Forespar MF 847 Vented Loop - 1-1/8"

The Forespar MF 847 Vented Loop - 1-1/8" is an essential anti-siphon valve designed to protect your marine systems from fluid loss and cross-contamination. Whether you're running through rough seas or sitting idle at the dock, siphoning between tanks can silently drain fuel, coolant, or waste—damaging engines and creating safety hazards. This vented loop is the industry standard on fishing vessels, cruisers, and commercial boats where system reliability determines your ability to stay on the water safely and productively.

The MF 847 features a simple but effective one-way valve mechanism housed in the upper loop section. When pressure equalizes, the internal valve opens to allow normal flow; when siphoning pressure develops, the valve closes instantly, breaking the siphon and preventing backflow. The 1-1/8" diameter suits standard marine cooling and sanitation plumbing, while the compact 6 x 2 x 8-inch footprint fits neatly in engine compartments and head enclosures. Forespar's proven design uses corrosion-resistant materials engineered to withstand years of salt spray, vibration, and constant pressure cycling—critical factors that separate marine-grade hardware from automotive substitutes.

Anglers and boat owners install the Forespar MF 847 in engine cooling circuits and marine head discharge lines to prevent costly tank-to-tank contamination and emergency engine shutdowns. Installation requires basic hose routing—place the loop at the highest point in your discharge line to maximize valve effectiveness. Compatible with standard 1-1/8" marine hose and fittings, this loop integrates seamlessly into new builds and retrofit projects. At just 0.5 pounds, it adds no meaningful weight while delivering years of silent, maintenance-free protection that keeps your vessel's systems isolated and functional.