Technical Information

The Autovents are operated by the expansion of a mineral wax.  The high rates of expansion are concentrated over the phase change solid-liquid.  The piston works directly in contact with the wax and the lowest temperature we have so far been able to utilise is about 55° Fahrenheit.  Other waxes and blends of wax can be used to give higher opening temperatures.

The viscosity of the wax causes a hysteresis giving a temperature difference of 5° Fahrenheit to 10° Fahrenheit, opening to closing, although this may be possibly reduced by careful blending of the wax.

Response time is somewhat governed by the load on the piston.  The energy to move the load is collected from the surroundings and is governed by the surface area of the tube in which the wax is contained.  For the smaller units we use a plain aluminium tube but for the larger we use a tube which is finned on both the outside and the inside bore.  Wax is a poor conductor of heat.