Gunner Quinn
(Continued from Part 1.)
I took the pressure cooker back into the house and washed and checked everything again.
Pressure cooker knocked over in use – Next, I wanted to know if a pressure cooker got tipped over or knocked off the stove, what would happen? I was expecting a steam release, but how much? I set up the stove and pressure cooker on a stump in my north 40. This time I just used water. I placed an old sleeping bag next to the stump to avoid damage to the pressure cooker when I pushed it over after attaining full boil.
I fired up the stove and once the cap was rocking, took a 10’ piece of PVC and pushed the pressure cooker over. I repeated it three times. The first time the cooker landed upside down resting on its steam vent, and the other two times on its side. In none of the cases did the cap fall off. The one which landed upside down had a muffled release, the steam vent was mostly blocked by the sleeping bag so the steam came out slowly. When it fell on its side the steam release was similar to the first two small blasts in Experiment #2. The cap didn’t fall off either time and even though the steam was released quickly, it wasn’t getting a lot of distance before moving upwards in the air and dissipating. It wasn’t as loud as I was expecting.
Later, I realized I should have kept the variables the same so I redid the experiment using chili and chopped canned carrots for another added food texture. The pressure cooker was disabled in experiment #4 so I had to use one of my good stainless-steel pressure cookers to repeat this experiment. With the pressure cooker on its side after falling off the stump, I expected chili and carrots to clog the steam vent tube and slow down the steam release as it had in Experiment #2, as if a valve were being turned off.
I redid the experiment with the same results, once it landed upside down, twice on its side. But surprisingly, the amount of the steam release was the same and nothing resembling a valve shutoff occurred.
Does the safety plug work? The last thing I wanted to test was how well the safety plug worked and what it looks like when the safety plug blows out. How long does it take for the pressure cooker to get to that point once the steam vent clogs?
I washed and cleaned the aluminum pressure cooker again, then added chili and carrots. Using a 4d nail wrapped in high-temperature plumbing tape, I plugged the steam-escape hole. I put a brick on the nail to keep the plug in, then lit the stove and backed up 20 feet.
I watched for the metal button to pop up indicating it was getting close to full pressure, then I expected the plug to blow shortly thereafter. The metal button popped up, but it took longer than I expected to see the steam blast, perhaps ten minutes. Finally, I heard a loud sound like an air compressor with the dust-blowing nozzle in use. There was a huge flash of steam before the pressure cooker headed due north, tumbling down a slight slope. It stopped 17’ away.
The Results
1. Constant burner on high under full pressure – nothing dangerous occurred when the burner was kept on high. The weighted cap didn’t blow off or tilt. The owner’s manual suggests turning the heat down once the cap begins rocking but as I discovered, it’s not for safety reasons. Keeping it on high can cause too much water to evaporate and burn the food as well as potentially warp an aluminum pressure cooker. With quick-cook foods like beans, this can’t happen if the recommended time and water level are used. On the other hand, my pulled pork with its 90-minute cook time would have problems if too much water boiled off.
2. Cap suddenly off – With my jury-rigged bailing twine I wasn’t able to get the cap to come off in a single pull so I didn’t get to see a geyser under full pressure. By the third pull when the cap finally came off, enough pressure had already been released so the geyser wasn’t as substantial as I was expecting. It was very peculiar however when the geyser stopped suddenly. When cleaning the pot afterwards, I discovered a tiny piece of bean skin from the chili had risen with the rapidly-vaporizing water and clogged the steam tube almost entirely. The skin was soft so it was a big surprise to see that something that small and soft under pressure could clog the hole and stop 98% of the remaining steam from escaping quickly.
With more tests to try to get the cap off under full pressure, it was catching on something and not lifting straight up without a lot of jiggling. I discovered another built-in safety feature.
On the underside of the weighted cap is a ½” deep hole in the center to keep the cap in place over the steam vent. At the edge of the hole are four small tabs and the steam vent tube has a head on it. If the cap gets bumped the tabs catch on the neck of the tube to keep the cap in place. If bumped hard enough, there will be a controlled steam release on one side but the cap should stay on in most situations. Since the steam is only coming out of one side, a hot pad or dish towel can be used to push the cap back into place.
3. Pot falling over – As in experiment #2, because of the tabs on the underside of the cap I wasn’t able to get the cap to come off when each pressure cooker tipped over three times. If the pot fell from a higher distance like a stovetop, the cap could possibly fall off sometimes when it hits the hard floor but it’s far more likely to tilt to one side as the tabs catch and keep it on. Since the cook who knocks a pressure cooker off the stove would be standing right there, even if the cap stayed on the steam release could potentially cause burns depending how quickly the cook could jump back out of the way. As with bumping the cap, I can’t imagine an actual scenario where I could knock a pressure cooker off the stove. My larger cooker has two handles that only stick out 2¼”, weights 7 lbs empty, and averages 12 lbs when food is inside cooking. My smaller one has a 6” handle but as an extra precaution, I keep it on the back burner with the handle turned to one side so it can’t be bumped.
What puzzled me when I repeated experiment #3 was why the steam vent on the stainless steel pressure cooker didn’t clog as expected. Food was almost certainly up against the vent after the cooker hit the ground so why wasn’t it clogging?
While cleaning the steel pressure-cooker pot before repeating the experiment, I noticed a difference between the two cooker lids. The steam vents underneath the cap on both cookers were identical: ¾” tall with a ¼” wide head on top and a 1/16th inch wide hole through the center of the tube. The bottom end of each steam-vent tube was very different though. On the aluminum lid it is only 1/8th inch long with a single hole. On the stainless-steel lid it’s 5/8th inch long, ½” wide and hexagonal shaped, with each of the six sides having a hole. The bottom of the tube also has a hole. With seven holes facing seven different directions it’s much less likely that food particles would completely clog the steam vent. When I examined the cooker after the first run of the experiment, I saw that three of the holes had slivers of carrots in them but the other four were still clear, allowing the steam to escape.
While not much help if the pot falls over, this type of steam vent is a huge overall benefit. In a pressure cooker with a blowout plug as the only safety mechanism, a hard-to-clog seven-holed steam vent would greatly reduce the chances of a blowout occurring.
4. Safety plug – In experiment #4 I wanted to know what it looked like when the safety plug blows. As mentioned, with today’s safety features the most dangerous thing that can happen with a pressure cooker is for the blowout plug to do its job, potentially causing 1st-degree and 2nd-degree burns if the user is close enough to the resulting geyser when the plug blows. Pressure cookers which have a safety valve are much safer since there’s no blowout plug and the excess steam is released more slowly in a very controlled manner.
In this last experiment with the aluminum pressure cooker, when the plug blew I expected the resulting geyser to go straight up in the air and for the pot to remain more or less stable, or possibly fall off the stump. As I watched the steam blast send the pot tumbling and stopping 17’ away I knew it wasn’t the right kind of motion a safety plug blowing out would cause. When I picked the pressure cooker up, I saw that two inches of the gasket had blown out from under the lid. The large steam release on the south edge of the pot it what sent it north. As they say, for every action there’s an equal and opposite reaction.
Why did the lid gasket blow instead of the blowout safety plug? Like so many other equipment failures in life, human error had caused the problem. There are two issues that should never be overlooked when using a pressure cooker in the kitchen. Because I was experimenting, outdoors, and standing back out of the way, the faulty gasket was used anyway in the name of research.
(To be concluded tomorrow, in Part 3.)
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