Meet Mr Hoover
- Alison and Dave Roberts
- May 22
- 2 min read
Updated: May 26
14th February 2022
The boiling point of water is the temperature at which the vapor pressure of the liquid water equals the pressure surrounding the water and the water changes into a vapor. Water at a high pressure has a higher boiling point than when that water is at atmospheric pressure. In other words, the boiling point of water varies with surrounding pressure. Water boils and turns to vapor at 212 degrees at sea level where the pressure is 14.696 PSIA and 0.0 inches of vacuum. Inside a vacuum chamber like the home-made model above water will turn to a vapor at 104 degrees at 27.75 inches of vacuum 1.066 PSIA.
Wood placed inside our vacuum chamber with heating pads on either side to heat the wood evenly when under vacuum will vaporize the water in the wood at a much lower temperature so there are less stresses caused to the wood thus there should be less cracking and warping. A temperature controller is used to set the parameters of the heat mats to control the wood temperature. Another important advantage is time; a piece of green wood can be dried in the vacuum kiln in as little as 7 days. One of the issues to the vacuum kiln is even heat distribution on the wood so rough turned bowl blanks need a heat mat that can shape to the contours of the bowls.
This book in the photo below is an excellent source on building your own vacuum kiln, by Joshua Salesin and available on Amazon.
Hoover came about through a few conversations and help from family. My brother William put me onto the idea, I then talked to my turning friend Glen who liked the idea as well. He mentioned it to his brothers Gord who is a pressure welder and Robert a steel fitter and before long his son Adam who is in HVAC also got involved. Before we knew it, we had a finished vacuum kiln and were ready to start drying turning wood.
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