Do you use the lid on your mash tun while fly sparging?

This might be a silly question, but for those of you with the cylindrical cooler mash tuns... do you keep the lid on the mash tun while you fly sparge or do you keep the top off?

My method so far has been: remove lid, pour my sparge water (dispersed with a colander) and then replace the lid. I do this about every 10 minutes for an hour and typically get great efficiency (lowest has been 75%, highest has been 85%.)

I've come really close to a stuck sparge though, and I think it has to do with suction. The mash tun just doesn't drain that fast when it's basically air tight. Towards the end, I've been leaving the top off so it drains better.

What do you do?

I use a copper coil in my cooler MLT for temp control so I don't use the lid at all.

I've been fly sparging with a hose draped on top of the mash in a 10 gallon cooler but I prop the lid over it to help with heat loss. I can also look to make sure I have a good bed of water on top and not run dry.

I take the lid off for the entire sparging process. I fly sparge by hand. Works for me. I consistently hit right at around 80% eff.

I keep the lid on during the sparge, but my lid is drilled to allow the sparge water to enter, and there is sufficient leakage around the hole to prevent any problems caused by a vacuum. If the vacuum is causing a stuck sparge, you could place the lid on the top, but not screw it down tightly. This would prevent any vacuum, but would also prevent most of the heat escaping.

-a.

Thanks all. Going to just set it on top a little more loosely next time. Mainly I just wanted to make sure I didn't get a bunch of people saying "OMG don't use a lid when you sparge!"