Matt
The Eclipse was a strange one. At least the dirty-fan version was. I never saw the clean-fan version as it was not on sale in the UK for long.
With the dirty-fan Eclipse, what happend was this; when the cleaner was stood upright, the cleaning head was raised off the floor and a flap was moved to block suction to the cleaning head.
On the back of the cleaner was the hose. The wand was stored in a hole which was solid. This meant that when the cleaner was stood upright with the hose stored, there was no airflow as all ducting was restricted. However, this was not quite the end of it, as underneath where the hose was permanantly connected to the cleaner there was a knob which activated another valve, though in many cases the knob had broken off. The point of it was to keep air out of the hose whilst the cleaner was being used as an upright machine. Turning it one way blocked off the hose altogther; turning it the other way allowed air into the hose.
I suppose to some extent it did help the amount of power avaliable at the cleaner head by having the hose shut off, but that power must have been minimal and as the hose termitated into a solid storage bracket, it was just as easy to leave the value set to "tools" even when using the cleaner as an upright. To that end it worked like the hose on the Hoover Turbopower Total System. The Eclipse was a half-hearted and overenginered attempt at an automatic changeover really.