Introducing the Backstop 12-TWH2 all stainless steel tankless expansion tank with air valve designed for use with all brands of tankless water heaters and point of use water heaters rated at 2 gallons or less. In stock at Friedman & Dorrans, this device absorbs thermal expansion and pressure surges in tankless water heaters to protect the heat exchanger. It can also be used as a shock suppressor (water hammer arrestor) for appliances with a fixture capacity of 11 (size A). The unit is durable and corrosion resistant and is tested & approved by IAPMO to the NSF61 standard for potable water.