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Forespar 903008 Marelon 1/2" Vented Loop Anti-Siphon 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

903008
06/01/2036 4:23 PM
Sale Price

$26.57

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Product Details

The Forespar 903008 Marelon Vented Loop is a vital safety component for marine plumbing systems, designed to prevent dangerous back-siphoning that could lead to flooding or sinking. This 1/2" vented loop valve allows air to enter the discharge lines when needed, breaking the siphon effect and protecting your vessel from unwanted water intrusion.

Key Features:

  • Constructed from glass-reinforced Marelon composite for superior corrosion resistance
  • 1/2" NPT thread connections for standard marine plumbing integration
  • Anti-siphon valve automatically opens to admit air when pump stops
  • Designed for installation above the waterline in head, galley, and livewell discharge systems
  • Non-metallic construction eliminates galvanic corrosion concerns
  • Durable composite material withstands harsh marine environments

Essential for preventing back-flow in marine toilet, sink, and pump discharge systems, this vented loop provides reliable siphon break protection. Install above the waterline at the highest point in the discharge line for optimal performance and safety.

Products specifications

Hose

1/2" Barb

Mount Type

MF845

Size

4-1/4" W x 5-1/4" H

Shipping was 5.00 on a 1.99 part but considering ebay was asking 18.00 for it I'm very happy

So good so far

Ordering went extremely smooth

good

Thanks. Best price + shipping I found.

Easy buying

great service!

Quick and easy.

Excellent price and quick delivery made my first purchase a great one. Will for sure be checking out Autoplicity for any future buys.

Best parts at the best price, will continue to order from Autoplicity. Shipping is also very fast.

Best price I could find! Shipped through UPS, great service.

Fast and inexpensive. Thanks.

Price was the lowest for the product that I wanted. That's including shipping price, which was still cheaper. Will definitely look into other products from them.

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