Mike,
I can think of three reasons. 1.The instructions are not very clear. 2. I wasn't able to figure out the correct technique on my own. 3. It's embrassing to ask for directions.
Actually I thought the blower just made the backwashing more efficient,

so it used less water to accomplish the task. So what does the opening the bottom gate valve do? Like I tried to explain earlier, the instructions say to open this first, but never tell you to close it back. Water pours out the 1.5" pipe, but clears quickly. I guess you close it then. They really need to write some backwashing instructions for Dummies. Like me.
Mitch
PS
That gate valve is actually a little dangerous. It opens quite easily and drains a *lot* of water. If it got opened accidentally by a child or a puppy it could totally drain some poorly designed ponds. It's like the main gasket blowing, but much, much worse.