Hose Debris Discussion

[chanik]

As the hose is crushed onto the fitting, it will thin (my hose is clearly thinner where it was clamped) and that material needs to move outward under the pressure and tends to flare open. Careful experimentation with weenie hot dogs and my clenched fist has verified this behavior. Pressed against sharp ridges of a barbed fitting, it will sheer the lining and strip it in many places as the lining is fairly rigid. The debris then is flowing upstream. One flaw of band clamps is that they tend to tighten unevenly which would exacerbate the formation of channels for the debris to escape the clamped area. I doubt it was before clamping since the mechanic who worked on it said he changed to the tighter clamps because the hose felt loose with the Oetiker clamps. That is an easy test though. Just take a short piece of tubing and jam it on and off a barbed fitting and look at it. I would image one of our mechanics would have noticed by now if that were enough to shave the lining. There was no evidence of any hose deterioration due to fuel exposure even where it is shaved or of the shavings themselves.

[Jim Meade]

I'm sorry, I just don't believe it. As a farmer, I've put a lot of hoses on fittings, both flared and barbed. I've done it on radiator hoses, oil cooler return lines, sprayer lines, garden hoses, diesel and gas fuel line hoses and I don't know what all. I've used mostly conventional clamps. Some I've tightened down with a wrench till they squeezed and distorted the hose. I have not seen the behavior described here. Where I have seen a flared hose is when the non-reinforced hose is very old and has been in service a long time, especially if there is any flex to the hose. It gets soft and expands. I've never seen a fluted hose.

 

It defies logic for me that a hose that is clamped and thus is displaced under the clamp and which therefore has the barbs cut into the hose where the hose is displaced would result in the debris suddenly moving over the barb which cut it in the first place and then goes up against pressure and the rest of the hose to fitting friction and restriction to get into the fuel line.

 

Pushing a hose onto a barbed fitting and then pulling it off is no test, to me. The OP was that the clamp did the damage. Nothing was said about pushing the hose on the barb and then pulling the hose off the barb. Everyone agrees that pulling the hose off the barb could result in the barb removing material from the inside of the hose. That has never been in question. Surely, we all agree that such debris would then be available inside the hose to migrate to the carb.

 

My contention has been that the type of clamp by itself is not going to put debris in the fuel stream and that debris is not going to go back up against the friction of the tube on the fitting and certainly not over the ridge of the barb.

 

Well, let's drop it. You are not going to convince me and I'm not going to try further to convince anyone else.

 

Let me say in conclusion that it does not speak well of the site management that the original post was locked. What in the world is this site for if not to exchange views and help us all learn? No matter what position one takes on the hose clamp barbed fitting issue, surely all of us have given it more thought and have perhaps arrived at our own more comfortable conclusion because of the exchange of views and ideas. Is the idea that site management can now use the locked message as a reference post to the unwary and not have to reveal that there was a good deal of contrary discussion about it?

 

 

 

[Ed Cesnalis]

Jim,

 

I agree with most of what you say. I called Gates and they confirm that their disclaimer is a primary concern. Barbed fittings and rubber hoses are not compatible. The locked post indicates there is a single cause of rubber debris and it is overclamping. If I compare the latest set of photos with mine the damage patterns are not similar so I would not hang my hat on a single cause such as clamping.

 

The common problem is the barbs, why are we using them? I guess because our CTs were originally fitted with them.

 

I can name multiple mechanics that have got good results with careful installations but then follow up with an installation that caused forced landings. We can't inspect the fuel line for damage, this method is problematic.

[Roger Lee]

There is no single cause, but that over clamping is a major problem. It has been one of our major issues in the CT debris. Also there is more than one clamp on fuel line. Over crimping the Band-It clamp will damage the hose because it tends to be even farthure out on the end.

[Aircraft Specialty]

I read on the Zenith site that there's a replacement for the standard rubber hose for the 912.

Seems like the replacement is a conductive stainless steel braid Teflon hose that doesn't have a life cycle replacement time and is cheaper than the current rubber hose.

 

Has anyone else heard of this replacement or if it's acceptable?

 

There may be hoses where the problems associated with rubber cease to exist.

 

We have now released the official 912 hose kit with an installation package for the RV-12. The cost of the complete kit including all conversion fittings is $599.95. This is for a total of 6 hoses, conversion fittings to change the 912 over to standard flare fittings, and a replacement of the rotax fuel block on top of the engine. Everything is stainless steel or steel (where stainless wasn't available) and all hoses are firesleeved. The RV-12 installation package may be slightly different than for other aircraft, and we are going to go model by model and slowly create more kits for other aircraft. We will also work on oil lines and coolant lines in the next year or so.

 

There is more info on the hoses at http://www.aircraftspecialty.com/rv-12.html

 

In addition, we have videos of hose fabrication there for those that are interested.

 

Hi Rich,

 

There are, but people complain now about hose prices wait until you pay for some of that hose and their fittings

 

Roger..... we can actually build conductive teflon replacements at a VERY REASONABLE cost. In addition, we assemble and pressure test all our hoses. Since you do extensive work with the 912 engines, I would love the opportunity to chat with you about this and about the possibility of using this package on SLSA aircaft.

[Roger Lee]

I sent you a PM. Give me a call.