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Forespar 903003 Marelon 5/8" Vented Loop Siphon Break Valve

Manufacturer

Forespar

<h3>About Forespar Products Corporation</h3><p><strong>Forespar Products Corporation</strong> has been a cornerstone of the marine industry since its founding in 1966. The company's origin story is as practical as the products it makes: <a href="/7351-forespar">Forespar</a> was started by lifelong boater Robert Foresman simply because he wanted a telescoping whisker pole — and couldn't find one good enough. That hands-on, solve-a-real-problem philosophy has guided every product decision in the decades since, growing Forespar from a single-product idea into a large and diversified supplier of sailing and boating products serving the world market.</p><p>Headquartered in Rancho Santa Margarita, California, Forespar operates a state-of-the-art manufacturing facility that handles the entire product lifecycle in-house. The team uses CAD/CAM design, a full machine shop, plastic injection molding, and carbon composite processing — capabilities that allow Forespar to maintain the tight tolerances and consistent quality that demanding sailors and powerboaters expect. This vertical integration is a key reason the brand has earned such a loyal following across the globe.</p><h3>Marelon&reg;: The Forespar Innovation That Changed Marine Plumbing</h3><p>One of Forespar's most celebrated contributions to boating is <strong>Marelon&reg;</strong>, a proprietary polymer composite formulation engineered specifically for marine plumbing applications. Marelon fittings — including seacocks, thru-hulls, and vented loops — deliver exceptional resistance to corrosion and electrolysis, two of the most persistent threats to below-waterline hardware. Because Marelon components weigh roughly half as much as traditional bronze equivalents, they help reduce overall boat weight without compromising structural integrity. The precision-molded plumbing systems built with Marelon are UL approved and meet A.B.Y.C. standards, giving boaters confidence that their below-deck plumbing is as safe as it is durable.</p><p>Forespar vented loops and thru-hull fittings are trusted by both sailors and powerboat owners who need reliable, maintenance-friendly solutions that hold up in the harshest saltwater environments. The corrosion-free nature of Marelon also means fewer inspections, less maintenance, and longer service life compared to metal alternatives.</p><h3>Sailing Performance Gear: Poles, Vangs, Furling &amp; More</h3><p>Beyond plumbing, Forespar is equally renowned for its performance sailing hardware. The brand's lineup of <strong>spinnaker poles and whisker poles</strong> — available in aluminum, carbon fiber, and composite materials — is designed to help sailors extract maximum downwind performance. The locking telescoping designs allow for quick adjustments on the water, and the carbon fiber options in particular combine a featherlight feel with impressive structural strength. For racers and cruisers alike, Forespar poles represent a genuine upgrade in sail handling capability.</p><p>The <strong>Leisure Furl</strong> in-boom mainsail furling system is another flagship product line bearing the Forespar name — a sophisticated solution for sailors who want easy, reliable sail stowage without sacrificing performance. Rounding out the sailing hardware catalog are boom vangs, sail handling hardware, davit systems, and safety equipment, making Forespar a one-stop source for outfitting a sailboat from deck to transom.</p><h3>Powerboat &amp; Cruising Accessories</h3><p>Forespar's reach extends well beyond racing sailboats. The brand's <strong>davit systems</strong> and the innovative <strong>Nova Lift</strong> make deploying and retrieving dinghies, tenders, and outboard motors significantly easier for cruising families and liveaboards. Forespar's marine lighting products offer dependable illumination for navigation and on-deck use. The Flopper Stopper — a uniquely Forespar solution — helps reduce uncomfortable rolling at anchor, a quality-of-life upgrade that any offshore cruiser will appreciate.</p><p>Whether you're racing offshore, cruising coastal waters, or maintaining a powerboat at the dock, Forespar has built products specifically for your challenges. The brand's commitment to innovation, quality manufacturing, and real-world boating experience has made it one of the most trusted names on the water for more than five decades.</p>

Part Number

903003
06/02/2036 5:57 PM
Sale Price

$29.10

In Stock (6)

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Usually delivered within 2 days

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Product Details

The Forespar 903003 Marelon Vented Loop is a critical safety component for marine plumbing systems, designed to prevent back-siphoning that could lead to flooding or sinking. This 5/8" vented loop features a float-operated valve that allows air to enter the discharge line when water flow stops, effectively breaking the siphon and preventing seawater from flowing back into the vessel.

Key Features:

  • Constructed from glass-reinforced Marelon composite for superior corrosion resistance and durability
  • 5/8" hose barb connections for secure fitting integration
  • Float-activated valve automatically opens to admit air when needed
  • Install above the waterline to prevent backflow in marine toilet, sink, and other discharge systems
  • Non-metallic construction eliminates electrolysis and corrosion issues
  • Translucent body allows visual inspection of valve operation

Marelon vented loops are essential for any below-waterline discharge system including marine heads, galley sinks, and livewell drains. The valve must be installed at least 6-12 inches above the waterline to function properly. Regular inspection and cleaning ensures reliable operation and protection against dangerous back-siphoning.

Products specifications

Compatibility

In-Line

Diameter

For 5/8" Line

Material

Marelon

Type

Vented Loop

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