Posted by Charlie on January 18, 2002 at 09:32:10:
In Reply to: Re: Re: Valve port blisters. posted by Duh... on January 18, 2002 at 09:22:46:
I will take a whack at it for you.
on piston tubas on the valves, there are 3 to 4 holes through the pistons where air travels when the pistons are in the up position and when depressed to carry air through the tubes for each piston. These holes in the pistons are called ports. In these holes, you will see little bumps inside where the lower or upper port next to it interferes with it and it causes this bump or blister.
hope this helps