- Jan 16, 2018 at 4:11 pm #3512746
Why boil water if you don’t need to? And if I want to pasteurize my water instead, how can I know I’ve done it right?
I’ve always been bugged about having to boil my water, because it’s not necessary to make water safe to drink and since fuel usage is more or less proportional to the temperature delta, I saw significant savings to be had there.
Up until now I had not seen a WAPI I liked enough and could justify bringing backpacking. It had to be ultralight, foolproof and reliable, preserve system efficiency and react quickly.
The well known beeswax in a tube with two washers indicator is tricky to build small enough to be ultralight and still requires lifting the lid to get a reading, plus the wax melting process is slow.
The use of thermochromic pigments could be better from a reaction time perspective, but you still have to lift the lid if it’s a floating indicator. Maybe it could be integrated into the paint of the pot, but that’s too involved for a diy project and I’m not sure how it would be affected by the termal conductivity of the pot or the variability of the outside environment.
Enters Nitinol! A memory shape alloy with a given activation temperature depending on chemistry. I feel I was able to build something that meets all my criteria with this, and it weight less than a gram.
Here’s the demonstration:
NiTi wire WAPI videoJan 16, 2018 at 7:16 pm #3512769
Rene RavenelBPL Member
Looks like the wire needs to be at least long enough to reach the edge of the bottom of the pot? And you wrapped the wire through 2 holes in the plastic stoppers so it would stay put even when it tries to straighten?
Just to get the spec’s in the thread, I see you used 0.5mm nitinol wire w/ an activation temperature of 70C (+/- 10C). Nexmetal currently offers this on Amazon for $2.50/ft. That error on the activation temperature suggests you should calibrate this with a thermometer before relying on it.Jan 16, 2018 at 7:42 pm #3512771
Yes, my crude implementation needs the wire to reach the corner of the pot when extended because the hole in the lid is too large. The force exerted by NiTi wire is quite impressive for its weight so one could design a small sleeve in the lid to make it pop straight up, but that’s only cosmetic.
The second disk has 3 holes and I threaded the wire down-up-down. I Would have liked to get small red beads epoxied in place instead for something cleaner, but all I had was silicone sheet scraps to play with and I was too eager to test the concept.
I’m really happy how well this works. You could actually just carry a small lenght, twist it and throw it in a pot to keep things simple. NiTi also seems safe, reportedly leaching nickel less then stainless steel. It is also used in stents.
The activation temperature error is no big deal as you can account for that in your holding time, but you are right it’s important to validate it. Once that is done though, it’s reliable.Jan 16, 2018 at 10:08 pm #3512795
Dean F.BPL Member
@acrosomeLocale: Back in the Front Range
I’m always amused by the people that insist that you have to boil water “for five minutes” to pasteurize it. I always tell them that if you just reach a boil- at any realistic elevation- you’re good. But they don’t believe me. :)Jan 16, 2018 at 10:24 pm #3512800
I like the clever, tech, geeky idea
Although you can just do it by ear. It starts getting noisy before it boils, use a thermometer to calibrate your ear. Your solution would be more accurate though.
If you bring water to boiling it instantly kills bugs. If you bring it up to 180 or something, you have to let it sit for a minute or so before bugs are killed. Anyone know some real numbers to kill Giardia, Crypto, E-Coli?Jan 17, 2018 at 12:08 am #3512821
Rene RavenelBPL Member
Wikipedia on pasturization confirms the 15 seconds at 70C metric, but it’s clear that this is intended for food born pathogens which including E. Coli, but makes no mention of Giardia or Cryptosporidium.
The CDC advises boiling for one minute below 6,500′ or 3 minutes above. https://www.cdc.gov/healthywater/emergency/drinking/making-water-safe.html
I use an inline filter on a hydration bladder, so I don’t actually need any sanitization; my personal interest in this is just a ‘hot enough’ indicator, which I suppose my ears could do as well. It’d be super cool if this could be rigged to turn off the stove.Jan 17, 2018 at 12:53 am #3512830
70 C = 160 F
E Coli is something you might encounter in the wilderness, so that’s useful
I filter about half my water, the other half that I boil anyway, I don’t filter
Rehydrating – bring water to full boil so it rehydrates better
instant coffee – 160 F would be fine
black tea – should be 195 F or so, and then brew for 5 minutes, so that should be fineJan 17, 2018 at 12:54 am #3512831
Seems like the hardest to kill is giardia. I feel safe with 75C and letting it sit in a cozy until it’s actually cold enough to drink.Jan 17, 2018 at 6:22 am #3512881
Rex SandersBPL Member
@rexLocale: Central California Coast
Clever! Unlike most WAPIs, no need to lift the lid to judge progress, saving even more fuel.
FYI: Pasteurization and WAPIs, we’ve been over much of this topic before:
Martin: Thanks for the WHO reference, good summary.
— RexJan 17, 2018 at 3:41 pm #3512893
WHO – that’s pretty authoritative, thanks
72 C (162 F) for 15 seconds to kill Crypto
You must be logged in to reply to this topic.