Over-pressure valve actuation pressure?
- Thread starter danstrider
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OP
danstrider
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@Coztick I hear the Rube Goldberg critique. That's fair when looking at the CVS at it existed. Yes, the current BC technology does work. Snicker and point if you like.
I'm the curious type. It could be fun and possibly there is some value in ditching or augmenting the BC. That's enough justification to me for having fun. You might play by using gear you bought to look at fish; I play by burning brain cells thinking about and building toys. To each his own.
@Luis H thanks for your eagle-eyes spotting 2psi in the patent. Understanding 4.5ft over-pressure was used before is a great design baseline.
I'm currently going to try an exhale and inhale direction vent, use a stiffer spring, and omit the equalizing air valve. I do have a power-inflator, so can equalize manually if needed. The If its behavior just doesn't work well, I might hack up a cheap second stage.
A clear tube for the pressure vessel (low differential still counts) should make it possible to actually see the air/water ratio and watch the valves operate. This first version will also be way oversized because it's cheaper and easier to cut the tube shorter than try to stretch it
Right now the projected system weight is 3lbs for the tube & endcaps & valves, plus 1.23lbs for the power-inflator with LP hose. The ScubaPro Litehawk travel BC lists at 5.28lb with straps and pockets and stuff, so currently we're in the same ballpark.
Also @Luis H, thanks for the short history lesson about early BC adoption and fears!
danstrider
I'm the curious type. It could be fun and possibly there is some value in ditching or augmenting the BC. That's enough justification to me for having fun. You might play by using gear you bought to look at fish; I play by burning brain cells thinking about and building toys. To each his own.
@Luis H thanks for your eagle-eyes spotting 2psi in the patent. Understanding 4.5ft over-pressure was used before is a great design baseline.
I'm currently going to try an exhale and inhale direction vent, use a stiffer spring, and omit the equalizing air valve. I do have a power-inflator, so can equalize manually if needed. The If its behavior just doesn't work well, I might hack up a cheap second stage.
A clear tube for the pressure vessel (low differential still counts) should make it possible to actually see the air/water ratio and watch the valves operate. This first version will also be way oversized because it's cheaper and easier to cut the tube shorter than try to stretch it
Right now the projected system weight is 3lbs for the tube & endcaps & valves, plus 1.23lbs for the power-inflator with LP hose. The ScubaPro Litehawk travel BC lists at 5.28lb with straps and pockets and stuff, so currently we're in the same ballpark.
Also @Luis H, thanks for the short history lesson about early BC adoption and fears!
danstrider
No judgement here sir!
We are all Dorks with our underwater toys.
Mine is ow sm... See I have a sense of humor!
Good luck with your "smart wing"!
Any dive gear is way cooler than golf.
OP
danstrider
Registered
OP
danstrider
Registered
A friend 3D printed a test part of the threaded boss and it works fine (even though it was an FDM printer and the threads were, um, unsightly). The sealing surface is workable. This confirms dimensions enough for me to get on with the endcaps themselves.
Those McMaster springs with 14 lb/in rate mentioned earlier were WAY too stiff. It hurt to unscrew the parts, as you have to hold the valve open from a thin cord while unscrewing. Other companies make springs in-between...
An easier way to increase the activation pressure is to decrease the size of the hole. I'm shrinking the hole from diameter of 0.75in (1.77in2) to 0.4in (0.5in2), which increases the activation pressure from 1.53psi (3.5ft water) to 5.42psi (12.5ft water). I can always drill it out larger, and this way the spring (and force on it) doesn't change.
The current pressure vessel is a 5.75in inner diameter, 18in long polycarbonate tube, cut down from the stock size of 24in. Based on the Nautilus CVS at 2/3 flooded of ~7.5gal being recommended, I'm still carrying less volume than the CVS and yet about twice as much as I think is needed. Cutting the tube shorter again is easy after this theory is confirmed. My main fear leaving it long is that the thin walled tube buckles (implosion direction) before reaching the 5.42psi activation of the pressure relief valve. Finite element analysis of buckling the way this would go can be tricky. I also need to reach the lower end valve to flood and drain the vessel, so it can't be too long.
Progress.
danstrider
Those McMaster springs with 14 lb/in rate mentioned earlier were WAY too stiff. It hurt to unscrew the parts, as you have to hold the valve open from a thin cord while unscrewing. Other companies make springs in-between...
An easier way to increase the activation pressure is to decrease the size of the hole. I'm shrinking the hole from diameter of 0.75in (1.77in2) to 0.4in (0.5in2), which increases the activation pressure from 1.53psi (3.5ft water) to 5.42psi (12.5ft water). I can always drill it out larger, and this way the spring (and force on it) doesn't change.
The current pressure vessel is a 5.75in inner diameter, 18in long polycarbonate tube, cut down from the stock size of 24in. Based on the Nautilus CVS at 2/3 flooded of ~7.5gal being recommended, I'm still carrying less volume than the CVS and yet about twice as much as I think is needed. Cutting the tube shorter again is easy after this theory is confirmed. My main fear leaving it long is that the thin walled tube buckles (implosion direction) before reaching the 5.42psi activation of the pressure relief valve. Finite element analysis of buckling the way this would go can be tricky. I also need to reach the lower end valve to flood and drain the vessel, so it can't be too long.
Progress.
danstrider
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