I wanted to post an update on my Taco 4900. I ordered a Caleffi Discal in 1-1/2" last week. Decided to go that route because of the good feedback and ability to easily service. I have posted a couple pictures of install and what I found in the 4900. The 4900 pall ring design seems a little restrictive after comparing to the Caleffi. We installed it yesterday. Removed the Temp well and T that was to left of air sep to give a little more space to pump. This is the inlet side of the 4900. Some of the pall rings (6-10) were stuck in a cluster. Not sure what the cause? grey film.