nessmiller
Guest
Can somebody please explain to me what is meant by an "upsteram" design in a 2nd stage? Along this line, why are the DIR guys so against this design? I'm an engineer, so please don't hold back on the technical details. Thank you!
"Upstream" regulator design
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Essentially, it describes the type of valve used in the regulator.
A downstream valve will fail in the free flow position. In other words, you won't be cutoff from your air supply if the valve goes south.
Conversely, an upstream valve will fail in the closed position.
I'll leave the DIR question to more knowledgeable folks. However, I thought that cavers still preferred upstreams for their deco bottles so that they wouldn't lose their deco gas in the event of a failure.
A downstream valve will fail in the free flow position. In other words, you won't be cutoff from your air supply if the valve goes south.
Conversely, an upstream valve will fail in the closed position.
I'll leave the DIR question to more knowledgeable folks. However, I thought that cavers still preferred upstreams for their deco bottles so that they wouldn't lose their deco gas in the event of a failure.
luvdiving
Contributor
Hi Northeastwrecks:
That about covers it.
That about covers it.
OP
nessmiller
Guest
Thank you for your reply, but I think that I'm confused.
This is what i understand, please clear up my thinking--in the event of a failure in the 1st stage, a downstream regulator will free flow while an upstream regulator will not. I assume this is why the upstream regulators have pressure-relief devices built into their hoses. This wouldn't help the cavers though, they'd still lose their gas.
In the event that the valve in the 2nd stage fails, a downstream regulator will free flow while an upstream will not. At this point, I assume that the diver using an "upstream" regulator would be cut off from their gas, but they wouldn't lose it. Is this correct?
This is what i understand, please clear up my thinking--in the event of a failure in the 1st stage, a downstream regulator will free flow while an upstream regulator will not. I assume this is why the upstream regulators have pressure-relief devices built into their hoses. This wouldn't help the cavers though, they'd still lose their gas.
In the event that the valve in the 2nd stage fails, a downstream regulator will free flow while an upstream will not. At this point, I assume that the diver using an "upstream" regulator would be cut off from their gas, but they wouldn't lose it. Is this correct?
They would then switch second stages and regain access to their gas.
OP
nessmiller
Guest
It looks like I'm beginning to understand. Thanks for enlightening me.
Interesting...it seems that something that was probably part of the original "requirements" - a safety feature - is interpreted by some (the DIR folks) as a liability.
Would one of the DIR gurus, for whom my respect is growing, please tell me what you folks don't like about upstream regulators?
Thanks
Interesting...it seems that something that was probably part of the original "requirements" - a safety feature - is interpreted by some (the DIR folks) as a liability.
Would one of the DIR gurus, for whom my respect is growing, please tell me what you folks don't like about upstream regulators?
Thanks
...but from what I remember it was because of the additional first stage failure point created by the overpressure valve (or in lieu of that the weird non-standard hoses required).nessmiller once bubbled...
It looks like I'm beginning to understand. Thanks for enlightening me.
Interesting...it seems that something that was probably part of the original "requirements" - a safety feature - is interpreted by some (the DIR folks) as a liability.
Would one of the DIR gurus, for whom my respect is growing, please tell me what you folks don't like about upstream regulators?
Thanks
OP
nessmiller
Guest
Please be patient with me. I'm confused again.
It sounds like there is an overpressure relief valve in both the 1st stage and the hose prior to the 2nd stage. Any idea why the design requires both of them? Is it just to ensure adequate venting to guarantee that the hose won't burst?
It sounds like there is an overpressure relief valve in both the 1st stage and the hose prior to the 2nd stage. Any idea why the design requires both of them? Is it just to ensure adequate venting to guarantee that the hose won't burst?
nessmiller once bubbled...
Please be patient with me. I'm confused again.
It sounds like there is an overpressure relief valve in both the 1st stage and the hose prior to the 2nd stage. Any idea why the design requires both of them? Is it just to ensure adequate venting to guarantee that the hose won't burst?
No, you only need one OPV on the lowpressure side of the 1st stage, but it can be anywhere. In some cases it's built into the 1st stage and in some cases, like Poseidon's old upstream 2nds, the OPV is built into the 2nd stage. In either case it's on the LP side of the system.
I want to correct one thing. While an upstream 2nd may respond to a free-flowing 1st by wanting to lock up it doesn't mean you won't lose any air. Of course you will. Either the OPV will open, with the obvious consequences, or a hose will burst in which case you will lose all of your air.
In either case the air will escape somewhere other than via the 2nd stage, which may partly explain why it's not DIR. The simplicity of the downstream design is probably also part of the answer and as someone already suggested the OPV creates one more thing that can go wrong.
R..
pescador775
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The purpose of the overpressure valve is to provide a safety in case of first stage failure, not failure of second stage. Should the first stage fail, and this is typically a small leak, air is vented from the valve and not through the second stage (mouthpiece). The diver can usually complete the dive without any disturbance to his breathing cycle.
Single hose, upstream designs use a tilt valve. The only failures of even remote likelihood would be a broken spring or damaged valve seat. I don't see how either of these could lead to shut off of air. Once the diver inhales against a broken spring the valve will jam open similar to the 'downstream' mechanism. Similarly, a damaged seat will cause a leak in either type.
The DIR people claim to avoid excess failure points and I can see that an overpressure valve might fail due to corrosion or whatnot. However, I feel that this is an exaggerated concern. This component is no more likely to fail than a piston regulator which is also subject to flooding. In addition, the downstream valve associated with this type of regulator is subject to tiny wear indentations which can lead to chatter or hard breathing or leaks. The upstream valve is not subject to this problem, to my knowledge.
It may be of interest that the typical diaphragm FIRST stage is an upstream design.
Single hose, upstream designs use a tilt valve. The only failures of even remote likelihood would be a broken spring or damaged valve seat. I don't see how either of these could lead to shut off of air. Once the diver inhales against a broken spring the valve will jam open similar to the 'downstream' mechanism. Similarly, a damaged seat will cause a leak in either type.
The DIR people claim to avoid excess failure points and I can see that an overpressure valve might fail due to corrosion or whatnot. However, I feel that this is an exaggerated concern. This component is no more likely to fail than a piston regulator which is also subject to flooding. In addition, the downstream valve associated with this type of regulator is subject to tiny wear indentations which can lead to chatter or hard breathing or leaks. The upstream valve is not subject to this problem, to my knowledge.
It may be of interest that the typical diaphragm FIRST stage is an upstream design.
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