Introduction: 2-Liter Bottle Compressor (No Moving Parts)
2-Liter bottles are amazing. They weigh almost nothing but can hold well over 100 psi of air or water pressure. In this instructable I use their unique properties to inflate a completely flat car tire without a compressor or electricity!
- a bunch of 2-liter bottles (I used eight)
- misc. air fittings
- 1/4" plastic water line (like for ice makers)
- an adapter to connect to a hose bib
Step 1: Collect a Bunch of Empty Bottles
My family drinks sparkling water instead of soda. But each time we finish off a bottle I can't bring myself to toss/recycle such an impressive pressure vessel. It would be nearly impossible to make anything like it at home without metal and a welder but even then it would way 10x more! So for months I've been hoarding 2-Liter bottles not knowing what I would use them for...until now!
Step 2: Design a Manifold
We need something the bottle can screw into with an air-tight seal. I had a number of ideas how to do this. The original cap for the bottle can be drilled and glued/epoxied with various fittings. I've taken the stem from an old bicycle inner-tube, inserted it from inside the cap and used it to inflate a bottle for classroom demos. I could also glue/epoxy the cap into a block of plastic or pvc fitting from the hardware store. Ultimately I decided this project is challenging enough I need it to work the first time, so I'm designing a custom manifold complete with o-ring for sealing. The bottle caps seal on the inside lip of the bottle mouth but the o-ring I chose seats on the tip of the rim.
Step 3: Fabricate Manifolds
This is the most challenging part. Any air leaks will limit the capacity and effectiveness of the compressor. The manifolds could potentially be 3D printed but I want them super robust so they don't crack under pressure. I'm using my mill I've converted to CNC (see my BUILD2 channel for details on that) to "thread mill" a small block of aluminum.
Step 4: Plumb Manifolds Together
I'm attaching the manifolds to a scrap 2x6 board I had lying around. Wood screws work great to pin them down. I threaded the in/out ports with 1/8" NPT on the mill which will fit a variety of fasteners. For convenience I'm using "push connect" fittings that accept 1/4" plastic line. The red tubing came with a Rancho adjustable shock kit I got years ago but the milky white variety works just as well for this and can be found at your local hardware store cheap. However you choose to do it, make sure to check for leaks and minimize them. Also be sure to connect everything in "series" so any air/water that enters from one end has to travel through each bottle to get to the other end.
Step 5: Connect to Hose Bib
The hardware store had plastic connections designed for an outdoor hose bib but they looked like junk to me. I wanted something metal with a pipe thread that would be secure and not leak. Fortunately they had this "Watts" water pressure gauge for pretty cheap and it comes with a nice brass hose bib adapter. Unfortunately that doesn't allow us to do anything other than read the pressure we have available. I purchased the "T" separately and am unscrewing the gauge from the adapter and putting it back together to allow monitoring pressure while using the water. A word of warning, the thread sealant the factory used is REALLY tough. I would have heated it to aid disassembly but that would melt the gauge. Brute force was the answer but it took everything I could muster.
Step 6: Putting It All Together
The exit end depends on what you want to use the compressed air for. I'm inflating a car tire so I'm attaching a valve, gauge and the working end of a broken foot pump. Screw all the bottles into their manifolds, shut the exit valve and stand the whole thing up. That way each bottle will fill before allowing any water into the next bottle. Here's the fun part. Open the hose bib and watch as the water flows in fast at first, then gradually slows down to a stop. My water pressure is kinda high (80 psi) so it can compress the air from all 8 bottles into the last 1.5 bottles at 80 psi. At that point I open the exit valve and let the air flow into the tire, being SURE to shut the valve BEFORE any water leaves the last bottle making its way into the tire. If the tire needs more air you must do the tedious job of unscrewing and emptying all the bottles (I used them to water my lawn) then start the whole process over. Seldom is a tire completely flat but if it is you'll probably need to do this process three or four times. But hey, no electricity or moving parts required!
Runner Up in the
Trash to Treasure Contest