This trap works on the difference in Enthalpy of Steam and Condensate. A capsule attached to a Bellow filled with precise amount of a Hydrocarbon, Expands and contracts in response to the rising/lowering of Enthalpy. Thereby shutting and opening the valve. Condensate has lower Enthalpy, causing the bellow to contract and the seat to retract which opens the valve and allow discharge of condensate. The reverse happens with the steam and its higher Enthalpy.