I am a senior mechanical engineering student. My specialty is design and prototyping. I have worked for several companies learning how to prototype, and this comes in really handy for some of my "other" projects. Here is a pretty simple one...
I was introduced to the gravity bong by a friend. He told me the full name as described to him was the "Afghanistan Gravity Bong". We were sitting around one night and decided to try one out.
While I could go into detail concerning the mechanics of the bong's operation, I don't think that is really necessary. The reason it is called a "gravity bong" and not something else is this is what someone called it, that is how they described it to their friends, and now it is an accepted term for the following setup. I have observed some people on the net arguing about gravity vs. pressure vs. whatever. If you have comments like this as a result of this description, I refer you to: alt.engineering.geeks. The type of argument I have observed would have been halted a long time ago by declaring a "TECH TIME OUT !!" at our school. Take a hit man. I feel better now having said all that, so... on with the important stuff...
Place the bottomless bottle into a water source such as a bucket of water, sink, bathtub, larger bottle, fishtank (just kidding), etc...When the bottle rests on the bottom, the mouth piece should be above the water level enough to grip the bottle. I'm not sure if warm or cold water is best, or even if it makes much difference seeing as the smoke is not bubbled through it.
Pack the bowl and place it on the mouth of the bottle.
Slowly! draw the bottle out of the water, while lighting the bowl. The herb should really burn and the smoke will look intimidating. Stop when: a)the herb is all ash (preferable), or b)when the bottom of the bottle is still an inch or so below the water level in the bucket. Begin preparing yourself for a huge hit.
Carefully remove the bowl without letting the bottle move downward (up a little is o.k., but don't let the bottom come out of the water), exhale deeply, and place your mouth over the opening. Inhale quickly and completely, allowing your head to move downward. Try not to drink any bong water as this kind of sucks! (although its like learning to swim, it's bound to happen a little).
Don't cough and hang on tight!
PACKED BOWL >> $$ I I I\/I BOTTLE >> / \ BOTTLE >> / \ / \ / \ | / \ | | / \ | |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~WATER~~~|~~~~| |~~~~|~~WATER~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| \__________________/ \__________________/ BUCKET BUCKET Step 1 Step 2 \/ = BOWL % $$ = HERB LIGHTER __ *% ** = LIGHTER FLAME >> |__|@** $$ SUCK /\ I\/I || || / . .\ || I..I || /. . . \ || /. . \ || /. . . . \ \/ /. . . \ |. . . . . | /. . . . \ BOTTLE >| SMOKE | |. . . . . | | . . . . .| | . . . . .| | |~~~~~~~~~~| | | |~~~~~~~~~~| | |~~~~|~~~~~~~~~~|~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~~~~~~~~~~~~~~~~~| |~~~~|~~~~~~~~~~|~~~~| |~~~~~~~WATER~~~~~~~~| |~~~~~~~~BONG~~~~~~~~| |~~~~~~~~~~~~~~~~~~~~| |~~~~~~~~WATER~~~~~~~| |~~~~~~~~~~~~~~~~~~~~| |~~~~~~~~~~~~~~~~~~~~| \__________________/ \__________________/ BUCKET BUCKET Step 3 Step 4
This worked o.k., but quite a bit of air flowed in for the quantity of herb which was consumed. Also, it was a pain to unscrew the cap after lifting the bottle. Overall, we all ended up having a great time and the first trial was still a success. I leave this historical description in here because: a)this may be a good enough system for you, or b)you are also in a pinch for something right away as we were!
Having decided the activity was fun enough to warrant further development of the gravity bong, and having access to a machine shop, I designed a bowl just for this purpose. This incorporates a nice sized burn chamber (approximately = to 5 bat hits from a small bat), a small screen, and an o-ring seal to prevent air from passing anything but the burning herb. It drops out a pretty hefty ash after each hit.
Here is a horizontal sketch of my gravity bowl design:
FITS ___ IN ____O| \ _______ BOTTLE >> / \__________/ _____| | |+ |-----------------------/ + << SCREEN HOLE >>>> |-----------------------\ + | __________ |+____ \____ / \_______| O-RING >> O|___/ BURN CHAMBER
You could make the dimensions to whatever you think may work best. I put a 1/4 in. hole through the bowl, with a 3/8 dia. burn chamber that is .400 in. deep. It fits nicely inside a 35mm film canister for storage and TRANSPORTATION to parties (no plans to build more, though several friends have already tried begging!).
This new bowl works very well and burns quite efficienty, filling the bottle with dense smoke. The only change I have made to the apparatus is to offer the option of a milk jug in place of the 2-liter bottle, with a plastic adapter atached to the jug which makes the mouth the same size as a 2-liter bottle.
I built my setup some time ago, but the other day someone on the net mentioned using a tuba mouthpiece. Not a bad idea. Also, people have said they used aluminum foil with holes poked in it. The point is to get a lot of burning done without using an overly large volume of air.
This has not been done yet, but the plan is to design a multi- user setup using a larger water bottle (like the Poland Springs).
To get really wacked, breath back into the bottle, allowing it to rise back up to the beginning of step 4, and inhale again. Do not however, deprive yourself of too much oxygen. I used this method and took a full minute to take the hit, breathing in and out, and was immediately wacked, staying that way for several hours from one hit!
Have a "Gravity Party" with many friends - lotso fun!
Some people like to push the bottle to the bottom, and then inhale. While this does act to push the smoke into your lungs (kind of like breathing in a balloon), I don't really feel it is any faster. If you try this, don't displace so much water that the bucket overflows.
If it is your first time trying the system, do some trial runs without packing the bowl and lighting it. This is a must for a first time user from the point of view of risk reduction (won't chance losing precious smoke).
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