahead.

__________________
Get a girlfriend you sad twat - a Rebreather is an unfaithful mistress - dont blind yourself to her faults just because she goes down on you