twin set - contents gauge

[pauls1149]

I have been diving with a twin ? with a manifold and isolator - set for a couple of years now and have had a debate about which side to place my contents gauge. Is it best coming from the side you normally breath from (you can see how much air you have in that cylinder if the isolator is not opened) or is it better on the other side (if you have to go onto the other reg flowing a free-flow you can see how much air is available once the free flowing reg has been turned off). I know there is no ?correct? answer ? but your comments are welcome.

[derek perry]

Hi

I have been diving the same twin set system for several years now and have 2 contents gauges. The left tank comes under my left arm and the right under my right arm. That way I know which gauge refers to which tank. I don't see you can do it any other way really; otherwise you will always be in the dark about one of the cylinder, unless you dive with the isolating valve open. If it helps most people who dive with ponies also have a separate contents gauge for that. For a few quid extra I think it's worth it

Derek


I have been diving with a twin ? with a manifold and isolator - set for a couple of years now and have had a debate about which side to place my contents gauge. Is it best coming from the side you normally breath from (you can see how much air you have in that cylinder if the isolator is not opened) or is it better on the other side (if you have to go onto the other reg flowing a free-flow you can see how much air is available once the free flowing reg has been turned off). I know there is no ?correct? answer ? but your comments are welcome.

[PeteM]

I have been diving with a twin ? with a manifold and isolator - set for a couple of years now and have had a debate about which side to place my contents gauge. Is it best coming from the side you normally breath from (you can see how much air you have in that cylinder if the isolator is not opened) or is it better on the other side (if you have to go onto the other reg flowing a free-flow you can see how much air is available once the free flowing reg has been turned off). I know there is no ?correct? answer ? but your comments are welcome.

If you dive with it off the secondary valve then it gives you a bit of extra info, in that if the isolator is closed it will not move so you know early that there is a problem, if you dive with it on the primary then it will still move so you are relying on spotting it move twice as fast.

Being able to see what is in either cylinder after an equipment failure is a red herring. If you have a problem that requires you to isolate then you are on your way up so it does not matter how much gas you have left in either cylinder.

Of course when you are diving without a problem then it does not matter which side it is on

HTH

Pete

[iainmsmith]

I have been diving with a twin ? with a manifold and isolator - set for a couple of years now and have had a debate about which side to place my contents gauge. Is it best coming from the side you normally breath from (you can see how much air you have in that cylinder if the isolator is not opened)

Assuming that you dive with the isolator open (I don't subscribe to the idea that you should dive with it closed, although I known that school of thought exists) then IMO, you should have the contents gauge on the opposite side to your primary regulator. That way, should you accidentally leave the isolator closed, you will realise after a short time into the dive when you notice that the contents gauge hasn't moved.

If you're diving anything but air, that in itself may by an indication to call the dive unless you are 100% certain that you know when the isolator was closed (ie you did it yourself) otherwise you have no certain knowledge as to what gas was put into which tank, ie you cannot be certain what you are breathing.

> or is it better on the other side (if you have to go onto the
> other reg flowing a free-flow you can see how much air is
> available once the free flowing reg has been turned off).

Why would it matter? If you've got a freeflow and have closed off a reg, you now have no AAS, so you abort the dive. You either have enough gas or you don't. If you don't, then you (ought to) have a very attentive buddy. If you haven't got that...'nuff said.

If it's a second stage free-flow, you may want to give it a minute or so to see if, having thawed out, it then behaves itself. If it does, then you can open the isolator again and see how much gas you have and can make a decision whether to continue or not. If it doesn't, then you are again on your way to the surface.

Iain

[Nigel Hewitt]

I have been diving the same twin set system for several years now and have 2 contents gauges.

I did this too. I clipped them off on my chest D rings so they came instantly to hand and just needed turning towards my face to read.

I've heard the 'failure points' matra recited but the only failure I've had on an SPG in the water is when one jammed at 180 bar. It took a while to register that it had stopped moving and hence I promoted it to my personal *if it's important take two* list. One of the things I trust least when diving is me so anything that makes faults more obvious is a good thing.

nigelH

[Dominic Humphries]

I've heard the 'failure points' matra recited but the only failure I've had on an SPG in the water is when one jammed at 180 bar. It took a while to register that it had stopped moving and hence I promoted it to my personal *if it's important take two* list

So presumably you use two SPGs on a single cylinder as well..?
:o)

[Matt]

I've heard the 'failure points' matra recited

Swivel!

Heh. Nothing to do with late 70s teen sitcoms ;-)

In the scheme of things the swivel joint at the SPG connection can be problematic. I have seen several fail over the course of 8 years. Often the failure is not catastrophic, just a steady stream of bubbles coming from the joint. Sometimes the leak only occurrs in a particular position, so it gets missed in bubble checks. A constant minor HP leak can be difficult to notice other than your gas useage being subtely higher than it should be. With Trimix the problem is compounded by the depth and Helium's ability to find the smallest of gaps to escape from.

One of the things I trust least when diving is me so anything that makes faults more obvious is a good thing.

One of the things I trust least is the tiny O'ring that seals the swivel joint. The two surfaces involved moved radially which causes wear on the O'ring. It is a good argument for binning SPG boots, so at least the swivel can be easily checked and serviced.

In fact I am on the lookout for an SPG that does not have a swivel.

[Nigel Hewitt]

>>I've heard the 'failure points' matra recited but the only failure I've had on an SPG in the water is when one jammed at 180 bar. It took a while to register that it had stopped moving and hence I promoted it to my personal *if it's important take two* list

>So presumably you use two SPGs on a single cylinder as well..?
>:o)

Dive a single? Do you think I'm mad?
Didn't I say that if something is important I take two?

nigelH

[Dominic Humphries]

Dive a single? Do you think I'm mad?
Didn't I say that if something is important I take two?

Ah, well, in THAT case, when can we expect to see some photos of your lovely new Twinspiration?
>:o)

[PeteM]

I've heard the 'failure points' matra recited but the only failure I've had on an SPG in the water is when one jammed at 180 bar. It took a while to register that it had stopped moving and hence I promoted it to my personal *if it's important take two* list. One of the things I trust least when diving is me so anything that makes faults more obvious is a good thing.


Did this actually fail underwater or get noticed underwater? If the latter a breath down test would have found it.

Personally the only underwater SPG failure I have heard of was when a swivel joint descided that it wanted really wanted to be a was quick release joint. That was fairly obvious to the person concerned

Pete

[Matt]

Assuming that you dive with the isolator open (I don't subscribe to the idea that you should dive with it closed, although I known that school of thought exists) then IMO, you should have the contents gauge on the opposite side to your primary regulator. That way, should you accidentally leave the isolator closed, you will realise after a short time into the dive when you notice that the contents gauge hasn't moved.

It is possibly not quite that simple. If your diving with a hot fill in cold water, the guage will have moved significantly by the time your on the bottom. The important bit is to comprehend what the guage reads, rather than just making sure it is not saying 'full' or 'not empty'. It also helps to be thouroughly drilled in reg switching and gas management in general.

So hactually I would rather people intially use indipendants or leave the manifold closed for a while. That way they will routinely practice the skills needed to spot and deal with a problem on a manifolded set.

I did not have much of an oppinion on this until a friend of mine blew his stops and ended up in the pot after diving with his manifold innadvertantly closed. He has been diving twins for a while and I was surprised at what happened. After we had talked it through we agreed that he may have avoided the drama if he had used indis for a time and paid more attention to basic drills like shut downs and air shares.

The isolator being shut is not a cause for drama. I am as sure that if my reg went tight I would switch to the secondary. Also that I would notice the SPG not behaving normally. I dived indis for a year before getting a manifolded set and I am certain it helped later, on the couple occassions I have inadvertantly dived in with a shut manifold.

Does anyone have a good reason for the SPG being mounted on the left post? That's where mine is but it is purely for ergonomic reasons. I am quite dissapointed not to be able to think of a better reason.

With the guage on the right and the manifold closed, the SPG will provide an obvious 'in the red' warning which might evoke more of a response than a guage which simply indicates 'not empty'.

[Dominic Humphries]

Does anyone have a good reason for the SPG being mounted on the left post? That's where mine is but it is purely for ergonomic reasons. I am quite dissapointed not to be able to think of a better reason.

The right post is usually the one breathed off, so is most likely to go wrong. Therefore the left post has the SPG as it's the one most likely to stay working.

[Nigel Hewitt]

>>Dive a single? Do you think I'm mad?
>>Didn't I say that if something is important I take two?

>Ah, well, in THAT case, when can we expect to see some photos of your lovely new Twinspiration?
>:o)

Huh??
Seven failure modes. Seven recovery drills.
Duplication doesn't have to be two of the same.

On a single there are two failure modes and no recovery drills so take a pony, a buddy you trust or stay at a depth where you can swim out of it.

I'd link a smug picture of me with a sidesling 7L turtleing but I don't have redundency on the http server and it's down. Paw marks on the keyboard last time.

nigelH

[Nigel Hewitt]

>> but the only failure I've had on an SPG in the water is when one jammed at 180 bar. It took a while to register that it had stopped moving

> Did this actually fail underwater or get noticed underwater? If the latter a breath down test would have found it.

I went in with about 270 and it seemed to be lasting well - I'm a bit of a heavy breather. The SPG was hanging up in the celler still reading 180 for ages and then I went to steal it's hose and bumped it and it now points off scale.

> Personally the only underwater SPG failure I have heard of was when a swivel joint descided that it wanted really wanted to be a was quick release joint. That was fairly obvious to the person concerned

Yikes. At least mine didn't try to throw my gas away and we had a plan with thirds and I had more gas than that so I wasn't happy but we just did the stops (all on backgas, this was before I was into accelerated stuff) and got out. I think it was about 110 bar apres dive but I can't remember.

nigelH

[janos]

My SPG failed underwater and yes it was the swivel. It produced a steady stream of bubbles, not catestrophic, but enough for me notice the change in my air consumption - it went up by about 50%. Fortunately I was on the 6m shelf at Stoney at the time so was quite relaxed about the whole thing.

GOing back to the original question, I would say SPG to the secondary post, not only for the free-flow reason before, but if you look at the guage and it hasn't changed, then you know the manifold is shut.

Laters,
Janos

[David Walker]

Assuming that you dive with the isolator open (I don't subscribe to the idea that you should dive with it closed, although I known that school of thought exists)

What is the reason for diving with it closed? If its closed during normal diving, and I can't see a reason you'd open it if you had a problem such as a freeflow, then when would you actually use the manifold?

David

[PeteM]

:=Assuming that you dive with the isolator open (I don't subscribe to the idea that you should dive with it closed, although I known that school of thought exists)

What is the reason for diving with it closed? If its closed during normal diving, and I can't see a reason you'd open it if you had a problem such as a freeflow, then when would you actually use the manifold?

The theory goes that you dive it like independents. If you get a freeflow or other equipment failure you shut down the offending valve then if safe to do so open the isolator to get access to all the remaining gas.

Personally I think it sounds like the worst of all worlds, the potential human failings of indy's and the potential mechanical failings of an isolator, YMMV

Pete

[Will Swift]

I had an SPG o-ring failure on-surface and without the tiny spare o-rings for the swivel had to replace the SPG with a back-up from a buddy, when it went - it went big time - and I was glad I was on the surface.

These O-rings are exposed to tank-pressure - do you really want to double up on these particular failure points?

If you close your manifold I assume you're on the way out and up - does the extra SPG add any value in that case?

If you're using EANx - have these O-rings been changed for viton? or were they changed on your last reg service - I believe neither was true in my case and now keep a few spare and change them myself.

I commend your honesty about not registering a stuck gauge but I trust myself, my taining, buddy and dive planning above my equipment.

I've heard the 'failure points' matra recited but the only failure I've had on an SPG in the water is when one jammed at 180 bar. It took a while to register that it had stopped moving and hence I promoted it to my personal *if it's important take two* list. One of the things I trust least when diving is me so anything that makes faults more obvious is a good thing.

nigelH

[dave humm]

I run a kevlar hosed SPG and an air integrated PDC each served off different 1st stages.

The only hose failure I've had was on the surface (pool side) and resulted in me having to change my shorts !

I agree with Nigel on the doubling up. But that's just me.

Dave

[Sarah Gauci Carlton]

If you are going to the trouble and expense of diving with manifolded twins with isolator, then you might as well have two pressure gauges, one on each tank. I don't know what type of diving you do, but if you are in any sort of overhead environment, you can't just go up if there is a problem. It is very helpful and reassuring to know exactly how much gas you do have left. Admittedly the extra pressure gauge is another failure point, but you can't have everything:-))
HTH
Sarah

:=I have been diving with a twin ? with a manifold and isolator - set for a couple of years now and have had a debate about which side to place my contents gauge. Is it best coming from the side you normally breath from (you can see how much air you have in that cylinder if the isolator is not opened) or is it better on the other side (if you have to go onto the other reg flowing a free-flow you can see how much air is available once the free flowing reg has been turned off). I know there is no ?correct? answer ? but your comments are welcome.

If you dive with it off the secondary valve then it gives you a bit of extra info, in that if the isolator is closed it will not move so you know early that there is a problem, if you dive with it on the primary then it will still move so you are relying on spotting it move twice as fast.

Being able to see what is in either cylinder after an equipment failure is a red herring. If you have a problem that requires you to isolate then you are on your way up so it does not matter how much gas you have left in either cylinder.

Of course when you are diving without a problem then it does not matter which side it is on

HTH

Pete

[iainmsmith]

If you are going to the trouble and expense of diving with manifolded twins with isolator, then you might as well have two pressure gauges, one on each tank. I don't know what type of diving you do, but if you are in any sort of overhead environment, you can't just go up if there is a problem. It is very helpful and reassuring to know exactly how much gas you do have left.

It may be reassuring, but I'm curious as to how it would be "helpful" to know exactly how much gas is left? What decisions are there to be made? Surely if you have had to shut down, you are on your way out?

In terms of reassurance, can a similarly warm and fuzzy feeling not arise from having planned and executed the dive properly, so that in the event of a shut down, the diver _knows_ that he has adequate gas on his back to exit...plus all that lovely reserve gas that his buddy has with him.

Iain

[David Walker]

It may be reassuring, but I'm curious as to how it would be "helpful" to know exactly how much gas is left? What decisions are there to be made? Surely if you have had to shut down, you are on your way out?

You may have just dropped your ?10,000 camera onto the sea bed - you can see it 5m below you just waiting to be picked up. If you know you have a lot of air in your second cylinder then you'd go and get it, if you had 10bar and a long ascent you'd get going up pretty quickly!!!
But in seriousness though, you may have deco to do, and you'd want to do as much of that as possible... but you *may* not have enough gas to complete the stops (obviously you should and thats just bad planning / air management), in which case you're going to need to know when you're down to 10 bar to save for your last 6m to get you out of the water.

David

[iainmsmith]

:=It may be reassuring, but I'm curious as to how it would be "helpful" to know exactly how much gas is left? What decisions are there to be made? Surely if you have had to shut down, you are on your way out?


But in seriousness though, you may have deco to do, and you'd want to do as much of that as possible... but you *may* not have enough gas to complete the stops (obviously you should and thats just bad planning / air management), in which case you're going to need to know when you're down to 10 bar to save for your last 6m to get you out of the water.

So where's your buddy? If you are concerned that you might have lost rather more gas than you would have anticipated, then why not simply breath your buddy's reserve gas on the way out and up? That way whatever you have is still there in the event of a subsequent seperation.

It may be that I'm just biased because the single most common failure point in my club last year was leaking from the SPG spindles, but I'm convinced that there are better ways to handle this situation without adding three or four o-rings (depending on which gauge is being used), a hose and a gauge, any of which can fail, thus increasing the chances of an aborted dive without actually adding anything significant in terms of safety.

Iain