WaterWorker G-12L Tank without Valve Water Heater Expansion Safety Tank, 4.4-Gallon Capacity, Green Product Description 4. 4 gallon, thermal expansion water heater safety tank, steel outer shell, polypropylene lined water reservoir, heavy duty butyl diaphragm that flexes, leak proof precharged air chamber, reduces pressure build up harmful pressure spikes in closed water systems, temporarily absorbs expanded water overflow. This product adds a great value. Product is highly durable and very easy to use. This product is manufactured china. From the Manufacturer WaterWorker Water Heater Expansion Safety tanks work on the same principle as pressure tanks. However, the diaphragm flexes up and down due to the pressure from the water expansion from heat in closed loop hot water systems. i.e., in-floor heating systems and hot domestic water systems. When water is heated expansions occurs within the water lines of the house. Excess pressure can damage solenoids, faucet disc and lift the pressure relief valve in the water heater. The Safety Tank absorbs that pressure and extends the life of the water appliances within the house. Features This product adds a great value Product is highly durable and very easy to use This product is manufactured China USA SHIPPING estimates delivery times and we work to get your item to you as quickly as possible and within those times, but please know it may take slightly longer than the estimate.