Enviro sealed first stage with stable ip

[buddhasummer]

Thank you Luis, I want to have my cake and eat it. The only issue for me using a conshelf with dry chamber fitted is that the hose routing when used with a DS is terrible. I will play with hoses and adapters and see if I can't come up with a cleaner configuration. My reason for wanting to use, if possible, an FSR is they like the conshelf are very simple regs service wise and require nothing other than a hex key to change the seat and the hose routing is much cleaner.

 

[buddhasummer]

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)

Thank you for your reply.

That accounts for increase in ip as tank pressure drops but does not account for ip increase at ever increasing depths. But I guess assuming the increase is only 1.5psi every 10 meters at 40 meters the increase will be around 6psi, my FSR swings around 3 psi full to empty so I guess only a total possible increase of maybe 10psi at 40m and 500psi and I'm not going to be at 500psi at 40m or I'll have bigger things to worry about. As Tom and Matt suggested, a conshelf is likely to handle that. I'll hook it up to a tank this weekend dial up to 150-155 and see what happens. I'll post back if anyone's interested. Cheers.

 

[buddhasummer]

I may well have turned nothing into something. For me an educational thread. Thank you to those who took the time to chime in and assist, it's been a learning experience. Cheers.

 

[Centrals]

The only differences between US4(non-sealed) and DS4(sealed) are the end cap, hydrostatic diaphragm and the hydrostatic transmitter.
The most basic Apeks package is US4 + XTX20 which I had regularly seen them used for rental. I had only used the US4 as deco reg at 21m max before.
Therefore if those three items on FSR have been removed, the reg should still work except it is no longer sealed.
My suggestion: (1) Write to Apeks for opinion (2) make the blanking plug (3) put it on the FSR and close it with the diaphragm and the end cap (4) use that FSR with another unmodified FSR/DS4 on a twin set and test them at 40m.(5) if you do not have twin set then use pony/stage instead (6) report it back please.

Cheers.

 

[buddhasummer]

The only differences between US4(non-sealed) and DS4(sealed) are the end cap, hydrostatic diaphragm and the hydrostatic transmitter.
The most basic Apeks package is US4 + XTX20 which I had regularly seen them used for rental. I had only used the US4 as deco reg at 21m max before.
Therefore if those three items on FSR have been removed, the reg should still work except it is no longer sealed.
My suggestion: (1) Write to Apeks for opinion (2) make the blanking plug (3) put it on the FSR and close it with the diaphragm and the end cap (4) use that FSR with another unmodified FSR/DS4 on a twin set and test them at 40m.(5) if you do not have twin set then use pony/stage instead (6) report it back please.

Cheers.

I've converted it to UFSR already and it works fine, all parts north of the valve lifter are the same. I was more interested in trying to keep it sealed without the overbalancing. As it turns out it may well pose no issue anyway. I'll try to see at what ip the conshelf free flows... Cheers.

 

[buddhasummer]

Couldn't wait, got a tank and had a play. Re fitted enviro seal. At its current setting the second stage started leaking at just over 150psi. Second stage was cracking at around .9" at 150psi ip after stopping leak. Tank pressure at 30bar. Dialed ip back down to 140psi and second stage is now cracking at around 1.1-1.2". Looks good enough. Think I'm good to go and shouldn't have any issues at the max depths I play at. Thanks once again.

 

[halocline]

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?

The MK2 compensates for depth in exactly the same way as the MK25, by allowing ambient pressure to, as you accurately put it, "assist the the main spring" by applying pressure to the ambient side of the piston head. That is exactly correct.

It has nothing to do with balancing, though. Balancing affects the way IP is related to tank pressure. In the case of the MK2, tank pressure pushes on the seat (attached to the piston shaft), essentially applying more pressure to keep the valve open. This results in higher IP (the force necessary to close the valve) when the tank is full. In the MK25, and all the other balanced pistons tank pressure does not push against the seat due to the geometry. Tank pressure does have a small effect on IP because the edge of the piston has some width to it, and this tiny width results in a very small amount of downstream force on the piston by the tank pressure.

Without depth compensation, no 1st stage would work for open circuit scuba.