PVC Pipe fittings

You would probably recognize what  PVC pipe is but just to bring every reader up to speed, I am referring to the white pipes that are now universally used for plumbing. PVC means polyvinyl chloride and it is the same as “vinyl”. The actual polymer is transparent but various pigments are added for color. White usually comes from titanium dioxide (or calcium carbonate), black comes from finely divided carbon (called carbon black) and other colors can be purple or gray or anything else. The colors code for usage so that if you encounter a pipe being used, you know what is inside of it. White carries potable water; gray electric wires; purple non-potable water and black, sewage. Transparent pipe costs a lot more even though it takes less pigment and allows you to see what is inside – a very nice plus where blockage can be a problem. When I was in graduate school at Yale, the new Chemistry building used nothing but glass pipe in its sanitary system for this reason. If I had to guess, I would say that the decision by the pipe industry to downplay transparent PVC is based on the feeling that the delicate, American sensitivity could not withstand seeing what is going on inside a pipe, especially a sanitary pipe.

What are the design choices that affect reuse? On the positive side, pieces of any length can be cemented together so a piece does not become unusable just because an end gets mashed. Where pipes of two different materials need to be joined (so they can’t be cemented), such as PVC to steel,  rubber connectors are sold. And there are available converters from one diameter to another. One thing that is not usually appreciated is that any color can be cemented to any other color and PVC pipe can be easily cemented to ABS pipe (often used for sanitary work) if the right cement is used.

The word cement is tricky and often misunderstood. Users are never told what the cement consists of and how to play around with its composition. It begins, classically, with three solvents mixed together, tetrahydrofuran (THF), cyclohexanone and dimethy formamide (DMF). All three are expensive organic solvents. It is the THF which gives the cement its sharp quality upon inhalation. Nowadays the Cyclohexanone is often replaced with cheaper methylethylketone (MEK). The reason for using this mix is that it will readily dissolve PVC plastic.  So any kind of scrap PVC pipe or pieces can be dissolved in the mixture and the resulting solution becomes the cement of plumbing fame. When the cement is applied to two surfaces and they are pressed together, some of each surface is dissolved and then the solvents evaporate, depositing the contained PVC in the space. The two surfaces are not just held together by some external glue but they literally fuse into one piece of continuous plastic.

Often in use, the cement container dries up as the solvents evaporate, becoming harder and useless. Plumbers will then discard the can. This is where a rich source of wasting comes from. All that is really required is for some new solvent to be added back. After a few hours or days in the can, the hardened plastic in the cement will redissolve so that the can, the included brush, the residual solvent in the can, the pigment and the formerly dissolved PVC will all be usable again.

Hardware stores used to sell the solvent for this purpose but then Big Garbage and Big Plastic realized they could stimulate wasteful discard by making the solvent impossible to get. Fortunately, there is a possible workaround.

It turns out that the cement has so much dissolved plastic that there is not enough free solvent left over to properly dissolve the surfaces of the pipes being joined. So some extra solvent is needed on the pipes before the cement is applied, to start the surfaces dissolving. The liquid that does this is called a primer and it is usually dyed bright violet. Since it dissolves the plastic, of course it is a form of the solvent mixture in the cement and can replace it. So all you need to do, when the cement is getting too hard and dry, is to add some of the primer to the cement. This defeats the insidious plan of the wasters and discarders, though they charge a pretty penny for the primer. Not to worry! They have more tricks up their sleeves. Like a cap for the container which easily gets dried cement on it which then prevents proper closing and allows the solvents to evaporate even faster. Or using low grade solvents in the primer that don’t actually replace the original solvents.

Clearly what is needed is a rethinking of the design of the container itself, and as always in a Zero Waste analysis, the system of use in which the container is embedded. No ZW design is complete by just changing one little feature of one product. Until that day however, you can cut down on the evaporation by storing the cement inside a sealed plastic bag when not in use. A closed glass jar is even better.

Let us now turn to the design of the fittings which fit over the ends of the piping. These are elbows, couplings, tees, size converters, nipples, unions and more. Some convert from a cemented end to a threaded end, thus allowing pipes to be connected by threading together. This also gives you a simple way to connect to the world of threaded iron or copper pipe.

 The sizing of pipes and tubings is critical for interconnectibility. The entire field of sizes in the US is an impossible mess with many competing standards, based on historical usage and varying geographically. There is a crying need for the entire field to be rationally defined by a design commission which starts over. However, if that were done today, reuse considerations would not even be recognized and the result would be just as chaotic as the current system. There is no particular reason for the use of stepped designations like 0.5 inch, 0.75 inch, 1.0 inch etc. For most pipe sizes, there is no measurement on the pipe which matches the size. Even though all three numbers describing a pipe are of separate interest – the inside and outside diameters and the wall thickness – they are all related and cannot be separately specified. This causes conflicts of priorities. 

Yet there is one more consideration that is of interest from a ZW viewpoint. PVC pipe especially was discovered by builders of all kinds – tents, awnings, fences, gates, small structures – to be extremely useful insofar as it is cheap, uniform, clean, lightweight and can be dismantled if not cemented. In other words, the sole emphasis on plumbing applications is misplaced. When fittings are designed, it is clear that all the designers care about is the inner surface of the fitting, what will snug up to the outside of the pipe, while the outer surface of the fitting is ignored. Often it has a brand or size embossed on it, which means that the outer surface is not smooth enough for a close slip fit or even for cementing since the embossing will create a leak. But what is worse, is that there is no attention paid to slipping one fitting inside of another in order to facilitate the assembly of fittings as slip joints. The sizes vary all over the place and never match any other size. Perhaps the greatest failing is that no size of larger pipe will ever fit tight over the outside of a smaller fitting. Even if standard sizes can’t be matched to each other, sleeves could be made available to adjust the inner size of a pipe to the outer size of a fitting but nothing like this is possible when the outer sizes are ignored by the designers and could be anything. They vary from brand to brand and from one schedule (wall thickness) to another. The whole system of using arbitrary and meaningless schedule numbers to denote wall thickness is primitive and counterproductive.

Thus fittings  which could have a function, and longer lifetime, determined by their matching outer dimensions are discarded because they were once cemented using their inner surface.

The situation deteriorates even further with specialized tubing systems such as for water hose or vacuum cleaner tubings. The latter seem to be purposely made incompatible with anything else, the better to motivate astronomical prices for simple replacement connectors. Vehicles again have extensive networks of tubing and hoses which once again are coordinated with no other sized tubing. The lack of standardization is always a recipe for unnecessary wasting, reduced versatility and higher prices.

The whole field presents a glorious opportunity to apply Zero Waste principles of intelligent design built around standardization and interchangeability.  It would not cost more (except in the changeover from wastefulness) and would actually save all kinds of waste, inefficiency and the frustration of forcing incompatible parts to somehow work together.


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