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GGDT Help

A place to ask general spud cannon related questions.
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GGDT Help

Unread postAuthor: pat123 » Fri Dec 21, 2007 12:13 pm

With ggdt how do you get the flow coef, open time, and dwell time of a valve. I wanted to know for a barrel sealer and a modded sprinkler. also how do you find the friction of the projectile? For the init position is it the distance from the tip of the barrel to the projectile or from the end of the barrel closest to the valve to teh projectile?

thanks
pat
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Unread postAuthor: boilingleadbath » Fri Dec 21, 2007 3:22 pm

Sentence 1, 2: you look it up, calculate it, or guess. The GGDT website is an excellent resource. (hint: generally, you should model burst disks/barrel/chamber sealing/hammer valves with the option designed for that valve type.)

Sentence 3: friction basically doesn't matter. Ignore it.

Sentence 4: Play around with the number... figure it out on your own.
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Unread postAuthor: MrCrowley » Fri Dec 21, 2007 3:25 pm

A post from Clide on Spudtech:

GGDT inputs for 1" and 3/4" Orbit Watermaster valves

Valve Type: Barrel Seal
Flow Coef: Still trying to work on figuring these out, for now I would go with current estimates... around 6 for 1"
Seat Diam: .95" in a 3/4"...1.1" in a 1" (diameter measured at where the seat actually seals if anyone is wondering where that came from)
Piston Diam: 1.8"
Piston Mass: .8 oz
Vent diam: .05" with solenoid, .1" to .2" depending on the blowgun. .2" usually requires modification on most blowguns.
Pilot volume: 1 in³
Dead vol: up to the end of the threads. 1.5 in³ in 3/4", 2.2 in³ in 1"


For a barrel sealer it's different with every valve even if they are the same diameter and in the same tee as one could be heavier then another or seal against a smaller port. That should be obvious.

And by the way GGDT doesn't have open time and dwell time inputs for a barrel sealer valve.

Have you even used GGDT yet? Also look on his website it has a whole page for questions like this.

Initial position is the position from the end of the barrel to the projectile I think.

And for friction, i'm not entirely sure, I just leave it as is, but I think there was a thread where someone had a simple way of guessing it.
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Unread postAuthor: pat123 » Fri Dec 21, 2007 8:27 pm

yeah I've been playing around with it some so for a sprinkler valve do you select generic as the valve type?

edit: sorry i now see in your quote it says barrel sealer what type of valve would be generic, a ball valve or something like that?
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Unread postAuthor: Hailfire753 » Fri Dec 21, 2007 8:44 pm

Well this topic is still alive... Can anyone give me a the stats of a 3/4" McMaster QEV? I also want to GGDT it, but I could not find all of the required deets. A link, maybe?
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Unread postAuthor: MrCrowley » Fri Dec 21, 2007 9:10 pm

Generic would be a ball valve, butterfly valve etc.

Some people put sprinkler valves under generic but it's better putting it under barrel sealer.

@Hailfire

I've asked around but no one seems to have any solid figures, I think JSR had some for a British QEV, I can't remember, well someone had some figures for a British QEV anyway, but not the McMaster one.
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Unread postAuthor: Hailfire753 » Fri Dec 21, 2007 9:13 pm

Oh well. When I get and moddify it I will post the specs.
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Unread postAuthor: pat123 » Fri Dec 21, 2007 11:17 pm

I used GGDT for my black marble gun and it said 407ft/s. It really doesn't seem that fast, how accurate is ggdt normally?
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Unread postAuthor: MrCrowley » Fri Dec 21, 2007 11:25 pm

Accurate to a certain degree, though I've had a problem where i've measured a golfball i've fired at 380m but GGDT says 260m maximum, i've tried everything to get the range to go up but it just doesn't.
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