Thursday, November 12, 2009

Plumbing and indirect causation

In both my price theory textbook (webbed) and Hidden Order, I point out that one cannot safely assume that changing one thing in a system leaves everything else unchanged; the context there is the effect of changing one element in a transaction, such as the price, the terms the good is sold at, or the quality of the good, on the other elements. In order to figure out what will happen, you need to understand the causal links. My four examples can be found in Chapter 2, under the subtitle "Four Wrong Answers."

I recently encountered another example of the same principle, in a rather different context. Our shower had been persistently dripping. After the tenth time my wife reminded me of the problem, I decided to do something about it. My conjecture was that the valve needed to be replaced, adjusted, or cleaned out, so I attempted to disassemble the mechanism to get at the valve.

I was unsuccessful in my attempt, but managed, in the process, to fix not only that problem, without knowing I was doing it, but two others as well.

How did I work that miracle? I succeeded in disassembling the shower head,and discovered that its filter was clogged. Cleaning that out was easy. I reassembled it, making a mental note that we still had to do something about the dripping. Had I thought more about it, I would have made a further mental note that while doing so, perhaps by hiring a plumber, we might also try to do something about the low water pressure and how long it took the shower to heat up.

If I had, I would have been wrong—because I had just fixed all three problems. With the filter cleaned, the water could get through the shower head, so the low water pressure problem disappeared. As I should have expected, but didn't, the problem of heating up the water disappeared too. With the water free to go through the pipe and shower head much faster than before, it took much less time to empty out the cold water in the hot water pipe, so instead of waiting for a minute or two to start taking a shower, it now took only ten or fifteen seconds.

The dripping stopped too. I conclude that it wasn't a problem with the valve at all. Presumably, the stopped up filter meant that the shower head filled up with water, and that was what was dripping.

A nice lesson in interconnected causation.

I had thought of using this as a lead-in to a discussion of what might go wrong with current health care reform, due to the interrelated causation of that much more complicated system, but I think I will leave that to a later post.


Arthur B. said...

You almost committed a crime here

Gary McGath said...

You were lucky. In my experience, fixing one plumbing problem is more likely to expose two others than to fix two others.

Anonymous said...

You may well have fixed the valve too. Often the valve will get a mineral deposit on a seal and the manhandling of the valve trying to get at the works frees the deposit.

I have had people ask me to replace their 1/2" pipe with 3/4" pipe hoping to over come this shower problem. I usually ask them to hand me my drill and look the other way.

Water use is not a national issue but a regional one. Living in the Midwest and surrounded by 5 rivers, the people on The Hill should not concern themselves with the volume of my flush.

Anonymous said...

The WSJ article referenced by Arthur had some funny lines.

"So the hunt is on for a technological fix. For years, auto makers have used turbochargers, which force more air into the engine, to boost power without burning more fuel."

"But as always with new technology, there are downsides. Small water droplets cool faster than big ones, so aerated shower heads often require hotter water -- and according to some estimates, roughly 10% more energy -- than traditional models."

The 2 quotes show the hunt is still on for the perpetual motion machine.

Note: for the non car people, turbochargers require more fuel. We can utilize combustion more efficiently, but we can't change the rules of combustion.

Beastin said...

Couldn't you equally well take this experience as an indication of what might go right with current health care reform?

Anonymous said...
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Unknown said...

This is a great little story and I was interested in it because I heard something similar from a friend of mine a couple of weeks ago. He knows nothing about plumbing systems and, as an experienced plumber myself, he was about to call me as a friend and ask if I could come over and have a look at his dripping tap. Needless to say he took a quick look himself and fixed the problem!

Unknown said...

This is such an easy answer to a plumbing problem that most people have no idea about. Cleaning the filter is so easy to do but people don’t have a clue about these simple plumbing jobs and end up paying well over the odds for a plumber to come out and fix it for them. There should be some basic tutorials in schools that teach kids how to do simple household repairs including changing a washer and similar.