Mash tun ideas

Currently I use a 10 gallon Rubbermaid cooler. The cooler has a copper manifold that does double duty for adding steam and draining. I drain using gravity into the boil kettle. For double batches of bigger beers, the cooler isn't big enough so I want to convert a 15.5 gal keg.
I'd like to keep using the same manifold but would also like to add a pump for recirculating during the mash to cut down on the length of the brew day. How does pumping out of the MLT work? Do I need a grant so grain doesn't get sucked out once the MLT get close to empty?

The main problem you will encounter when pumping from the MT will be compaction of the grain bed. A grant is one possible solution. Another is to simply cut the flow rate with a valve on the output side of the pump. When pumping without using a grant, it will be very hard to determine how fast to pump and how much suction you are applying to the MT. I solved this by installing a vacuum gage on the suction side of the pump. Another problem is that the grain bed compaction can happen gradually and the only indication of an approaching stuck mash will be a slowing of the flow rate. By that time, it's usually to late to avoid the compaction problem. The gage allows you see what's going on with much more precision. It made a world of difference for me.

Grain shouldn't get sucked out as you empty the MT. Typically, you would be fly sparging and there will still be plenty of liquid remaining in the MT when you reach your pre-boil volume. I seldom run the MT completely dry. There is no need to do so when fly sparging as it works on a displacement principle, unlike batch sparging where you would drain the MT completely.

Recirculating during the mash will likely lengthen your brew day rather than shortening it. The reason I say this is that you will probably start doing a mash out and maybe step mashes too which add to the time involved. You don't necessarily need to do these operations, but when you can it's likely you will. Just speaking from personal experience here. My brew sessions are rather lengthly, but I don't mind it as I enjoy the whole process and I'm never in a hurry when I brew. Batch sparging is probably the fastest and simplest brewing method if you want to save time.

I batch sparge now and obviously vorlauf before each drain. I always steam up to mash out (which is very fast compared to a HERM/RIMS) and sometimes do step mashes with the steam (again, very fast). If I could simply recirculate toward the end of the mash to clear it (instead of vorlaufing), I could save some time. I was thinking about a grant with 2 float/level switches, one to turn the pump on and one to turn it off. That way there's no real change from my current process besides a little automation and saved time. I have no idea yet how to wire in the level switches or even what switches to use. A vacuum gauge sounds like a great helper but if I continue to use gravity, I don't have that worry about bed compaction.

Yes, you could certainly do it that way with the grant and level switches, but if you are only planning to do the recirculation for a short duration it might be more trouble than its worth. Recirculating toward the end of the mash "is" vorlaufing IIRC. You shouldn't have problems pumping directly if you go slowly and it's only for a short duration. I'd give that a try before I'd invest the time and effort to set up the grant and switches.

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