"Actuation" înseamnă în românește "de acționare/de comandă.
Lower valve este clapeta din partea de jos a buncărului.
"Actuation unit" = actuator
https://www.google.com/?gws_rd=ssl#q=actuator
“An actuator is a type of motor that is responsible for moving or controlling a mechanism or system. It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion.”
http://www.mec.tuiasi.ro/diverse/Curs_Actuatori_Neconv.pdf
“actuatori cu cursa nelimitata (micromotoare de curent continuu, micromotoare de curent alternativ asincrone si sincrone, micromotoare electrostatice) actuatori cu cursa limitata (micromotoare liniare de curent continuu, microelectromagneti)”


--------------------------------------------------
Note added at 3 hrs (2016-02-26 18:12:04 GMT)
--------------------------------------------------

O clapetă cu "actuator" de la un asemenea furnal:
http://russianpatents.com/patent/252/2524870.html
“The rotary setting of the linear actuators 52, 52' achieved with installed on top of the casing of the actuator pins 58, 58'”