Built with heavy-duty butyl diaphragm system to absorb the expansion of water volume and help prevent dangerous pressure build-up. This Everbilt Expansion Tank will absorb pressure increases when properly installed on your closed water system. Most local codes now require an Expansion Tank on residential closed water systems. Water pressure over 80 psi can shorten the life of your water system and appliances. Stainless steel 3/4 in. MIP with Hex Factory pre-charged at 40 psig Certified with cUPC and NSF 61 compliant Brass air charging port with O-ring seal 16-Gauge cold rolled steel shell High quality coating prevents corrosion 100% butyl rubber diaphragm lined with polypropylene Maximum pressure of 150 psi Maximum temperature rating of 200F Protects water heater, fixtures and appliances