Sunday, February 28, 2010

Draining a Water Heater

My house's basement has no floor drain, so when my almost 19-year-old water heater sprang a leak I had to come up with a way to drain the thing. The main sewage pipe has a clean-out, so I uncapped it, shoved one end of a length of garden hose down it and connected the other end to the water heater's drain-valve fitting.

Problem solved, eh? Not quite.

The leak was at the top of the tank, so I closed the drain valve after what I thought should be sufficient draining. I had the cold water supply valve to the heater shut off, of course, but I could still hear water dribbling in the pipes and the tank. I took that to be just some remaining upstairs water making its way down that wouldn't amount to much.

A little later, I looked in on the heater and the leak was back; the tank had fully refilled. At least part of the dribbling noise I'd heard must have been from a faulty cold water supply valve that wasn't closing properly.

So now I had to leave the drain hose in place overnight until the guys could come and replace the water heater, and I didn't want to leave that gaping hole open like that all night. Never mind what manner of gaseous emission might belch forth, I've heard stories about what dwells in sewers, and I didn't want any urban myths slithering about in my basement while we slept.

I could have just shoved a wadded up towel in alongside the hose, I suppose, but that's no fun when you have a fairly well-equipped workshop. I took a few dimensions, rummaged through my bin full of off-cuts, spent a bit of time at the table saw and drill press and came up with this.

It's a scrap of 1/4" firply with three holes drilled through it. That hose has no fitting on its downstream end, so it just fits nicely through a 3/4" diameter hole.

All was still well the next morning. The guys came and did a fine job of installing a new water heater and cold water supply valve, so the house is back in business as it ought to be.

I must hang my plywood drain-hose adapter on a nail nearby for safe-keeping. I want to see if I live long enough to need it again.

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Saturday, February 20, 2010

Reader Beware

I've long been inclined to 'look stuff up'; to seek information in books. Civilization places high value on the written word, and I internalized that value very early on.

All well and good, but there's a potential problem always lurking -- just because information is printed on the pages of a book doesn't make it true. It may be damnable nonsense. How does one sort out the wheat from the chaff?

I wish I had a good answer to that. I don't, except to advise that one bring a healthy scepticism to bear on one's reading.

The more that I've learned about machinery and woodworking and metalworking through actual experience and empirical study, the more I'm able to spot nonsense in print. And the amount of it that I find amazes me. It's everywhere. It's to the point where my scepticism is bordering on disdain. Following is but one small example.

This example is from a book titled "Small Gas Engines -- How to Repair and Maintain Them" by Paul Weissler, published by Sterling Publishing Co. Inc. of New York. The cover bears the imprint of Popular Science, a respectable American mainstream magazine. It's a 282 page soft-cover published in 1987. It's copiously illustrated. It has the look of authoritativeness about it.

On page 208, there's a photograph purporting to show how one begins to dismantle a recoil starter. The photograph is preposterous. [I lack the equipment to reproduce the subject photograph here. Please bear with me while I try to paint a word picture.][1]

A typical recoil starter has a stamped sheet metal shell that houses a spring-loaded pulley/clutch with the pull-cord wrapped around it. Extending from the circular shell are the mounting ears for bolting the unit to an engine's cowl. Bolted in place on an engine, the stamped steel shell is a very strong item. Off the engine, the shell has its weaknesses and mustn't be subjected to thoughtlessly applied, inappropriate forces.

A starter that's off the engine reveals a central screw that holds the pulley/clutch affair in place. The screw must be removed in order to service the unit's innards. The screw is very tightly in place; one that I encountered in the course of repairing a broken pull-cord showed evidence of having been installed with a thread locking compound applied to it.

Now, a helpful tool for loosening stubborn screws is an impact driver -- a hammer powered specialty screwdriver. The driver contains a mechanism that converts the axial force of a hammer blow at the end of its handle, to a rotary force at its tip. In order for it to work effectively, the item containing the screw to be loosened must be rigidly backed up, and secured against rotation; else the driver simply cannot work -- a hammer blow's force will dissipate to no useful effect.

In the photograph mentioned earlier, the recoil starter is suspended by its mounting ears across the wide-open jaws of a big mechanic's vise. We see the impact driver held to the screw head and a hammer poised above. The photograph is patent nonsense. Such a setup could not possibly work. All that could result from it would be bent mounting ears on the starter.

And there's more. On the occasion that I had to dismantle a similar starter, I ended up breaking the screw; it was that tight because of the thread locking compound. Had I known, I might have held a big soldering iron to the screw's head for a while to heat it up and soften the thread locker first (although that might have been problematical; I seem to recall that the screw's shoulder was the spindle for the plastic pulley). That may have worked, and saved me the trouble of having to fabricate a replacement for the broken screw. Nowhere in the book's photos or text is there any mention of the possibility of thread locker being present, or the application of heat to soften it.

The photographs go on to show a fully disassembled recoil starter. How the author got from the ridiculous to the sublime is a mystery to me.

Such hogwash is not uncommon. One wonders what's behind it. How can writers present patently false information as authoritative gospel?

Some of it may be due to deadline pressures, although I'd expect those to be more operative in periodical publications than in books. The curious thing about the example cited above is that it would have been no more time-consuming or difficult to illustrate a correct setup for impact driver use than it was to compose that ludicrous tableau at the vise.

Another thing that may be at work is what I call 'plausible extrapolation'; a tendency to write on further about a subject than one actually has any right to, given how much one truly knows and has experienced of the subject. I know I'm not immune to that. I occasionally find myself lapsing into it, and I have to figuratively grab myself by the shirt collar and shake myself loose from it. I suspect that a lot of technical writing is riddled with flimsy 'information' of that provenance.

And it could well be that some authors are simply out of their depth, and/or contemptuous of their subject matter and their readership. But they have a job to do filling up blank space with text and illustrations, so they fill it up with text and illustrations. Job done.

In any case, be wary. Publication is no guarantee of veracity in technical books and magazines. There's a lot of insubstantial, misleading 'information' that gets printed and bound between covers. It's an unfortunate irony that the target market for such tripe is precisely those who genuinely want to learn.

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Note -- SATURDAY, MARCH 21, 2015:

[1] I've acquired a camera since. Here's a photograph of the subject photograph:

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Saturday, February 13, 2010

Gas Furnace Thermocouples

I'll begin this post with its conclusion:

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If you have a gas furnace with pilot light ignition, a good thing to have on hand is a spare thermocouple (the pilot light sensor). That's what this whole thing boils down to.

If you care to read on, here's my pilot light story.

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On Tuesday last, I got a phone call at work from home; it seemed that the furnace wasn't coming on. I dropped everything and drove home.

The pilot light was out. I lit it and let the furnace run to warm the place up. I switched off the furnace before it was entirely done and let it sit. After a few minutes, I checked on it and the pilot light had gone out again -- not a good sign. I lit it again and started sizing up the situation. Calling in a serviceman was an option I'd rather not have had to exercise. I didn't want to hear, "Ya need a new furnace or ye're all gonna die! I've got one on the truck. $3,000.00 installed -- they're on special this week."

The pilot light burned nicely whenever I'd relight it; a healthy little blue flame, not anemic or sputtery. That suggested a thermocouple fault. I noticed there was a screw on the valve body labelled "PILOT ADJ." The visible screw turned out to be just a cap over a little well with the actual adjustment screw down inside it. Here's a close-up of the gas valve -- you can see the location of the adjustment screw's cap.

I removed the cap and tweaked the little screw down inside to make the pilot light flame bigger, and that worked -- and continued to work for the rest of the week.

On Wednesday, I found a furnace parts dealer right near where I work. I went there and they had what I needed. They only carried a single Honeywell universal thermocouple, so it appeared that furnace thermocouples are a highly standardized item, which suited me fine. (The item is a Honeywell Model Q340A 1439, 36" universal 30 millivolt output thermocouple; about $20.00 list price.) Here's a view of what I got in its blister-pack.

On the rear of the package card, there are drawings of three possible mounting arrangements.

My furnace has the arrangement shown at the left in the above photo. I could have used the existing receptacle, but I thought it best to replace it with the new one. The receptacle has a 1/2" A/F hex on it. The valve control end has a threaded collar with a 3/8" A/F hex.

Here's an overall view of the installation.

And here's a close-up of of where the thermocouple resides alongside the pilot light's fuel delivery tube and jet.

It all went fairly smoothly, and saved me some serious money.

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How a Thermocouple Works

First, a word about why it's there. It's a safety feature to ensure that should a pilot light go out for whatever reason, the gas supply to its jet is shut off. So, the 'why' of it is pretty obvious -- it will prevent a sustained gas leak that could have dire consequences. (It's also a good example of what's meant by the term 'fail-safe'. A fail-safe component or system is one in which failure results in a safe condition. A thermocouple's failure can only result in the gas supply being shut off. It's impossible for a thermocouple to fail in such a way that the gas supply would remain on.)

Strictly speaking, a thermocouple is a junction at the ends of two dissimilar metal wires. When heated, such a junction generates a small electric voltage, sufficient in this application to supply enough current to hold open what I surmise to be a tiny solenoid valve. (It's not easy to find detailed information about the innards of furnace gas valves.) The probe end of what's called a furnace thermocouple is the housing for that junction. Bathed in the pilot light's flame, the thermocouple constantly generates the voltage/current required to keep the gas valve open that supplies the pilot light. Should the light go out, the thermocouple cools and the gas supply to the pilot light's jet is soon shut off.

All well and good, but there's an obvious potential for trouble; if the thermocouple's output falls off, or fails entirely, you'll have a pilot light that won't stay lit. I was fortunate in that the thermocouple hadn't failed outright, and turning up the flame bought me time to get a replacement and install it at a time of my choosing. It could as easily have been an outright failure outside of business hours, requiring a costly emergency service call. So, as I said at the outset, a spare thermocouple is a good thing to have on hand.

The length of the unit's lead is not critical; it just has to be long enough. That's no doubt why the furnace parts dealer only stocks the longish 36" item. (There are shorter ones made.) What that copper-tube-looking lead is, by the way, is a two-conductor coaxial cable. The outer copper jacket is one conductor; running down its length inside and insulated from it is the other conductor.[1]


There really isn't any. I've seen advice to clean the probe, but I don't buy it. My thermocouple was well over a decade old, and there was only a slight sooty coating on it. As long as the probe end is well positioned in a proper flame, and the valve control end is snug, all you can do is replace it if it appears to be at fault. Cleaning it is unlikely to have much, if any, effect.

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[1] I like to see everything, so I cut the old thermocouple's cable to see how it's constructed. Here's a view of it.

The 'cable' is a copper tube, with a clear enamel-insulated solid copper wire inside it. This is a low-resistance cable if ever there was one.

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Sunday, February 7, 2010

A Huge Rusty Spoon

One finds the oddest things in one's backyard at times. Last summer, a freakish sequence of wind gusts brought down a huge old Manitoba maple at the bottom corner of my yard. Before the tree removal crew came to deal with the thing, I went down and relocated a stack of fence boards that I'd piled near the tree some time ago, so the crew would have unimpeded access to the stump area. While I was rummaging around down there, I found this rusty old spoon. The thing is huge. 'Looks like something you'd use to give cough syrup to a hog. (Do hogs get coughs?) I'll see how well I can clean it up. It's in pretty rough shape.

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It's still ugly as sin, but in a clean sort of way.

I wire brushed it on a 6" wheel, scoured it with a scouring cleanser and gave it an application of GM Blue Coral Preservative Sealer. And it turns out that I have something of an antique item in the workshop (see below).

It would take extraordinary efforts to get this item to a truly pristine condition, so I'll leave it at this. I've made a place for it to hang on one of my toolboards. If I ever have to administer cough syrup to a hog, it'll be right at hand.

GM Blue Coral Preservative Sealer

It's a paste wax, basically. It has a blue colour in the jar. I don't know when it was last available. I must have bought the jar pictured in the late sixties for the chrome on my Austin-Healey Sprite. Most of it is still left.

There's someone in Kernersville, North Carolina who has an empty jar of it on Craigslist -- asking price is $1.00.

There is an outfit known as Blue Coral that makes car cleaning products, but they don't appear to have any connection to this GM Blue Coral.

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Scissor Sharpening

Scissor sharpening is a chore that I never much liked doing before I acquired an upright belt sander that takes 1" x 42" belts. The machine makes many sharpening jobs easier, scissor sharpening notably so.

The finest belt I've been able to get so far for the machine is 120-grit, which is just barely fine enough for the task. The aluminum oxide abrasive works well on carbon steel, not so well on stainless steel but well enough. I find that the belt 'grinds' with much less heating effect than one gets from a grinding wheel -- a big bonus.

It's helpful but not essential to have a pair of scissors taken apart for sharpening. The latest pair that I did had a nice screw-and-nut pivot that came apart easily.

Present each scissor to the belt with its operative face down, so the belt is leaving the cutting edge corner rather than approaching it as it goes by. Make smooth, moderate passes from pivot point to tip until you've turned a 'wire edge' the entire length of the cutting edge. At that point, the machine has done its work. Hone the operative face of the scissor with a pocket stone just enough to rid it of the wire edge effect and you're done.

Use blue threadlocker when reassembling the pivot. Once you've got the tension to where you like it, set the scissors aside for the threadlocker to cure for an hour. Lubricate the pivot with light mineral oil.

The only part of the operation that demands a bit of skill is presenting the scissor's edge to the sanding belt consistently at the same angle for every pass made. I'm thinking of making an oversize table for my sander. Then I could fabricate some manner of 'sled' fixture that would pretty much deskill the process entirely.

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