The impact of tubing sizes

[spookmineer]

Ok, if we're being pedantic, there's pressure that is less than atmospheric pressure before the pump inlet, causing the atmosphere to push in and attempt to crush the tubing.

There have been numerous posts from various people where they've shown that with soft-walled tubing, all you need to do is to slightly restrict the run into the pump inlet and the tubing will collapse. Sticking a restrictive block before the pump inlet will achieve the same effect.

If you don't believe me, I'll set up a test and video it in effect for you, using a DDC-2. Believe me, it happens.

It wasn't meant to be pedantic...

Thanks for the explanation. I don't have a watercooling setup (yet) but your post is very plausible, no need for a video.

If anything, my post was to question at how much head pressure there could be a problem, as quick fittings don't (potentially) cause problems just before the pump, but even before this:

I'm only wondering at what amount of head pressure it's not wise to use push fittings anymore.
Is 2 ft too low, is 5 ft good enough?

[edit]
I hope I'm correct here, 1 bar equals 10.2 meter of water pressure (= 33.46 feet).
I guess manufacturers give out specs of overpressure? Assuming that's the case, then people who experience collapsing tubes are having more pressure loss through their loop then the specs given by manufacturers... (going below 1 bar)
Their loop is more restrictive then the pressure from specs can handle, and the pump intake is indeed below 1 bar.

Or Gabe's explanation is the cause of the problems with push fittings:

Negatives in a nutshell:
Safety
- push-in fittings were designed for applications where pressure is <2-7> bars. They were never intended for low pressure environments.

[/edit]