Unsealed Conshelf Supreme IP spec

[Six2Life]

Check Wolfinger's book, page 141, 2nd paragraph from the bottom.

He is talking about a change in IP from 0 to spec IP but I noticed a change when simply adjusting the IP. Say from 135 to 145.

There will be a limit to how much seat thickness can be used (in this specific 2nd stage) for adjustment since the thinner the seat is, the closer the metal poppet surface will be to the flat metal surface next to the orifice. Once those metal surfaces meet, that will be the end of the adjustment range in that direction. Also if the seat mating surface sits below flush with the poppet, the edge of the orifice will be somewhat shrouded by the poppet. Not sure if that would have any noticeable effect on airflow. I thought about using an awap seat, which was about 2/3 the thickness of OEM, but decided against it for those reasons.

 

[halocline]

Regardless of what you read in reg savvy, the ONLY way that adjusting the IP is going to move the 2nd stage lever is by moving the seat. I'm sure you understand that. There's just not that much movement that the seat can have before it starts freeflowing. So, if adjusting the IP up does move the seat a bit, just take that tiny bit of slack out the lever.

I doubt that the poppet edge would have any noticeable effect on air flow, but I do get how eventually that edge might limit adjustment range. My guess (and its only a guess) is that it would only take a very slightly thinner seat, maybe a few hundreds of an inch, to make a pretty big difference. A quarter of a turn on an adjustable orifice make a big difference, and that can't be much more than .010" or so. It's worth a try if you can get good material and have enough interest in it. If it really worked, you could always file down the edge of the poppet, I suppose.

Have fun!

 

[Luis H]

Keep in mind that the soft seat works a bit like a secondary spring when it is contact with the volcano orifice. The spring constant of the seat is a function of the rubber hardness (rubber durometer) and the geometry. Part of the geometry is the thickness of the seat, the thicker, and the lower the spring constant.

The amount of compression on the seat is going to be proportional to how soft is the rubber and how thick is the seat.

It is true that the travel of this spring is very short, but there is a bit of compression. The compression is higher when there is IP (or low IP) and the compression is somewhat relieved when there high IP (see note below).

I am sure you have you have seen the lever drop when the second stage is pressurized. That is why you should always adjust the lever height when the regulator is pressurized (or compensate for it).

The seat motion is very small, but the mechanical advantage of the lever is a multiplier for the lever displacement. The mechanical advantage in most second stages ranges from about 5:1 to, I believe, as high as 7 or even 8 to 1. I can’t speak for all regulators. That means that a small motion of the seat carrier is amplified at the lever tip.


BTW, a single stage Mistral has a mechanical advantage of about 25:1. The compound lever system is made up of two levers each having a 5:1 mechanical advantage and therefore the end result is the multiplication of both lever’s mechanical advantage.


Note: when you adjust the volcano orifice (on a second stage with adjustable orifice) it is always recommended to press the purge button to relieve the pressure on the seat. This avoids cutting the seat while turning the orifice. But, if you are using an in line adjustment tool, it is OK to turn the volcano orifice as long as the regulator is pressurized. There is no need to press the purge button since the force on the seat is very small; most of the force is taken by the pressure thrust of the IP.

Being able to adjust the volcano orifice while pressurized is part of what makes an in-line adjustment tool so effective and so quick. I have been using them for years. I still have to do it the old fashion way on my Poseidon Cyklon second stages and I can get it in a few tries, but the tool is great for a 109.

 

[halocline]

I'm sure there is substantial movement of the seat (and resulting movement of the poppet or seat carrier) when going from unpressurized to IP. I was referring to a very small amount of movement as a result of adjusting IP.

Here's the interesting part IMO. When the seat goes from being unpressurized to pressurized, does it A)compress, B) expand in thickness, or C) both? My guess is that it mostly expands, especially in the 'ring' where the orifice contacts it and outside of that. If the lever drops, the seat carrier must move, and if the reg does not freeflow, the seat must expand in thickness to remain in contact with the orifice. But, there is now force (IP) acting directly against the area of the seat inside of the orifice, so if the seat is a compressible material, it must compress in that area. Right?

 

[Luis H]

The motion is directly proportional to the pressure change (not necessarily in a linear fashion, but proportional). Meaning when the pressure changes from 110 to 145 psi, the seat will deform about 30% of the amount as when the pressure goes from 0 to 110 psi. An elastomeric (rubber) spring is not linear, so this is only a rough approximation.

To answer your second question, think about the contact area of a knife edge volcano orifice versus the area of the circle where the IP produces its pressure thrust.

Yes, when there is no IP rubber gets compressed a lot more because the force on the very small surface area on the edge of the volcano orifice. When you apply air pressure that indentation is in large part relived. It can not be fully relieved because there have to be enough contact force to create a seal.

The area under IP pressure will have some compression, but due to the larger surface area the deformation is relatively small.


Note: how much actual force is required to create a seal is dependent on several variables, including surface roughness (of both surfaces), imperfections, rubber hardness, etc. I think some engineers have made a living studying this subject for some complex applications.

 

[Zung]

... But, if you are using an in line adjustment tool, it is OK to turn the volcano orifice as long as the regulator is pressurized. There is no need to press the purge button since the force on the seat is very small; most of the force is taken by the pressure thrust of the IP.

Being able to adjust the volcano orifice while pressurized is part of what makes an in-line adjustment tool so effective and so quick. I have been using them for years. I still have to do it the old fashion way on my Poseidon Cyklon second stages and I can get it in a few tries, but the tool is great for a 109.

Thanks Luis for legitimizing an act I've been doing secretly for a while behind all the gurus' back!