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Old 02-21-2010, 04:11 PM   #31 (permalink)
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Thanks, Mayvik. Sorry yours was giving you so much grief.



I decided to see at what velocity an unmodified SA-8's relief valve would open. Short answer: I don't know!

Long answer: The shots weren't registering on my Radarchron. I had the reg turned in maybe six turns from the ~280fps range. I backed out the adjuster in about 1/2 turn increments and finally saw one read 429fps. The next shot was 350-something, and then I was out of powderballs.

I wasn't trying any inverted gun funny business, either. At whatever velocity those earlier shots were, it was frickin' loud. Wishing-I-had-ear-protection loud.

Conclusion:

If I had to guess, I would say that the only purpose of the overpressure relief on the SA-8 is to keep the valve chamber from exploding. Maybe it would vent on a hot summer day sitting in the sun with liquid in the valve, I don't know.

So my current plan is the same as before: I'm not shooting at a person with my SA-8 until I get a proper pressure relief.
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Old 02-21-2010, 05:08 PM   #32 (permalink)
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Quote:
Originally Posted by drg View Post
Can you post the numbers from the T8 that back up your conclusion?
No. I have no more 12 grams nor do I have any motivation test a marker that's been on the market for years. I do have like 4 years of anecdotal experience using it on the field though, many times as a primary and only marker. During none of that time do I recall seeing +/- 40fps swings.
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Old 02-21-2010, 05:33 PM   #33 (permalink)
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Originally Posted by MondoMor View Post
I backed out the adjuster in about 1/2 turn increments and finally saw one read 429fps.
The one thing I didn't understand was why didnt the gun shoot 429 when inverted? you would think the liquid would be boiling off, with the pressure creeping up to 800psi.

There are lots of possibilities, like the boiling process is cryogenic. Just as when you rapid fire with a co2 tank, it can chill itself down to 300-400psi. Perhaps thats what is happening in the giant dump chamber. The liquid flashed, but chilled at the same time? Especially with the tight passages which probobly act like a condensor.

Or perhaps the SA8/T8 does not use a typical regulator. The 50fps jump is what you would expect if the liquid simply flashed in the barrel. This is what would happen with every non-regulated poppet-valve gun on the market. (ie Spyder, Tippmann, etc).

Looking at the parts diagram, the reg uses a ball-valve instead of a poppet-valve. In that regard, the reg is different then the AGD-type reg. Then perhaps the liquid is capable of creeping back?

Who knows. It would be very, very nice if Eric from Tiberius is capable of giving us THOUGHTFULL, INTELLIGENT answers. By "capable", I am referring to what his lawyers will allow, which we all suspect is nothing.

What I really do not want is another condescending rant like from 10-Shot telling us how stupid we are for using guns not designed for paintball, while he goes on to brag about using his own "vent-less" guns, not to mention his cow-marking nelspots. That is simply insulting, and we expect better. Much better
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Old 02-21-2010, 05:59 PM   #34 (permalink)
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I did some back-of-the-envelope fuzzy-math calculations from eyeball measurements I took of reg components.

The ball in the reg is forced into its seat by a spring, it requires about a pound to unseat it (with no gas in the system). The I.D. of that seat o-ring is about .1", and so I went with 0.010 square inches of area to make the math easy. At 800psi from the 12 gram, that's about 8 pounds of additional force pushing that ball into its seat, for a total of 9 pounds. So the pressure required on the other side of the ball to unseat it is about 900psi. That's around triple the usual operating pressure of a T8 (350psi I think?), and maybe double the SA-8 pressure.

Even if my numbers are all stupidly off (likely!), I don't think the reg seat would open to equalize pressure before the relief opened up.


There's a lot of volume on the piston side of the reg, and a relatively small orifice and tight passages leading to the dump chamber. Maybe liquid is boiling right at the reg piston (and closing it) before much gas or liquid has had a chance to make it to the dump chamber?
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Old 02-21-2010, 08:57 PM   #35 (permalink)
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maybe the valve is only to keep the gun from exploding catastrophically, not for hot shots
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Old 02-22-2010, 05:03 AM   #36 (permalink)
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Quote:
Originally Posted by Mayvik View Post
No. I have no more 12 grams nor do I have any motivation test a marker that's been on the market for years. I do have like 4 years of anecdotal experience using it on the field though, many times as a primary and only marker. During none of that time do I recall seeing +/- 40fps swings.
Then again your T8 hasn't been new for quite some time now.

Have you actually shot long strings of shots over a chrono from a T8? I know for me at least, I was always tempted chrono as few shots as possible, since it eats the powerlet and current mag's rounds.
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Old 02-22-2010, 10:28 AM   #37 (permalink)
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A friend of mine (Tim aka "Thalion") did some testing with his T8. I added some pages to the spreadsheet with his data.

He had a lot of trouble with that old horrible D-Day paint. But his inverted testing is interesting. He noted one small puff from his relief valve, but the velocities weren't badly affected.
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Old 02-22-2010, 10:59 AM   #38 (permalink)
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Originally Posted by ajmidget View Post
maybe the valve is only to keep the gun from exploding catastrophically, not for hot shots
Loctite the valve, and find out for sure
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Old 02-22-2010, 11:02 AM   #39 (permalink)
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Originally Posted by HP_Lovecraft View Post
What I really do not want is another condescending rant like from 10-Shot telling us how stupid we are for using guns not designed for paintball, while he goes on to brag about using his own "vent-less" guns, not to mention his cow-marking nelspots. That is simply insulting, and we expect better. Much better
Not going to happen. If anyone comes into this thread and takes that kind of non technical armchair lawyer dump please report it and the post and it's author will be dealt with.

As you can see the other thread has been locked and another one has been moved because people can't seem to keep calm and not argue.

E
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Old 02-22-2010, 12:57 PM   #40 (permalink)
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Originally Posted by MondoMor View Post
A friend of mine (Tim aka "Thalion") did some testing with his T8. I added some pages to the spreadsheet with his data.

He had a lot of trouble with that old horrible D-Day paint. But his inverted testing is interesting. He noted one small puff from his relief valve, but the velocities weren't badly affected.
Thanks for the test data from both you guys. From the current sets of data the results seem clear enough for me. Would have been nice if the paint in the t8 would have held up better tho
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