Question Regulator Physics

[TrimixToo]

If water is allowed to enter the 2nd stage (no mouth on the 2nd stage regulator) the pressure will be equalized in and outside the 2nd stage, the diaphragm won't move and depress the demand lever and the valve (poppet against orifice) will remain shut.

If there is a mouth on the 2nd stage that keeps water from ingressing and the same amount of air/same air that there was on the surface remains in the body of the 2nd stage, then the ambient pressure while decending will push against the diaphragm and cause the demand lever to depress which will open the demand valve and allow air to flow from the hose connecting the 2nd stage to the 1st stage. Air will flow out the hose into the 2nd stage until the pressure in the 2nd stage balances with the ambient pressure outside the 2nd stage. The first stage HP valve will open as a result of the drop in pressure in the hose between the 1st and 2nd stage, and will subsequently close when that pressure equals the IP pressure the 1st stage is set to...that coincides with the 2nd stage demand valve closing.

-Z

So...what, exactly, did you disagree with?

 

[Lorenzoid]

So...what, exactly, did you disagree with?

I'm thinking Zef disagreed with nothing. He just offered a different way of explaining it.

 

[Zef]

So...what, exactly, did you disagree with?

I disagree with the notion that IP is relative to ambient pressure. As I understand it, IP is a fixed setting...adjustable on a diaphragm 1st stage, and based on spring strength/length (modifiable with shims) on a piston 1st stage?

Unless I am mistaken, IP remains constant regardless of depth and only changes when cylinder pressure drops too low to sustain the IP the 1st stage is set to....cylinder pressure is unaffected by depth.

-Z

 

[Lorenzoid]

I'm thinking Zef disagreed with nothing. He just offered a different way of explaining it.

I stand corrected. Still, I liked Zef's explanation.

 

[TrimixToo]

I see. You contend that the IP is maintained at an absolute pressure and not a relative pressure. So, at 321', where the ambient pressure is about 9.7 ATA, I should expect my Abysss (with an IP of 140 or so) to have an IP of about zero PSI relative to ambient pressure? As it was easy enough to breathe it there, rather than impossible, I rather suspect not.

The IP setting really needs to be maintained relative to ambient pressure for the regulator to continue to work well as you descend.

I disagree with the notion that IP is relative to ambient pressure. As I understand it, IP is a fixed setting...adjustable on a diaphragm 1st stage, and based on spring strength/length (modifiable with shims) on a piston 1st stage?

Unless I am mistaken, IP remains constant regardless of depth and only changes when cylinder pressure drops too low to sustain the IP the 1st stage is set to....cylinder pressure is unaffected by depth.

-Z

 

[Zef]

I see. You contend that the IP is maintained at an absolute pressure and not a relative pressure. So, at 321', where the ambient pressure is about 9.7 ATA, I should expect my Abysss (with an IP of 140 or so) to have an IP of about zero PSI relative to ambient pressure? As it was easy enough to breathe it there, rather than impossible, I rather suspect not.

The IP setting really needs to be maintained relative to ambient pressure for the regulator to continue to work well as you descend.

Ok, I did some thinking about what you posted and here are some thoughts:

1. You are correct IP is relative to ambient pressure but I think you didn't really explain this very well.

2. IP for the 1st stage is set and the "setting" doesn't change, but because the 1st stage is open to the pressure of the ambient environment (piston 1st stage, or unsealed diaphragm 1st stage)**, the realized IP is actually the set pressure amount above ambient pressure...

...in the case of your Mares 1st stage, the IP would be set at @ 142psi....the IP setting itself does not change, but because because the ambient pressure acts on the side of the diaphram in the spring chamber, the membrane experiences the ambient pressure + the pressure of the spring set to 142psi. At 321ft of sea water, the diaphram would have 142psi of the spring acting on it + 142psi of the water pressure of that depth acting on it.

**(an environmentally sealed diaphragm 1st stage acts/responds to ambient pressure the same way as an unsealed diaphram 1st stage due to the action of the piston-like pressure transmitter between the sealing diaphragm and the main diaphragm.)

3. Here is a good video that explains this concept much more clearly than either of us have done:



4. While this is all good info and makes for great academic discussion, I believe its technical nature exceeds the understanding the OP was seeking in their initial questions.

-Z

 

[L13]

Pressure can be measured as "gauge"(relative to ambient) or absolute pressure.

A 1st stage regulator maintains a constant "gauge" (relative to ambient) IP pressure, which means absolute pressure changes as ambient pressure changes.

The term "gauge pressure" is used because most gauges report relative pressure.

SPG's report absolute pressure.

 

[TrimixToo]

Ok, I did some thinking about what you posted and here are some thoughts:

1. You are correct IP is relative to ambient pressure but I think you didn't really explain this very well.

2. IP for the 1st stage is set and the "setting" doesn't change, but because the 1st stage is open to the pressure of the ambient environment (piston 1st stage, or unsealed diaphragm 1st stage)**, the realized IP is actually the set pressure amount above ambient pressure...

...in the case of your Mares 1st stage, the IP would be set at @ 142psi....the IP setting itself does not change, but because because the ambient pressure acts on the side of the diaphram in the spring chamber, the membrane experiences the ambient pressure + the pressure of the spring set to 142psi. At 321ft of sea water, the diaphram would have 142psi of the spring acting on it + 142psi of the water pressure of that depth acting on it.

**(an environmentally sealed diaphragm 1st stage acts/responds to ambient pressure the same way as an unsealed diaphram 1st stage due to the action of the piston-like pressure transmitter between the sealing diaphragm and the main diaphragm.)

3. Here is a good video that explains this concept much more clearly than either of us have done:



4. While this is all good info and makes for great academic discussion, I believe its technical nature exceeds the understanding the OP was seeking in their initial questions.

-Z

1. Communication is a shared responsibility. I don't claim to be able to write a perfect explanation. Sorry you didn't understand what wrote. When you don't understand, please ask questions. Perhaps, as in this case, you will (a) learn something and (b) discover that you don't disagree after all.
2. You're catching on.
3. No plan to watch it.
4. Thanks for the opinion.