In the cannabis culture, gravity bong is a term that can refer to one of two devices usually used for smoking cannabis. Gravity bongs differ from regular water bongs or water pipes in the fact that they usually do not filter the smoke through water, they have a far larger chamber, and the smoke is much denser than possible in a standard bong. Additionally rather than the operator reducing the air pressure inside the device this is achieved with either falling water or by lifting the device while it is in a bath of water. These devices get their name because of the role that gravity plays in creating suction when trying to restore the pressure equilibrium of the inside of the bottle with the outside air. Both devices described below are known as gravity bongs and not all people will be familiar with both versions; many may know their device as a gravity bong instead of using the more specific term for each device.
A gravity bong utilizing a bucket, also known as a bucket bong, bucket, bucket kit, compression bong, depth charge, or turbo, can be constructed in many different ways, allowing for variations in material availability. In all cases, however, some sort of a bottle and a bucket are needed. The size of the bottle is very important to operation; a larger bottle is generally preferred. The larger the bottle is, the more volume that is available to fill with smoke. The size of the bucket is contingent on the bottle; it is ideal that the bucket can, when filled with water, allow the entire bottle to be submerged.
The bottle is prepared by cutting the bottom of the bottle off, leaving it as tall as possible. Also some sort of bowl or stem is somehow placed in the bottle cap, usually by cutting a hole. It is absolutely vital to the proper operation of the Gravity Bong that the seal on the hole in the cap is air tight, such that the only air that can enter through the cap is through the bowl or stem. Also common is a small hole placed near the top of the bottle to be used as a shotgun or carb. The purpose of which is to allow clean air into the bottle from another source than the cap, if necessary. A simpler method is to remove the cap and place tin foil over the bottle top. The foil is shaped into a bowl shape, pierced with small holes, and then filled with cannabis.
The bong is operated by submerging the bottle in the bucket, with only the open top of the bottle protruding from the surface of the water. The bowl is filled with a substance to be smoked, and then screwed onto the top with the bottle still in the water. The bottle is then slowly lifted out of the water while the carb is being covered with a finger, at the same time as a flame is applied to the bowl. The pressure will pull the flame into the bowl burning the substance and pulling all of the smoke into the bottle. Once all of the material in the bowl has been burnt, and the bottle is full of smoke, the cap is removed and the user places their mouth over the opening. The bottle is then pushed down, forcing the smoke into the user’s lungs.
When the bottle is pulled out of the water with the carb covered, the air flow into the bottle is restricted to whatever is allowed through the bowl. Thus any air that enters the bottle must come through the burning material, thus the air is consumed during the combustion process and the only gas that enters the bottle is very dense smoke. Typically the amount of smoke entering the bottle is not enough to account for the change in volume which results from pulling the bottle out of the water. Thus to keep the pressure inside the bottle the same as the surrounding air the water level inside the bottle raises above the water level of the rest of the bucket.
The force of gravity pull on the water inside of the bucket creates the suction that pulls air through the bowl. The force of the suction is directly proportional to the level that the water in the bucket is raised above the surrounding water level. The higher the water level is pulled creates more a higher force due to gravity, because of a larger volume of water being suspended higher.
The pressure inside the bottle is governed by the equation p=rho*g*h, where p is the pressure of a fluid column, rho is the density of the fluid, g is the gravitational acceleration, and h is the height of the fluid column. As the water levels in the bottle and bucket separate, the difference in height causes a pressure difference between the bottle and the atmosphere. A larger pressure difference means that air will be sucked through the bowl at a higher flow rate which is not always the most ideal. A high rate of air flow may result in the substance in the bowl burning faster than is ideal to maximize the amount of smoke. Another complication resultant from excessive air flow may be the substance is pulled through the opening of the bowl before it is fully burned, producing wasted material.
After the bottle is full of smoke, and all combustible material is burned, the user forces the smoke into their lungs by pushing the bottle down. The effect that is produced from pushing the bottle down is the opposite obtained from pulling it. When the bottle is pushed down the water level in the bottle is pushed lower than the top of the water, which results in the gravitational forces on the surrounding water to force the water level back to equilibrium in the bottle. To maintain equilibrium, the gas in the bottle is forced out the now open top into the lungs of the user at a higher force than usual.
According to some, this bong maximizes the effect of the substance smoked like no other method can. This is due mainly to a number of factors, the enormous density and volume of the smoke, and the velocity at which the smoke is forced into the users lungs. A Gravity Bong produces a hit that contains much more volume than one produced from normal methods, because the user usually stops before they’ve sucked in a gallon of smoke, however a Gravity Bong is a large bottle, completely filled, thus ensuring a maximum potential. Critical to the large volume is the high density of the smoke which is produced due to the restricted source of air flow, only through the bowl. Combining these factors with gravity forcing the smoke into the user’s lungs at an increased rate, the outcome is a method that surpasses any other in the amount of effect that produced from the smoked substance.
Optional bucket bong accessories include a water bong guard. A guard consists of a buoyant sphere, often a ping-pong ball, which is placed within the bottle before the hit is drawn. Slight modification of the bottle will keep the ball inside the bottle at all times. Instead of having the entire bottom of the bottle cut off, wedges of the bottom may be cut out. When flat, they will not allow the ball out, but when gently twisted the gap is large enough to allow pong ball access in and out of the bottle.
Another modification is a percolation tube that draws the smoke down into the water by connecting to the male slide piece. The bottle must be raised so that the mass of the volume of water inside the device above the water surface can gravitationally pull the smoke through the percolation tube. If the tube is long or the device is not airtight, it will not work. This method produces a toke that is generally more potent and also decreases the damaging heating effect of the conventional gravity bong.
Similar in design to the bucket method is the fountain method, also known as a waterfall bong. A Fountain usually consists of a plastic bottle with a hole punched at the bottom and a removable bottle cap with a bowl in it, or an alternative to that is a guass, which is usually a piece of round metal that fits on the bottle with a mesh inside. The bottle cap or guass is removed, the hole is covered by a finger. The vessel is filled with water and then while holding a flame to the bowl, finger is removed. Gravity causes the water to flow out creating a vacuum inside the chamber and smoke begins to flow into the chamber; see the section on the bucket bong for a more detailed description of this process. When all the water has run out the user removes the bottle cap or guass, places their mouth over the opening at the top of the bottle, and inhales the contents. The colloquial term fountain is used frequently in Europe and Australia, waterfall is the American translation.
Depending on a number of geographic differences, the term gravity bong may be interpreted as either device. There are supporters for both viewpoints who raise arguments that support their stance. While each contends for the title, they share similarities that are critical to their operation. At their core they both use the gravitational force of water to create a vacuum. The resulting suction created draws air through the bowl to fill a container with smoke. Where they differ, however, is the technique that is used to control or constrain the rate of air flow through the bowl. In the Southwest United States a gravity bong is also referred to as a bosh, for reasons unclear.
Supporters of the waterfall method claim that gravity makes the water fall from the device, thus forming a very simple machine utilizing the potential energy of stored water at a height. Because the machine stores all the energy required to do the work, the waterfall proponents feel their device is worthy of the gravity bong name. Mostly in South Australia, the waterfall method is also known commonly as a fountainy or fountain bong. In the North of England they are commonly called deffies. This method is also referred to as a flow, because of the way the water flows out of the bottom of the bottle. Made by cutting three holes in the bottom of milk jug, etc.
As with the waterfall method, the bucket method uses gravity to create a vacuum, its claim for the title of Gravity Bong is supported mainly by the argument that it relies more on the force of gravity. The bucket method uses gravity pull both to create a vacuum, and to control the air flow. When the bong is pulled using the bucket method, the air flow rate is directly proportional to gravity force due to the difference between the water levels of the bottle and the surrounding bucket.
Some argue that the bucket method in fact does not need gravity at all, all it needs is a device to create a vacuum; therefore it can also be referred to as an air displacement bong, or pressure flux bong. Gravity merely holds the water in place (making it resemble a liquid piston), if a solid piston is used instead of the liquid piston, the direction of gravity is irrelevant