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Valve compression issues on new instruments?



 
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bassguy
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Joined: 25 May 2016
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PostPosted: Thu Apr 20, 2017 12:22 pm    Post subject: Valve compression issues on new instruments? Reply with quote

Specifically how is valve compression measured? How quickly can valve compression diminish on a new indtrument? I just ordered an instrument & a credible THF messaged me about his experience with the same product, describing low valve compression & premature lacquer wear around the valve casing
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Richard A
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Joined: 11 May 2005
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Location: Rhode Island, USA

PostPosted: Thu Apr 20, 2017 12:59 pm    Post subject: Re: Valve compression issues on new instruments? Reply with quote

bassguy wrote:
Specifically how is valve compression measured?


James Becker at Osmun Music has a leakdown tester. He can quantify compression.

bassguy wrote:
How quickly can valve compression diminish on a new indtrument?


It would depend on how tight it was to start and how faithfully you kept it cleaned and lubed.
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Richard III
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PostPosted: Thu Apr 20, 2017 2:31 pm    Post subject: Reply with quote

Ignore this if it is too annoying, but I play instruments all the time that are 40-60 years old with fine compression. Any brand that has that bad of valves is not worth having at any price. Oh wait, any price seems to be little silly. If some guys says, hey man, here's a horn for a dollar that you just have to use 30 weight motor oil to make the valves work, I might be tempted.
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Richard

Holton H378 French Horn
Adams F1 Flugelhorn
1962 Conn Victor Trumpet
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rufflicks
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PostPosted: Thu Apr 20, 2017 2:41 pm    Post subject: Reply with quote

How does it play???
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James Becker
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Joined: 02 Sep 2005
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Location: Littleton, MA

PostPosted: Fri Apr 21, 2017 4:15 am    Post subject: Re: Valve compression issues on new instruments? Reply with quote

Thank you Richard for mentioning our ability to quantify valve seal.

Under a load of 1 psi of static air pressure our test can detect the "blow by" or pressure loss of piston and rotor valves. Keep in mind the sound pressure you produce inside a wind instruments does not exceed 1 psi, so this is a realistic amount of pressure.

When new, top end manufacturer's valves will typically score 95% air tight with 5% pressure loss, while student models typically score 85% air tight with 15% pressure loss. Instruments that loose greater than 20% from when new are candidates for rebuild.

Longevity of seal is improved when valves are fitted to closer tolerances to begin with, are cleaned regularly, and oiled daily. The purpose of oil is not only for lubrication but also to displace the damaging effects of trapped condensation from your breath. As with any unprotected brass, oxidation will occur allowing copper carbonate deposits to build up inside your instrument. Corrosion removes zinc from the alloy and copper carbonate will act as an abrasive accelerating mechanical wear.

This diagnostic test is provided free of charge for our repair customers so we can more intelligently advise them as to whether a rebuild is needed or not.

FWIW we've witnesses a Bach Stradivarius C trumpet that was played daily for seven years need a valve rebuild and replacement leadpipe due to "red rot" (de-zincification). So you'd do well to keep up your instrument's maintenance.

I hope this is helpful.
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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 http://go.mappoint.net/ups/PrxInput.aspx
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Richard III
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Joined: 22 May 2007
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Location: Amador County, CA

PostPosted: Fri Apr 21, 2017 5:46 am    Post subject: Reply with quote

I do a plug the bell test and blow. This is how I found out that an old cornet had an issue with it's tuning slide water key. It seemed okay. The cork wasn't bad. But the spring was weak and it wasn't sealing completely. Easily fixed as part of my tech person's fixing of all issues. The first valve has some blowby also that was made worse by old valve guides. Still an issue that thicker valve oil doesn't fix, but the horn plays fine. I may have it rebuilt in the future.
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Richard

Holton H378 French Horn
Adams F1 Flugelhorn
1962 Conn Victor Trumpet
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Paladin53
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Joined: 27 Sep 2015
Posts: 22

PostPosted: Fri Apr 21, 2017 12:49 pm    Post subject: Reply with quote

James,
Could you please explain how you go about the compression test?

What gauges do you use?
Assuming two gauges, where are they placed?
Where do you apply the 1psi air?
Where do you measure the leakage?
How do you measure the leakage?
Is it a certain amount of time, then check loss?
Or is there a measure of blow by flow?

I am familiar with compression test on engines but having a hard time understanding how one would go about it on trumpets.

Pictures would really be nice.
Thanks,
Floyd
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James Becker
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Joined: 02 Sep 2005
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Location: Littleton, MA

PostPosted: Fri Apr 21, 2017 2:07 pm    Post subject: Reply with quote

Thanks Floyd for asking about our leak tester.

To be perfectly honest I'm not comfortable listing details on a public forum. Our tester was developed specifically for wind instruments and is not the magnehelic popular with woodwind technicians. We feel it's more effective than the "Mag" machines in providing us the data we need to perform our jobs.

Anyone is welcome to come in our shop for a compression test and evaluation free of charge.
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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 http://go.mappoint.net/ups/PrxInput.aspx
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