Description
Non Return Valve – Backdraft Shutter
This inline damper simply falls shut when no fan is forcing air through your ductwork. Hence the alternate name: Gravity Shutter.
Galvanised Steel construction. Butterfly Damper.
Non Return Damper – 315mm
Non-return damper preventing reverse airflow in ductwork. Non Return Damper automatically closes when the fan stops to prevent backdrafts. Lightweight blades for minimal resistance to forward airflow. Ideal for extraction and exhaust systems.
£16.90
20% VAT added at checkout
In Stock – Available for next day delivery
Order before 3pm today for delivery by Monday 14th September
Select Size
Frequently Asked Questions
What does a non return damper do?
It lets air flow one way only. When the fan runs, the airflow pushes the damper open; when the fan stops, the damper simply falls shut, preventing backdraughts, cold air ingress and reverse flow through the ductwork. This is why it is also called a gravity shutter or backdraught shutter.
How is it constructed?
It is a butterfly-style damper in galvanised steel, an in-line unit that fits within a run of circular ducting. There are no motors, springs to wind or controls to connect — operation is entirely automatic, driven by the airflow from the fan and by gravity when the fan is off.
What sizes are available?
The range covers circular duct diameters of 100, 125, 150, 160, 200, 250, 315, 355 and 400mm. Choose the size matching the duct run it will connect into or the fan spigot it will serve (a female connector joins the damper to a fan spigot) — the damper installs in line, in the same way as a standard spiral duct component, and should be secured and sealed like the rest of the run.
Where should a non return damper be fitted?
Typically downstream of a fan, or wherever ductwork could allow unwanted reverse airflow when the system is off — for example extract runs terminating outside. Because the blades rely on gravity and airflow to operate, follow the fitting guidance supplied and ensure the damper’s orientation allows the blades to close freely when the fan stops.
Delivery Information
In Stock
Next Day Delivery — order before 3pm Monday to Friday for dispatch the same day.
Delivery Options
| Service | Estimated Delivery | Cost |
|---|---|---|
| Standard Delivery (UK mainland) | Next working day from dispatch | £15.95 +VAT (£7.95 for small items) |
| Free Delivery | Next working day from dispatch | Free on orders over £400 ex VAT |
| Click & Collect | Collect from our Leicester branch | Free |
| Scottish Highlands & Islands | 2-3 working days from dispatch | £36.95 +VAT |
Delivery Area
We deliver to all UK mainland addresses. Scottish Highlands and Islands deliveries may take a little longer. We are not currently delivering to Northern Ireland — Click & Collect remains available.
Questions about delivery? Call us on 0116 246 0031 or email sales@alphaair.co.uk
Returns Policy
Six-Week Returns — No Restocking Fees
We want you to buy with confidence. You can return any standard stocked item within six weeks (42 days) of delivery for a full refund — 100% of the item price, no restocking or handling fees. Trade and business customers get exactly the same rights as retail customers. See our Returns Policy for full details.
Return Conditions
- Items must be unused and in original packaging
- Custom-made, bespoke or powder-coated items are made to your specification and cannot be returned unless faulty
- Items must be returned with proof of purchase
- Return shipping costs are the responsibility of the customer unless the item is faulty
How to Return
- Contact our customer service team to arrange a return
- Pack the item securely in its original packaging
- Include your order number and reason for return
- Ship the item to our returns address
Faulty Items
If you receive a faulty or damaged item, please let us know as soon as possible — ideally within 48 hours of delivery, so we can claim against the courier on your behalf. We will arrange a free collection and send a replacement or issue a full refund. This does not affect your statutory rights.
Questions? Contact us at sales@alphaair.co.uk
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