The thickness of the small black plastic frame of the screen must be installed under the gasket for the lens to seal properly.

Or are you missing a screen or shim?

There is an important design aspect of the Beckson ports to be aware of. The ports are designed to accept a fly screen installed in a gap provided between the gasket and the plastic frame of the port. In fact it is the gasket that holds the screen in place. But without the thickness of the screen's frame behind it the lens will not compress the gasket adequately and therefore won't seal. The screen must be in place for the lens to seal properly.

Beckson ports were originally shipped from the manufacturer with both the screen and a plastic spacer the shape of the screen's frame. Now ports are shipped without the spacer. Over time and a series of owners, even if they were there when new, the screen or the spacer may have been lost.

One more caution: If you happen to have both the spacer and the screen, never install both at the same time. Either use the screen or the spacer. Attempt to install both at the same time and you will break the hinges or frame when you tighten the dogs.

We carry replacement screens, gaskets, and lenses for both of the port sizes used by Catalina, the 5" X 12" and the 4" X 10".