Non Return Valve

Non return one way check valves for boat bilge outlets and other marine related hose use. Popular hose barb sizes from 12mm, 19mm bilge hose, 25mm upto 32mm and 38mm larger pump hose sizes.

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  • Sale! Non Return Valve Medium Size

    Non Return in-line Valve 12mm 19mm 25mm

    Original price was: £15.97.Current price is: £12.99.     Add to basket
  • Sale! Large One Way Valve

    One Way in-line Valve 25mm 32mm 38mm

    Original price was: £21.97.Current price is: £18.99.     Add to basket

    • In-Line Non Return Valves for Boat Hoses

    Preventing bilge backflow shouldn’t mean reducing your pumps output  performance. Our in-line graduated size barbed non return valves feature a high water flow flap valve mechanism housed in ultra rugged, marine grade polypropylene plastic. Engineered to splice directly into your existing flexible boat hoses of various diameter, these one way valves provide an airtight seal against backflow without the high cost, weight, or corrosion risk of older more traditional metal fittings.

    Whether you’re stopping water from trickling back into your bilge or securing low pressure gravity deck drains, our heavy duty stop valves offer the perfect balance of durability, easy installation, zero maintenance and reliability.

    The Benefits of a Heavy Duty Non Return Valve

    Why choose an in-line one way flap valve over a spring loaded or older style metal valve? The engineering makes all the difference in low pressure boating and marine plumbing:

    • Zero Corrosion Risk Plastic Construction: Polypropylene Plastic is completely immune to saltwater corrosion, scale buildup, and electrolysis damage. It is impact resistant and won’t degrade under the chemical harshness of bilge cleaners or trace fuel elements.

    • Low Release Pressure Flap Valve Design: Unlike stiff spring loaded check valves that force your electric bilge pump to work twice as hard, our internal flap (or flapper valve) opens with minimal fluid pressure. This maximises your pumps gallons per hour (GPH) output.

    • Ribbed Hose Barb Ends: Molded directly into the valve body, the heavy duty barbed ends provide a high friction grip for marine hoses. Once secured with stainless steel hose clamps, they form a leak proof connection that resists heavy engine vibrations.

    • Graduated Hose Fitting Sizes: Our non return stop valves are available with multiple hose diameter fitting size options. The heavy duty ABS construction graduated in-line barbs allow for use with hose sizes from 12mm upto 38mm.

    Boat One Way Valve Installation Best Practices

    Match Flow Direction Correctly:

    Pre-installation check.

    Locate the flow arrow molded onto the valve body plastic housing. The arrow must point in the direction you want the water to flow (away from the pump, toward the thru-hull exit).

    Cut and Clean the Hose:

    Preparation for valve install.

    Cut your flexible marine hose cleanly at a 90 degree angle using a sharp knife or a pipe cutter for plastic pipe. Ensure the interior of the line is free of debris that could jam the internal flap valve open.

    Seat the Barbs Fully:

    In-Line stop valve assembly.

    Push the hose firmly over the ribbed barbs until it seats flush against the center shoulder of the valve.
    Top Tip: If the fit is incredibly tight, dip the hose end in hot water for 10 seconds to soften the plastic hose.

    Double Clamp for Safety:

    Final securing in-line one way valve.

    Secure each side using two marine grade (316) stainless steel hose clamps, alternating the screw positions to distribute clamping pressure evenly.

    Available One Way Valve Sizes & Specifications

    Our inline heavy duty boat check valves are available in standard marine hose diameters to drop straight into your water system:

    • 12mm 19mm 25mm: Perfect for many standard automatic bilge pump outlet sizes.

    • 25mm 32mm 38mm: Ideal for shower sump drains, manual bilge pump outlets and other medium size drain or bilge systems.

    Application Warning: While non return flap check valves are the gold standard for bilge lines and gray water drains, flap style valves should never be used as a stop valve on critical below the waterline suction plumbing (like engine cooling intakes). For those applications, always use a manual seacock as the last line of defense against water ingress.