Reliance RWC AVEN012 auto air vents

I need to use 2 of these on my power shower hot and cold supply pipes because a potential air trap exists due to me having to go over joists and back down again. Because these air vents will be fitted in my loft does anyone have experience of these becoming stuck and releasing water as well with the ensuing damage that will result? There does not appear to be a fitting to extend the air vent port to a remote safe location where water being emitted will not cause problems. thanks guys.