Aquarium immersion heater with dry operation prevention thermostatic switch

摘要

An aquarium heater includes a tubular glass housing provided with a temperature control circuit in the upper part thereof for switching on and off a heating element disposed in the lower part of the housing and comprising an elongated non-metallic support tube on which a helical resistance heating wire is wound. A temperature responsive bimetallic breaker switch enclosed in a metallic housing is coupled within a feed line to the heating wire and is located in the interior of the support tube slightly below the upper end thereof and extends within a number of turns of the heating wire, with length of the breaker switch representing a small fraction of the length of the support tube. The interior of the housing and the support tube are filled with sand to the extent that the breaker switch and heating wire are completely enclosed by sand to improve heat transfer between the heating wire and breaker switch thereby making the breaker switch quickly responsive to dry operation of the heater to deenergize the heating wire.