Question about pressure cooker "jiggler weights"

  • #1
Old style pressure cookers regulated pressure by having a vent tube in the lid with a weighted stopper that sits atop it, known as a jiggle or jiggler weight. The jiggler weight seals the vent tube until enough pressure builds to move the weight, which releases pressure until the weight falls back into a sealing position. Some of them included multiple jiggler weights, such as one for 5, 10, and 15 PSI regulation. The lighter the weight, the lower the PSI regulation.

My question is: what is the relationship between weight and pressure? Is it a simple linear relationship, i.e., twice the weight = twice the pressure required to move the weight? For example, if a 1.5 oz. jiggler weight regulates the pressure at 5 PSI, how heavy would it have to be to regulate the pressure at 10 and 15 PSI?
 

Answers and Replies

  • #2
CWatters
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Yes. Pressure = Force / area

Force is provided by the weight and area is the area of the vent tube.

For example, if a 1.5 oz. jiggler weight regulates the pressure at 5 PSI, how heavy would it have to be to regulate the pressure at 10 and 15 PSI?

1.5oz = 5 PSI
3oz = 10 PSI
4.5oz = 15 PSI

However there should be a safety valve somewhere in case too much weigh is applied or the weight becomes jammed in the vent tube. If there isn't a safety valve don't use it!
 
  • #3
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If you are thinking about pressure and what steam temperature you might have, don't forget that you are talking gauge pressure, not absolute pressure. With no weight the pressure is atmospheric (14.69 psi at sea level) and if you double the weight from 1.5 to 3, the pressure increases from 19.69 psia to 24.69 psia. For safety, gauge pressure is the right stuff. For cooking and temperature control, absolute pressure is the right stuff.
 
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  • #4
Thanks for the helpful replies and the advice.
 
  • #5
garrymcgaw
Do things take longer to cook if you use a 1.5 oz jiggler compared to using a 3 oz one?, same size pot.
 
  • #6
jbriggs444
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Do things take longer to cook if you use a 1.5 oz jiggler compared to using a 3 oz one?, same size pot.
Yes. The temperature of boiling water at the lower pressure is lower and that at the higher pressure is higher.
 
  • #7
With all due respect, My question is why would a jigler have multiple weight markings on the same jigler when the weight is the same no matter which hole you use. Ten, 15 or 5 lb.
 
  • #8
If you are thinking about pressure and what steam temperature you might have, don't forget that you are talking gauge pressure, not absolute pressure. With no weight the pressure is atmospheric (14.69 psi at sea level) and if you double the weight from 1.5 to 3, the pressure increases from 19.69 psia to 24.69 psia. For safety, gauge pressure is the right stuff. For cooking and temperature control, absolute pressure is the right stuff.
Unfortunately, the jigler on my pressure cooker and nearly every one I have ever seen has multiple weights markings on the same jigler. 5, 10 and 15 lbs. The holes are the same size and no matter which hole I use, the weight of the jigler is absolutely the same because IT'S THE SAME JIGLER.
That means at least two of the holes are simply a lie.
 
  • #9
jrmichler
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Same jiggler weight, different pressure area. Photo of multi pressure jiggler and pressure cooker vent pipe from Amazon:

Jiggler Weight.jpg

Cross section of the vent pipe with weight on it (not to scale):
Jiggler.jpg

The top of the vent pipe is cone shaped. The multi pressure jiggler weight has three different diameter seats, marked DIM in the sketch. The largest diameter seat has the lowest pressure, the smallest diameter seat has the highest pressure. Same weight, different area equals different pressure.
 
  • #10
sophiecentaur
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That means at least two of the holes are simply a lie.
That's always a possibility but I suggest that you have not measured the relevant area where the pressure actually applies. There are so many cookers like that and they do work.
If you are thinking about pressure and what steam temperature you might have, don't forget that you are talking gauge pressure, not absolute pressure.
Perhaps that just needs to be made clearer. Absolute pressure is what governs the boiling point of the water. A mechanism for controlling the pressure in the chamber may or may not be affected by external air pressure but a simple weight will be affected.
The maximum pressure that you can expect inside a domestic pressure cooker won't be much more than 2Bar and that gives a cooking temperature of about 120C. Expected variations in ambient pressure are only about 5% so you could expect that sort of error in cooking temperature. Thankfully (for cooks), that's not much.
 

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