Enviro sealed first stage with stable ip

[Pao]

The mainspring does not "resist the HP valve from opening" it KEEPS the HP valve open. IP is what closes the valve.

Sorry about that. I got a little confused.

I was thinking more along the line of the unbalanced piston 1st stages like the MK2. I thought that was what the OP wanted to achieve. A blanked out diaphragm 1st stage would behave exactly like that without balancing/depth compensation.
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But would water pressure exert enough force on the underside of the piston to assist the main spring to produce some form of depth compensation?

 

[rhwestfall]

I was thinking more along the line of the unbalanced piston 1st stages like the MK2

again, the pressure of the tank closes the system, even on a MK-2.....

 

[Pao]

again, the pressure of the tank closes the system, even on a MK-2.....

I was using it as an example for an "unbalanced" 1st stage, and not as an example of how IP is generated

 

[tbone1004]

Sorry about that. I got a little confused.

I was thinking more along the line of the unbalanced piston 1st stages like the MK2. I thought that was what the OP wanted to achieve. A blanked out diaphragm 1st stage would behave exactly like that without balancing/depth compensation.
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But would water pressure exert enough force on the underside of the piston to assist the main spring to produce some form of depth compensation?

what he is trying to say is that balancing and depth compensation are different. The MK2 is an unbalanced regulator, but it is still depth compensating.
What that means is that assuming the tank pressure doesn't change, the IP will remain at a fixed value above ambient. I.e. IP directly associated with depth.
At the surface that is 135 psi, at 100ft/4ata, that is 179psi. What it does mean is that the IP is going to be a function of tank pressure and will also change as the tank pressure changes. I.e. IP is variable with tank pressure and IIRC is about 20psi swing across tank pressures.

A "normal" balanced first stage has the IP fixed as a function of tank pressure, and since it is depth compensating, the IP is directly associated to depth.

When you put a blanking plug in the DS4 or any other sealed diaphragm, it is still a balanced first stage which means that the IP is going to remain fixed as a function of tank pressure. What you are doing here is fixing the IP at a constant pressure and removing the depth compensation. I.e. when you go to 100ft with a plugged regulator, instead of 179psi that it should be, it is still at 135psi. This is crucial for proper CMF flow rates on a rebreather, but is detrimental to a second stage. If you plug it, ambient pressure is 44psi, so instead of the 135psi that your reg is tuned to, it will be functioning as if it was being supplied by 90psi and will be very hard to breathe

 

[buddhasummer]

Was about to order a couple but something was nagging me, thought I'd wait overnight to see if anyone else had a comment. Glad I did.

Was lying in bed last night thinking something was wrong with this idea in relation to my proposed application. I don't know regs like the gurus but was thinking why are there no regs that are solid sealed units, there is always a diagpragm exposed to water to allow for changes in water pressure.

Thank you for your detailed replies, I've learnt more about reg function. I'll look for a more suitable reg.

Thanks again.

Does anyone know of a non over balanced sealed diaphragm reg? Cheers.

 

[buddhasummer]

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.

Thanks. Herman crunched the numbers in another thread and said there would be an approximate ip increase of 1.5 psi for every 10 feet. That would equate to an increase in ip of around 15 psi at 100 feet and almost 20 psi at 130 feet. I think that would tip the conshelf over. Guess only way to know for sure is to test it by either diving or simply hook it up to a tank and steadily increase ip to see at what point it tips. Most of my diving is in the 100-130 feet range. As you stated Tom/Halocline it may not be a problem in reality. Cheers.

 

[tbone1004]

@buddhasummer I think @herman may have confused feet and meters. At least on the Apeks it's about 1.5psi/10m which is a lot less wonky.

 

[runsongas]

does the sherwood sr2 also have an overbalancing issue? if not, anyone know the ip swing?

 

[207diver]

Don't be afraid of using an over balanced first stage. If you tune your unbalanced 2nd stage to the desired cracking effort at the highest possible IP which would be on a 500psi tank that you will not experience a "free flow" as the tank pressure decreases. Although the cracking effort may be a bit higher with a full tank (lower IP)

 

[Luis H]

Does anyone know of a non over balanced sealed diaphragm reg? Cheers.

If what you are asking is of a non-over-pressure compensated regulator, the Conshelf and the Titan (Conshelf derivative) with the dry environmental chamber are not over-compensated.

I have tested them with a submersible IP gauge down to near 100 ft deep and the IP followed the ambient pressure without changing. It stayed constant for the entire dive profile. The intermediate pressure was the same amount above ambient at all depths.

I have posted pictures in other threads of the setup I have used with the submersible IP gauge. The gauge is open to measure the pressure above ambient.

The only modification I did is to drill larger holes to the case to be able to rinse it as soon as I surface to limit corrosion.

Note: Herman and awap were diving with me at least one of the times I used it. Awap actually used it to test one of his regulators.

The effective area of internal diaphragm has the same effective area of the external diaphragm.

Somewhere there is a post where I explained in the past the mechanics behind the dry environmental chamber and what I mean by "effective diaphragm area". The explanation is not difficult, but it is late. Let me just say that it involves the area of the diaphragm and how that flexible diaphragm area is affected by edge clamping. The actual diaphragm stiffness plays a part also.