Advice on valve compression please

[richarddownunder]

Hi All

got some magnehelic measurements made on my (newish) trumpet - I don't know what the units are but assuming they are a standard unit for this type of measurement. I wondered if there were thoughts on whether these are acceptable. The manufacturer says they are within their spec.

First set dry, second set oiled

1ST VALVE UP 3.0 2.3
1ST VALVE DOWN 3.0 2.3
2ND VALVE UP 3.2 2.0
2ND VALVE DOWN 4.0 3.1
3RD VALVE UP 3.4 2.1
3RD VALVE DOWN 3.4 2.6

The guy who did the measurements was very helpful and thought they were OK, but, I think, not very good... but the key is how the horn plays.

Just interested really in any wisdom from those knowledgeable in such things.

Cheers
Richard

[Richard A]

I’ve only seen compression measured with a leak down tester. My suggestion would be to measure at some interval, perhaps annually, and see how it changes. Then find a friendly dealer who will let you measure a brand new horn or two and compare your results.
_________________
Richard Ashmore
I am a Mechanical Engineer and have many years of Social Distancing experience.

[zaferis]

I've never seen measurements like this done on valves..

In my mind, compression (the lack of compression) will have an effect on the valve movement before there is air leakage around the valves during play (so worn or untrue that the valve is hanging up). My reasoning is that the amount of air actually moving through the instrument creates much less standing pressure than the instrument can handle - the air can easily escape from the bell. You would have to be moving an inordinate amount of air for the pressure to "back up" enough to get forced around the valves, unless the compression was very low - by the time the valves have that little compression you would have more issues with them hanging up.

The interesting number(s) would be, how low can the compression be before leakage during play has impact upon tone. Then, how different is that with various mutes? I can imagine it's different with a Harmon mute.

I own a couple instruments that have I've had for 30+ years (continuous use) that have no "pressure" issues and still perform well. I think any realtively new instrument would be well within playable ranges - again, unless there is an mechanical/physical issue from damage or extremely poor construction.
_________________
Freelance Performer/Educator
Adjunct Professor
Bach Trumpet Endorsing Artist
Retired Air Force Bandsman

[shofarguy]

Richard,

Back about 10 years now (wow, it HAS been that long!) I owned a 1976 vintage Benge 5X. It had really... No, extremely loose slotting. Eventually, it began to leak water and bubbles out between the tubes of the 3rd valve slide and the 2nd valve slide would blow off when I played. I had to hold that with my middle finger when I played it!. Then, the 1st valve piston began to hang up.

I had all the pistons rebuilt and all of the slides refit. The change in slotting and resonance was dramatic. Now, the horn landed notes confidently and changed partials crisply.

So, I recommend that you focus on the slotting and resonance of your horn. If it plays well and sounds good, if it works mechanically, don't worry! If it feels and plays loosely, it might be time to check it out further.
_________________
Brian A. Douglas

Flip Oakes Wild Thing Bb Trumpet in copper
Flip Oakes Wild Thing Flugelhorn in copper


There is one reason that I practice: to be ready at the downbeat when the final trumpet sounds.

[OldSchoolEuph]

Magnehelic is a brand name for precision pressure gauges. The only application that relates to valve compression is to stop the bell and pressurize the horn slightly (clamping spit key too) and at a very light induced pressure of a few inches water column (1"WC=.036PSI), and then measure the leak-down over a set amount of time. As the first number is not the same in each line, I don't know if these are best and worst leakdowns from multiple runs, or if that is starting and ending in a unit time - and then how much time?

I have done this to demonstrate poor quality valve fitting on some new (and surprisingly major/expensive) horns, but it only provides a comparative frame of reference. How much is too much also depends largely on the geometry and other properties of the individual horn. Long before a horn's valves flop around, higher frequencies will begin to leak through excessive valve gaps. This makes intonation more challenging, leads to frequency based variation in resistance, and eventually degrades the tone quality. But there is no leak-down = degradation chart one can make, so really, this sort of measurement is just a crude yard-stick to demonstrate a problem to non-playing engineers.
_________________
Ron Berndt
www.trumpet-history.com

2017 Austin Winds Stage 466
1962 Mt. Vernon Bach 43
1954 Holton 49 Stratodyne
1927 Conn 22B
1957 Holton 27 cornet
1985 Yamaha YEP-621
1975 Yamaha YEP-321 Custom
1965 Besson Baritone
1975 Olds Recording R-20

[kalijah]

zaferis wrote:

[richarddownunder]

Hi and thanks for the replies. I figured this was a standard analysis of valve state as a similar set of results had been produced by another tech. Apparently it's 0 to 10 scale and my understanding was that above 5 was considered ready for refurbishment. However, maybe it's not such a common approach as I was led to believe.

I'm hoping to replace the horn later this year as I'm not that happy with it anyway. I was just interested in whether this valve tolerance could be a contributing factor in my not really getting on with it so thought I'd ask as I had some numbers.

Thanks again
Richard.

[Wondra]

Whenever I've had valves checked for compression, it's been stated in terms of the clearance between each piston and respective valve casing. Using this measurement, clearance of .0005 to .001 is considered a good fit.
_________________
Dave Wondra

Don't make me get the flying monkeys...

[LittleRusty]

[Wondra]

[James Becker]

In our workshop we use a leak tester that measures the amount of pressure loss at 1 lb of static air pressure. Understanding that the sound pressure in wind instruments doesn't exceed 1 lb, this test provides us a realistic load by which to judge go or no go.

In our industry there are two tiers of valve fit manufacturers typically go for.

The most common are student valves that are ground or honed to a target diameter that allows them to be dropped into the casing without further hand fitting. On average these will lose between 15 and 20 percent, or score 80 to 85 percentage points on our test. This more relaxed fit allows valves to move freely with enough seal to allow for playability.

For professional grade instruments the standards are higher. Final hand fitting of pistons in casings is required to achieve a tighter seal. Typically the better makers score 95%, while some may relax their fit to 90% but not less than 85%.

Our diagnostic leak test allows us to determine when a valve rebuild is in order. We final test our rebuilds to insure they meet or exceed industry standards. We offer this diagnostic test free of charge to our customers, you simply have to ask.

A film of valve oil can bump these numbers by as much as 5 percentage points. Hetman #3 Classic oil can be an excellent stop gap to improve the seal of leaky valves until such time a rebuild can be done.

I hope this is helpful.
_________________
James Becker
Brass Repair Specialist Since 1977
Osmun Music Inc.
77 Powdermill Road Rt.62
Acton, MA 01720
www.osmun.com

Our workshop is as close as your nearest UPS store https://www.ups.com/dropoff?loc=en_US

[etc-etc]

[snowjam]

I should change by id to cheapbstrd because I can sure vouch for the Hetman #3 oil improving valve compression! $15 in oil delayed my having to replace my sons horns for 12 months so far!

He really wants to complete a rebuild of an an old Conn '46 22B, were down to dents and tuning slides now.