Question about pressure cooker "jiggler weights"

[MaximRecoil]

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?

 

[CWatters]

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!

 

[betadave]

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.

 

[MaximRecoil]

Thanks for the helpful replies and the advice.

 

[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.

 

[jbriggs444]

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.

 

[polyglot12]

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.

 

[polyglot12]

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.

 

[jrmichler]

Same jiggler weight, different pressure area. Photo of multi pressure jiggler and pressure cooker vent pipe from Amazon:

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

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.

 

[sophiecentaur]

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.

 

[afrasiab]

It means jiggler holes have diffrent area for specified pressure? Vent pipe dia is same in all cases...can some one explain P=F/A with refrence to pressure jiggler weight...

 

[sophiecentaur]

I thought they use different weights. Much easier to implement.

 

[sophiecentaur]

explain P=F/A with refrence to pressure jiggler weight...

The name "jiggler" is a clue to the detail of its operation. If you used a piston with a given force on it then the F would be constant and (I think) you'd have no problem. But a jiggler isn't stationary; it oscillates up and down about a mean position where the average area and the average force set the average pressure. If you had some sort of braking / damping mechanism to suppress the movement, the area wouldn't change and everything would be steady. (No need for that and just another thing to go wrong.)
I imagine that the profile of the pin could reduce or accentuate the jiggle and a good design would be less rattly. Otoh, you could use the same idea to produce wild oscillations if you wanted to - not in the kitchen though.

 

[afrasiab]

Thanks for the reply... but i still have some confusion. Force that is acting on jiggler, here 30lbs ( absoulute pressure, right?).
Is jggler having 3oz weight is countering that much force?? I am confusing to link jiggler weight ( unit in pounds ) with pressure ( unit in pounds per sq inch). How that simple eq ( P= F/A) relates with weight of jiggler.

 

[sophiecentaur]

What’s the area of the hole? That’s the area that counts. 4mm square ish? Small A small F.

 

[jbriggs444]

Thanks for the reply... but i still have some confusion. Force that is acting on jiggler, here 30lbs ( absoulute pressure, right?).

Looking upthread, I see 2 atmospheres quoted for 120 Celsius. Looking at a steam table, I see 120 C as 1 atmosphere, gauge. So yes, 30 PSI would be absolute.

Of course, the top of the jiggler is under ambient pressure, so the net force relevant for the jiggler is gauge pressure. 15 PSI instead.

Is jggler having 3oz weight is countering that much force??

A 3 ounce weight on a surface area of 1/75 of a square inch would counter it handily.

 

[afrasiab]

Thanks to all who tried to explain the concept.

 

[sophiecentaur]

Thanks for the reply... but i still have some confusion. Force that is acting on jiggler, here 30lbs ( absoulute pressure, right?).
Is jggler having 3oz weight is countering that much force?? I am confusing to link jiggler weight ( unit in pounds ) with pressure ( unit in pounds per sq inch). How that simple eq ( P= F/A) relates with weight of jiggler.

Ah yes. The juggler produces excess pressure over ambient. 100C boiling point corresponds to NO jiggler in place. Sorry I took that for granted.

 

[afrasiab]

P= F/A...A constant ( vent pipe area)...while F is also constant ( F equals jiggler weight, here in cooker case ) ..only p changing with respect to heat under cooker. When P reaches 5 lbs, 1.5oz jiggler will counter this much pressure. When P reaches 10lbs 3oz jiggler weight will counter that presure. When P reaches 15lbs pressure 4.5oz jiggler weight will counter that force.What happens to temprature in side ? it will reach 130C at 30lbs pressure. From my previous threads i learn this. If some mistake please explain that with refrence to cooker.

 

[Nugatory]

I thought they use different weights. Much easier to implement.

However, one weight with three differently machined openings is a much more useful product - only one thing to misplace instead of three and the one thing is always in use so less likely to go missing.

 

[Nugatory]

P= F/A...A constant ( vent pipe area)...while F is also constant ( F equals jiggler weight, here in cooker case ) ..only p changing with respect to heat under cooker.

Look at the diagram by @jrmichler in #9 of this thread. The relevant A is not the area of the vent pipe opening, it is the area of the jiggler that is subject to the pressure (because it’s the jiggler that is being pushed around) and that is determined by the geometry of the hole machined in the jiggled.

 

[sophiecentaur]

However, one weight with three differently machined openings is a much more useful product - only one thing to misplace instead of three and the one thing is always in use so less likely to go missing.

That could make sense. But the images, where they actually show the jiggler, seem to suggest multiple weights. Something else to lose at the back of the junk drawer in the kitchen.

 

[Nugatory]

That could make sense. But the images, where they actually show the jiggler, seem to suggest multiple weights. Something else to lose at the back of the junk drawer in the kitchen.
View attachment 295871

Whereas the only ones I’ve seen are of the one-weight three-hole design. I expect both styles are in use, wouldn’t be surprised to find it matters which continent we’re on, and might even be a side effect of some decades old patent.

 

[sophiecentaur]

Whereas the only ones I’ve seen are of the one-weight three-hole design. I expect both styles are in use, wouldn’t be surprised to find it matters which continent we’re on, and might even be a side effect of some decades old patent.

Do you have an image? Bearing in mind that the weight needs to be long, for stability. I couldn't figure a way to drill multiple holes but there again, a number of holes could actually cross each other inside the weight .

To be honest, I've never used a pressure cooker and a microwave oven cooks very rapidly without needing a high temperature on the surface of the food. But they must have their uses; my son has just bought one and they love it.

 

[Nugatory]

Do you have an image?

I don't, but #9 in this thread has a photo of a three-hole weight They're quite stable because they only lift a few millimeters each burp, not enough to lift off the the vent tube.

 

[afrasiab]

Look at the diagram by @jrmichler in #9 of this thread. The relevant A is not the area of the vent pipe opening, it is the area of the jiggler that is subject to the pressure (because it’s the jiggler that is being pushed around) and that is determined by the geometry of the hole machined in the jiggled.

Yes,it jiggler seat area but that must be equal to vent pipe area to enshure proper seal... am i right?

 

[afrasiab]

I don't, but #9 in this thread has a photo of a three-hole weight They're quite stable because they only lift a few millimeters each burp, not enough to lift the off the the vent tube.

I don't, but #9 in this thread has a photo of a three-hole weight They're quite stable because they only lift a few millimeters each burp, not enough to lift the off the the v

Do you have an image? Bearing in mind that the weight needs to be long, for stability. I couldn't figure a way to drill multiple holes but there again, a number of holes could actually cross each other inside the weight .

To be honest, I've never used a pressure cooker and a microwave oven cooks very rapidly without needing a high temperature on the surface of the food. But they must have their uses; my son has just bought one and they love it.

In 3 hole single weight, i think area on which pressure will act will be diffrent, machined according to calculation.. i tried to google its crosection pic but can't found. If some can share its x-section image disscusion will close at all.

 

[Nugatory]

Yes,it jiggler seat area but that must be equal to vent pipe area to enshure proper seal... am i right?

Not right - look at the diagram again, and the accompanying photo ofthe vent tube. The bottom of the machined cavity in the jiggler sits on the cone of the vent tube and seals no matter the shape and dimensions of the cavity above. So the cavity is at the same pressure as the interior of the cooker, and the upwards force on the jiggler depends on the area of the upper face of the cavity.

 

[sophiecentaur]

I don't, but #9 in this thread has a photo of a three-hole weight

I couldn't make much sense of the figure because 1. The static part of the valve seems to be shown upside down
and 2. the sketch makes little sense as it suggests the weight is perched right on top of the device (the convex curve that's been drawn). In fact the 'shaft' of the fixed part must extend way up into the weight to keep it stable - not just against being blown off by the steam but from falling off if the pot is nudged and to limit any pitching motion, which could damage the seating.
It does make sense to me now. Either design is elegant in its lack of 'articulating parts' and springs. I imagine there's always a risk of food bits getting up into the jet and causing excess pressure. Hence the additional safety valve

 

[jrmichler]

Sketch of jiggler weight in Post #9 was sloppy, so redrawn to be a little better. The sketch shows only one of the three different pressure holes in the weight. Each of the three holes extend almost to the center of the weight, so the larger diameter portion of each hole guides the jiggler on the spout. Each of the three holes has a different minor diameter (DIM in the sketch), which sets the pressure for that hole. Smaller minor diameter equals higher pressure.

Normal cooking does not put food particles up against the hole in the spout. However, cooking the mash to make moonshine does make a foam that can block the hole. In that case, a foam trap is needed both to keep the still from exploding and for finished product quality.