The Walchem WBL400-1N5U controller is now obsolete and the closest equivalent is the WBL600PSNNN-AN controller. The new WBL600 series has upgraded features; for reference, here is the description of the old model:
Boiler controller - bleed & feed, 120 VAC, prewired, no 4-20 mA output, standard electrode (up to 250 psi), integrated datalogging and config file import/export via USB flash stick.