Measurement Suggestions Sought

A weight biased relief valve; ie a 1/4 hole in the top w/ a ((1/4)^2 * .7854 * 15) pound weight sitting on it?

Hul

Erik wrote:

Can you just take the faggy thing apart and see if there is wear or something wrong with the regulator?

Personally, I'd never trust a pressure cooker with plastic parts, but unless you shop at the garage sale, that's all your getting these days.

We did have a bean block the valve on an old Miro? pressure cooker once. The safety slug melted and blew the entire contents out and into the ceiling. New plug from the harware store and everything was back in business.

Put a temperature sensor to outside wall (use a couple of turns of mig wire around to press sensor firmly against wall), with some wool around for insulation. The temperature drop from the wall is small, and the wool keeps temperature drop to surroundings small.

Test first in normal kettle boiling at 100C, first sensor in water (around 100C), then on the outside as described above. Should work nicely. After verification, measure your pressure cooker temperature.

I just tried reading bare and sooted areas of a stainless tea kettle with two IR thermometers. Both varied considerably across the surface and never came close to 212 F. The boiling water inside reads 204 F, so they aren't all that accurate anyway.

I've had better luck with thermocouples than anything else, as long as the tip can be tucked tightly against or inside the metal somewhere, like under the rim. These come with very flexible K probes with fast-responding fine tips. The two I have are accurate to 1 degree C in slush and steam.

The plug prongs are indeed thicker than on my Omega plugs, but both fit the socket. They resolve to 1 degree C as in the specs, not 0.1 C like the Youtube video.The price jumped from $6.99 shortly after I bought mine.

It's really difficult to make good enough thermal contact to get an accurate reading from a surface. I put sheet copper probe clamps under the knobs of my pots and still see only about 195F at boiling, with a thermocouple that reads 212.1 F inside the boiling teapot. jsw

Maybe you could rig up a rubber-tipped air nozzle tee'd with a low-pressure tire gauge to measure the relief setting. jsw

Good advice. I'd add a tension spring to the binding wire to allow for thermal expansion and shifting from handling. jsw

How much to replace the pressure related parts?

Why not measure the temperature of the outside? That is pretty much regulated by the fluid inside it. Do you have one of the hand-held IR thermometers?

Are you sure about that last figure? :-) I think that should be about 127 C. 260C in a pressure cooker is *scary*. :-)

Is the regulator replaceable? I would suggest swapping out the regulator -- or testing it with compressed air a gauge and a regulator.

Good Luck, DoN.

It's hard to measure pressure without refitting (and causing safety concerns). One could use a temperature-indicating device (there are disposable test strips that could be put into a jar and cooked in normal fashion, that would read out the highest temperature attained).

Or, you could try to measure the surface of the pot (put a dot of black paint onto the pot, and read it with an IR thermometer, if you don't mind the sticker shock on a Fluke 62). A bit of glue and some insulation from the air, and maybe you could make the same measurement with a thermocouple.

The easiest way is a thermocouple inside the cooker, which leads to the problem of getting the thermocouple leads from inside to outside.

One can get very thin thermocouple wire, thin enough that one can just put it under the normal pressure seal, and ignore the slight steam leak where the cooker main seal (some kind of rubber) doesn't quite conform to the wire. Only thing to be careful of is that the wires doesn't short to the cooker metal. Kapton tape will do the job.

One can also thread the wire right through the seal rubber with a hypodermic needle, removing the needle after the wire is through.

When done, just cut the wire on one side, and slowly pull it out of the seal, which will seal the hole.

Joe Gwinn

The wire that comes with the readout I mentioned is thin and flexible, but its braided fiberglass insulation wouldn't pass easily through a needle hole in the gasket. It might work under the gasket if gooped with RTV. jsw

Look around on the Omega.com website. One can get other insulations, like teflon and I think kapton.

Joe Gwinn

Omega sells good wire. The 30 AWG type J I bought recently reads 212.1 F in boiling water.

I prefer the PFA (TT-) insulation within its limits, fiberglass (GG-) above. Wood stove gasket cement stabilizes the cut end of the braid.

I made an electrically isolated metal probe by winding fiberglas yarn around the end, dipping it in gasket cement and stuffing it into a

Navigating Omega's site can be confusing. Here is wire:

You need acetylene to weld the junction, a good reason to use the probe that came with the display. Propane doesn't even reach the top limit of the operating range. I've welded both ends of all my spools of wire. jsw

While acetylene does work, it isn't required.

I always used a 100-watt 110-volt incandescent lamp and a carbon rod, connected to 110 volts. Twist the two wires together, heat, dip in borax. Connect the wires to the hot side of 110 vac through the lightbulb. Connect the carbon rod to neutral. Touch the wire to the rod, then pull back, drawing an arc. The wires will weld into a nice little nugget. Heat and dip into water to remove the fused borax.

I learned this trick in the 1970s, where the university still distributed 110 volts DC, and this trick was used for such things as welding platinum tube ends closed. As I recall, the tube was positive and the rod was negative, so most of the heat went into the tube end.

Joe Gwinn

Thanks, that sounds like a good and inexpensive alternative.

I'm perhaps overly cautious about the safety aspects of what I suggest to strangers on the Internet. That's why I often mention general possibilities and keywords but leave the details to Google.

jsw

Neat!

What's the (ball park) resistance of the TC wire? I'm thinking about how much current will be flowing through them. The lamp limits it to an amp, but I'm thinking that's a bit much. Of course, it will only be briefly, but ...

Bob

The 1 meter Type K probe that came with the TM-902C measures 3 Ohms, with both 0.25mm wires in parallel. jsw

I don't recall that any grad students were fried, but they're expendable.

One can also use a lab power supply, if it's big enough and will do constant current into a short.

By the way, one can also soft or hard solder the wires together. The accuracy is very slightly reduced, and welds hold up better at high temperatures, but for 100 C this will work just fine.

Why does this work? Because if one has three kinds of wire in series, say chromel, copper, alumel, and the copper part and its two junctions are all at the same temperature, the net result is as if the copper link were not there and the chromel was welded directly to the alumel.

Joe Gwinn

Segway had a capacitive discharge spotwelder for attaching tabs to batteries that could join thermocouple wires, but I just liked playing with acetylene better. jsw