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Removing human error from pneumatics...

A place to ask general spud cannon related questions.
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Unread postAuthor: Technician1002 » Thu May 13, 2010 1:08 am

I was reviewing my photos for the audio chronograph and realized a properly designed piston valve is pretty foolproof. The pilot is simply opened, the pressure vents, and when the balanced pressure is crossed depending on the valve ratio, the valve pops open. It is very predictable in a well built valve.

Attached is an audio wave of a piston valve opening. It shows the hiss followed by the boom. A slow pilot does not slow the speed of the boom, but only delays it.
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Unread postAuthor: saefroch » Thu May 13, 2010 5:42 am

So there is no detectable difference between a well-made piston valve, a QDV, a burst disc, a piston valve that is piloted perfectly and instantly, a QDV opened with infinite speed, and a burst disc that tears open instantly, leaving no shrapnel behind? :shock:

EDIT: I'm confused... It seems like there should be
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Unread postAuthor: Technician1002 » Thu May 13, 2010 1:00 pm

Sorry for the confusion. The topic was on Human variable. There is a difference between the valves. They all have finite opening times and differing flow properties when open. Not all those valve types are the same.

All I was referring to was how much a human operator can influence the opening property of any one of the valve styles. For example, a ball valve can be opened very slow, or fast by variations in the human operator. A burst disk on the other hand will simply burst when burst pressure is reached. There is no such thing and deciding to burst one slowly.

Properly made piston valves simply pop open when the forces balance point is crossed. The QDV simply pops open when the o ring unseats in the front, etc. The opening times on a regular piston valve and a QDV are finite. One by design is faster opening. Both open slower than a burst disk. All these designs are faster than a manual ball valve.

To sum up
Burst disks open in under .1ms
QDV, QEV and sprinkler valves opens under 1ms.
Most piston valves open under 5ms.
Most ball valves open slower than 30ms.

Flow when open also vary. This is the flow coefficient seen in GGDT and other fluid dynamics models.

In regards to flow issues, ball valves are great along with bust disks. My QDV is somewhere in this category. Normal piston valves in a T, QEV, and simular flow path valves are next and sprinkler valves with lots of turns and bends is bottom of the list with lots of resistance to flow at near supersonic flow.

All valves have their good and bad. In spudding a very fast valve is desirable. A good flow is desirable. If this is all you want, the burst disk is on top. If you want ease of use, wide pressure range, easy to trigger, etc, then bust disk is less popular. You can't buy a QDV, so for cost, ease of use, modified sprinkler valves, QEV, and ball valves are popular. A step up in performance is home made piston valves, either conventional or QDV.

Due to the acceleration properties of most spuds, almost any valve with an opening time under about 2ms makes very little performance difference. Model various valve speeds in GGDT. Other than flow, the opening times of most pistons, sprinkler valves, QEVs, etc have little change on performance. Only valve flow efficiencies make huge differences.

A ball valve is slow enough, variations in human operators makes huge performance changes.

I hope this helps.
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Unread postAuthor: saefroch » Thu May 13, 2010 2:16 pm

:shock: Wow. Yes, that helps a lot. Thanks so much, guess I'll be doing some work with GGDT now. Purely for design purposes, have you ever thought of a tee-housed QDV?
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Unread postAuthor: POLAND_SPUD » Thu May 13, 2010 2:17 pm

I think that tech has explained the difference between burst disks vs. piston/QDV valves quite well

Let me just stress one more time that the valveless launcher design can theoretically combine the best of both worlds...
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Unread postAuthor: saefroch » Thu May 13, 2010 2:21 pm

Valveless launcher design? Where was this mentioned?
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Unread postAuthor: Technician1002 » Thu May 13, 2010 2:29 pm

saefroch wrote::shock: Wow. Yes, that helps a lot. Thanks so much, guess I'll be doing some work with GGDT now. Purely for design purposes, have you ever thought of a tee-housed QDV?


You are welcome for the information. I used GGDT a lot after I built some launches. It is being used for a future plan on some supersonic marshmallow launches and possibly a supersonic golf ball. That is iffy.

Yes, but it is way into the future. I have other builds on the table before I get to one. Finishing the 2.5 inch is first, finishing the copper 1/2 inch is second, the Gumball machine gun is third, a 4 inch QDV is a possibility, and then maybe a QDV in a T. It is low on the list due to the bend in air flow and more distance between the air chamber and valve. Coaxials have no inlet plumbing at all. A T will have some inlet constriction.

A quick sketch of one built in either a 3 inch galvanized T or in 4 inch ABS T could be done for you if you would like to see what possibilities are on the drawing table. Both would be 2 inch valves.
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Unread postAuthor: saefroch » Thu May 13, 2010 2:47 pm

Wow... somebody's got the future really planned out. With all those QDV models we should be able to come up with some actual data on the effectiveness improvements of a QDV over other valves. I can visualize the construction of a tee QDV, I understand those just fine once I actually looked at the diagram you had the internals of the valve setup sitting on in the explanation video.
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Unread postAuthor: POLAND_SPUD » Thu May 13, 2010 2:57 pm

uhmm it was mentioned here -> http://www.spudfiles.com/forums/valvele ... 12569.html

if you have a look at the last pic on the first page you'll realise that this is very similar to the QDV valve (but should offer better performance than the QDV
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Unread postAuthor: saefroch » Thu May 13, 2010 3:52 pm

That is almost exactly a QDV, except you push the piston forward and the piston is the projectile. Wait...

Couldn't you just use the outside of a QDV type piston as a sabot and just catch that on the end of the barrel? It would still be a high-precision build but a system like that with a small piston in the back unlike JSR's post, more like the patent could work.

EDIT: And why would JSR be looking up projectiles to trigger avalanches?
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Unread postAuthor: Technician1002 » Thu May 13, 2010 4:27 pm

I have performance data. There is a thread on it. :D
Link http://www.spudfiles.com/forums/ggdt-and-in-tank-quick-dump-valve-performance-t18090.html

In an embarassing moment, I seated the piston too far forward in the cellular core cannon and launched the piston. The 2 inch cannon has been safety tested by hitting the golf ball in an attempt to launch the piston. The rod, nut, and screwed on golf ball with pins is able to prevent the piston launch. It safely vents air out the control rod path. The marshmallow cannon has a physical pin to prevent the piston from going too far forward.
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Unread postAuthor: saefroch » Thu May 13, 2010 4:48 pm

So what you found there is basically that GGDT is not built for QDVs. Has D_Hall addressed this? I don't mean to shoot down the awesomeness of the QDV or anything, but I highly doubt that a QDV is as effective as a burst disc, even within normal measurement capacity. While you have shown that the QDV is extremely effective, I think we will see some deviation if you try to operate a QDV at higher pressures, even at 200 psi. The only troubles with operating a QDV at high pressures is the force of that piston coming back...

I have my doubts about the data, but it is compelling. As ever, I want more extensive data, and distrust GGDT despite all the accuracy simply because it was not designed for a QDV.

Thought about my valveless reverse QDV proposition?
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Unread postAuthor: POLAND_SPUD » Thu May 13, 2010 5:03 pm

@saefroch
I don't think there is any reason to overcomplicate things.... something as simple as this Image should work

yeah I know it is a hybrid but you get the idea
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Unread postAuthor: Technician1002 » Thu May 13, 2010 7:28 pm

I have my doubts about the data, but it is compelling. As ever, I want more extensive data, and distrust GGDT despite all the accuracy simply because it was not designed for a QDV.


I didn't use GGDT to model the QDV. I used GGDT to compare the GGDT to known designs. i don't have a full collection of all the other designs to do side by side comparisons. I have done 2 field side by side tests with the QDV cannons. The ABS cannon was pittted against a spray and pray ABS cannon of the same size. We were matched for range when I used about 30 PSI. At 60 PSI it was game over.

The 2 inch 3 gallon was compared side by side with a 1.5 inch sprinkler valve. Both cannons are using a 3 inch barrel. The instrumentation we had for that was a high speed camera. This is where the apple splat on the water bottle video was made. The two cannons are not in the same league.

Photo of a side by side comparison.
Image

What data would you like? Much of it is posted. On this page is some high speed photos. There is a 5 foot long measure right behind the flight path. Feel free to check the results yourself. The apple launch was at 80 PSI.
https://inteltrailblazerschallenge.wikispaces.com/Photos
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Unread postAuthor: saefroch » Thu May 13, 2010 9:12 pm

I have seen that design before on the forum, and even considered building one. But the issue is still ammunition that can seal. Ball bearings would work fairly well but may become a limitation with size. The biggest issue with that design is creating enough of a pressure spike to force the ammunition past the o-rings without causing the mechanism to load another.

I am aware that you have already shown the QDV design is in a totally different league than sprinkler valves, combustions, and other types of piston valves. I am interested in data about the performance of a QDV versus other valve types as a function of pressure, and am fully aware that such data is not readily available. I also saw that you experimentally determined an optimal pressure. Do you know what most tightly correlated with? EDIT: What I mean here is more like "What could you do to get the greatest increase in muzzle velocity?" I love the use of the high-speed camera, that really shows how fast the valve opens. Wow.
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