Tkanks and sorry for my bad english...........the Aqualis XT reservoir comes wit a pressure equalization menbrane that , if I'm not mistaken , it's necessary for the proper functioning of the fill level sensor ............. my question was if I could or not to use a different pressure valve ( the koolance pressure valve , for example ) and , if so , whether this would affect the proper functioning of the fill level sensor
No. The Aquacomp is a very free flowing air valve that always keeps the pressure in the res at the same as atmosperic. If it didn't the fill level sensor would change without the actual fill level changing because it works by sensing pressure.
The Koolance model is a saftey valve that only trips at a certain pressure above atmospheric. Other models like the Bitspower are purely manual models and fill levels would be all over the place unless you regularly manually cycled it.
Of the ones I know of only the Aquacomp will maintain proper fill level sensor function.