The evaporators mod. OV are indirect steam generator: these use a thermal source (diathermic oil) different from fire and for this reason can be exonerated from qualified conductor. It are always combined whit a diathermic oil heater which supply the necessary feat for working.

The quality of steam is better respect to the traditional steam generators, as is not a violent vaporisation, but it is gradual and costant which avoids water enrainment. The coil of primary fluid (thermal oil) is of type whit four passes whit tube welded to the plates of the evaporator and distribution heads of the oil; this design permits an easier inspection an maintenance of the tube nest repect to the evaporators with extractable ā€œUā€ type tubes. The thermal insulation of the shell is obtainedi with a mattres of mineral wool at high insulating capacity and it is protected from alluminium steel sheet.