Can I perform a pressurized transfer with the FTSs flat lid?

Yes  

In fact, we recently introduced a 1.5" TC weldless compression fitting accessory which will allow flat lid users to perform pressurized transfers without switching to their domed lid.  More specifically, the weldless TC flange allows flat lid users to utilize our existing Pressurized Transfer Fitting, in addition to other TC accessories with their FTSs flat lid.

Here is a list of parts you will require to install and perform a pressurized transfer:

1.5" TC Weldless Compression Fitting

Pressurized Transfer Fitting

1.5" TC Clamp and Gasket

17 mm Plug

42 mm Hole Saw

#7.5 Silicone Stopper OR 1.5" TC Flange to 1/2" barb

Begin by drilling the 42 mm hole in a previously unoccupied area of your flat lid, use the high-speed setting on your drill for the cleanest cut.  Once the hole is drilled debur any sharp edges with a household razor blade.  Next install the TC Compression fitting from the top of the lid, ensuring the silicone O-ring forms an air tight seal to the top of the lid, and then tighten the locknut from the underside.

Install the 17 mm plug in the previous blow off port, since you will now be using the new compression fitting for both blow-off and pressurized transfers.  Keep in mind, If you do not install the plug, there will be no way for pressure to build within the vessel when you go to transfer.

Your FTSs lid is now ready for use.  During active fermentation, rig a blow-off by attaching a 1.5" TC Flange to 1/2" hose barb to the 1.5" TC compression fitting (as shown in photos below).  Then you can run a 1/2" piece of silicone tubing into your blow-off container. You may also use a silicone stopper with an airlock, however, a blow-off is always recommended.  Lastly, do not attempt to use the Pressurized Transfer Fitting as a blow off fitting, the 3/8" hose connection can become easily clogged from an overactive fermentation.

When your beer is finished fermenting, and you wish to perform a pressurized transfer.  Remove the blow-off fitting from the weldless TC compression fitting, and then install the Pressurized Transfer Fitting.  Finally, connect the pressurized transfer fitting to your regulator. Then run a length of tubing from your racking valve to a cleaned, purged, and sanitized keg. 

Remember to turn down the pressure on your regulator to 0 before beginning the flow of gas.  A quick burst of CO2 in excess of 2.5 PSI can cause damage to your lid clamps.  Slowly turn up your gas to roughly 1-2 PSI, and open the racking valve to begin the transfer.