This is the brag zone. If you have an interesting bit of information regarding your launcher to make it unique, post it here. Photos and links to videos are welcome.

Now that the submissions are all in for judging, it's time to share a little.

To get things started, here is a photo series of how a technician makes a valve core without a lathe or round stock. To make a fast valve, we wanted to create a valve that was fast, has a short flow path, large opening, and reliable.

We chose these goals to beat average designs and their limitations. Sprinkler valves are fast, but have flow problems as they have limited sizes, complex flow paths, and many tend to re-close early as the surge supply is depleted faster than the trigger bleed. For this reason, many of them make great air horns unless modified. Ball valves while having a short straight through flow when open, it's opening time is limited by the ability of an operator to get it open without the partly open valve severely limiting the energy transfer to the shirt. Our final design is taken from a piston valve design that was modified to meet the speed and flow design needs while eliminating many of the pitfalls of piston, sprinkler, and ball valves.

Most piston valves are opened by releasing the air pressure holding them closed which brings up the first problem many piston valve builders face. It is very difficult to get an initial seal in order to build pressure. The second problem is the mass of the valve piston. They are often long and large in diameter. The third problem is often related to the slow rate the trigger pressure bleeds off while the tank pressure dumps, causing an early re-close limiting the launch power. To solve all three problems, a solution was considered. To reduce the diameter and length of the piston to reduce the mass of the moving piston a small diameter is used. The use of o-rings is used to eliminate a large difficult to seal flat orifice seal and permit using a piston much shorter than many piston valves. A manual trigger for a reliable open and close is used while retaining the speed of an air opened piston valve.

An air operated version of this style valve is often referred to as a quick dump valve. They are often used to quickly dump chemical tanks. They are seldom used for air as commercial quick exhaust valves are used instead. Building a reliable quick exhaust valve without a machine shop for the tight tolerances needed is very difficult. The quick dump valve did not need any special high precision machining, springs, or other hard to manufacture parts. The o-rings that fit the pipe were located at a local hardware store as a replacement part for a kitchen faucet. They were 60 cents each. The valve core was turned to fit these o-rings.

The initial opening speed was considered to get the opening avalanche started faster. It was decided to decouple the trigger rod from the valve core to reduce moving mass further and permit an impact to start the core motion. This operation is much like a cue stick hitting a billiard ball for a short acceleration time. The last item to increase opening speed was the selection of the material. Light and strong is desirable. The ability to work with it was a must.

Aluminum is more than twice the mass of water. High density polyethylene is less than the mass of water. It floats. It is the same stuff milk cartons are made of. It is not very fragile. Many cutting boards are made of it. It is also the same stuff the gas company uses for moderately high pressure city gas lines. If 100 PSI natural gas won't blow it apart, it should work fine in a thicker form as a valve core. Without a ready source of round HDPE stock, I shopped locally and located some sheet HDPE at Tap Plastics in Portland. They had some in their scrap bin for $1.70/lb.

The Gas company welds the pipe segments together because it is highly resistant to almost all glue and solvents, so I needed to learn to weld it in thick layers.

With the help of a custom thermostatically controlled flat heating unit I picked up from Goodwill for $6.00 we began laminating layers of sheet HDPE to build up the valve core. After it was built up to size, it was cut to the rough shape. Then it was turned on a drill press that was picked up new on sale from Harbor Freight for about $40.

Supplies needed; Flat Thermostaticaly Controled Lamination Heating Unit, HDPE cut to the correct size with room to trim, and a Clamping Device.

After clamping the plastic will return to a solid. Here you can see the outer edges are cooling first with the area next to the block is still liquid. That is not a hole, it is liquid plastic where it squished out when clamped. After cooling it is a single solid piece.

HDPE turns clear when liquid and squishes like melted cheese

Laminated block will be ready for turning into a valve core on the drill press after a little trimming with a saw.

Squished core block Melted HDPE is much like melted cheese.

I didn't get a photo of turning the big block of plastic, but I did photograph a test run before laminating the big core, just to see if it was feasible.

First a hole was drilled part way into the block and threaded onto a bolt with the head cut off. This provided a way to mount it in the drill press.

Drilling for the mounting bolt

The stuff was too tough to hand tool, so a wood chisel was fastened down in the drill press vise and the material was lowered past it in several passes cutting it round and true. This was much harder with a bigger chunk as it wanted to chatter when in areas not near the chuck. This would have been much easier on a lathe. The vibration when trying to make it round was very bad, but settled down once it was round.

Test machining, round and true

This assembled unit slides inside the valve cylinder inside the tank. The ports are located near the outlet inside the tank so the flow path is very short. The valve core is free to move under air power for about 2 inches. The golf ball is pushed in to seat the valve into the closed position. The rod is yanked out to use the nut on the end of the rod to strike the core getting it started moving to open. Air pressure from the uncovered ports in the air tank blast the valve the remaining 3/4 inch or so to fully open while the pressure also starts to move the t shirt it's first inch or two. After the valve is open, the discharge air pressure ensures it remains fully open against the stop until the 700 cubic inch tank pressure is depleted in about 20-50 ms depending on the mass of the load.

This valve was designed to fully open in less than 3 inches of t shirt travel in the launch tube as the mass of the valve core is less than the shirt. Our launch acceleration measurements confirm this. The orange golf ball was chosen from my used collection to resemble a basketball. If you look closely, you can see the small pin used to close the valve between the foam stopper and the valve core. Very little force is required to push the valve closed, so the small pin works fine and easily retracts into the stopper tube before the valve is triggered open. This is not the final version of the stopper assembly. This one was tested and the forces pressed the foam into the tube and the piston broke the reset pin. The foam on the left was eliminated. A cap was turned to fit between the tube and foam, and a thinner heaver foam pad was cut from a knee pad for gardening that was picked up at Fred Meyer for about $4. There was lots of pad, so I cut lots of spares and donated half the pad to the Arlington team to use in their launcher. It makes you feel cheap donating a half of a $4 pad, but I knew they could use it. A single kneepad can make over a dozen launcher pads. If you build one of these, drop me a line. I have extra pads. Not shown in the photo is the cavity in the front of the piston. It is just large enough for the nut to retract into the piston about half way. This permits more rod movement to provide a faster strike and more room for the reset pin to retract through the foam into the tube out of range of the piston. As a bonus, it reduces the moving mass for an even faster valve.

Assembled core assy

This is the valve body which is brazed inside the tank. There are 3 ports cut 1 inch by 2 inch. 1-1/4 inch of travel of the core is all that is needed to open this all the way. The air path from the tank out the pipe is about 2 inches long from air chamber to the t shirt. This is the outlet end. The golf ball goes on the other end. The ports were cut by hand using a hacksaw for the long cuts. The short cuts were done with a drill with a series of small holes which were joined by using a larger size, and then finished with a file. It isn't the prettiest thing a machinist would be proud of but it works well for a proof of concept prototype. It also shows that it can be made without a fully equipped machine shop. The idea is to be able to build one with the tools in a typical high school shop.

Valve ports inside the tank are beveled on the inside to help the O rings glide into position.
When the valve is closed the core sits in the gap of the ports with an o ring on each side. Air trying to escape pushes both directions equally so the core does not move. Air pressure seats the o rings so the additional pressure helps the core remain stationary until the rod is yanked so the core is knocked to the left. Once the front o ring lets air escape, the rising pressure finishes blowing the piston all the way open in very little time. The pin in the rod used to close the valve is retracted back into the stopper assembly at this time so the fast valve does not strike the pin and break it. This is a safety item for the operator. The force on the valve opening is not driving the golf ball into the operator's hand with high force. This low moving mass helps the valve open quickly.

How well does it work? Here is a t shirt launch.

The weekend before the big game provided nice weather for a little friendly shoot off and final power adjustment testing. When the engineering prototype and school team launchers and launch tubes are all gathered together, we have an impressive arsenal.
Here is a photo of the collection. The launch tubes are mixed up a little. Mostly on the left is the Arlington tubes and on the right Technician's tubes. In compliance with rule 12 we got creative in naming the garment launch tubes to cover socks, underpants, t shirts, skirts and jeans. We can launch an entire wardrobe into either the lower decks with the short tubes or upper decks with the longer tubes. The collection includes tubes from 1.5 inch to 4 inch in half inch increments except a 3.5 inch. The 1.5 inch tube is inside the 2.5 inch Cheap Seats Shot tube. It has a flare so it won't fall out. It is used as a push rod when not launching stockings.
It is hard to believe the big 4 inch tube was still accelerating the foam ball as it left the tube when powered by the smallish air tank, but it was. That tank has enough expansion volume to do the job. Technician's best shot was with the 3 inch ABS tube with only 30 PSI pressure.

From left to right is the breech loader short 3 inch, 3 inch with brake, 3 inch solid, Arlington tank, hand pump in back, 2.5 long rifled with 1.5 inch inside, the bit cut off the 10 footer with muzzle flair for easy loading, 2 inch ABS, 2.5 long, pushrod, 2.5 inch cheap seat shots with brake, mentor tank, 3 inch ABS with rifling, and 4 inch foam ball tube with foam ball. Thin stockings, mens dress socks and briefs fit the 2 inch, camisoles, small t shirts, rolled boxer shorts, thick rolled gym socks fit the 2.5 inch, X large rolled t shirts fit the 3 inch, and small jeans and skirts fit the 4 inch. Small shoes fit the 4 inch one at a time. Our garment launchers are ready.

Non garment items also fit. Gateraid fits the 3 inch tubes. Watch the recoil. These kick hard. Soda cans fit the thinner wall 160 PSI rated 2.5 inch but won't fit the thicker wall 200 PSI pipe. With the smaller cross section area and less weight, they don't kick nearly as hard. Depending on the apple they fit 2.5 and 3 inch. Smaller spuds fit the 2 inch without trimming or the 1.5 inch with an air tight seal.

Here is the landing of a Gateraid bottle next to the 50 yard line. It was launched from the shop out near the street on the far side of the school from the track. If it was launched from the outside edge of the track behind the goalpost behind me, it would have landed way up the hill behind the scoreboard and tennis courts.

Gateraid Landing

Here is a video of the Gateraid launch. I should have taken my keys out of my pocket. The hard recoil gave me a bruise where my keys got squished into my leg. Note the recoil. Even though I braced for the launch, I still needed to take a step to keep balance. Video by Mr C.

Pop cans don't survive the landing, even on grass.
Pop can burst on landing

An apple made it into the far end zone by the scoreboard.

Apple in the endzone

Here is a video frame grab of the 4 inch foam ball heading to the field from the shop. It landed in the shot put pit in the gravel behind the white sign next to the track. Can you spot the scoreboard from the shop? The side of the gym is the curved top building. The bus barn is around the corner on the edge of the track past the parking lot. 2 photos up will give you an orientation to the track around the field. The track and football field is behind the white sign. The field lights are easy to see. In proofreading my posts, I noticed this is the 4 inch ABS tube, not the 3 inch silver tip ABS tube.


Quick Dump Valve construction photos by Technician