What is a Hot Liquor Tank/Mash Tun?

This doesn't have to do with homebrewing, and more to do with commercial brewing, but I've been finding a bunch of 7-10 barrel brewing systems online (just for fun...) that have a Hot Liquor Tank/ Mash tun combo. These are two vessel systems (so no lauter tuns). So it's basically a three in one: Mash/Lauter/HLT with a kettle/whirlpool.

I don't understand how there can be just one vessel for these two very different purposes (mash tun and HLT). For example, where would your sparge water come from if your Mash/Lauter is full of mash?

I'm confused, any thoughts? Also pictures would be awesome, if you guys have any. I want to see these peculiar mechanisms...

In systems I've seen, mash and sparge take place in different vessels.

One vessel is the HLT, mash tun and BK. The other vessel is the Lauter Tun.
Water is heated in the HLT/MT/BK, grist added and mashed.
Then the entire contents (i.e., with grain) are pumped to the Lauter Tun.
Sparge water is heated in the HLT/MT/BK and pumped into the lauter tun.
The wort is then transferred back to the HLT/MT/BK for the boil.

The combo you mentioned is one vessel, but separated top and bottom, with the water on the top, and the mash underneath. Kind of like two vessels stacked. The water is gravity fed from above during lautering, and pumped into the kettle.

Budzu said:

The combo you mentioned is one vessel, but separated top and bottom, with the water on the top, and the mash underneath. Kind of like two vessels stacked. The water is gravity fed from above during lautering, and pumped into the kettle.

Click to expand...

Not the way it works... the hot liquor tanks are on the bottom, mash tun on top. Water is pumped up to be mixed with the grist as it falls or is augered into the mash tun.