A thermal actuator comprising: a first fluid flow housing having an inlet, an outlet, a first end and a second end opposite said first end, said first fluid flow housing being used for the controlled passage of a first fluid between said inlet and said outlet; a first bellows housing having a proximal end and a distal end, with said proximal end being operably affixed to said first end of said first fluid flow housing; a second bellows housing having a proximal end and a distal end, with said proximal end being operably affixed to said second end of said first fluid flow housing; a first bellows operably positioned within said first bellows housing, said first bellows having a fixed end affixed proximate to said first end of said first fluid flow housing and a movable end opposite said fixed end, said first bellows being surrounded by a first bellows region within said first bellows housing, said first bellows containing a medium therewithin; a second bellows operably positioned within said second bellows housing, said second bellows having a fixed end affixed proximate to said second end of said first fluid flow housing and a movable end opposite said fixed end, said second bellows being surrounded by a second bellows region within said second bellows housing, said second bellows region containing a second fluid therewithin; and an actuation rod that extends internally from said movable end of said first bellows, through said first fluid flow housing, to said movable end of said second bellows, characterised in that said actuation rod has a fluid passage disposed therewithin to alternatively block, and enable, the flow of said first fluid from said inlet to said outlet; said actuation rod, said first bellows and said second bellows collectively forming a reciprocating actuator capable of moving between a first position for blocking said passage of said first fluid and a second position for enabling said passage of said first fluid, said second position serving to align said fluid passage of said actuation rod with both said inlet and said outlet of said first fluid flow housing, thereby enabling the controlled passage of said first fluid to flow from said inlet through said fluid passage and into said outlet. a first fluid flow housing having an inlet, an outlet, a first end and a second end opposite said first end, said first fluid flow housing being used for the controlled passage of a first fluid between said inlet and said outlet; a first bellows housing having a proximal end and a distal end, with said proximal end being operably affixed to said first end of said first fluid flow housing; a second bellows housing having a proximal end and a distal end, with said proximal end being operably affixed to said second end of said first fluid flow housing; a first bellows operably positioned within said first bellows housing, said first bellows having a fixed end affixed proximate to said first end of said first fluid flow housing and a movable end opposite said fixed end, said first bellows being surrounded by a first bellows region within said first bellows housing, said first bellows containing a medium therewithin; a second bellows operably positioned within said second bellows housing, said second bellows having a fixed end affixed proximate to said second end of said first fluid flow housing and a movable end opposite said fixed end, said second bellows being surrounded by a second bellows region within said second bellows housing, said second bellows region containing a second fluid therewithin; and an actuation rod that extends internally from said movable end of said first bellows, through said first fluid flow housing, to said movable end of said second bellows, characterised in that said actuation rod has a fluid passage disposed therewithin to alternatively block, and enable, the flow of said first fluid from said inlet to said outlet; said actuation rod, said first bellows and said second bellows collectively forming a reciprocating actuator capable of moving between a first position for blocking said passage of said first fluid and a second position for enabling said passage of said first fluid, said second position serving to align said fluid passage of said actuation rod with both said inlet and said outlet of said first fluid flow housing, thereby enabling the controlled passage of said first fluid to flow from said inlet through said fluid passage and into said outlet.