WAPI production

Below is detailed information about buying and/or making Water Pasteurization Indicators (WAPIs).

Purchasing WAPIs from Solar Cookers International

WAPIs can be purchased from Solar Cookers International (SCI) in any quantity (online order form).

The advantages of buying WAPIs from SCI are:

1. You will receive the wholesale price--$3.00 each for quantities over 25. It would be hard for you to make them yourself for a lower unit cost.
2. If you make them yourself you run into quality control issues. Here is how Bob Metcalf handles quality control on the ones he makes. After he makes them, he puts them into hot water so that the wax melts and runs into the bottom of the tube. Then he inspects them visually for any holes in the tube and for the other indicator of a problem: water inside the tube. Then he repeats the process a second time. You can melt the wax of a batch of WAPIs at one time, rather than heating one individually. When heating them in water, watch for wax coming to the surface of the hot water. That will be a sign that one or more of the WAPIs in that batch definitely are leaking. Whether or not you see wax on the surface of the water, each and every WAPI should be visually inspected after both of the hot water tests. Any WAPI that shows any sign of leakage is thrown away in a place where it will be sure not to get mixed up with the good WAPIs. Bob says he throws away 1 out of every 10 or 15 WAPIs he makes, so you can see that there is a cost factor to consider.
3. Making your own WAPIs is a major pain. The tubing comes in 8-foot lengths, which makes it a little hard to handle. Bob uses a band saw available at his university to cut them, but he describes the cutting process as a "bother."
4. In addition to purchasing the wax and the tubing, you'll also have to purchase the fish line and the washers.

Making your own

Bob Metcalf is willing to give you a small supply of the wax, which he estimates will be more than enough for 500 WAPIs and perhaps enough for 1000.

The wax for use inside the WAPI is available here:

Quest International
5115 Sedge Blvd.
Hoffman Estates, IL 60192
USA

Tel: +1 (847) 645-7000
F: +1 (847) 645-7064

The type of wax we use is called Myverol, and the specific product is known as Myverol 18-06, which has a melting point of 69° C. Apparently, the smallest unit that they sell this product in is a box about 1 foot square, which weighs about 45 pounds (20 kg). Bob Metcalf has not yet used up one box and I'm not sure he even expects to in his lifetime--it would be enough for untold thousands of WAPIs.

The tubing we use is .373 inches outside diameter, and the wall thickness is about .060 inches. It is important to be sure that you use a polycarbonate tubing, which Lexan is, but double check with your dealer, because other plastics (ones that are not polycarbonate) lack either the temperature stability or the optical clarity that is needed.

The Lexan tubing can be obtained from McMaster-Carr in Los Angeles. This is the contact info:

McMaster-Carr Supply Co.
P.O. Box 54960
Los Angeles, CA 90054-0960
USA

Phone: 562-692-5911
F: 562-695-2323

http://www.mcmaster.com

The product number is 8585K11. It comes only in 8 ft. lengths. at 60 cents a foot. The measurements I gave you above were more exact than what the company's website gives--it says 3/8 inch exterior diameter and 1/4 inch interior diameter, which is pretty darn close to the figures I gave you above.

I have been instructed by the higher authorities to once again stress with you the idea of quality control--checking every WAPI twice, and looking to see if ANY water has gotten inside the WAPI, because water will affect the wax, which will then possibly melt at temperatures below pasteurization temperature.

Bob Metcalf says, that when you make the WAPI's you put enough wax in the tube to fill it about half way. (The wax comes dry and powdered, looking a lot like fine grated Parmesan cheese.) After the first time it melts, it will be a solid chunk at the bottom of the tube.

External links

• How to make WAPIs