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The Lennox 77W66 is a genuine OEM 3-way brass ball valve featuring an L-port configuration, sized at 2 inches and rated for 400 PSI WOG (27 Bar), designed to provide dependable directional flow control in compatible Lennox heating, cooling, and hydronic systems. Unlike the T-port design, the L-port configuration allows flow to be directed from one port to another without a mixing function, making it ideal for diverter applications within Lennox systems. Signs of valve failure include stiff or stuck operation, leaking around the ball or stem, or improper flow routing, and replacing it with this direct OEM part ensures a factory-accurate fit and lasting reliability.