Need Help Creating a Flap Valve

How about a return spring?

I appreciate the reply! That's a great idea! So are you suggesting to attach a return spring to a flap? Do you think that a small ball would create enough pressure to push through the flap?

Look. The forum knows nothing about you, nor what it is you are trying to accomplish.

A "small ball" has no meaning to anyone, except to you.

PVC pipe comes in many sizes as well.

Springs come in all sizes and tensions also.

Try giving the size and weight of the ball and the diameter of the tube into which you will drop it and from how high above the flap.

The more detail you provide the better your responses from the forum will be.

You're totally right. Sorry about that, it's my first post!

So I'm trying to make a pneumatic tennis ball launcher. I would like to be able to load the barrel by dropping a tennis ball through a pvc pipe that's placed vertically from the base of the barrel. I would drop the ball into the vertical pvc pipe, it would push through the flap, the flap would close behind it, and the ball would land at the base of the barrel. The flaps function would be to prevent compressed air from escaping through the loading entry point (from the vertical pvc pipe).

Let me know if I missed something or wasn't clear enough!! Thanks :)

1. How will you release the flap once it has x pounds of pressure pushing up against it after the ball drops?

2. Sealing is a problem, because a gasket will be required, and a surface it can seal against.

3. You will need a surge tank or something to store an accumulated supply of compressed air.

Look at some of these before you go forward.

Compressed Air Tennis Ball Mortar - Instructables

How to Make a Tennis Ball Mortar: 14 Steps (with Pictures) - wikiHow

The Tennisball Canon - Safe way to build a Tennis Ball Cannon

1. How will you release the flap once it has x pounds of pressure pushing up against it after the ball drops?

correct me if I'm wrong, but are you asking how the flap is going to take the upward pressure pushing up against the flap?

If so, do you think it would work if:

1) I cut the vertical pvc pipe into two pieces

2) attach a flap with a return spring to a gasket ( the flap would be bigger than the gasket opening so that it doesn't get pushed through with the air pressure).

3) apoxy the gasket with the flap in between the two pvc pieces. Essentially, the vertical pvc pipe would consist of: half a pvc pipe attached to a gasket with a flap, attached to the other half of the pvc pipe.

2. Sealing is a problem, because a gasket will be required, and a surface it can seal against.

I believe if answer to #1 is possible then this wouldn't be an issue

3. You will need a surge tank or something to store an accumulated supply of compressed air.

Why would this be necessary? Wouldn't the air go out of the end of the barrel?

Thanks!

This isn't like firing a gun where the pressure increases inside the barrel due to burning gases and expanding air pressure. Pressure keeps building until the projectile exits the barrel at a high rate of speed.

In an air cannon, all the energy is stored in the chamber where the ball is (in your design) and that pressure begins to drop immediately when the seal is broken.

Look at these: Free Air Cannon Plans - PVC Ballistics They all have an accumulator or a large chamber to store lots of compressed air.

I think we may be on totally different pages (completely my fault for being terrible at explaining). So hopefully this will clarify what I'm looking to do.

I'd like to create a pneumatic launcher exactly like the YouTube video below (except the fishing line). Instead of having to load the launcher from the top of the barrel, I would like to have a vertical pvc pipe that I could just drop the ball into and the ball land at the base of the barrel.

What I am trying to solve is how I would be able to drop the ball into the vertical pvc pipe that is connected to the barrel and have the launcher function the same way (or as close to it as possible) - which would require a way to prevent the air from escaping out of the vertical pvc pipe. So now that I believe I have explained myself more clearly, how would you go about doing this?

Just a side note, I will be regulating the pressure output from the tank. (not sure if this will impact the solution). Thanks!!

https://m.youtube.com/watch?v=u9OdiCja8vs

Sorry. now I get it.

Not going to ask why.

The first thing that comes to mind is a T of the same size as the pipe. You'd want a Tee Socket x Socket x Thread and a threaded plug of the correct size.

Unscrew plug, insert ball, tighten plug. Teflon tape it for a seal.

It get's more complicated if you want something more sophisticated.

Maybe someone else has an idea.

Yea this is a bit complicated. The top of the vertical pvc pipe would have to remain open so that you could have the option to continuously load balls through it (only one in the chamber at a time though)

The T goes at the bottom, not the top. The threaded part is vertical so the tube is always open at the top.

I'm still not understanding you.

What we have here is, failure to communicate. (A line from a movie, Cool Hand Luke)

Try it, and see.

A drawing would help a lot! At first I was assuming that this vertical PVC pipe WAS the barrel. Now I believe that the barrel is a second PVC pipe at some other angle (45° for maximum range?)

Any such flap/valve MUST be at the point where the vertical pipe joins the barrel. otherwise you will lose air pressure into the vertical pipe.

My initial suggestion would be a half-cylinder sliding joint. you would load a stack of balls into the vertical pipe, and each time you slide the joint (perhaps by pulling back on the barrel), one ball would fall into the barrel. Sliding the barrel forward would seal the joint.

I would use a laser activated trip switch to a solenoid to open the flap, and a spring return setup....

...but I have no idea of the scale or purpose of this device you speak of....so really just a shot in the dark....

Very interesting, thanks for that! I replied with more detail to Lyn if you have any other ideas:

"So I'm trying to make a pneumatic tennis ball launcher. I would like to be able to load the barrel by dropping a tennis ball through a pvc pipe that's placed vertically from the base of the barrel. I would drop the ball into the vertical pvc pipe, it would push through the flap, the flap would close behind it, and the ball would land at the base of the barrel. The flaps function would be to prevent compressed air from escaping through the loading entry point (from the vertical pvc pipe).

Let me know if I missed something or wasn't clear enough!! Thanks :)"

....but why do you need the flap, the barrel isn't pressurized until you fire it, then you don't want any flap in the way....why would you alter the design that is all over youtube and proven to work well, what do you hope to improve....the only reason to alter the design is if you hope to improve the design or use it for a specific purpose other than just shooting balls....

It is for a purpose other than shooting balls. I just need to figure out how I can make this happen so I can apply it to an undisclosed project. If you have any input, I'd highly appreciate it!

<Beam me up Scotty>

Apparently not

Well have you considered a mechanical launch mechanism instead of pneumatic?

Go Big, or go home....haha

https://patents.google.com/patent/US20140109887

Can't you make your vertical drop point near the end of the barrel? and let it roll in

Or a double ramp? >

Unless you can make the flapper come down on top of the ball in the shape of the PVC pipe with a perfect seal the exhaust gas will move around the ball and bubkis will be the result.

If you use a return spring, the force on the flap should be less than the force exerted by the small ball, for it to open, that means that the small ball should be of solid metal and the flap far lighter.

Non return vertical valves for solids, is always a million dollar question.

I cannot watch videos at work so I'm not sure that I get what you are trying to do with your project.

However, I do have a caution. If you are going to rapidly pressurize and de-pressurize PVC pipe it will fail and failing PVC pipe tends to shatter under high pressure. At minimum you need to place a guard around it or even better, use a different material.

Good luck!

I built one of these using a Shindaiwa EB630 backpack blower to shoot tennis balls. I took the existing blower tube and cut a hole in it large enough for the tennis ball to pass through. I then took some approximately 3/32" thick rubber sheet and pop riveted the upstream edge of the rubber to the inside of the tube so that the rubber curved to match the wall of the tube. No return spring was required. We also shot empty pop cans.

Initially we just pushed tennis balls into the rubber until it went through the hole in the tube and air pressure took the tennis ball and returned the rubber to tightly seal the opening in the tube. Later we set up a second tube that lined up with the opening and you could shove a stack of balls down the tube, past the rubber sheet and out the blower tube for burst fire.

Tennis balls won't go of their own weight, you have to push them through. The rubber flap had the beneficial effect of blocking the tube as the ball was pushed in which caused the blower to race a bit and give a little more oomph when the ball finally took off.

We used this for a fun event at a landscaping equipment distributor meeting with distance and accuracy competitions.

We also developed the "Shindaiwa Landscape Decorating System". It consisted of a mandrel on bearings mounted at the blower tube nozzle using an offset bracket. You placed a double roll of toilet paper on the mandrel and pulled out about three feet of paper. The air stream of the nozzle would pull the paler off of the roll, entrain it in the airstream and deliver it at some distance and elevation from the blower.

We developed a rating system for the EB630, EB801 and the EB8510. The EB 630 was rated 5 seconds, that is, it would take a double roll of toilet paper and empty the roll in 5 seconds, delivering the roll at up to 85 feet high in the air. The EB801 and EB8510 had ratings of 3.3 and 3.0 seconds, but required a ball bearing support for the roll mandrel. Plain bearings had enough drag to tensile fail the paper in about 5 foot lengths as it came off the roll. During the same distributor meeting we had three landscape decorating systems in operation and let the distributors "decorate" the interior of one of our warehouses as part of the fun event.

I would add that we used a metal strip along the upstream edge of the flap and pop riveted through the strip, rubber and tube. The metal strip held the seal between the rubber and tube at the upstream end of the flap. Otherwise, the upstream edge of the flap would flutter and sometimes scream in the airflow.

I agree with the comment about pvc being dangerous since it shatters when it fails.

That warning past wouldn't a large swing check valve work? The spring may need to be modified depending how stiff it is.

Depending how much pressure you use perhaps a modified dryer heat diverter where you add a spring or weight and close the boxed vent. Not sure if that would be strong enough for your use.

If I was doing something like this I would opt for a more bolt action type device. It would require sliding a section forward and backward to load but not much more difficult than dropping a ball in.

I might also consider making some of the parts more prone to fail out of metal or hdpe.