I sounds like the bladder has failed. To replace, all you need to do is turn the water off, unscrew the old tank, and screw the new one in place. The tank should be pressurized to equal the PRV setting. Watts recommends using a hand pump,like for a bicycle, but if you are careful, a regular compressor will work. Just remember the volume of air is actually quite small, so go slowly and keep checking with a gauge.