Wednesday, June 28, 2006

Is That an Expanding Pipe, Or Are You Just Happy To See Me?

Greetings Squaddies! Welcome back.

Today's question comes from Greg Howley, the owner and proprietor of GregHowley.com. Greg has impeccable taste in handheld video game systems and wives' names. He's also a frequent visitor to this site and as such, is better than probably 80 - 85% of the world's population. His question is:

In the house where I grew up, I used to be able to tell when the shower
water got hot by listening - the pitch of the water would change as it heated
up. Recently, I noticed the same thing with our sink - as the water heats up,
the pitch goes up. What is the connection between water temperature and
pitch

Well Greg, it sounds to me like you have a Class 5 Ectoplasmic Entity, also known as a "Squealer". Most likely, at some point, someone in your family tree did someone wrong and once the victim, perceived or actual, died, he or she set out to torment your family for all of eternity. They found you at your old home, took up home in your pipes and have found you yet again. Your only recourse is to do right by the spirit and lay it to rest.

Ha! Kidding. My extensive research of the vast plumbing resources on the web point to two explanations for what you're hearing, however neither help us understand the connection between water temperature and pitch. Now, the connection between water temperature, the thermal expansivity of the pipes and pitch is something we can work with. And so we shall.

Thermal expansion is, in a nutshell, when certain substances expand in size due to an increase in temperature. As the substance is heated, the heat energy is absorbed by the bonds that keep the subtance's molecules together. As these bonds absorb energy, they lengthen, causing an increase in size. Some items, like mercury, expand a whole bunch, while others, like diamond and, ironically enough, water, expand very little. Copper, which your pipes are most likely made of, has a thermal expansion coefficient of 17 (forgive my lack of units) which corresponds to about a 1.12 inch increase in length of a 100 ft pipe when heated by 100 degrees. Now, how this corresponds to a higher pitch depends on what is causing the sound in the first place, which brings me to the two things I found out.

The first, and less common idea, is that the water pressure in your home is too high. When the pressure is high, and the water gets heated, the pipes will heat, expand and raise the pressure even higher. This results in a high pitched wailing, akin to a banshee or a cat trapped in a garbage bag, or a banshee cat trapped in a banshee bag. This can cause bigger problems down the line as high pressure can screw with all of the various gaskets and plumbing seals in the house. It can be fixed for less than 200 bucks by a new pressure valve where the water comes into the house. I speak from experience on this as we had the same high pressure problem, minus the keening, wailing sounds when we bought our current house.

The second answer, and the one I found as being the most common, is that the expansion of the pipes is causing them to rub against their brackets and hence the high pitched, squeaking noise. Pipes are attached to walls, joists and floorboards with brackets, usually metal, which then causes a charming metal on metal squeaking when the pipes expand.

This second cause may be harder to fix, depending on where the squeaky bracket actually is, namely behind a nice, finished, painted wall. Should you be able to find the bracket, you can either use a bigger bracket, or put something around the pipe to act as a buffer between the bracket and the pipe. You can also swap out all of your plumbing with pipes made of diamond, the pipes of choice for the discerning homeowner.

Another option would be to investigate pipes made of a polymer of copper and zirconium tungstate, provided such a polymer is ever invented. Zirconium tungstate shrinks when it gets colder, over a much wider range of temperature than other materials with negative thermal expansion. If a combination of copper and zirconium tungstate were created, in effect the copper's thermal expansion would be cancelled out by the zirconium tungstate's negative thermal expansion. Currently there aren't any plans to make plumbing supplies from zirconium tungstate, however it is being investigated for fillings, so that when you wash down your popsicles with hot coffee, your fillings don't explode and blow your jaw off.

While I'm sure the squealing sound is annoying with copper pipes, it could be worse. Your pipes could be made of mercury which would a) require you to keep your house at a frosty 38 below zero so that the pipes stay solid b) expand all to hell once heated even a slight amount and c) invariably kill you as any water flowing through mercury pipes would melt your nervous system.

Sources:
Wikipedia - Coefficient of Thermal Expansion
Wikipedia - Mercury-in-glass Thermometer
LiveScience.com - Strange Shrinking Material

4 comments:

k o w said...

Now I had the same problem in my old place that was built around the turn of the century. Cast iron piping feeding old copper pipe. In the new place built circa the late 60's everything is copper and I have no sound from the hot water. BUt I also have one of those low pressure kit thingamabobs installed so maybe thats it.

suburbanjoe said...

Iron has a slightly lower coefficient of thermal expansion than copper, so it still could have been expanding and making noise. Most likely, your low pressure thingamabob is keeping everything in check. It's the thingamabob to have when you need a thingamabob.

Greg said...

Cool - expanding pipes makes sense.

I think the sound is just the sound of water flowing rather than bad piping - it's not an overly noticable noise, I just have a good ear. And our house is less than a year old, so it's not old pipes.

Booster MPS said...

Interesting phenomenon although I dont think that I have ever noticed the sound in any of the homes I have lived in. Cool!