Fail safe design

[Bambright]

For second stage reg. there are Downstream and Upstream Valve. How about First Stage? Will we categorize as Down and Upstream also?

For the balanced diaphragm first stage, the valve move against the air flow direction when open. Is this fail safe design? Should we call this type of valve the Upstream valve?

Hope this is not too technical. I could not find the answers any where.

Thanks,

Bambright

 

[DA Aquamaster]

Diaphragm first stages do use an upstream poppet design. The mainspring in combination with the ambient pressure acting through the diaphragm provides the force needed to lift the soft seat off the orifice. If the mainspring were to break with this design, the smaller seat carrier spring would hold the seat against the orifice and the first stage would fail closed. For this reason, designers are careful to ensure the mainspring is never over compressed and remains comfortably within its working range.

With a piston regulator the poppet is a downstream design and the mainspring holds the piston mounted hard seat off the soft seat. If this spring were to break, this force would no longer be available and the IP would then be very low due to the change in the balance of forces acting on the piston. But theoretically, if you inhale the pressure on the compression side of the piston head should be low enough to suck the piston upward and open the seat enough for at least some air to pass through the reg. Whether this air is enough to be useful is where the difference between theory and practice will become a very personal issue.

So in either case, breaking a mainspring is a very bad thing to have happen.

 

[rescuediver009]

I am not sure that this would be the case with an overbalanced design, such as apeks.... I think that the reality of this actually happening should also be taken into consideration...

 

[Bambright]

I am not sure that this would be the case with an overbalanced design, such as apeks.... I think that the reality of this actually happening should also be taken into consideration...

Would you please elaborate more....

 

[rescuediver009]

Would you please elaborate more....

I was just bringing up the thought that the extra boost of air that pushes the hp seat on to the cone, might be enough to keep it off the cone if it wasn't there. And then if the main spring were to break, then the diaphragm may not necessarily seal the mechanism shut.... Just a thought, I don't know if it would work, I have never tried it or anything. Really I think that this is all a little over the top to tell you the truth, I mean with the main spring breaking and all.

 

[DA Aquamaster]

It is pretty much a theoretical argument. I have never heard of a mainspring breaking unless it was the wrong spring for a regulator or was badly over shimmed and operating outside it's normal working range.

 

[rescuediver009]

It is pretty much a theoretical argument. I have never heard of a mainspring breaking unless it was the wrong spring for a regulator or was badly over shimmed and operating outside it's normal working range.

Ok I get you. I was just worried that someone was actually worried about that happening. But hey, I am all for theoretical discussions too. What is your take on the overbalanced construction being failsafe "theoretically" ?