We have a school with a chilled water system. The system is 300 tons of d.x. and quite large in reference to the piping layout and length of run.We are gong to replace the verticle expansion tank due to a ruptured bladder. My question is ,what is the formula for figuring out what to charge the new tank to . I'm told it will come pre charged to 12 psig,but I dont think that will be enough pressure to satisfy our verticle lift . Many thanks in advance.