Where should the pressure gauge be mounted and what are the advantages of this configuration?

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Kofferfisch

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Hello together,

last week there was a discussion in my diving club how the pressure gauge should be mounted for cold water diving. My instructor is of the opinion that it should be mounted on the primary first stage. Unfortunately, I do not see any advantage in this and when asked, they could not tell me one. Then I looked at the recommendation of my association (VDST) with the result "Individual decision, safety-wise it makes almost no difference".

My own opinion:
The pressure gauge should be screwed into the secondary first stage. That has the advantage if the primary first stage should ice up and the corresponding valve is closed you still sees how much air is in the tank.

Are there any advantages that favor a different configuration that I have not yet thought of?
 

Wibble

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The DIR configuration for twinsets is you've a left-side and right side. The SPG is connected to the left side along with your necklaced backup regulator, your longhose is on the right side.

If the isolator's closed when you dropped in (and failed to check it when getting into your kit on the surface), you'll notice that your gas pressure doesn't drop (you're breathing from the RHS). Just undo the isolator underwater.

Should the longhose go pop, you'd shutdown the RH valve and breathe from the backup -- gauge would still be reading pressure.

There's very few failure modes that would require the isolator to remain closed. The isolator valve is often the first thing to close when you've a "boom" -- bubbles all around you. Once you've worked out which "hose" has burst, you shut down that side and breathe off the other. Then you'd open the isolator valve to ensure you've got all gas available.


You'll probably find that the real reason for connecting the SPG to the LHS is simply that the RHS is reserved for the donation process in a DIR-compliant rig. This means the RH side of the whole rig's reserved to enable the longhose deployment, i.e. the longhose could be entangled with the SPG hose if that was on the RHS and you had to donate just at the moment you were reading the gauge. Same reason for not mounting any stages on the RHS.
 

Kofferfisch

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The DIR configuration for twinsets is you've a left-side and right side. The SPG is connected to the left side along with your necklaced backup regulator, your longhose is on the right side.

If the isolator's closed when you dropped in (and failed to check it when getting into your kit on the surface), you'll notice that your gas pressure doesn't drop (you're breathing from the RHS). Just undo the isolator underwater.

Should the longhose go pop, you'd shutdown the RH valve and breathe from the backup -- gauge would still be reading pressure.

There's very few failure modes that would require the isolator to remain closed. The isolator valve is often the first thing to close when you've a "boom" -- bubbles all around you. Once you've worked out which "hose" has burst, you shut down that side and breathe off the other. Then you'd open the isolator valve to ensure you've got all gas available.


You'll probably find that the real reason for connecting the SPG to the LHS is simply that the RHS is reserved for the donation process in a DIR-compliant rig. This means the RH side of the whole rig's reserved to enable the longhose deployment, i.e. the longhose could be entangled with the SPG hose if that was on the RHS and you had to donate just at the moment you were reading the gauge.
Thank you for your explanation. You show some things that I have not yet considered. Unfortunately, the longhose is "demonized" in my diving club. Basically, this can also be transferred to a configuration with short hose or am I missing something?
Wherever you think is best for you! What suits one person is not suitable for others.
I think to know what works best for you, it is important to know the pros and cons of each option. But at the moment i do not think it is a good idea to screw it into the primary first stage.
 

Vitesse2l

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I assume the OP is diving an H valve single cylinder?

What sort of diving are you doing where ice may be a problem? My own diving is uk based and H valve is rare in rec diving over here.
 

Wibble

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@Kofferfisch

The longhose needs a little practice, but there is not much to it.

It's a pity that your club doesn't like it; seems like an old-school attitude (or they're avid cave divers).

If I'm diving on a single cylinder, I will have a longhose and the small hose with a necklace bungee. Both are connected to the same first stage. It works exactly the same way as if I were diving a twinset/doubles.

Longhose donation: simply take out the regulator in your mouth with your right hand, over your head and push it into the face of the diver who needs it. With your left hand you scoop up the necklaced backup and put it in your mouth and breathe. When the other diver's grabbed the longhose from your right hand, you then release the rest of the hose from under your belt (normally behind a battery). Then back away from that diver a bit.

Needs a little practice, but is very easy.
 

Ulfhedinn

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Once you have had to donate air... you will appreciate the long hose. Open water or not.
 

BlueTrin

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Is the reason for having the SPG on the left side with a DIR configuration to not trap the long hose?
 

Kofferfisch

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I assume the OP is diving an H valve single cylinder?

What sort of diving are you doing where ice may be a problem? My own diving is uk based and H valve is rare in rec diving over here.
In fact, I dive sidemount with a longhose. So my question is not about myself. I find the question interesting and would like to know what the reasons are for the two options. In Germany, I rarely see anyone diving specifically with an H valve, but a redundant 1st stage is actually now standard.

The longhose needs a little practice, but there is not much to it.

It's a pity that your club doesn't like it; seems like an old-school attitude (or they're avid cave divers).

If I'm diving on a single cylinder, I will have a longhose and the small hose with a necklace bungee. Both are connected to the same first stage. It works exactly the same way as if I were diving a twinset/doubles.

Longhose donation: simply take out the regulator in your mouth with your right hand, over your head and push it into the face of the diver who needs it. With your left hand you scoop up the necklaced backup and put it in your mouth and breathe. When the other diver's grabbed the longhose from your right hand, you then release the rest of the hose from under your belt (normally behind a battery). Then back away from that diver a bit.

Needs a little practice, but is very easy.
I have no problem with this configuration since I also dive it myself and also see the advantages. I also agree that with a little practice the long hose is not a problem. The argumentation is that when diving on vacation, you rarely meet divers who also use a configuration with a longhose. But that is not what this topic is about.

Once you have had to donate air... you will appreciate the long hose. Open water or not.
That is not what the topic is about. I also think the topic longhose is discussed many times. No need to start again here.

Is the reason for having the SPG on the left side with a DIR configuration to not trap the long hose?
Thank you Wibble also mentiont that.
 

Wibble

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@Kofferfisch — I’d made the assumption that you were new to the longhose so answered as if you were a novice. Others may have done that too :)

On holiday, I’d use the longhose every time on open circuit — sidemount, backmount doubles or a single. Not my problem if others are unfamiliar with that configuration although it only takes a second to demonstrate for them to understand.
 
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