Depressurizing plugged first stage

[WarrenZ]

Less risk because.... ??

150ish psi vs 3000psi forcing the threads together.

Lp port should have less stiction holding it in place as it is slightly smaller with less pressure holding it there.

 

[eelnoraa]

I know this is a stupid question but lets just treat it as a thought experiment.

Let's say you plug all the ports on a first stage and connect it to a tank, then you pressurize it. How would you remove the first stage afterwards (depressurize it)?

I did exact the same twice, both had to do with mistake in regulatoe maintenance routine. Just close valve, crank open HP port. The amount of air inside is little, plus HP port flow rate, really not much beside a medium pop, not even as lousy as my tank pressure gauge release button.

 

[Justin Bove]

Less risk because.... ??

I would think the LP port would be around 100-200 PSI while the HP port would be 3000-3500 PSI or whatever the tank pressure is.

 

[rhwestfall]

unless the valve is open there is negligible volume of pressurized gas available to do much of anything of any consequence aside from ruining an o-ring...

 

[happy-diver]

I know this is a stupid question but lets just treat it as a thought experiment.

Let's say you plug all the ports on a first stage and connect it to a tank, then you pressurize it. How would you remove the first stage afterwards (depressurize it)?

It's an easy thing to do by mistake. I was once troubleshooting an issue and disconnected the primary 2nd stage, the LP inflator hose, and the SPG from the first stage, and replaced them with plugs. I was about to connect an HP gauge to the regulator and thought about it. "If I do this and open the valve, there will be no way to depressurize the system and that would be bad".

You see, not a stupid question at all

I did exact the same twice, both had to do with mistake in regulatoe maintenance routine. Just close valve, crank open HP port. The amount of air inside is little, plus HP port flow rate, really not much beside a medium pop, not even as lousy as my tank pressure gauge release button.

 

[RainPilot]

I have done this several times (on my CCR the system purges the O2 when you shut down, if a student forgets to turn the O2 tank off when it's shut down or if it's opened with it shut down, I need to go through the whole start cycle to get to depressurise to remove the tank).

An allen key and a few slow turns on a port plug and it will hiss for a second and then the pressure is gone. The actual volume of gas in the system is pretty low, even more so if it is just a first stage. You can regulate the rate by how much you open the port as well. So far I haven't had to replace an o-ring but it wouldn't hurt.

 

[АлександрД]

I do like such topics! with "near-stupid" quesions.
near - because it absolutelly useless, but could occur.... and with interesting ways for solution...
but not for this case, because:
- length of the thread on the HP or LP connectors much bigger than o-ring thickness.
- when you has unscrew any HP or LP plug - all that you can have - brocken o-ring, and no more. BUT! you have to do it with closed tank valve and until it starts to "psst"
- it is much more easy to open LP port plug, because a) diameter of LP plug is less than HP. b) pressure for LP is always less or the same than HP. a+b=>c) force to unscrew the LP plug is always less than HP.

But you have another way, more dangerous (not only for your but for regulator) - you can try unscrew DIN thread (with Yoke connector I think it is much more simple and with ease).
P.S. I always use that whay, when detach regulator from valve... but alway do it with depressured around 20-30bar...

... 2. When you try to disconnect 1st stage from tank - after closing valve do not drop the pressure less than 20bar. Then try to disconnect DIN or Yoke carefully from valve. It will make "psssst", and stops. Do not press purge button on 2nd stage after! You should stay pressure in the hoses.
When you make this step - you can loose HP o-ring, be carefully. Put it back to the sink.
Than close hole in the 1st stage by finger, and then put regulator to the fresh water and shake it storngly.
THAN shake it from water drops, remove finger, AND SLOWLY press purge button.
When pressure in the hoses will drop less than IP (setup pressure or Intemediate Pressure), you 1st stage will opening, and air starts to go from hoses, over regulator, over the filter to the out.
It allow you to get some dividents:
Your filter will be cleaned from any possible drops of water.
You filter will be cleaned from any rust particles from the tank.
And you be able to see, how it clean, when you will put you palm before air stream. All particles will stay on your wet palm (I hope you are freshed regulator before )
And also that allow to prevent water ingress inside regulator when you will freshening it.

 

[buddhasummer]

I've done it before, undid the hp port plug until it started leaking, nothing bad happened, I'm still here.

 

[Jimbo2]

A firefighter was killed recently doing something similar. They had some scuba cylinders for their dive team where the valve had frozen shut. He loosened the burst disc plug until air started draining then went on to another cylinder. The burst disc plug then gave way, causing the cylinder to take a tumble and break the valve off, after which the cylinder became airborne and struck the firefighter in the head. Lesson learned would be to strap the cylinder to something before you start releasing pressure. I would do an lp port over an hp port once I had it strapped down, because 3000 psi can be dangerous in ways that are not obvious.

Visual of the Ohio fire station interior and the track of the cylinder that struck the firefighter in the head.
NIOSH LODD Report: Ohio Firefighter Dies after Being Struck by SCUBA Cylinder

 

[tridacna]

Visual of the Ohio fire station interior and the track of the cylinder that struck the firefighter in the head.
NIOSH LODD Report: Ohio Firefighter Dies after Being Struck by SCUBA Cylinder

In that accident, the valves were stuck. The tank pressure was the problem. You had a full tank of air at tank pressure to deal with.

In this scenario, the valve is closed so we are dealing with an exponentially smaller amount of air. Only the volume that is contained within the first stage chamber. There is thus much lower risk of danger.

(Assuming you are smart enough to close the tank valve of course).