What are you trying to insulate, valve itself, operational unit or pipeline and unit?
Fluid, pressure, size? Chiller?
Apart from this you ask for a general insulation between minus 40 deg C and plus 60 deg centigrade if my conversion tables are correct.
If this is correct you have three problem areas:
A. Fairly low temperatures where valve material quality and operational possibillities could have to be considered. Heat tracing, and/or completly inbuilt solution with heating possibillities recommended. Material choice of valve and valve sealing, stem sealing operational at lowtemp?
B.Midrange around zero where condensation on inside of insulation could be a problem. Insulation air and waterthight against pipeline wall, else to be solved as A.
C. Heat, moisture and rain. No problem if material quality and general protection else is correct. May require extra protection of outer surface.
Apart from this I think your idea could work under most conditions. I would however have a look at possible shrinkage under heat conditions of your insulation material, and you wold probably need a more resistant outer and inner surface.
Suggestion: Expanded polyurethane? Anyway: ask sub-suppliers of expanded foam or producers of smaller yachts, life buoyous etc. If your valve is relatively small and simple you could probably try a 'do it yourself test' - again look to smaller boats or housebuilding 'do it yourself' arena.
There also exists insulate 'jackets' ready-made to protect from heatloss for steam pipeline valves.. Depending on quality and form this could perhaps be used for some of your conditions, but are of course generally not constructed to protect against rain.
