well preasure tank question

Concidently, we just had a pressure tank problem solved last Friday. The tech doing the work had to install a new tank to replace one with a broken bladder. Our pump cuts in at 40 psi, shuts off at 60 psi. The tech set the precharge in the tank at 35 psi -- the spec calls for 2 psi below the pump start pressure, but the tech said he preferred to have a slightly larger margin. Regards --

Yes, 2psi below cut-in (with tank empty) is correct but it isn't critical. All the pre-charge does is provide a 'spring' for the system to operate against. The 2psi optimizes pump run time. Difference between 35 and 38 psi would probably be non detectable without precision measuring equipment. That said, I do have a problem with techs and their "I prefer..." opinions vice what the manufacturer says.

Harry K