Water pipe percolator
A water pipe percolator is a small additional sub chamber within the shaft of a water pipe that provides in-line smoke-water interaction via heat exchange and dissolution. Percolators come in different forms, such as dome, pedestal, tree, helix, and the more recent honeycomb and fritted disc percolators. Depending upon the form of the percolator, it may or may not be diffused. However, the primary purpose of the percolator is to act as an extra chamber to filter smoke through water.
Function and purpose of a percolator
A percolator works by utilizing a pressure differential between its bottom and top in/outlets. Reduced pressure at the outlet end is usually provided by the user's lungs. The fluid at the inlet (i.e.: a smoke, vapor, and air mixture) is directed to the bottom of a column of water, where the pressure differential causes the inlet fluid to pass though the water in small pockets (liquid bubbles), and then rise to the outlet. In short, diffusers make smoke cooler, and rise evenly through the pipe, due to the water bubbles hitting the surface simultaneously. The following is a diagram illustrating the diffusion process of a tree percolator:
The diffuser serves the primary function of cooling the smoke and combustion vapors that pass through it. The surface of the bubbles come into direct contact with the water, where the temperature difference causes an exchange of heat between the hot smoke/vapor, and the cool water. The tree percolator design incorporates a number of small openings instead of large singular ones in order to diffuse the smoke into a larger number of smaller bubbles. This serves the purpose of increasing the surface area of the smoke that is in contact with the water and increasing the efficiency of heat transfer. In short, the primary function of the diffuser allows for cooler, cleaner and even rising smoke.
A secondary function of a percolator is to trap certain components contained within the smoke. Water soluble substances enter into solution as the smoke/vapor contacts the water, while less soluble substances pass through with relative ease.
A tertiary function of the diffuser is to hydrate the air-smoke-vapor mixture. Humidity of the air passing through the water is increased. The increased humidity reduces the irritation to the upper respiratory tract experienced by users according to anecdotal claims.
There are a number of percolator designs on the market today. The two most prevalent are the tree and dome designs. Pedestal, helix, double helix, serpentine, inline, dewar, ring, coil, honeycomb; tree twist and even "frit" percolators also exist, but are uncommon. All of these are ordinarily known in scientific production as 'traps'. Each chambered percolator, or trap, filters smoke. Multiple percolators will cause increased filtration, as well as drag, but minimize elements such as nicotine or any other resin. Multiple percolators in one piece can also cause cleaning issues and vacuum pressure resulting in trapped particulate matter, or water travelling into the bushing for glass on glass water pipes. A new trend for more artistically shaped percolators has resulted in many new styles.
Tree percolators usually utilize between 1 and 10 but can go up to 19 (or more, if the manufacturer is capable) individual flow paths for the smoke to enter the water. In general, smaller work is more difficult to manufacture. Recent variations include bent arm and twist trees. The size of each slit and the number of slits combined should equal the inside diameter of the up stem for equivalent air flow.
Dome percolators instead use a single encircling cylindrical piece to direct smoke to the bottom of the water column. Dome percolators can be diffused in many different ways, some have triangular slits along the bottom. While others have either a few large holes or many small holes around the bottom of the dome. The size and number of holes, or slits is determined by the inside diameter of the up stem for correct air flow. Sometimes colored art is applied to the dome resulting in a 'zig zag' pattern common in traditional soft glass paperweights and vases. pH(x) glass holds the patent for the dome percolator design (USPTO 6,935,345 ) and has sued other paraphernalia manufacturers in US Federal Court. Dome percolators may be the first type of secondary filtration used in water pipes.
Coils limit or increase air flow based on the number of wraps and outside diameter of the tubing and increase the amount of distance smoke must travel before reaching the user. Coils are often seen in a sealed glycerin-filled chamber, meant to be frozen to increase heat exchange with the smoke. They were the first associated with the 'slow-draw' style trap for water pipes.
Dewar percolators correct an early problem associated with domes, whereby a vacuum creates back pressure pushing water up the bushing. The Dewar contains a jacketed dome that stands up off the bottom of the percolator chamber eliminating the issue. *Jacketed Dewar sections containing a coil immersed in freezable glycerin are believed to represent the first models.
The Ring is a variation on the tree containing a single bent up stem attached to a u-bend. The u-bend wraps around the up stem and contains either holes or slits. This would be a "slow-draw" percolator and is usually found in shorter pieces. Altering the air flow for intentional drag is claimed to create a smoother hit, thus allowing harsher tobacco products to be consumed. While no studies have shown this to be proven, recent federal laws on tobacco products exhibit a trend in this direction.
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Artistically combining a Dewar with low-set arms in a swirl pattern, the Pinwheel is a re-engineered version of the Ring. Only two are known to exist, although tested and shown to be 'slow-draw' water pipe percolators; the 'slow-draw' system is not yet proven to provide benefits. *Footnote.
Multiple Action Dewar
M.a.d.s are jacketed Dewars with round or compressed spheres inside. Holes at the top of the sphere inside the Dewar allow smoke to billow intensely filling the jacket before channeling out slits in the bottom. They act as air diffusers and water percolators in one piece. A sub-category of M.a.d.s include the Atomic Mushroom and Snake Egg.
Inline percolators resemble the tree with one larger arm sealed inside a jacketed Dewar. The Inline contains slits and is usually found in the first chamber of the water pipe. The Inline can be made with slits of varying diameter, allowing increased diffusion and creating visually entertaining bubble patterns. Coined 'Harmonic', the pattern resembles waves of bubbles similar to a sound wave pattern. The glass artist 'Hops' is credited, along with 'Toro', for origination of terminology and design.
Honeycomb Diffusers are very efficient diffusers because there can be as many as 100 individual holes for a single trap. Honeycomb Diffusers rest above the water, parallel to the surface. As air is drawn into the piece, and bubbles are created in the water, the bubbles are forced to contact the Honeycomb and pass through the holes, reducing the size of the bubble, increasing surface area interaction between the smoke and water, and providing a large amount of diffusion with a low amount of drag.
The fritted disc, or "frit" diffuser makes use of glass fragments which are bound together leaving very small spaces between one-another. This results in a very large number of holes which become venues of diffusion. The frit perc, having such small (though plentiful) holes requires more frequent cleaning. An ash-catcher can be useful to reduce the need for solvent cleaning.