Check the listing for details. Inline Check Valve w/ 3/8" Quick Connect (Push Connect) Fittings for Reverse .... Condition: New. Listed at 17.99 USD. Inline check valve prevents water from flowing back through the line. It is used on reverse osmosis systems to prevent backflow through the membrane. When the check valve malfunctions, it can allow the tank to empty back through the membrane and down the drain line. Inline check valve prevents water from flowing back through the line and is necessary on RO systems 3/8" quick connect fittings make connecting the check valve quick and simple 3/8" for higher flow units Free shipping is for orders shipping within the contiguous USA only. Outside provinces, HI, and AK will be sent an invoice for the additional amount due. International shipping orders will use ebay global shipping program unless other arrangements are made with us in advance. 785 735 9769