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I recently acquired a 10-year-old Miraphone 291 with vented valves. 3 of them work as they should, but 2 do not. On the 3 working valves I can see the valve cover the vent hole when I press the valve, but I don't see that on the first and third, so I'm led to believe that the vent hole is plugged on those valves. I'm tempted, but hesitant, to stick a small wire in the hole to dislodge the suspected plug. Doing so would push any substance into the valve chamber, which hopefully would just fall through the horn, but I do worry a bit about it causing trouble in the valve chamber. I would appreciate any insight into this. Thanks!

Shoot water into the large vent in the bottom of the piston.

Were the holes drilled in the correct location? I seem to recall that being a big deal with rotors.

@Dan - thanks for the idea, but this is a rotary valve horn.

@Ryan - yes, all 5 are drilled in the same location; 3 work fine, 2 do not.

Thanks, both!