Flap Valves – HDPE Tidal & Outfall Flap Valves, Made in the UK
At AQUIKO, we supply a comprehensive range of high-quality flap valves engineered for robust flood-defence, drainage and sewer applications. Designed to prevent reverse flow and ensure reliable operation, our flap valves deliver dependability in demanding UK environments. Whether you need wall-mounted, pipe-mounted, side-hung or bespoke units, you’ll find the right solution here.
Why Choose AQUIKO Flap Valves
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Proven reverse-flow prevention — our flap valves are designed to close quickly and effectively under back-pressure, reducing flood risk and protecting infrastructure.
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No corrosion — our standard flap valves are UV-stable HDPE, which won’t rust in sea water, sewage or aggressive ground. Stainless steel 316 is available for bespoke designs.
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Minimal maintenance — large opening angles and flush design components ensure debris is less likely to cause jams, giving you lower lifetime costs.
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UK-made and UK-stocked — AQUIKO makes its flap valves in the UK and holds standard sizes in stock, so most orders ship quickly with local technical support.
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Bespoke capability — if your project demands unusual dimensions, unique mounting or specific materials (e.g., stainless steel 316), our custom flap valve service has you covered.
Our Flap Valve Product Range
Browse by configuration:
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Wall-Mounted Flap Valve — ideal for mounting on outfalls, culverts or headwalls where a standard plate solution fits easily.
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Pipe-Mounted Flap Valve — designed for insertion into pipes, enabling end of line non-return protection for drainage or sewer systems.
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Side-Hung Door Flap Valve — perfect for providing a fish friendly solution to flood defence.
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Square Flap Valve & Custom Variants — for bespoke projects, larger openings or special materials requirements.
Installation & Service Considerations
When specifying a flap valve, please consider:
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Minimum required opening angle – ensuring full flush out of debris and achieving the fastest response on closure (studies show larger opening angles reduce head-loss and improve performance).
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Material choice – if your installation is coastal or in chemically-aggressive environment, ask us about stainless steel 316 options for enhanced corrosion resistance.
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Finish, flange type and access requirements – integration with your headwall or pipework should be seamless; our team will advise on custom modifications and site-fit details.
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Maintenance access – our designs require minimal maintenance.
Why AQUIKO
AQUIKO designs and makes flow control and flood protection products in the UK, backed by decades of flood-defence and hydraulic engineering experience through our sister company Aquatic Control Engineering. Every flap valve comes with drawings, datasheets and specification support.
Ready to specify your flap valve? Get in touch with our sales team today for:
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Stock availability and lead-times
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Bespoke sizing and materials
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Support with specification, drawings and installation advice
01777 819 734 | info@aquiko.co.uk
What is a flap valve?
A flap valve is a non-return valve fitted to the end of a pipe or to an outfall wall. A hinged flap hangs over the opening. Water flowing out of the pipe pushes the flap open; when the water outside rises higher than the water in the pipe, for example a river in flood or a high tide, the flap is pushed shut against its seat and stops water flowing back up the drainage system.
Flap valves are used on surface water outfalls, culverts, attenuation tanks, pumping station outlets and tidal outfalls. On the coast and on tidal rivers they are often called tidal flap valves, because they close as the tide comes in and open again as it goes out.
Tidal flap valves
A tidal flap valve protects outfalls on the coast and on tidal rivers. As the tide comes in, sea water pressure pushes the flap shut against its seat so it can’t travel up the drain. As the tide goes out, water held in the pipe pushes the flap open and the pipe drains.
HDPE suits tidal outfalls because it doesn’t corrode in salt water, and the light flap opens at a low head, so the pipe starts draining sooner on a falling tide. Our HDPE flap valves come in standard sizes from 100mm to 1500mm, with larger sizes made to order as custom flap valves.
See our tidal flap valves.
Flap valve types
| Type | How it fits | Best for |
|---|---|---|
| Wall-mounted flap valve | Bolts to a headwall, chamber wall or outfall face | Outfalls and headwalls, new or existing |
| Pipe-mounted flap valve | Spigot fits into the end of the pipe | Pipe ends with no headwall |
| Square flap valve | Bolts over a square or rectangular opening | Box culverts and chambers |
| Side-hung door | Hinged at the side rather than the top | Fish-friendly outfalls |
| Custom flap valve | Made to suit | Sizes over 1500mm and special requirements |
Round flap valve sizes
Our standard round HDPE flap valves are made in the UK in sizes from 100mm to 1500mm. Choose your size for drawings, datasheets and a quote:
| 100mm | 150mm | 200mm | 250mm |
| 300mm | 400mm | 500mm | 600mm |
| 700mm | 800mm | 900mm | 1000mm |
| 1100mm | 1200mm | 1300mm | 1400mm |
| 1500mm | Over 1500mm: see custom flap valves | ||
HDPE flap valves
All AQUIKO standard flap valves are HDPE flap valves, made from UV-stable high-density polyethylene rather than cast or ductile iron. That gives you:
- Light weight: far easier to handle and fit, often without lifting gear on smaller sizes.
- No corrosion: HDPE doesn’t rust in sea water, sewage or aggressive ground.
- A low opening pressure: the lighter flap opens with less head, so water drains away sooner.
- Little scrap value: unlike iron, plastic flaps are not a target for metal theft.
Stainless steel is available for bespoke designs or special requirements. Read more in Why HDPE for penstocks and flap valves.
Flap valve, duckbill or WaStop®?
A flap valve isn’t the only way to stop backflow. A duckbill valve uses rubber lips that press together, and a WaStop® inline non-return valve uses a membrane that sits inside the pipe. Flap valves are robust, simple and suit most outfalls, especially larger ones. A WaStop® is better where there is no headwall, the pipe is vertical, or odour is a problem. Not sure which suits your site? Ask us and we’ll recommend the right one.
Flap valve FAQs
Is a flap valve a check valve?
Yes. A flap valve is a type of check valve, also called a non-return valve or backflow valve: it lets water flow out and stops it coming back. The flap is the moving part that opens and closes.
How does a tidal flap valve work?
As the tide rises above the level in the pipe, the water pressure outside pushes the flap shut so seawater can’t travel up the drain. As the tide falls, the water building up in the pipe pushes the flap open again and the pipe discharges.
Do I need a headwall for a flap valve?
Wall-mounted flap valves fix to a headwall or wall. If there is no wall, use a pipe-mounted flap valve. We also supply precast headwalls that can be supplied with a matching flap valve.
What sizes do you make?
Standard sizes are 100mm to 1500mm. Anything over 1500mm is made to order as a custom flap valve.
Do flap valves need maintenance?
Check them during routine inspections and after floods. Clear any debris caught under the flap and make sure the hinge moves freely. Installation and operation manuals are on our documents page.
How do I get a price?
Trade customers can log in to see prices. Otherwise request a quote or call 01777 819734 and we’ll come back the same working day.
What is the difference between a flap valve and a flap gate?
They are the same product. “Flap gate” is more often used for larger square or rectangular openings, and “flap valve” for round pipes.
More answers in our flap valve and penstock FAQs.
