Fly Sparging - Theory Question

I've got a question about the theory behind fly sparging. I've always been taught to match the inflow rate of the sparge with the outflow rate of the wort to the kettle. (Slow, so you don't collapse the grain bed or create channeling).

Here is my theory question - if you have a slow outflow or drain to the BK, you are not collapsing the grain bed. If you sparge in a way that does not create channeling - ie, not just dumping a ton of liquor on the top of the grain bed....why would it matter to match the inflow and outflow rate? So, essentially, once I have a few inches of sparge water on top of the grain bed, what would be the harm of adding the remainder of the sparge water as long as it doesn't channel?

I am with you on this. I wouldn't think it would matter as long as the outflow is less then the inflow and you are not dumping the sparge in large amounts that would disturb the grain bed.

Technically, I'm trying to figure out how to not buy another pump, and not have to move kettles around for a gravity drain...which gets tough with 10g batches.

That said, I'd be a lot cooler with a second pump, and I'm sure it would come in handy.

In theory: solute (sugar) will diffuse upward into whatever water mass you place in the MLT. By adding a large margin of water above the grain bed, you are essentially creating a more attractive gradient for dissolved sugar to "hang out" in.. therefore more sugar will be left over in the MLT liquid when you cut the sparge after reaching boil volume.

Reality: Ya it won't matter. I would lauter about half your MLT volume to pull the really concentrated liquid out first (mini batch sparge initially). Keep the grain bed submerged of course. After that the sparge water above the grain bed stays pretty clear so you aren't losing any sugar and it will save you some hassle if you don't have a sparge pump.