Enviro sealed first stage with stable ip

[buddhasummer]

PS I love the good folk on SB and the wonderful resource and exchange of information that it is.

 

[buddhasummer]

What! You're not making one?

I'm gonna do both.

 

[buddhasummer]

In the blurb they write the following:

This little delrin plug is used to fix the inter stage pressure on an Apeks DS4 first stage.

It will stop the regulator from compensating the I.P with depth and keep it to where you set it.

This is for use with KISS type O2 injection using constant mass flow


DO NOT BUY THIS UNLESS YOU KNOW WHAT IT IS AND HOW TO USE IT....USING THIS ON OPEN CIRCUIT EQUIPMENT COULD BE VERY DANGEROUS

I fail to see the danger, am I missing something? Cheers.

 

[Pao]

In the blurb they write the following:

This little delrin plug is used to fix the inter stage pressure on an Apeks DS4 first stage.

It will stop the regulator from compensating the I.P with depth and keep it to where you set it.

This is for use with KISS type O2 injection using constant mass flow


DO NOT BUY THIS UNLESS YOU KNOW WHAT IT IS AND HOW TO USE IT....USING THIS ON OPEN CIRCUIT EQUIPMENT COULD BE VERY DANGEROUS

I fail to see the danger, am I missing something? Cheers.

Think of it as diving deep using an unbalanced first stage. You will run into all sorts of problems related to increased work of breathing and CO2 retention which could lead to all sorts of problems including increased susceptibility to DCS, narcosis and O2 toxicity to name a few. But with recreational depths it should not be a problem, especially with "air-balanced" 2nd stages.

 

[tbone1004]

do NOT blank the top

@Pao you don't want to make the IP constant in terms of a fixed IP. You want to make the IP constant as a function of depth. If you block the end like is done with CMF CCR's then you remove the depth compensation. That will end particularly poorly for an unbalanced second stage.
There are 2 types of balancing that the first stage sees, one is a function of tank pressure, the other is a function of depth. Most of the regulators out there are pretty good as a function of tank pressure, but the sealed diaphragms are over-balanced because the thumb tack rule in the transmitters. If you want to remove the over-compensation for depth, then you have to remove the whole mechanism. If you blank it, you remove the depth compensation which is really critical if you want good work of breathing at depth.

Since I dive Poseidons which are also an unbalanced second stage, I am currently on the hunt for similar regulators since I want a 5th port and swivel. If you want a reg with no over-compensation that is good in the cold, then the Poseidon MK3 is going to be the best. Sadly it is very expensive and doesn't have a swivel or a fifth port, but it doesn't need to be sealed, and is very stable.
That said, I would be hard pressed to imagine that you will be able to tell a 10psi difference on a Conshelf, but I could be wrong.

 

[halocline]

Basically the transmitter adds to the mainspring pressure to resist the HP valve from opening. Increasing the spring pressure forces the reg to Increase its IP to "balance' this increased pressure. Without the hydrostatic transmitter spring pressure, and consequently IP, will be constant.

The mainspring does not "resist the HP valve from opening" it KEEPS the HP valve open. IP is what closes the valve. Increase in ambient pressure does increase the IP. This is absolutely necessary for a first stage to function. Its called depth compensation, it has nothing to do with balancing. If you try to disable the mechanism for depth compensation (i.e. with a plug design for use in a CCR) the regulator WILL NOT WORK.

Sealed first stages with larger external diaphragms than internal ones, coupled with a mechanical transfer device (the plastic piston-sort-of thing that connects the two diaphragms) do result in IP rising slightly more than the change in ambient with increasing depth. The companies call this "overbalancing" but it's really just "over-depth compensating." As far as one of these first stages causing an unbalanced 2nd stage to free flow at depth, I guess it is possible, but I would try it out with your conshelf. My guess is that you won't have a big problem. You might have more of an issue with increased venturi assist if you tune the 2nd stage a bit too hot.

If you need a sealed 1st stage that has absolute IP stability as a function of depth I would simply pack a MK10 or MK5, or find any number of sealed diaphragm regs that don't have a larger external diaphragm. They've got to exist. You could also try a sealed atomic 1st stage if you want spend a bundle.

 

[underH2Oman]

If you are trying to keep the 1st stage balanced but not overbalanced just fill the chamber between the 2 diaphragms with liquid silicone and leave the hydro static balancer out. I believe the overbalancing is caused by the vacuum created on the air in the space. if you fill it with silicone it should still balance with depth but maintain the set pressure above ambient.

 

[halocline]

Think of it as diving deep using an unbalanced first stage. You will run into all sorts of problems related to increased work of breathing and CO2 retention which could lead to all sorts of problems including increased susceptibility to DCS, narcosis and O2 toxicity to name a few. But with recreational depths it should not be a problem, especially with "air-balanced" 2nd stages.

You are totally confusing depth compensation with balancing, they are completely different things. All first stages (and 2nd stages) all compensate for depth in exactly the same way regardless of being balanced or unbalanced. If they did not do so, they would not work for scuba diving at all. Regulators compensate for depth by introducing ambient pressure into the regulator so that any pressure changes in the regulator are related directly to that ambient pressure...i.e IP is always Xpsi over ambient or cracking effort is always X "/H20 over ambient.

 

[halocline]

I believe the overbalancing is caused by the vacuum created on the air in the space. if you fill it with silicone it should still balance with depth but maintain the set pressure above ambient.

The so called 'overbalancing' is because there are differing areas of diaphragms, with a direct mechanical connection. As an example, imagine a 1st stage with a diaphragm that has an area of 1sq in. At the surface, air is pushing on that diaphragm with a pressure of about 15 lbs (15psi atmospheric pressure). Descend to 33 ft, now you have about 30 lbs of pressure on that diaphragm, an increase of 15 lbs. This exactly matches the increase in ambient pressure.

Now add a larger external diaphragm, lets say with an area of 2 sq in. Connect the two with a piston. Now when you descend to 33 ft, the external diaphragm has 60 lbs of pressure on it (double the total pressure due to double the surface area) and the mechanical piston transfers all the pressure to the internal diaphragm. This causes IP to rise much more than the increase in ambient.

The "vacuum" of air in between the diaphragms has nothing to do with it.

In reality, the area of the external diaphragm is only very slightly larger than the internal diaphragm, and so the increase over ambient is slight. Otherwise you'd have regs free flowing at depth like crazy.

 

[tbone1004]

@halocline it's not actually the internal diaphragm, it's the delta between the silicone sealing diaphragm and the metal spring carrier, but the concept is obviously right.