Newbie question about port plugs

[ZapDiver]

Hello, I've recently acquired one 3100 Series Regulator. It came with a second stage and hose attached, so I asked my vendor about the unused LP port plug and he told me:

"You will always be short one LP plug per 1st stage no matter the regulator manufacture, it's how they come. It's a safety issue."

This left me wondering why is it so, and what safety issue is this covering. Can you answer my doubts?

I apologize if this is not the proper forum to ask the question. If so please tell me in which forum it should be placed.

Thanks in advance.

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Zapdiver

 

[guruboy]

I don't completely understand you post.

However, if you have a 1st stage, it seems very likely you will attach a 2nd stage. The manuf can save themselves a plug by leaving one LP without a plug.

 

[fisheater]

Could it because were someone foolish enough to hook up a first stage with all of the ports plugged to a tank that there would not be any way to release the pressure to remove it?


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[Jim-SAR]

I don't know of any reason during diving that you wouldn't have a 2nd stage installed on an LP port. So, the number of port plugs would always be one less than the number of ports.

If you have a 2nd stage installed and you're still missing a plug, then that's a problem. Just buy a plug.


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[sharkbait1]

I don't know of any reason during diving that you wouldn't have a 2nd stage installed on an LP port.

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Dry suit inflation system would not have a second stage connected to a LP port. In this case you would install an overpressure relief valve.

In the case of you're typical regulator set up, the second stage "is" your over pressure relief valve. Most free flows (not all) are a result of an issue with the first stage not the second stage.

To answer the op's question, someone else sort of answered it. If you were to put the (fully plugged) first stage on a fully pressurized cylinder and open the valve, you would you not have "good/safe" a way to relieve the pressure to remove the first stage from the cylinder.

Another scenario might be if the HP seat started creeping, pressures could rise in places that are meant for working pressures or IP (Intermediate Pressures). Generally in the neighborhood of 120psi to 140psi depending on the reg.

 

[ZapDiver]

Could it because we're someone foolish enough to hook up a first stage with all of the ports plugged to a tank that there would not be any way to release the pressure to remove it?


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Thanks for the answer, this really makes sense, but, if I were to buy a first stage just to have as spare (not connected to any hose) wouldn't I need all of the ports to be plugged to avoid dust or other crap to get into the regulator?

 

[Dr. Lecter]

Honestly, I'm not sure how unsafe it would be to have the LP ports all plugged. Yes, you'd have to wrench on a plug-either HP or LP-to drain the pressure and remove the reg, but the seal is at the top of the threads rather than the bottom so I wonder if they're really going to come shooting off the reg. Then again, the DIN plugs I use to seal gas in my tanks during transport vent out a small hole in the DIN valve when I wrench them off under pressure... maybe the threads themselves would actually hold pressure?

It's probably just a case of why pay for 5 or 7 LP plugs when only 4 or 6 are needed by the customer. Though maybe it's also the case that wrenching off plugs under pressure might not be good for the brass threads.

If you have a spare reg and you want to plug it for storage, tape works fine. If you're an obsessive, buy an extra LP plug.

 

[doctormike]

Thanks for the answer, this really makes sense, but, if I were to buy a first stage just to have as spare (not connected to any hose) wouldn't I need all of the ports to be plugged to avoid dust or other crap to get into the regulator?

I guess if you need an extra first stage as a spare, wouldn't you also need an extra second stage? A second stage would be just as likely to fail as a first stage (if not more so, I don't know).

So you should plug the last LP port on your spare first stage with your spare second stage. That should keep the dust out!

 

[elan]

All my scubapro first stages were coming with a plastic plug which was protecting from the crap pretty well. Not sure how DR regs come

 

[guruboy]

Dry suit inflation system would not have a second stage connected to a LP port. In this case you would install an overpressure relief valve.

You don't use a 2nd stage reg with a dry suit?