Labtecpowers (soon-to-be) quick dump valve cannon

[Labtecpower]

First of all, I want to thank Technician1002 for making the design, and making the QDV clear to me.


I decided to make a QDV, because of the power reached with relatively low pressures. I found some stuff around the house, and decided to start.
At school I turned a nice piston out of PVC (may be brittle, if it breaks, I will make one out of nylon)
The valve will be housed in a 42 mm ID steel pipe.
It has a nasty burr in it, but that problem will soon be solved with a lot of sanding.
I already removed a huge amount of the burr, and I have cut the ports for venting the chamber. I use three ports, as the piston will be perfectly centered in that way.

Here are some pics:





The ports are nice and smooth by now, and I will sand an angle on the edges, to make sure that the piston slides in and out nicely.
I'm searching for O-rings now. Does anyone have some information on what dimensions I should use? It will be a floating O-ring design.

Tell me what you think, and please tell me what I could improve!

[jackssmirkingrevenge]

Looking good, piston brittleness should not be an issue with an adequate bumper.

Why do you want a floating o-ring? It's not like you want air to be able to flow past in one direction but not the other in a QDV, as there's no pilot area.

[Lockednloaded]

I think floating o-rings have less friction in QDVs

[Labtecpower]

That's right. floating O-rings have far less friction, because they get compressed less than in an ordinary O-ring seal.

[Technician1002]

Very nice start for a QDV. Is this going to be a coaxial design or will this valve be built inside a T?

As far as PVC is concerned, I used a PVC piston in my ABS cannon with a good bumper and have had no problems after years of service.

In regards to floating o rings, they can be made to seal in both directions. This is very common in pneumatic air cylinders where small amounts of leakage is acceptable. The floating rings greatly reduce friction. My ABS cannon does not use floating rings, but the rest of my QDV cannons all use floating o rings. When in storage, sometimes the ABS cannon will get a stuck piston which needs a hammer to get it loose with grease. The other cannons don't have that problem at all. They are easy to pull. One of my videos show the low pull friction on the floating rings. I can open the valve simply by giving the small cannon a shake.

The rings tighten some when air pressure seats them. They seal well when all the surfaces are smooth for the o rings. Floating o rings are used for more than just one way valves.
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For sizing o rings, find ones that will fit inside your pipe with the least amount of compression possible. It must be large enough to touch the pipe along the full circumference to make an initial seal. With the initial seal, air pressure will finish seating the ring for pressure.

O ring test fit. I pick them to fit the pipe.

[Labtecpower]

The cannon will be coaxial. that design has the highest flow.

I believe that the ports have an area of 36 cm2

The air tank will be made of a refillable "campingaz" butane tank.
I know butane tanks can't hold as much pressure as propane tanks, but this one is pretty thick walled and heavy.

I think i'm going to TIG-weld the connection begtween the pipe and the tank.

[dewey-1]

Not knowing your country. I will go with US sizes. That is why I wish people would state their location even if it is only by the closest country or continent.

A #332 has OD of 1.645 inches, ID of 1.225 inches and Width of .210 inches.
If your pipe/tube is actual 42mm measured this would be 1.6535 inches.
What is the actual measured ID?

See McMaster Carr pn 5018T345.

Some hardware stores carry o-rings and use the AS568A numbering system.

See McMaster Carr pn 9262K406 for metric size of 42mm OD.

[Labtecpower]

I live in Holland. Over here we measure everything (thank GOD) in MM's.

To be precise, my pipe ID is 42.12 MM.

Would I be fine with an O-ring of 43.00 MM, or is this too big?

I found some O-rings with a diameter of 42.50 mm. However, they are made out of Viton. Does it's sealing capability match with NBR O-rings?

And... One question. Don't you Americans dislike using Inches?
It looks horribly inefficient to me. I wouldn't like calculating with all those bits. (1/2, 1/4, 1/8, 1/16, etc.)

[dewey-1]

I live in Holland. Over here we measure everything (thank GOD) in MM's.

And... One question. Don't you Americans dislike using Inches?
It looks horribly inefficient to me. I wouldn't like calculating with all those bits. (1/2, 1/4, 1/8, 1/16, etc.)

After 40 years of using both dimension systems it becomes second nature.
There are many different fields of work that use multiple dimension systems.

What are the actual dimensions of the piston: OD, o-ring width groove,
OD of groove?

I don't think o-ring material type will have all that much dimensional differences in operation.

[Labtecpower]

Internal Diameter pipe: 42,00 mm

O-ring groove width on piston: 5,10 mm

O-ring groove depth: 6,09 mm


And, I indeed think understanding inches is a matter of experience. But, it makes it somewhat harder to understand American cannons.

[dewey-1]

http://www.herculesmx.com/forms/ORingSizeChart.pdf

http://www.sealanddesign.com/category/2 ... 65/65.aspx

P39 looks like the number you need for metric.

38,7 +/- ,37 for ID and 3,5 +/- ,10 for Width.

[Labtecpower]

I forgot to tell that I can very easily widen the grooves on the piston.
I will first try to find nice O-rings in Holland. If I don't succeed, I will import them.

[Brian the brain]

Probeer het hier eens:

http://eriks.nl/nl/producten-en-dienste ... /o-ringen/

[Gun Freak]

And, I indeed think understanding inches is a matter of experience. But, it makes it somewhat harder to understand American cannons.

How do you think we feel It is sometimes hard to understand cannons from other countries too.

On topic, this looks like a great start to a QDV! Good luck with the rest and I can't wait to see the final result!

[Labtecpower]

Well, I feel like you should start using millimeters But you are probably thinking the same

Ik denk dat ik mijn O-ringen bij Technirub ga bestellen. Dat is een veel overzichtelijker bedrijf.