X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fed1rmmtao105.cox.net ([68.230.241.41] verified) by logan.com (CommuniGate Pro SMTP 5.1.12) with ESMTP id 2373066 for flyrotary@lancaironline.net; Sat, 06 Oct 2007 21:18:50 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.41; envelope-from=alventures@cox.net Received: from fed1rmimpo01.cox.net ([70.169.32.71]) by fed1rmmtao105.cox.net (InterMail vM.7.08.02.01 201-2186-121-102-20070209) with ESMTP id <20071007011813.WPLF25304.fed1rmmtao105.cox.net@fed1rmimpo01.cox.net> for ; Sat, 6 Oct 2007 21:18:13 -0400 Received: from BigAl ([72.192.143.193]) by fed1rmimpo01.cox.net with bizsmtp id xDJB1X0094AaN600000000; Sat, 06 Oct 2007 21:18:11 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: Hose clamp myth busters Date: Sat, 6 Oct 2007 18:19:10 -0800 Message-ID: <000001c80888$725ab1e0$6401a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C80845.643771E0" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.3138 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C80845.643771E0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable If those hose clamps are not constant torque clamps, please consider upgrading them before first flight. They're available from McMaster. =20 =20 Mark; =20 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 = sold. Certainly not picking 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). 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=94 diameter. So the aluminum expands about 0.000037=94 on the diameter = while the SS expands only 0.000012=94; a huge difference of 0.000025=94. 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=92t be a bad thing. =20 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. =20 So whether they are regular good quality clamps, properly tightened (not over-tightened), or constant torque clamps properly tightened; I=92d = suggest 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 = can be expected to last 6 =96 9 years. The other thing, of course, is that on = our planes we will probably change out the hoses every second annual or so anyway. =20 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. =20 Sorry; did I go on too long:-)? =20 Al G ------=_NextPart_000_0001_01C80845.643771E0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable

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.=A0 But I will express my conclusion/opinion = that this clamp thing has been over sold. =A0Certainly not picking on you, and I = know our friend on the other list makes a big issue of the constant torque = clamp.=A0 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). =A0Doing the math will show that this = is less than infinitesimal.=A0 The temp change of the coolant may be about 80 C = cold to hot.=A0 The clamp heats up maybe 15C less than the aluminum. Assume a 1 = =BD” diameter.=A0 So the aluminum expands about 0.000037” on the = diameter while the SS expands only 0.000012”; a huge difference of = 0.000025”.=A0 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 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 – 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 suggest 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 – although = contemporary automotive coolant hose can be expected to last 6 – 9 years.=A0 = The other thing, of course, is that on our planes we will probably change out the = hoses every second annual or so anyway.

One more thing.=A0 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. = =A0It 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

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