XT1 1st stage failed CLOSED at depth

[redacted]

Hard for me to understand how they could fail closed. Please explain?

On any 2nd stage, break the lever.

On any BP 1st stage, break the main spring.

I don't use diaphragm 1sts so have not examined their failure modes.

 

[redacted]

Why? Can't those fail closed too?

Maybe but it is not obvious to me. A spring failure should not lock it closed like with the balanced design but it probably will not provide enough gas flow to be useful. I suspect cracking pressure may be very uncomfortable as IP when it locks up will be quite low. Maybe someone will test it.

 

[guruboy]

Maybe but it is not obvious to me. A spring failure should not lock it closed like with the balanced design but it probably will not provide enough gas flow to be useful. I suspect cracking pressure may be very uncomfortable as IP when it locks up will be quite low. Maybe someone will test it.

Assuming all unbalanced designs are flow-by piston, that makes sense.

 

[BRT]

On any 2nd stage, break the lever.

On any BP 1st stage, break the main spring.

I don't use diaphragm 1sts so have not examined their failure modes.[/QUOTE
OK, if the lever broke or the diaphragm ruptured your 2nd stage would not flow. Have you ever seen a lever break? And if the first stage spring broke it would mess with intermediate pressure. I don't see how it would cause complete air shutdown but I guess if it broke into little pieces that would shut off pressure entirely. Have you seen that happen? Neither of these would fix themselves and work later.

 

[redacted]

I have never seen either of those failure modes. But, no matter how unlikely, they remain possible.

I have screwed around with a BP 1st trying to lower IP way below spec which allowed the piston knife edge to seal in the seat to a point that lowering IP to ambient would not cause the piston to withdraw from the seat.

I would hope someone with an interest in diaphragm regs might do a part by part failure analysis to deternine what might have happened to cause that symptom (spg shows pressure but no gas flow).

 

[2airishuman]

I believe this is the same internal design as the HOG D1 and the Deep Six regulator. Perhaps someone can confirm.

Almost any rgulator can fail closed. It really makes you appreciate the simplicity of an unbalancd piston 1st.

I just rebuilt my US Divers Aqarius which is an unbalanced piston regulator.

I believe that it could fail closed in at least three ways:

1) Broken main spring. Since, like many piston designs, the adjusting spring applies closing pressure on the piston, I believe this would result in zero air flow.

2) Stuck piston due to adhesion of the piston o-ring to the wall of the regulator.

3) Clogging, at least in theory.

Hard for me to understand how they could fail closed. Please explain?

I don't use diaphragm 1sts so have not examined their failure modes.

It depends on the design. I haven't had my D1s all the way apart. On my Conshelf regs, there's a pin that pushes the seat open. If that breaks, the reg could fail closed. It is possible for the seat to become delaminated so that it doesn't open when the pin pushes on it. Clogging would appear to be theoretically possible.

 

[BRT]

I believe this is the same internal design as the HOG D1 and the Deep Six regulator. Perhaps someone can confirm.



I just rebuilt my US Divers Aqarius which is an unbalanced piston regulator.

I believe that it could fail closed in at least three ways:

1) Broken main spring. Since, like many piston designs, the adjusting spring applies closing pressure on the piston, I believe this would result in zero air flow.

2) Stuck piston due to adhesion of the piston o-ring to the wall of the regulator.

3) Clogging, at least in theory.




It depends on the design. I haven't had my D1s all the way apart. On my Conshelf regs, there's a pin that pushes the seat open. If that breaks, the reg could fail closed. It is possible for the seat to become delaminated so that it doesn't open when the pin pushes on it. Clogging would appear to be theoretically possible.

Trying to imagine what kind of glue I would use to adhere the o-ring to the cylinder so the spring couldn't move it.

 

[Bryan@Vintage Double Hose]

Maybe but it is not obvious to me. A spring failure should not lock it closed like with the balanced design but it probably will not provide enough gas flow to be useful. I suspect cracking pressure may be very uncomfortable as IP when it locks up will be quite low. Maybe someone will test it.

You are correct. A tiny bit will get by but no where near a breathable amount.

 

[tbone1004]

@2airishuman they are similar, but different manufacturers. What happened on my Poseidon was that something wasn't aligned 100% accurately and the diaphragm wasn't able to depress when you pulled negative pressure from the second stage. To get it to depressurize I had to press on the diaphragm with an allen key and it then worked perfectly fine. It pressurized, but it couldn't depressurize which was the fail closed. I think this was an alignment issue somewhere internally. It is now working just fine, and has been for 2 years with no repeat of the problem

 

[2airishuman]

I have screwed around with a BP 1st trying to lower IP way below spec which allowed the piston knife edge to seal in the seat to a point that lowering IP to ambient would not cause the piston to withdraw from the seat.

I want to add that, there was a recall on the U S Divers Cousteau regs, back in the day, because the seat could come loose and move towards the piston, resulting in a "fail closed" condition. It had happened once on an actual dive but no one was hurt. The fix was to add a retainer for the seat.

For those not familiar with the Cousteau, it's a flow-through piston design.

Trying to imagine what kind of glue I would use to adhere the o-ring to the cylinder so the spring couldn't move it.

Corrosion, in such a shape to make a ramp.