I have a Courtois .525-.547 trigger horn. The valve section bore measures .547. When I look from the receiver end through the gooseneck with the tuning slide off a portion of the valve obscures a small part of the airway..enough to notice. Can this be a factor in how the horn blows? Are valves supposed to leave the airway completely open? or not?

Depends what you're looking at. You wouldn't expect to see straight path through, given the curvature of the knuckles.

But if you're seeing the edge of the rotor core with the valve either at rest or fully engaged, then it's misaligned and the bumpers either need replacing or trimming, depending on the direction of correction required. Checking the markings on the valve stem and bearing plate (under the screw cap) should confirm - these aren't always perfect from the factory, but they're better than guessing.

The Meindlschmidt 'Flow' as pictured on its' website show a perfectly circular pathway...? What I am seeing is the curvature of the knuckles

[quote="Gribnes"]The Meindlschmidt 'Flow' as pictured on its' website show a perfectly circular pathway...? What I am seeing is the curvature of the knuckles[/quote]
Right, a valve that is different and is mounted differently looks different.

Almost all rotors do not have full circular cross sections for the air paths. The ones that do often advertise something like a "fully in-tact duct" or some such.

Almost no rotors have a straight path through the valve. One of the Meinl's, Shires Tru-bore, etc. try for this.

These "issues" are pretty much WHY we have so many options in valves today. I have no idea what rotor is on your Courtois, but most rotors do not provide a clear, unobstructed circular path.

Cheers,

Andy