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Repair Techs: Venting Rotay Valves
Posted: Tue Jul 03, 2012 2:24 pm
by Z-Tuba Dude
For any Techs who care to answer:
Do you know if the act of venting a rotary valve causes any degradation of tone/pitch?
Thanks in advance!
Re: Repair Techs: Venting Rotay Valves
Posted: Tue Jul 03, 2012 2:49 pm
by tubaguy9
It does not do anything really to the tone. However, if it is not done right, it will cause a leak in the circuit while you are depressing the valve.
Re: Repair Techs: Venting Rotay Valves
Posted: Wed Jul 04, 2012 11:26 pm
by Z-Tuba Dude
bump
Re: Repair Techs: Venting Rotay Valves
Posted: Thu Jul 05, 2012 12:07 am
by Ed Jones
After 17 years of self debate, I finally had the rotors on my venerable old Neptune vented. I noticed no difference in tone or pitch. The advantage is that valve slurs are much smoother, especially those pesky cross slurs (adding tubing, and going up in pitch: low C to Db). The only disadvantage is that I can no longer make annoying sounds by pulling the 4th valve and slowly depressing the valve.
Re: Repair Techs: Venting Rotay Valves
Posted: Thu Jul 05, 2012 8:27 am
by Rick Denney
If the hole in the casing is the right size and in the right place, it will not cause a leak and if it doesn't leak it won't change the tone.
The effect Ed mentions is caused by a couple of factors, I think. One is that the air inside the valve tubing, being vented to the outside, has a wide resonance curve instead of the narrow peak resonance of the closed tubing. It keeps a narrow resonance from fighting a buzz on a different frequency during the slur. Once the valve has completed the change, the resonance is restored, but by that time the buzz and the tubing should agree on the correct pitch for the resonance.
The other is that no residual pressure or vacuum in the valve tubing will cause a pulse that could upset the resonance of the buzz.
The hole is placed in the narrow opening between the ports when the valve is not depressed. But it will be on the narrow septum between the ports in the rotary valve when the valve is depressed. That septum is narrow and if the hole is too big, it might leak. Some technicians will drill the hole slightly off-center to place it in a thicker part of that septum when the valve is depressed, but still such that it will be in the opening when the valve is not depressed.
Don't do it if the valves are worn and leaky. Fix that first.
Rick "recalling that some Miraphones had vented rotary valves from the factory" Denney