Hose Debris Discussion

[Jim Meade]

I'd like a little more explanation of the comment that improper clamp application and barbed fittings causes the debris that can affect the jets.

 

When one connect the hose to the barb, typically one slides it on and leaves it. In the case under discussion, the hose is slid over the barb and then a clamp is tightened. Allegedly, the clamp is over tightened and thus causes the barbs to cut into the hose.

 

The hose is pretty snug on the barb and then it is clamped. Fuel can not get past the clamp, and maybe not even past the first ridge on the barb.

 

How does any debris migrate back upstream to get from between the hose and the barb into the fuel stream? The cut parts are most likely behind the ridges on the barb. No fuel can get there to flush it back upstream.

 

I welcome any and all discussion of this subject with the objective of better understanding whether the proposed cause for debris is likely or even possible, and under what circumstances.

 

 

[Runtoeat]

I'm also wondering how the pieces of rubber can get past the barbs once the clamp is tightened. Like Jim, I would think the hose pieces would be trapped. The only way I can visualize the pieces getting into the fuel system would be if the clamp is loosened to reposition the hose or to do some sort of maintenance? I still am considering taking some sand paper and reducing the sharpness of the barbs if/when these are exposed during maintenance (or during the next 5 year replacement - arrrggghhh!)

[Ed Cesnalis]

Rubber hose and barbed fittings are not compatible even if they are used together in many cases. The barbs puncture the hose and the hose is not designed to be punctured. The only reasonable fix is to use beaded fittings.

 

Good results on a hose change only mean that the amount of damage done was minimal.

 

My CT sustained the most rubber debris pollution that has been seen to date and it wasn't caused by clamping. I have replicated the damage pattern to my hoses without even using clamps, forcing tight fitting hose over barbs can be all that is needed to sustain a high degree of damage.

[Rich]

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.

[Roger Lee]

Hi Rich,

 

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

[Jim Meade]

CT, I think I hear you saying that people are scalping the edge of the interior of the hose when it is pushed over the edge of the barb. That kind of scalping could occur on any kind of fitting except one with a reduced diameter, rounded end. I didn't see you saying that the damage occurred down the hose and somehow migrated up past the ride and the clamp to get in the fuel stream.

 

I don't hear anyone explaining how the Safety Officer's scenario works. See my questions in the OP.

 

If I replace my hose, I'll put on the teflon. Once and done.

[Ed Cesnalis]

Jim,

 

I don't know what 'people' are realizing just myself. The shaving that i am victim of does not occur when beaded fittings are used, Beaded fitting that are now commonly used on high pressure fuel injected systems do not have barbs that puncture the inner wall to gain purchase. SO's scenario works if barbed fittings are replaced with beaded fittings

[FredG]

Jim,

 

I can only find braided stainless steel teflon-lined hose in a maximum size of

-06 (specs: 0.32 in. hose ID, 0.43 in. hose OD). I looked mainly at websites for race car builders. I am familiar with elastomeric hose with braided stainless steel wrap in larger sizes, but it's not teflon lined. Where do you source teflon-lined hose in the size we need for our Rotax 912 engines?

 

Thanks.

[Jim Meade]

CT, how does the debris get upstream? Where does the shaving take place? I can see it taking place at the very end of the fitting, but I can't see any cutting done at the ridges of the barbs being able to get back upstream.

 

Fred, I thought Kent talked about this very hose. Is my recollection faulty?

[Doug G.]

Does the cut allow fuel to get behind the surface and cause deterioration?

[Jim Meade]

Does the cut allow fuel to get behind the surface and cause deterioration?

 

Doug,

How does fuel even get there? This would be past the ridges on the barb. Fuel should never get past the first ridge on the barb. That is why this whole explanation is hard for me to understand?

 

Wouldn't it have been easier if Roger/SO had just left the original thread open so it's easier to see and cite the OP(but, I digress)?

[Ed Cesnalis]

All of my debris was shaved off the ends. Every hose was changed and damaged a both ends, it all goes down stream.

[Tom Baker]

Jim, most of the barbed fittings in question are brass with machined barbs. The barbs are very sharp. The biggest problem is that the fitting OD is too large for the ID of the fose going over it. You really have to work to get the hose slid in place. I try very hard to make sure the hose slides straight on, but I would bet that some rock the hose from side to side getting it worked in place. This side to side movement with the hose being so tight on the sharp barbs would cut little slivers of hose from the ID. These slivers could be pushed into the hose because of the rocking motion, and the cuts from the barbs would go all the way to the end of the fitting.

One other thought is the last barb on the fitting goes right to the end forming what would be like a gasket punch. If you are not careful in getting the hose started on the fitting you could shave some off right there real easy.

[mocfly]

Guys,

On all barb fittings that are used in hydraulic lines that service servo valves I was taught by a rep from Parker Hannifin that one has to break or radius the leading edge of the barb fitting or what certain people are experiencing can happen. Your mechanic can do this with emory paper alone or a file if he has some pretty good skills and then smooth it out with some emory.

The other thing that will help from experience is using a light film of the same type of lubricant that is used in the line to coat the exterior of the barb prior to insertion into the hose. In the case of the fuel lines plain old Vaseline would be acceptable.

 

[Jim Meade]

Tom,

I understand what you are saying, but still don't see how anything that is cut off by the barbs can work back upstream and get into the hose in a position where it can move into the fuel stream. Surely, the only place where any sliver cold be free to move would be at the first ridge, and even those slivers would be toward the fitting end of the barb, not the open end. How can they get over the barb if the hose fits so tightly? You must be saying that a person pushes (walks) the hose on and where a barb cuts a sliver (before the clamp went on? the OP was talking about a clamp causing the problem) and then a person pulls the hose back over the barb and in doing so drags a sliver with it. Maybe, but I'd have to see it. And, this doesn't address the OP point on the clamp problem.

 

Anything cut off by the second or further barbs has to get by the first barb. Sorry, I am not convinced.

The slivers cut off by the punch like sharp end of the barb - absolutely. What CT and mocfly talk about is very clear and understandable, and chamfering the barb end seems to make sense.

 

When lubricating fittings and o-rings that cannot use petroleum products, for example on my herbicide sprayer, I use soy cooking oil.

 

[Ed Cesnalis]

 

Jim,

 

To get a pattern like these all barbs give the hose a shave and the shavings are then pushed into the connected hose. After that they can flow downstream.

 

On the 1st photo you can see 2 big shavings that are still attached.

[Jim Meade]

I don't agree with your analysis, My thoughts on what happens over time as the hose is pushed - even walked - onto the barb does not support what you are proposing.

 

And, none of this addresses the initial proposition that it was the clamps.

 

Hey, how about the clamps, anybody?

[Ed Cesnalis]

I can sit in my office and insert a barbed fitting into gates FI barricade hose and get the result in my photos above. No need to clamp, no need to wait or even add fuel. Instant damage that pollutes downstream.

 

There have been reports of hose degrading, I'll buy that. Reports of damage from over clamping, I'll buy that. I report that a large amount of debris can be created by inserting the barbed fitting.

 

There maybe 3 ways for fuel line to produce debris and a 'bad batch' isn't something that we can do much about. The other 2 methods go away if we switch to beaded fittings. The failure rate after 5 year changes has been too high to ignore. The safety issue is huge and the costs can be big as well if the debris leads to a violent start up and it finishes off your sprag clutch.

[mocfly]

CT,

Put a .060 radius on the fitting and insert the fitting per my advise then try your test again.

[Ed Cesnalis]

Chris,

 

I know the damage can be minimized. The original installations on our CTSWs worked well but the 5 year replacement worked poorly, technique means everything. None the less Gates has it correct, barbs cut into tubing to gain purchase by design and that makes them a bad choices when using rubber hose. I notice my new fuel pump comes with beaded fittings and I'm sure everything on an FI installation has to be beaded why should we remain mismatched and prone to failures?

[Jim Meade]

Someone talk me through it one millimeter at a time.

Scenario:

A fitting screwed into some kind of metal fixture with a hose connected to the resulting open end.

We're not talking about scalping the inside of the hose with the sharp end of the fitting - that is a given and we all accept that. Chamfering the end may help.

1. OP

The original question was that the clamp will cause pieces of rubber to come off the inside of the hose.

My objection is that I don't see how those pieces of rubber can get back up into the fuel stream, especially if the clamp is applied. How does rubber get back toward the open end of the fitting so that it can enter the fuel stream? The reason I don't believe it is because the hose fits so tightly that I don't believe any debris from any source could move. This is reinforced because the clamp further compresses the hose. I believe that if this is a smooth, bulbed fitting the bulb will further block movement and if it is a barbed fitting the barbs will block movement of debris.

 

2. Second comment that arose is that barbed fittings can make cuts (disregarding the clamp). I don't doubt that barbs can make cuts. It would seem to me that the cuts would be where the sharp, highest raised part of the barb is. This is away from the front of the fitting and the barb itself would have to be surmounted by debris along with getting past the tight hose fit along with getting bast the clamping pressure. I just don't see how this can happen.

 

All bets are off if one pulls the hose back off without either cutting a new, clean end or being sure there is no debris in or on it or the fitting before replacing hose. But, that's not what the OP talked about, nor am I.

 

I grant that Tom's point about walking a hose on may raise more questions but am not convinced on that. But, that's not what the discussion is about.

 

Some of us have reservations about the claims by the Safety Officer in his/her blocked post and I don't believe the other comments are addressing the issues point by point.

[chanik]

If the hose is clamped too tight, then the barbs will shave and roll lots of little pieces off. The hose tends to flute open on either side of the clamp so that lets debris through and then any pushing or twisting of the hose, which is almost certain considering you need to clamp the fire-sleave and most mechanics are going to test tug on the hose is all enough to send lots of little pieces down stream. (Roger is referring to my hose, BTW) Even after cleaning out the carbs and bowls (13 debris peices), 5 more new pieces were found when I made it to Roger. Also I momentarily lost a carb again on my flight down to Tuscon. So I have lost power in flight 3 times so far. There is some minor abrasion on the bulbed end (on the pump) But definitely this is a massive risk factor on the barbed fittings. I would concur that they should all be replaced, especially on the banjo fitting where the fuel distributes. That is the one hose that has no filter between it and the carbs (the new fuel pump has an internal filter screen)

[Roger Lee]

And why do people think I'm the Safety Officer. Other than a mustache I look nothing like him. I'm much heavier in build and much meaner.

[sandpiper]

You can easily tell the difference between Roger and the S.O. One of them is much better looking. The problem with the S.O. is that he wants to lick your face. :wacko:

[Jim Meade]

If the hose is clamped too tight, then the barbs will shave and roll lots of little pieces off. The hose tends to flute open on either side of the clamp so that lets debris through and then any pushing or twisting of the hose, which is almost certain considering you need to clamp the fire-sleave and most mechanics are going to test tug on the hose is all enough to send lots of little pieces down stream. (Roger is referring to my hose, BTW) Even after cleaning out the carbs and bowls (13 debris peices), 5 more new pieces were found when I made it to Roger. Also I momentarily lost a carb again on my flight down to Tuscon. So I have lost power in flight 3 times so far. There is some minor abrasion on the bulbed end (on the pump) But definitely this is a massive risk factor on the barbed fittings. I would concur that they should all be replaced, especially on the banjo fitting where the fuel distributes. That is the one hose that has no filter between it and the carbs (the new fuel pump has an internal filter screen)

 

This is the best commentary so far. Here is my reaction:

"If the hose is clamped too tight, then the barbs will shave and roll lots of little pieces off."

It seems logical that the ridges or edges of each barb could cut the hose. Shave? Why would it "shave" them? Roll? How does clamping "roll" pieces of the inside of the hose - the hose lining? My question is how does the clamping dislodge pieces of the hose (as opposed to make cuts or slices in the hose)?

 

"The hose tends to flute open on either side of the clamp..."

 

By fluting I assume you mean it opens channels, like the flutes on a stone column. What evidence do we have that a hose does that when the hose is so tight that as Tom says it has to be forced on? Even if it does open a channel, how far back would the clamping pressure hold that channel open, as it would have to to allow debris to move through it?

 

When you say "downstream" it seems to me that we really mean upstream. That is, the debris would have to go up against the flow and pressure of fuel until it emerges from the tight space between the fuel line and the fitting and enters the fuel stream.

 

Do I have barbed fittings? I don't know. I haven't changed the hoses. It seems to me there are many CTSWs flying around with this kind of fitting that are having no problems whatsoever. I have no objection to changing fittings, but I still don't see any conclusive evidence that excess clamping causes debris to go upstream against all the physical impediments to enter the fuel system.

 

Obviously, we need some good experimental data. I have looked for more info online but so far haven't found anything.