Sight glass calibration question

Hey guys,


I was calibrating my sight glass using the method that BobbyfromNJ on recommends on Youtube.

I noticed a discrapancy between volume and weight however. After pouring 4 cups of water 4 times into a larger container from a Pyrex measuring cup that the accumlated water weighed 8 lbs 4 oz when a gallon is supposed to weigh 8 lbs 5.6 oz. I used a digital kitchen scale and zeroed the scale with the empty pitcher on it first. I was also *very* careful and meticulous when pouring the water into the Pyrex and then into the larger pitcher, so I'm 99% my volume was correct, but which do I trust?

I know I'm prolly splitting hairs here, escpecially since it's only 1.6 oz we're talking about, but what should I trust more? The volume or the weight?

Cheers,



Nick

Pyrex measuring cups are known to be not very accurate. I used a 1 gal bucket that I filled from a flask that was calibrated.

Was it distilled water?

No, it was softened tap water.

The thing is, based on other sight glass on keggle examples I've seen online, I was worried that my marks on the sight glass might be too high, not too low. If I went with the weight as opposed to the volume they would get even higher.

JRems said:

Pyrex measuring cups are known to be not very accurate. I used a 1 gal bucket that I filled from a flask that was calibrated.

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Yeah, I was worried about that, but as a test I filled the Pyrex up to the 4 cup mark using a 1 cup measuring cup and it read perfectly.

The scale could be a little off too. Splitting the difference is probably a few drops more than your volume measurement or probably within the typical reading error anyway.

Bobby_M said:

The scale could be a little off too. Splitting the difference is probably a few drops more than your volume measurement or probably within the typical reading error anyway.

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Yeah, good point. I figured either way I'm darned close so I should be ok.

CanadianQuaffer said:

Hey guys,

I know I'm prolly splitting hairs here, escpecially since it's only 1.6 oz we're talking about, but what should I trust more? The volume or the weight?

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The discrepancy could also be due to temperature. The weight per given volume of water is measured at the temperature of water's greatest density, which is something like 34 degrees F, IIRC. That, and the slight inaccuracies in the markings on your pyrex measuring cup, and the vagueries in the scale weight measurement would probably account for what is going on.
Since measuring at the correct temp would be difficult, I would trust the volume more than the weight. You'll be quite close either way, though.

I dunno how different sanke kegs can be from one another, but my 3 gallon mark ended up being about 2-3/8" above the bottom weld line while the 15 gallon mark is 1/2" above the top weld line.

Is that a good reference to go buy in comparison to others or do different sanke kegs have subtle differences in their dimansions?

I would trust my scale more than I would trust my (L)eyeball. Any inaccuracy in measuring 4 cups is multiplied 4 times for each gallon. 132oz is 98.8% of 133.6oz.

I was looking through some others posts but still am not real sure on this. When calibrating do you do it with all your diptubes, pick ups and false bottms installed? I get that you would want to as without them it would change the reading and i think you would want to do it just like you would on a brew day??

PorterBoy said:

I was looking through some others posts but still am not real sure on this. When calibrating do you do it with all your diptubes, pick ups and false bottms installed? I get that you would want to as without them it would change the reading and i think you would want to do it just like you would on a brew day??

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Yeah, you definitely want everything in the kettle like it would be when you're actually using the sight glass.