Tidal Flap Valves – HDPE Flap Valves for Coastal and Tidal Outfalls

A tidal flap valve stops sea water and tidal river water flowing back up a drain or outfall. AQUIKO tidal flap valves are made in the UK from UV-stable HDPE, which doesn’t corrode in salt water, in standard sizes from 100mm to 1500mm.

How a tidal flap valve works

A hinged flap hangs over the end of the pipe. As the tide comes in and the water outside rises above the level in the pipe, the water pressure pushes the flap shut against its seat, so sea water can’t travel up the drain. As the tide goes out, water held back in the pipe pushes the flap open again and the pipe drains.

Why HDPE for tidal outfalls

• No corrosion: HDPE doesn’t rust in sea water, so there’s no corroded hinge or seat to replace.
• Opens at a low head: the light flap opens with less water behind it, so the pipe starts draining sooner on a falling tide.
• Light weight: easier to handle and fit on exposed outfalls, often without lifting gear on smaller sizes.
• Little scrap value: unlike iron, plastic flaps aren’t a target for metal theft.

Stainless steel 316 is available for bespoke designs.

Choosing a tidal flap valve

• Wall-mounted flap valve: bolts to a headwall, sea wall or outfall face.
• Pipe-mounted flap valve: fits into the end of the pipe where there is no wall.
• Square flap valve: for box culverts and rectangular openings.
• Custom flap valve: for sizes over 1500mm and special requirements.

We also supply precast headwalls with a matching flap valve. See our full range of HDPE flap valves.

Tidal flap valve FAQs

How does a tidal flap valve work?

It closes as the tide rises and opens again as it falls. Outside water pressure holds the flap shut against its seat; as the tide drops, water building up in the pipe pushes the flap open and the pipe discharges.

What sizes do tidal flap valves come in?

Standard sizes are 100mm to 1500mm. Anything larger is made to order as a custom flap valve.

Do tidal 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.

More answers in our flap valve and penstock FAQs.