Aquascape 3" Dual Union Check Valve prevents backflow in ponds and water features while also providing a professional plumbing connection inside skimmers and pondless waterfall vaults. Perfect for larger installations that use large pumps and filters. The heavy-duty, swing-style check valve flapper is built to last and maximizes water flow through the valve when open while preventing the backflow of water when the pump is shut off or during a power outage. Union connections on both sides of the valve make maintenance quick and easy without the use of tools. Designed for use with Pondless Waterfall Vault w/ Extension, Large Snorkel Vault, Grande Skimmer, Tsurumi 12PN Pump and Aquascape 10,000 Pump.