X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from wx-out-0506.google.com ([66.249.82.224] verified) by logan.com (CommuniGate Pro SMTP 5.1.12) with ESMTP id 2373592 for flyrotary@lancaironline.net; Sun, 07 Oct 2007 07:34:19 -0400 Received-SPF: pass receiver=logan.com; client-ip=66.249.82.224; envelope-from=msteitle@gmail.com Received: by wx-out-0506.google.com with SMTP id i27so891599wxd for ; Sun, 07 Oct 2007 04:33:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=beta; h=domainkey-signature:received:received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; bh=w26KLGjqlDIaoUe/ZR+aNGcvZaY2UTpRyJD4w6YnUCc=; b=IDUggVkYPhsvuSU6gCden6W5w9RbZXElzR042bXJwLTZhhZajB/sqs/0IFlft4ZRxG+JfPmtcOcpFRxRam71aTU9QJRNqj/5P6fBam84I9R2cuH0aE6cVccBCZMUHT2Nh2v+WLhlMftDDgfbyZQ48THV1+9/E3HgEG1EItLBUts= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:to:subject:in-reply-to:mime-version:content-type:references; b=jp/4S9hwsGo1DBNYo0Sa3sDqA1IqvztitJqPgDmOGzXCjw8sB9PxEJmJvPTD3MGCqhGEpcriCMp4wLzyl9LoPw29dxJcLEwPgtw1YakBcmEBvxxoS2LNlv4091v4+Y+2pQ8h8jPfziE+OfxQKGKyerEYWCgF0QaxATOFotsgWzA= Received: by 10.90.96.7 with SMTP id t7mr2040788agb.1191756820513; Sun, 07 Oct 2007 04:33:40 -0700 (PDT) Received: by 10.90.35.16 with HTTP; Sun, 7 Oct 2007 04:33:40 -0700 (PDT) Message-ID: <5cf132c0710070433i694466dcjb1ac53bcded86ccb@mail.gmail.com> Date: Sun, 7 Oct 2007 06:33:40 -0500 From: "Mark Steitle" To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] Hose clamp myth busters In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_Part_37671_24111632.1191756820503" References: ------=_Part_37671_24111632.1191756820503 Content-Type: text/plain; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Al, Thanks for the analysis. I always wondered why cars, which use the "old fashion" clamps, don't blow hoses left and right. I guess I'm just a belt and suspenders kind of guy. I like the fact that they adjust to the expansion. Mark S. (I used "Wiggins" couplings) On 10/6/07, Al Gietzen wrote: > > If those hose clamps are not constant torque clamps, please consider > upgrading them before first flight. They're available from McMaster. > > > > Mark; > > > > I have no objection to the use constant torque clamps, of course. But I > will express my conclusion/opinion that this clamp thing has been over so= ld. > Certainly not picking on you, and I know our friend on the other list ma= kes > a big issue of the constant torque clamp. IIRC, the main point raised wa= s > the effect of thermal expansion, more exactly the differential thermal > expansion between the inner metal tube (aluminum in this case) and the cl= amp > (usually SS). Doing the math will show that this is less than > infinitesimal. The temp change of the coolant may be about 80 C cold to > hot. The clamp heats up maybe 15C less than the aluminum. Assume a 1 =BD= " > diameter. So the aluminum expands about 0.000037" on the diameter while > the SS expands only 0.000012"; a huge difference of 0.000025". I am > certain that this effect on the thickness of the elastomer hose is entire= ly > negligible. And besides, having that clamp just a wee smidgeon tighter wh= en > it is hot and pressurized can't be a bad thing. > > > > Now, it is true that over time the elastomer loses some of its elasticity= , > mostly over the first few months, and then very slowly over the next few > years =96 depending on the type of elastomer, of course. > > > > So whether they are regular good quality clamps, properly tightened (not > over-tightened), or constant torque clamps properly tightened; I'd sugges= t > that the important factors are: re-torque the clamps after a few weeks or= a > month of use; use the widest clamp for the diameter, and consider high > quality silicone hose =96 although contemporary automotive coolant hose c= an be > expected to last 6 =96 9 years. The other thing, of course, is that on o= ur > planes we will probably change out the hoses every second annual or so > anyway. > > > > One more thing. Consider putting a Schroeder valve on the system > somewhere so you can easily pressure test the system before you fly (or > before you start your engine), and maybe at annual time. It is so much > easier to deal with any leak while things are cool and on the ground. > > > > Sorry; did I go on too longJ? > > > > Al G > ------=_Part_37671_24111632.1191756820503 Content-Type: text/html; charset=WINDOWS-1252 Content-Transfer-Encoding: quoted-printable Content-Disposition: inline
Al,
Thanks for the analysis.  I always wondered why cars, which use t= he "old fashion" clamps, don't blow hoses left and right.&nbs= p; I guess I'm just a belt and suspenders kind of guy.  I like the= fact that they adjust to the expansion. =20
 
Mark S.
(I used "Wiggins" couplings)

 
On 10/6/07, = Al Gietzen <ALVentures@cox.net= > wrote:

<= span style=3D"FONT-SIZE: 12pt">If those hose clamps are not constant torque= clamps, please consider upgrading them before first flight.  They'= ;re available from McMaster. =20

<= span style=3D"FONT-SIZE: 12pt"> 

Mark;

 

I have no objection to the use = constant torque clamps, of course.  But I will express my conclusion/o= pinion that this clamp thing has been over sold.  Certainly not pickin= g on you, and I know our friend on the other list makes a big issue of the = constant torque clamp.  IIRC, the main point raised was the effect of = thermal expansion, more exactly the differential thermal expansion between = the inner metal tube (aluminum in this case) and the clamp (usually SS). &n= bsp;Doing the math will show that this is less than infinitesimal.  Th= e temp change of the coolant may be about 80 C cold to hot.  The clamp= heats up maybe 15C less than the aluminum. Assume a 1 =BD" diameter. = So the aluminum expands about=20 0.000037" on the diameter while the SS expands only 0.000012"; a huge diffe= rence of 0.000025".  I am certain that this effect on the thickness of= the elastomer hose is entirely negligible. And besides, having that clamp = just a wee smidgeon tighter when it is hot and pressurized can't be a bad t= hing.

 

Now, it is true that over time = the elastomer loses some of its elasticity, mostly over the first few month= s, and then very slowly over the next few years =96 depending on the type o= f elastomer, of course.

 

So whether they are regular goo= d quality clamps, properly tightened (not over-tightened), or constant torq= ue clamps properly tightened; I'd suggest that the important factors are: r= e-torque the clamps after a few weeks or a month of use; use the widest cla= mp for the diameter, and consider high quality silicone hose =96 although c= ontemporary automotive coolant hose can be expected to last 6 =96 9 years.&= nbsp; The other thing, of course, is that on our planes we will probably ch= ange out the hoses every second annual or so anyway.

 

One more thing.  Consider = putting a Schroeder valve on the system somewhere so you can easily pressur= e test the system before you fly (or before you start your engine), and may= be at annual time.  It is so much easier to deal with any leak while t= hings are cool and on the ground.

 

Sorry; did I go on too long J?

 

Al G


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