[the Kergan]

I have an auto opener on my greenhouse window. Does anyone know how it works, the science behind this strange mystical gadget!

I know something happens in the barrel, or I think it does.
Is it heat in the greenhouse that prompts it to open or hot sun on the barrel of the autovent?

Only reason I ask is that I want to shade the greenhouse and I'm wondering if I shade the glass in front of the opener will it stop it from working properly.

[arugula]

Have a look at this (other brands may vary):

http://www.baylissautovents.co.uk/shopcontent.asp?type=TechnicalInformation

I could have typed it all out again, but....

[JayG]

Mine is a Bayliss and it works fine (it's not a precision scientific instrument although Bayliss certainly take their technical information quite seriously based on the info in Argyllie's link!)

It doesn't really matter whether it's shaded or not provided yours has some adjustment so that it starts to open at the temperature you want it to.

[mumofstig]

I've just disconnected the hydraulic tube on mine, It wanted to open because it's warm in there, with the door all but closed.

The door is nearly closed because it's blowing a hoolie right in the direction of the door. Last year the open window was pulled out of the ridge groove by the wind 

I didn't fancy that all over again 

[GrannieAnnie]

I think mine's a Bayliss, but this year it didn't work, but not bad as Brian bought it for his Mum in 1966!