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Post by james1979 on Jul 10, 2020 12:43:19 GMT -8
JB, This fitting isn't changing the type of valve, what it is doing is adding a point of adjustment. In a traditional downstream poppet valve, you have 3 forces affecting the poppet; Spring preload holding it shut, Intermediate pressure trying to open it, and the lever levering it open. The closer IP is to spring preload, the less force needed on the lever to open the valve.
The spring preload is defined by the spring strength (or rate), length, and the distance from the orifice (or hard seat) and where the back of the spring seats in the valve body.
In an ordinary 1058 second stage (or Scubapro 108, or any similar reg), that distance from orifice (hard seat) is fixed... so your only breathing effort adjust available is to raise the IP to offset the spring preload more. With this fitting we can set the spring preload to nearly anything we want, which means we can tune it for as easy or difficult of cracking pressure as we want, independent of the IP. I think that made sense... but I usually think I do even when I don't! In theory, you might have a Conshelf (pick your number) that has the perfect match of specific tolerance variations that it will breathe optimally at the IP you want... but that is vanishingly rare due to minor part variations.
Respectfully, James
Nice description. I love my SP109's. I have the same in-line adjustment tool shown earlier. M I'm too cheap to buy an inline tool... so I still do it the hard way of adjust, pressurize, check, depressurize, repeat.
James
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Post by nikeajax on Jul 10, 2020 14:26:17 GMT -8
James, excellent, I think I get it: I'll have to reread it a few times to get what you're saying JB
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Post by vance on Jul 11, 2020 13:55:40 GMT -8
Yup, this thing basically only adjusts the poppet spring preload. This just means how compressed the poppet spring is. Looser=less cracking pressure, which is good until IP overcomes the spring. The spring can hold against the seat at too low tension, but the reg will freeflow catastrophically when the lever is depressed because the spring can't reseat the poppet. Most opinions I've heard on this are that you shouldn't go lower than .5" cracking. Anything less may prove insufficient, leading to problems. Tighter= more positive seating of the second stage, but cracking pressure is excessive. I might be wrong on this, but I think the stock cracking pressure is around 1.5"? So, this means there's an inch or so to work on. I made this so that the extended position of the hard seat is the same ( plus a bit) as the stock 1085 seat. I figure there's no present need to exceed the stock tightness. The end of the new fitting is relieved a bit to allow the poppet to extend into the fitting for the adjustment and to insure enough fitting length inside the reg body for strength. The orifice/seat opening is threaded to allow the hard seat to move forward or back into the fitting for adjustment. In the pictures, the hard seat/orifice is the shiny crome bit sticking up out of the plastic fitting. It is extended up midway in the picture.
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Post by vance on Jul 12, 2020 14:33:54 GMT -8
I'm shipping the new ones off to James for testing and final approval.
I cut back the relief on the seat end due to concerns about reduced airflow when the poppet enters the relieved area. I'm not sure that the poppet will ever get that close, but IDK.
We need flow tests and manometer tests, and an actual measurement on just how far the seat moves up and down between the stock seating preload and failure to seat/reseat. I think it's a very small range. Of course, the range between stock and the least possible functional preload will be even less. Like hundredths. Nowhere near 1/16". Dunno. No data yet.
I could be wrong. Have been before.
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Post by james1979 on Jul 12, 2020 14:49:19 GMT -8
I'm shipping the new ones off to James for testing and final approval. I cut back the relief on the seat end due to concerns about reduced airflow when the poppet enters the relieved area. I'm not sure that the poppet will ever get that close, but IDK. We need flow tests and manometer tests, and an actual measurement on just how far the seat moves up and down between the stock seating preload and failure to seat/reseat. I think it's a very small range. Of course, the range between stock and the least possible functional preload will be even less. Like hundredths. Nowhere near 1/16". Dunno. No data yet. I could be wrong. Have been before. I promise, I'll make my manometer.... finally. Failing that, I'll take it to the LDS and use their magnahelic. I'm also going to reach out to someone with a flow bench, and see about flow test comparisons to stock fittings. Both with and without the recess.
And again, thanks Phil!
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Post by vance on Jul 12, 2020 17:26:55 GMT -8
No rush, James. We'll git 'er dun.
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Post by james1979 on Aug 19, 2020 15:16:59 GMT -8
Well, this project isn't forgotten.. just on a slow simmer! A friend with a flow bench came back with what amounts to "it flows more than you'll need, and doesn't restrict flow even at the settings I was worried about." I also got some math applied to the structural aspect, and that came back as plenty strong for design loads... not computed for abuse loads! But should be just fine short of gross negligence. Pending another prototype round, I will be reaching out to see if VDH is interested in producing them, otherwise I'll look into small batch production myself... It's finding a reasonable source for small batch chroming that worries me! And, because I can't stay on one thing at a time.... I also started working on replacement exhaust T's for the old screw on version of the 1085... first draft is usable, second draft needs printing but should be better. I'll get around to the longer style in the future.
First draft pictured next to factory T and installed
Respectfully, James
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