3 Inch 304 Stainless Steel Exhaust Rain Cap with Gravity Counterweight Flap for Truck Exhaust Stack

A vertical exhaust stack on a working truck is an open chimney. This 3 inch 304 stainless exhaust rain cap closes that opening with a gravity flapper that lifts under exhaust pressure and drops back the moment the engine stops. The 76 mm inlet slides over a standard 3 inch stack and locks with a stainless clamp band.

The shell and flap are formed from 304 stainless steel rather than aluminised mild steel, which matters on trucks that run winter roads treated with salt. 304 keeps a stable oxide layer after repeated heat cycling, so the flap hinge does not seize and the sealing face stays flat. The counterweight is tuned for light-duty diesel engines: it opens at low idle and closes firmly without slamming, which keeps cab noise and flap rattle under control at traffic lights.

• 76 mm clamp fit: the inlet collar is rolled to 76.2 mm and slots onto standard 3 inch exhaust stacks with a 1.5 mm clearance for sealant or graphite paste.
• 304 stainless construction: shell, flap and hinge pin are all 304, avoiding the dissimilar-metal corrosion that eats riveted mild steel caps.
• Gravity counterweight flap: calibrated so the flap lifts at idle back pressure and returns fully closed within one second of shutdown.
• No-weld installation: a 30 mm wide stainless band with a T-bolt takes the cap from box to fitted in under five minutes.
• Weather lip: the flap overhangs the collar by 6 mm so run-off drips clear of the stack wall instead of tracking down the pipe.
• Fleet serviceable: hinge pin is a removable stainless clevis, so a bent flap can be swapped without scrapping the whole cap.

The 3 inch exhaust rain cap is the volume seller in our auto spare parts range because 3 inch stacks are the most common size on light and medium trucks. Typical installations include:

1. Light trucks and box vans with vertical stacks behind the cab
2. Tipper and flatbed fleets that park outdoors all year
3. Small agricultural trailers running PTO-driven equipment
4. Workshop standby engines where the stack exits through a wall collar