Thermal switch

Abstract

There is disclosed a thermally responsive switch that is ideally suited for responding to the ignition and extinguishment of a flame. The switch is provided with two switch poles, one that is biased normally open and the other that is biased normally closed. The response of the switch to the presence of a flame is very sensitive and precise to open the normally closed contact within a few seconds after ignition of a flame and, shortly thereafter within another controlled time period, to close the normally open contact. Upon extinguishment of the flame, the switch reverses its movement, opening the normally open contact within a short time interval, and, thereafter, closing the normally closed contact. The switch mechanism employs a thermally responsive, tube-in-tube member with the inner tube connected to a push rod which resiliently carries a switch lever. The switch lever has lateral tabs which are captured within first and second slots of brackets which are on the switch blade and which have predetermined widths to provide lost motion connections between the switch lever and the switch blade. The switch blade is biased resiliently towards the normally closed contact and this bias is laterally unbalanced to provide a stepping action of the switch lever. The switch lever also resiliently receives and is carried on the push rod whereby it accomodates thermal deformation of the tube assembly which is in excess of that necessary for the opening and closing functions of the switch.