This is an idea for checking pressure canner gauges at home. It seems to work for me and I give it the “if it breaks into pieces, you get to keep all of the pieces” guarantee. In other words, use this for ideas, use your best judgement and don’t blame me if it doesn’t work for you.
Normally I’d just take the canner to the local USDA Extension Service office to get the gauge checked, but the office is closed because of Covid…so no gauge checks.
The last time I did have the gauge officially checked, checks were done at 5, 10 and 15 psi and if those readings were correct, the intermediate values were presumed to be correct. The person doing the tests also told me that the gauge should be replaced if the readings were incorrect by by more than 1/2 psi.
If you can get the gauge checked officially do that. Or, better yet, convert the canner to a “jiggle weight” pressure regulating system The jiggle weight replaces the gauge and needs no yearly check.
Yet another advantage of the jiggle weight is that the temperature control is much less critical and instead of having to continually watch the gauge, you can listen to the hissing of the weight while doing other things nearby.
Anyway, in a prior post, Pressure Canner Gauge Check. Part 1. I talked about making a manometer and about different methods of reducing the height of the manometer so I wouldn’t need such a tall structure to make the 15psi measurement.
Well, a friend loaned me a 40 foot tall “push up mast” that (before satellite television) was used to hold up the large television antennas and this gave me an idea to just make a “well manometer”. This is one that just uses one piece tubing going straight up, instead of a U shape. This saves a lot of tubing as I only need 35 feet, instead of three times the 35 feet amount–35 foot on each side of the U, plus another 35 feet to get the top of the U back to the bottom.
If you have a tall enough tree, you could use the tree instead of a pole, but you will need to ensure the tube goes “straight up”. In any event, it’s the height that’s important, not how things are supported.
I dug around in my bucket of brass plumbing fittings and came up with enough stuff to “give it a try”. Basically it’s a T-fitting with one end connected to the water supply, another end connected to the vent pipe on the canner and the third side connected to the tubing that extends up the pole.
In the picture, the water hose is obvious. the tube going up the pole is on the right hand side of the T and the hose going to the canner vent pipe goes from the left side of the T. I used that small valve on the water hose side of the T to control the water flow from the water hose and it made things a lot easier for me.
I have a Presto canner and a 1/4 inch ID tube fits perfectly over the vent pipe, so I matched the tube fitting on the T to that size.
I currently didn’t have any way to secure a 40 foot pole so I tried this as a proof of concept by using a 15 foot tree trimming pole. I used electrical tape to secure the top of the tubing and the tape measure near at the top of the pole and also at intermediate points on the pole. It doesn’t look it in the picture, but the pole is vertical…I used a level to check. Later I’ll mention why it’s “moderately important” to have the pole (and tube and measuring tape) as close as possible to vertical.
So, once everything was hooked up, what I did was to start the water flow, very slowly, so that the pressure in the canner began to slowly rise. At the same time, water also was flowing into the elevated tube. When the pressure gauge began to register and water began to flow out of the top of the elevated tube, I slowed the flow of the water so only a slight trickle was flowing out of the top of the tube. The slower the water flow, the better and just a few drips per minute from the top of the tube is great. If you can turn off the water flow and the pressure settles to a constant value, that’s even better as the water flow won’t cause an error…and it is a good test of the canner gasket.
When the water was merely a trickle from the top of the tube, I measured the distance between the top of the canner and the top of the water tube…13 feet.
Note that this is a surveyor’s tape and instead of the feet being divided into inches, the divisions are tenths and hundredths of a foot.
Note how I said “top of the canner”. This is important.
It turns out that 1psi will push water up 2.31 feet. More formally this 2.31 figure is for distilled water at 39F degrees, but tap water at temperatures comfortable to humans wearing light clothes is so close to 2.31 feet per psi that it doesn’t change anything enough to matter.
So, to get the pressure. In this case, a 13 foot tall column of water, at 2.31 psi per foot, I divide 13 by 2.31, which is 5.6psi. It’s hard to tell because of the the camera was not directly in front of the gauge, but the gauge needle was slightly closer to the 6 mark than the 5 mark on the outer scale, which is right where it should be. So, the gauge is accurate at 5psi.
When I figure out how to get a taller system, I can check the gauge at 10 and 15 psi.
Now, I need to figure out how to get the tube 35 feet in the air. What I plan on doing is calculating the heights i need for 5, 10 and 15 psi and using a string and pulley to raise the tape measure and tube to the correct heights and then letting the water trickle out the top of the tube. I thought about putting the tube at full height and measuring how high the water is pushed up the tube, but it is hard to see clear water in a clear tube from that far away. So, instead I plan on the “trickle out the top” method. As long as I keep the water flow to the absolute bare minimum, it will be fine.
The heights are 11.55 feet (11 feet, 6 5/8 inches) for 5psi, 23.1 feet (23 feet, 1 1/4 inches) for 10 psi and 34.65 feet (34 feet, 7 3/4 inches) for 15 psi.
The amount of tubing on the ground doesn’t matter as the manometer only “cares” about water above the height of the canner. So, it’s OK to have a lot of tubing laying on the ground.
The diameter of the tubing doesn’t matter. A larger diameter tube has more water, which weighs more, but the water is spread out over more square inches. The math works out that no matter how large the tube diameter is, it is always the case where each psi of pressure will push the water up 2.31 feet. It also works out that the tube varying in size along it’s length will have no effect…the 2.31 foot value is the same. This 2.31 value for water is for earth, but I doubt that will be a limitation. 🙂
Since errors in pressure for a canner can have dire consequences, some thought as to the various errors is worth while. Also, keep in mind the gauge is considered “OK” if the gauge error is less than 0.5psi.
The 2.31 foot per psi value is for distilled water at 39F degrees. Changing temperature from just above freezing to around 100F degrees would cause a 0.1 psi error. In this case, the error at 100F would be “gauge reads lower than the calculated manometer pressure”, so if the manometer calculation says 15psi, a perfect gauge would show 14.9 psi.
Tap water is not distilled water and and this can mess with the accuracy of the measurements, but it turns out that if the water tastes OK, the worst the error would be is a few thousandths of a psi (0.001 psi), so tap versus distilled water errors are not worth worrying about.
Another potential error is gravity being different from “standard”, but you don’t have any control over that. On Earth, the lowest value for gravity is atop a mountain in Peru and the highest value for gravity is on the oceans around Antarctica. But even at those extremes the error for a 15psi reading is around 0.06psi, so again, this isn’t an issue..
Another source of error is if the “uphill” tube is not vertical, so use a level to ensure the support pole is vertical. You can see what happens if you were tip the pole sideways…you can see that the pole length not the same as the height of the tip of the pole. At it’s most extreme, the pole laying on the ground, the pole tip height is zero, but the pole is still its full length. If the tip of the pole is “off of straight up” by a few inches, the pressure error will be less than 0.1psi, so pretty close to straight up and down is OK.
Yet another error is making a mistake in the height measurement. Even a foot error will only cause a 0.5 psi error and I’m quite certain the measurement can be made within an inch or so with no issue. A one foot error is “worth” about 1/2 psi error and a inch is 1/12 of that, so one inch works out to be about 0.04psi of error. This error can creep in if the tape measure and tube are not kept together, but again, even a slight imperfection does not cause a huge error.
The final source of error is letting the water flow too quickly. This is the biggest source of error and is the one that is most easily controlled, so go slow and if possible, stop the flow of water and let things “settle” before deciding if the gauge is correct at the desired pressure. I had a tiny bit of leakage around the safety plug on the caner, so I could not completely stop the flow of water, but I was able to slow the water flow to where only a drop or two of water per minute was coming down the pole.
If you’re careful, you should be able to check a canner gauge to ensure safe canning. But again, I’m not “there”, so I can’t tell if you’re making mistakes…so be careful.
is i. If you’re an engineer, it would be j to avoid confusing electrical engineers with imaginary numbers and current. 
is 8.
, is the summation symbol.
is the number called “pi”. 