I wonder if anyone can help. I'm keen to know what wax is used in thermostatic valves as I'm constructing an odour releasing system that releases smell at <20 C but not any higher. I figure that the expanding wax could be used to block the opening of the container.

I'm not hung-up on using wax, any other materials that fit the bill are greatly received, although anything with electronics is not suitable because the device needs to be v. cheap!

Many thanks in advance.
Ian

If you're using a wax that liquifies above 20 C, is the wax going to close off an opening that allows an odorant to come through? If so, does the device also need to reopen when the temperature drops below 20 C again? How do thermostatic valves work? Do they seal the wax inside a bellows assembly? Would a bimetalic element work better?

Yes, the odour would need to be released time&time again <20C, and close off >20C. The thermostatic valve works by the wax liquifying and consequently expanding which pushes on a button that closes off the water input to a radiator. So your bellows analagy is correct! My system needs to be deployed outside in the elements so I'm not sure a bi-metallic strip is up to it.
Thanks.
Ian

a simple light sensor circuit wit a theromometer blocking the light when it surpasses 20C wolud work

A bellows assembly with wax inside won't be cheap unless you're making a lot of them. Expect to pay $400 -$1000 (US) for a handful of prototypes. If you buy 100, the price may drop 10 fold. (I've priced bellows assemblies before.) I suspect if you're into mass production they can be relatively inexpensive though.

If you're doing wax, then your wax supplier should be able to provide you with the product that melts at a given temperature. I'd rely on them to provide the right stuff, it can't be that difficult. Go to Thomas Register and do a search on wax. See if this link works, if not go to Thomas Register and simply put in "wax".

Wax at Thomas Register (http://www.thomasregister.com/SearchHeading.aspx?search_string=wax&page=1&sid=0412190756523500007501LW8&uuid=TRGuest)

I seem to remember that thermostatic valves can be adjusted though, without changing the material. I'm not sure exactly how that works.

If you're not looking at mass production, then going this route will be way too expensive. I might suggest some alternitives if that's the case.

I wouldn't rule out bimetalic elements. They're used outdoors all the time (circuit breakers for example). Also, you may consider using something which changes from a liquid to a gas at a given temperature. They're used in valves all the time as well.

Most car radiator caps are wax filled thermo valves,but open a too high a temp for you. Try a bi-metal strip, they're cheap.