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chinaman9
Secret Asian Man

Registered: 11/02/18
Posts: 63
Loc: 'Murica
Last seen: 12 hours, 53 minutes
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Re: High altitude cubes? [Re: teladi]
#25751547 - 01/18/19 02:04 PM (5 years, 11 days ago) |
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Quote:
teladi said: The guage just measures the relative pressure between inside and outside the PC.
Thank you! I did not know that. Now I fully understand!
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: High altitude cubes? [Re: chinaman9]
#25751844 - 01/18/19 04:22 PM (5 years, 10 days ago) |
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That's not true of pressure cooker pressure gauges. They make special ones that you can calibrate to zero called altitude psi/pressure gauges.
They're most often used to measure the height of water in a tank because regardless of volume and circumference the height of the water dictates the pressure at the bottom of the tank. Since you can set them to zero and then chart the pressure as a known volume of liquid fills the tank and chart it out to make a correlation.
If you imagine the one on a cooker which cannot be calibrated the internal pressure is 14.7 there's a diaphragm with the outside world. If the outside world is less than 14.7 the dial is trying to read less than 0 but it cannot because of the needle stop. Once pressure hits 14.7 cumulative it starts to move off of zero.
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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The inside of a geared gauge looks similar to this. Like an eardrum. The pressure inside the gauge is calibrated to sea level unless otherwise specified. The diaphragm is attached to a gear rack as it travels inwards it moves a gear attached to the dial. The needle stop prevents the diaphragm from being sucked outward in an environment of less than 14.7 psi to some degree. In enough of a pressure differential the gauge would pop open
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chinaman9
Secret Asian Man

Registered: 11/02/18
Posts: 63
Loc: 'Murica
Last seen: 12 hours, 53 minutes
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DAMN! Thanks bodhisatta!!! Great info! I love to learn new things! You the man!
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teladi
FUNKSOULBROTHER


Registered: 06/27/17
Posts: 1,189
Loc: South Africa
Last seen: 5 months, 21 days
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Quote:
bodhisatta said: That's not true of pressure cooker pressure gauges. They make special ones that you can calibrate to zero called altitude psi/pressure gauges.
They're most often used to measure the height of water in a tank because regardless of volume and circumference the height of the water dictates the pressure at the bottom of the tank. Since you can set them to zero and then chart the pressure as a known volume of liquid fills the tank and chart it out to make a correlation.
If you imagine the one on a cooker which cannot be calibrated the internal pressure is 14.7 there's a diaphragm with the outside world. If the outside world is less than 14.7 the dial is trying to read less than 0 but it cannot because of the needle stop. Once pressure hits 14.7 cumulative it starts to move off of zero.
It is true of most PC gauges.
Pressure inside versus pressure outside is indicated on the gauge. Gauge pressure is the pressure relative to atmospheric pressure. Diaphragm spring, force on diaphragm from outside, force on diaphragm from inside are added mechanically and displayed on the gauge.
The absolute pressure outside may be 14.7 psi absolute. It'll be 14.7 psi absolute before start of cooking. When the gauge hits 1 PSI, it'll be 15.7 PSI absolute inside and 14.7 PSI absolute. Relative/gauge pressure is 1 PSI.
There may well be fancier pressure gauges found on some PCs, but the simple ones found on most PCs measure relative or gauge pressure.
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: High altitude cubes? [Re: teladi]
#25753570 - 01/19/19 11:56 AM (5 years, 10 days ago) |
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Prestos and all american cookers use geared gauges.
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spuitzakje

Registered: 11/11/21
Posts: 30
Last seen: 12 hours, 52 minutes
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Re: High altitude cubes? [Re: bodhisatta]
#28535061 - 11/09/23 03:54 AM (2 months, 18 days ago) |
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Hey. Used the search function to understand how gauges on a PC work. Came across multiple topics on the subject. I still get confused tho. Here it says that the Presto PC is calibrated and in another topic the same guy says:
Quote:
It still takes longer at altitude even with a pressure cooker unless you go to a higher psi to make up for the less psi of the atmosphere. The two pressures get added together.
All American actually goes over that in their manuals. I do not think presto does.
So is the pressure on the gauge relative to the outside pressure or is it calibrated to sea level?
How about PC's that don't use a gauge like this one:
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bodhisatta 
Smurf real estate agent


Registered: 04/30/13
Posts: 61,889
Loc: Milky way
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Re: High altitude cubes? [Re: spuitzakje]
#28535073 - 11/09/23 04:29 AM (2 months, 18 days ago) |
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Relative to the difference between the inside and outside of the cooker.
If you're at 15 psi on your cookers gauge Then If you're at sea level it's 14.7+15 psi At altitude it's something less than 14.7 + 15psi
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rocky_raccoon
Not a number


Registered: 12/12/22
Posts: 94
Last seen: 5 days, 4 hours
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Re: High altitude cubes? [Re: bodhisatta]
#28535135 - 11/09/23 06:06 AM (2 months, 18 days ago) |
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Back to the initial question: Ecuadorians are said to be derived from a specimen found in the andes at over 1100 m altitude.
-------------------- Nothing in life is to be feared, it is only to be understood. -Marie Curie
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spuitzakje

Registered: 11/11/21
Posts: 30
Last seen: 12 hours, 52 minutes
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Re: High altitude cubes? [Re: bodhisatta]
#28535180 - 11/09/23 07:12 AM (2 months, 18 days ago) |
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How you mean relative to the difference between the inside and outside of the cooker? When the PC is not operating, the inside and outside difference is always the same, no?
Let's say I were at 6000ft altitude, would I have to bring the PC up to 15psi or more since I would be higher in altitude?
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PBJ710
Strangler


Registered: 07/05/19
Posts: 2,623
Last seen: 18 days, 6 hours
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Re: High altitude cubes? [Re: spuitzakje]
#28535248 - 11/09/23 08:28 AM (2 months, 18 days ago) |
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Higher altitudes mean you either have to use higher pressures or longer PC times to get the same effective sterilization as 15psi @ sea level. 6000' is about the equivalent of losing 2psi of pressure.
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