AI transmitter on hose - leave transmitter O ring or not?

[scubadada]

Has this question come up before? I do not recall reading about it in previous threads on the topic of direct connection or short hose for a transmitter.

 

[broncobowsher]

Thanks, I removed the extra O ring.

That is the correct thing to have done.

The transmitter threads are the same as a SPG and those are the same as a HP hose. The transmitter is machined to work either way. Unlike the male side of a hose or an SPG.

The HP hose uses a static O-ring for sealing. It is an SAE hydraulic hose design. The threads are sealed inside the pressurized area.

The SPG uses dynamic O-rings, so the gauge can swivel on the end of the hose. That is what the spool is for. The way the female side of the hose is made, it is the only option. On a dynamic O-ring the threads are not sealed, the threaded nut is free to spin on the crimped insert into the hose. If you tried to pressurize the threads there will be a large leak where the nut spins on the hose.
Although you don't care if the transmitter swivels on the end of the hose, it is sharing the same connection method as an SPG. So treat the same as an SPG to a hose. Only O-rings on the spool.

 

[Divin'Papaw]

That is the correct thing to have done.

The transmitter threads are the same as a SPG and those are the same as a HP hose. The transmitter is machined to work either way. Unlike the male side of a hose or an SPG.

The HP hose uses a static O-ring for sealing. It is an SAE hydraulic hose design. The threads are sealed inside the pressurized area.

The SPG uses dynamic O-rings, so the gauge can swivel on the end of the hose. That is what the spool is for. The way the female side of the hose is made, it is the only option. On a dynamic O-ring the threads are not sealed, the threaded nut is free to spin on the crimped insert into the hose. If you tried to pressurize the threads there will be a large leak where the nut spins on the hose.
Although you don't care if the transmitter swivels on the end of the hose, it is sharing the same connection method as an SPG. So treat the same as an SPG to a hose. Only O-rings on the spool.

Great explanation! This is exactly what I did. The spool provides the o-rings and the transmitter itself should not have one. It isn't hurting anything but it isn't doing anything either. It would NOT hold back the pressure if the o-rings on the spool leak. I instinctively removed it when I set up the transmitter on the hose as I'd setup SPGs multiple times in the past. So it just seemed logical without much thought but I can sure see this tripping you up.

 

[gqllc007]

Does anyone have a link to the hose and the spool? Would like to make sure I get the correct ones....I have the Shearwater Perdix AI on the way

 

[Divin'Papaw]

Does anyone have a link to the hose and the spool? Would like to make sure I get the correct ones....I have the Shearwater Perdix AI on the way

All spools and HP hoses used in scuba are the same. Here is just one source but any dive shop, online or brick and mortar, can provide them.

DGX Air Spool w/ Viton O-Rings for SPG Swivel

High Pressure Rubber Hose

 

[Zef]

Connect the transmitter exactly the same way you would an SPG, just the spool.

I have researched this question in the past for Suunto transmitters.....Suunto transmitters call for the o-ring to remain whether attached directly to the 1st stage are connected to a HP hose.

-Z

 

[Mike1967]

I have researched this question in the past for Suunto transmitters.....Suunto transmitters call for the o-ring to remain whether attached directly to the 1st stage are connected to a HP hose.

-Z

Hmm I thought they just used a different spool but ok, we're talking about proper gear here anyway

 

[broncobowsher]

And keep a spare spool or two in the save a dive kit. Even if you don't need them, when that little O-ring lets loose it is faster to just change the whole spool than to try and change the O-ring on the spool. And as cheap as they are, not worth the fight either. I've done it as people were splashing and wasn't late to the party, just not the first one there. And you are the hero to someone not prepared as well. That $2 spool can get you an $8 burger after the dive.

 

[Divectionist]

Does anyone have a link to the hose and the spool? Would like to make sure I get the correct ones....I have the Shearwater Perdix AI on the way

What JimBlay linked there is all you need.

I got the same 'shoulder design' viton air spool with the metal separator in the middle rather than a simple tube, and a Scubapro kevlar HP hose in 10cm/4in. The hp hose length is your main decision point. Some people go for a minimum 15cm hose and perhaps Miflex, but I don't want it to flop around or require being tied to another hose, just enough to not be grabbed by people and get out of the way of a fully inflated wing.

The spool spare in the SAD kit is a good idea.

Steps
1. Take O ring off the transmitter
2. Insert one end of the air spool into the transmitter (make sure you have no other flow restrictor installed in the transmitter of course)
3. Screw the transmitter onto the hose and gently tighten with two wrenches (to hand tight, but it's better than twisting the plastic housing of the trans).

It definitely felt off with the squished exposed O ring, but it's not something I wanted to just remove without confirming, so thanks once again for everyone's help.

Attached is a picture from pressure/IP testing after, 10.5l tank for scale (maybe called LP85 in your neck). The trans can still move 2cm in either direction but otherwise holds itself there when pressurised. When diving I usually tilt the 1st stage slightly so that the inflator hose pokes up a bit and the transmitter tucks away behind the wing rather than straight out the side. It's an inverted MK17 so the trans coming out the top is extra dicey otherwise.

 

[scubadada]

DGX currently only has a 9" rubber hose, but a 6" braided hose. I guess I would still ask myself, do I want something sticking out from my 1st stage? I guess you can restrain it, see @Divectionist above. I've only had a transmitter directly attached to my 1st stage for a few over 1500 dives, so far so good. I have never seen it mishandled by anyone. AI transmitter damage when directly connected to 1st stage