2nd Al's motion,

 

I fly helicopters for a living (the certificated versions ....)

The last one has some of the hydraulics system (low pressure to/from the cooler) and the turbine oil to cooler hoses clamped with 2 regular clamps on each end. Though the hoses are capped off with a metalcap that has to prongs that go under the clamps, just to hold the cap on the hose end.

Constant pressure is good, but good regular clamps will do fine. You can safety wire them too, allthough the ones on the helo are not.

Then, I have to do a daily pre-flight inspection that includes to grap and pull the hoses somewhat. Short work of makeing sure the clamps are not loose, too.

 

If you do not or cannot preflight the engine like that before every flight, safetywire will give you some peace of mind..

 

Wiggins is the "smoothest" custom touch though! Max points for coolness too.

 

Sometimes cool is nice, even if you need "people in the know" to appreciate details like "Wiggins"

 

Cheers,

 

TJ

 

On 10/7/07, Mark Steitle <msteitle@gmail.com> wrote:

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 <ALVentures@cox.net> 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 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 ½" 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 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.  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.  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 long J?

 

Al G