Revitalizaire Heavy-Duty Spring-Loaded Backdraft Damper. Install in Any Orientation Without Sealants or Solvents. Galvanized Steel Casing, Aluminum Blades and EPDM Rubber Seals. (4 Inch)

I sprayed it with silicone lubricant before mounting in dryer duct as it did not appear to be easy opening. Hopefully after use it will become more easy to open. Duct is made of heavy gage metal and gaskets provide a good seal when mounting in 4” round metal or flex duct. On dryer duct, I would check periodically to see it is still working as lint may clog it. Not a fault in manufacture.

Works as advertised. I have an a/c's 6" exhaust and a 6" duct fan running into a 6" X 4" Y reducer with a 4" booster fan controller by a thermostat that takes the hot air outside (through 20' of 4" pipe). A/C runs all the time, and the duct fan runs only when the lights are on. Inserted one of these in 1 side of the "Y" and an Aldes back draft preventer in the other side. No hot air vents back into the room. When the booster fan kicks on, the damper opens slightly to relive the negative pressure. Would definitely recommend.

hopefully spring force could be adjusted

This is my 2nd purchase of this product. Well built and sturdy.

The piece is sturdy, came quick and should work great for my purpose. Some reviews said the spring was too strong, but this hasn’t been the case for me. I do have a pretty strong fan behind it but it is also down the line from the fan about 2 to 3 feet and opened easily.

This is a very high quality damper. It appears to seal almost completely. Unfortunately the spring is so strong that the butterfly dampers inside only open halfway reducing the effective area for air to flow when my bath fan is on causing it to work harder and creating extra noise. My fan is rated at 110 cfm which should be plenty of power to open the damper completely. It's too bad that this is the case because every other component on this backdraft damper is top notch. I would say that the spring is at least 2 or 3 times stronger than it ought to be to function correctly.

Nice design, however will nt work with a dryer, it doesn't have the push or strong enough flow to open the flap. Make sure you have a strong fan behind this.

Very well made, fit's together like a watch. But needs a lot of static pressure to open. My bathroom fan could not push the doors open.