Wilbur, I wish I could advise you on your pressure question, but I can't. Someone should be able to though. I would like to ask that you post a picture of the circulators when you have a minute. I'm curious to see what they are, plus it might help someone answer your pressure question, too.

You can either use Photobucket. Flickr, Picasa or the like or email pics to [email protected] and reference the URL of this thread.