Valve stroke

Discussion in 'Trumpet Discussion' started by Wlfgng, Oct 23, 2008.

  1. Wlfgng

    Wlfgng Piano User

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    While practicing today my mind started to wander a bit. Why do the valves on my trumpet have a longer stroke than the vlaves on my cornet?

    The stroke on the cornet is about half of what it is on my trumpet.

    Wouldn't a short stroke valve on a trumpet be the thing to have?


    Or should I just quit wondering and go back to practicing?
     
  2. Clarence

    Clarence Mezzo Forte User

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    Welcome to the world of custom horns!
    I love how my Pheaton and stage 1, have that short stroke thing going on!
     
  3. veery715

    veery715 Utimate User

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    It's just a design variation. Tubing must all be closer together, vertically, where it intersects with the valves. My guess is it's more difficult to assemble a horn with less clearance between the tubes in the valve section. A smaller bore would facilitate this, but it is unlikely that your cornet's bore is much smaller than your trumpet.
    On the pistons the ports would need to be closer too, but that doesn't represent the same level of construction obstacle as the tubing does.
     
  4. Puukka

    Puukka Pianissimo User

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    I doubt. I guess, it´s just an optical trick like at the Conn Vintage One and 52B.
    The rim of the top valve case is just higher than the inner part.
    Herbert
     
  5. oldlou

    oldlou Forte User

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    Sorry, Veery, the amount of bearing surface above and below the ports is designed to be optimal. Some designs, such as is found in the York Airflow trumpet and cornet have the shortest stroke I have ever found. I asked A.J.'Bill' Johnson, the designer of the Airflows about this and he stated that "the port spacing is just about average, but, the length of piston above and below the ports is very short. This 'could' show up as excessive wear if the valve plating and fit is less than very close to perfect". This of course could then result in valve leakage if the manufacturing quality was less than what he demanded. Bill said that he took a chance in his design, but, backed it with closer tolerances and the finest lapping that he could attain, along with the very best grade of nickel silver plating.


    OLDLOU>>
     
    Last edited: Oct 24, 2008
  6. veery715

    veery715 Utimate User

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    But Oldlou, if the port spacing is average how will that enable a short stroke?

    When the piston is depressed 2 different ports/passages in the piston line up with the inlet and outlet tubes instead the one port/passage that was in line with them when not depressed. One of the two ports in the down position allows incoming air/sound to enter the added length of the slide tubing and the second port/passage allows it to exit back into the outlet tube. You know this, of course.

    Now that I think about it the length of travel is determined by the space between the single port on the bottom and the lower one of the pair above it. That upper one "displaces" the lower one, and the vertical distance between them is equal to the length of travel. Of course, the uppermost port/passage must also line up with the exit tube, so that port will need to be relocated downward as far as the one below it. The slides must be moved lower as well, to line up with the new lower position of the "diversion" ports, unless the passage geometry within the piston is changed. While that is a possibility, it hurts my head to try and analyze it. Leaving the slide where it is while lowering the in and out ports would mean longer diagonal tunnels through the piston and a weaker structural design. Now it does hurt!

    Inlet and outlet tubes can also be adjusted, but the limiting factor is still the piston port spacing - that is where changes in travel length occur. And changes to that will necessitate relocation of the slide tubes and or inlet/outlet (inter-valve) passages in the final design.

    Of course, bore size is a constraint. Small bores would allow shorter travel than large, simply because the piston must travel at least the diameter of the bore plus inter-port distance.

    I am not trying to get all technical, but want to truly figure out what short- or long-stroke entails.
     
  7. Ed Kennedy

    Ed Kennedy Forte User

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    There may also be some accoustic considerations in the bend radius of the valve slide bows which would dictate the stroke of the valve.
     
  8. veery715

    veery715 Utimate User

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    Ed, I don't think it matters. Pretend the 2nd valve slide is a bigger radius and the ends where it meets the valve cylinder are now a whole inch apart, with the bottom end in the same place but the upper end closer to the top of the cylinder. The length of travel is still the distance between the piston bottom port (up position) and the "diversion" ports (down position). The lower slide port which connects to the inlet would not need to be moved, but the port which connects with the upper end of the now elongated slide would require an elongated diagonal passage in the piston that would reach from that higher upper port down to the outlet port. Maybe a longer piston (and cylinder) would be needed to accommodate the longer diagonal tunnel, but length of stroke would not be different. With a change in geometry, all ports still move the same distance. How far apart the slide in and out ports are only changes slide and piston tunnel configuration, not length of piston travel.
    In other words, you push the valve down to move the up-position port down out of the way and the down-position ports down into line with the inlet. The distance you move the valve - the distance between those ports on the piston, gives you the stroke length of the valve.
     
    Last edited: Oct 24, 2008
  9. nieuwguyski

    nieuwguyski Forte User

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  10. rowuk

    rowuk Moderator Staff Member

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    The length of the stroke has NOTHING to do with the fact that it is a cornet or trumpet. It is simply a design parameter from the manufacturer. Disregard the fact that ad people can always create a story for facet of anything.

    I am sure that 150 years ago, the stroke was longer due to manufacturing techniques and shortcomings. Modern manufacturing allows any length of stroke without changing the quality of the "seal" of the valves and ports. There are different strokes for different folks because that it what they feel comfortable with.

    I use to have a Benge and it had the longest stroke of any horn that I ever owned. It did not change my ability to play Clarke technical studies at any particular speed. It became a non-factor after a couple of weeks of play.
     

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