[philthespark]

I spoke to a chap this afternoon, he'd used a lot of pretty big valves in his job years ago. I mentioned this thread to him and he'd seen this phenomenon at work, they did a few tests and came to the conclusion that valves can and indeed do become damaged from being stored on their sides.
He reckons it's to do with the fact that they are normally used in the vertical position, and are designed as such, therefore there will be stresses and strains set up when stored in any other position.
Thinking about it it makes sense, any metal will distort over time and distortion will have an effect. in simple terms think of it like this.
If you stand a length of 4mm steel rod vertically and clamp both ends so it cannot move, it will remain straight. now turn it horizontally and after a period of time, days, weeks, months, you will notice that the rod develops a bend in the middle.
This is probably what happens with valves, it's irreversible and then you have a damaged valve. I seem to remember them being packed vertically, say a dozen individually packaged units in a bigger box, but don't recall any storage warnings. Today you see lots of items having storage instructions on the box, quite often you see the warning "store in an upright position" or "store vertically".
Maybe this fact was just one of those things that was obvious to the radio men of yesterday. a bit like we were brought up to know that hot coffee can scald you. today every coffee cup from fast food outlets has "warning contents may scald" written on it.
Mind you I'd rather admit to needing someone tell me a valve should be stored vertically, than admit I needed someone to tell me a hot drink could scald.