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Forespar 903000 Marelon 1-1/2" Vented Loop Anti-Siphon Valve

Manufacturer

Forespar

<h3>About Forespar</h3><p>Founded in 1965 and headquartered in Rancho Santa Margarita, California, <strong>Forespar Products Corp.</strong> has built a decades-long reputation as one of the marine industry's most trusted manufacturers of sailing hardware and below-the-waterline plumbing systems. From competitive racers to bluewater cruisers, sailors around the world rely on Forespar's engineering precision and material innovation to keep their vessels safe, light, and seaworthy.</p><h3>Marelon®: The Material That Changed Marine Plumbing</h3><p>At the heart of Forespar's identity is <strong>Marelon®</strong>, a proprietary polymer composite formulation the company developed to address the chronic vulnerabilities of traditional bronze marine hardware. Marelon® components are inherently immune to corrosion and electrolysis — two of the most persistent threats to any vessel's underwater fittings. Whether above or below the waterline, Marelon® delivers structural integrity that matches or exceeds its metal counterparts, all at roughly half the weight of equivalent bronze parts. This weight savings matters significantly on performance sailboats where every pound of displacement counts.</p><p>Forespar's precision-molded Marelon® plumbing systems carry UL approval and meet A.B.Y.C. (American Boat and Yacht Council) standards, giving sailors and surveyors alike the confidence of knowing these components have passed rigorous independent testing. The result is a complete line of <a href="/7351-forespar-seacocks-200913">seacocks</a> and <a href="/7351-forespar-sea-strainers-200906">sea strainers</a> that are lighter, longer-lasting, and easier to service than traditional bronze or brass alternatives.</p><h3>On-Deck Innovation: Tiller Extensions &amp; More</h3><p>Forespar's innovation doesn't stop below the waterline. Their <a href="/7351-forespar-tiller-extensions-accessories-201068">tiller extensions and accessories</a> are engineered for responsive, fatigue-free helming, whether you're racing around the buoys or hand-steering offshore. With ergonomic designs and quality materials built to handle the stresses of saltwater sailing, Forespar tiller gear is a staple aboard racing dinghies and performance cruisers alike.</p><h3>Protecting Your Vessel Above and Below</h3><p>Forespar also addresses some of sailing's less glamorous but critically important concerns. Their <a href="/7351-forespar-ground-plateslightning-protection-products-200501">ground plates and lightning protection products</a> offer sailors a proven method for safely dissipating electrical charge during storms — a genuine life-safety consideration for any offshore passage-maker. Meanwhile, the marine environment's constant humidity makes mold and mildew an unavoidable challenge aboard any boat. Forespar's line of <a href="/7351-forespar-mold-mildew-products-200690">mold and mildew products</a> helps boaters protect upholstery, bilges, and living spaces from the biological growth that thrives in wet, enclosed environments.</p><h3>Why Sailors Choose Forespar</h3><ul style="list-style:disc"><li><strong>Proven material science:</strong> Marelon® is a proprietary composite trusted for corrosion and electrolysis resistance</li><li><strong>Weight advantage:</strong> Marelon® components weigh approximately half as much as comparable bronze parts</li><li><strong>Industry certifications:</strong> UL approved and A.B.Y.C. compliant plumbing systems</li><li><strong>Breadth of catalog:</strong> Over 100 products spanning deck hardware, plumbing, safety, and maintenance</li><li><strong>American heritage:</strong> Privately held and California-based since 1965</li></ul><p>Whether you're outfitting a new build, replacing aging through-hull fittings, or upgrading your helm station, Forespar offers a rigorously engineered solution backed by six decades of marine expertise.</p>

Part Number

903000
09/19/2036 1:33 PM
Sale Price

$26.40

In Stock (10+)

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Usually delivered within 2 days

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Product Details

The Forespar 903000 Marelon Vented Loop is a critical safety component for marine plumbing systems, designed to prevent dangerous back-siphoning that could lead to flooding or sinking. This 1-1/2" vented loop valve allows air to enter drain lines when needed, breaking the siphon effect that can cause water to flow backward into the vessel.

Key Features:

  • Constructed from glass-reinforced Marelon composite for superior corrosion resistance
  • 1-1/2" NPT thread size for standard marine plumbing connections
  • Prevents back-siphoning in sink, shower, and discharge systems
  • Must be installed above the waterline for proper operation
  • Non-metallic construction eliminates galvanic corrosion concerns
  • Durable marine-grade materials withstand harsh saltwater environments

Vented loops are essential for any through-hull discharge system including heads, sinks, and pumps. The valve automatically opens to admit air when negative pressure develops in the line, preventing seawater from being siphoned back into the boat. This Marelon construction offers significant advantages over traditional bronze fittings, including lighter weight, no corrosion, and excellent strength-to-weight ratio.

Products specifications

Compatibility

In-Line

Diameter

For 1-1/2" Line

Material

Marelon

Type

Vented Loop

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