Injector HP Fuel Line - How to Make?

[RaymondR]

Originally Posted by S/V Adeline

When we had a steel line fail we got a high pressure 'hose' custom made to get going again.
Seems to work fine.
We purchased 4 new steel lines and are keeping the hose for an emergency spare, as it will replace any line (and cost twice what the full set cost)

It may work in the short term and sounds like a good contingency solution however was the timing still correct given that the elasticity of hose is considerably more than steel. Secondly, would the hose give the thousands of hours of service before failure that the thick steel lines provide.

[skipperpete]

Originally Posted by Wotname

I'm curious (and pedantic) - does the pressure really drop back to zero?



I always understood it only dropped back to just below the injector breaking pressure with that pressure being held the non return valve at the outflow of the pump - maybe I have the horse by tail of course.

Maybe not zero but definitely way below injection pressure. The non return valve is really an unloader valve that has a collar on it that fits in a very close fitting bore and after injection it retreats and seals off the injector line at the pump and in doing so, lowers the line pressure. It does this to stop high speed pressure echoes in the injector pipe that cause the atomizer to drip after injection. Injector lines were once made all the same length because of the shock wave travel but it seems that idea has lost popularity on the newer non common rail engines.
I was very surprised that flexible HP lines are now available ...even from Stardiesel who actually supply the solid pipe swaging tools as well.

[RaymondR]

Originally Posted by Wotname

I'm curious (and pedantic) - does the pressure really drop back to zero?

I always understood it only dropped back to just below the injector breaking pressure with that pressure being held the non return valve at the outflow of the pump - maybe I have the horse by tail of course.

Lots of leakage paths in these systems.

There are no soft seals anywhere in the high pressure sections of these systems hence the requirements for the return line from each injector. The plunger which lifts the needle valve in the injector nozzle does not seal in the barrel and the volumes pumped on each injection stroke are very small hence a comparatively rapid bleed by and drop in the injector line pressure.

So even if a check valve at the individual pump outlets sealed the pressure drop will still occur.

[S/V Adeline]

Originally Posted by RaymondR

It may work in the short term and sounds like a good contingency solution however was the timing still correct given that the elasticity of hose is considerably more than steel. Secondly, would the hose give the thousands of hours of service before failure that the thick steel lines provide.

Don't know. Given the advances made by steel braid, and considering it was designed to operate at much higher pressures than the fuel pump produces it might last awhile. I know from the paperwork I received with the vessel that the steel line that failed was two years old. That is abnormal.

[RaymondR]

Originally Posted by S/V Adeline

Don't know. Given the advances made by steel braid, and considering it was designed to operate at much higher pressures than the fuel pump produces it might last awhile. I know from the paperwork I received with the vessel that the steel line that failed was two years old. That is abnormal.

Very familiar with hoses having used many during my working life including some 60' long and rated to 10,000 psi working pressure with 3" bore.

They are undoubtedly the best solution in many instances particularly where independent motions of parts of a device are concerned. However the cost, when compared to that of steel piping, is generally higher and reliability lower. It is also generally less durable than steel pipe.

The steel injector piping on diesels is usually considered a life-of-engine component and the manner of their manufacture in bulk the lowest cost production provider.

[S/V Adeline]

Originally Posted by RaymondR

The steel injector piping on diesels is usually considered a life-of-engine component and the manner of their manufacture in bulk the lowest cost production provider.

That could explain why my vessel is on its third set of steel lines.

[Compass790]

Originally Posted by S/V Adeline

That could explain why my vessel is on its third set of steel lines.

Wow that sounds crazy unreliable. What engine is it? Does it have any clamps on the lines or anti-vibration loops?
Our boat engine is a yanmar single that shakes the fillings out oF your teeth but it's injector line is 39 years old AFAIK
I sell parts for them & no-one has ever asked for an injector line so suspect you have a design problem there.

[S/V Adeline]

Compass790,
The first set survived 36 years, my remark was aimed at the second set, which lasted two years and seemed very prone to rust pitting when nothing else in the engine compartment is having issues. Probably inferior steel, cheapest production possible.

[Wotname]

OK, time for an update (I did say this was a long term project )

I have sourced 6mmOD (2mmID) steel tube ex China. It is available in Australia but at 2 or 3 times the price and probably comes from China anyhow.

I have sourced nipples from the UK; I couldn't find in Australia but the UK ones were quite cheap. These nipples are suitable for the injector end but will need a tiny bit of lathe work for the pump; the OD is a little too large for the female nuts used at the pump end - no biggie!

Now comes the next big question - what filler rod to use to braze the nipples to the pipe. In short, I am choosing between a silver solder (with 15% silver) which melts around 650C or a harder bronze rod at around 880C. So far it seems the silver solder flows much better using capillary action than the bronze rod but that maybe due to lack operator technique/skill i.e. I need more practice with the bronze rods. I am using a gap of about 2 thou between the pipe and nipple.

I note the previous posts below!

Originally Posted by svthreecheers

......
Please silver solder only,brazing won't last very long
How do I know? 45 years fuel injection.

Why is this?
Do others agree?

Originally Posted by jimbunyard

Hope nobody gets their panties in a wad here, but technically soldering or silver-soldering is brazing, i.e. the process of joining two or more pieces of metal together with a filler metal that melts at a lesser temperature than the metal being joined.

It is troublingly common on internet discussions for people with lots of experience to make declarative statements, with probably/usually good reasons for making them, and then stop dead, with no explanation and no information as to how to accomplish the job in the way they deem correct.

For instance, I know there are at least dozens of types of 'silver solder', probably hundreds, not counting those that are the same alloy but produced by different manufacturers. It seems to me that at the very least it would be helpful to include some kind of designation as to what alloy or brand or designation of which product years of experience has taught works best, as well as maybe a brief note regarding technique.
...........

This is so true and as I am at the pointy end of the project, it is time get down to the detail!

FWIW, I am comfortable to using the locally available common 15% silver bearing rod but I am wondering if the harder bronze filler rod is better or worse in my application. Both are stated to be suitable for steel to steel brazing and I have the recommended flux for both.

[Wotname]

The pipe and nipples...

I am using the arrowed one for the injector end and either that or the one to it's left for the pump end. The one to the right is the existing pipe end.

[RaymondR]

For steel to steel butt welds I'd oxy weld with a steel filler rod.

[Wotname]

Originally Posted by RaymondR

For steel to steel butt welds I'd oxy weld with a steel filler rod.

It's not really butt weld - at least not according to my limited understanding of what a butt weld is.

The pipe is inserted into the nipple to depth of about 6 to 8 mm. The nipples aren't nearby so I'm not sure of the exact depth. The work is vertical with the nipple lowermost and I'm applying the filler at the top of the interface.

Using silver, I am getting capillary action right down the interface but with the harder and hotter bronze, maybe only 1/3 down interface - but that maybe my lack of experience - or not!

[Compass790]

I suspect your problem with the bronze flow is getting the pipe hot enough inside the nipple for the bronze to flow without overheating the nipple. Hard to achieve even heat when the pipe is much heavier wall than the nipple & shielded by it. Maybe you can try "tinning" the pipe first, then heating it & the nipple & sliding it on but I think you risk deforming them at bronze brazing temp. I wouldn't try it but I'd be happy with silver solder.
As you've observed the silver solder flows much more readily but maybe somebody with experience doing both methods will chime in.

[RaymondR]

Originally Posted by Wotname

It's not really butt weld - at least not according to my limited understanding of what a butt weld is.

The pipe is inserted into the nipple to depth of about 6 to 8 mm. The nipples aren't nearby so I'm not sure of the exact depth. The work is vertical with the nipple lowermost and I'm applying the filler at the top of the interface.

Using silver, I am getting capillary action right down the interface but with the harder and hotter bronze, maybe only 1/3 down interface - but that maybe my lack of experience - or not!

OK, a slip on type connection.

I suspect that the shear strength of the two options (copper and silver based filler rods) would not be far apart but that the better wetting action you have found with the silver solder would result in a far stronger joint overall. I'd favour the silver solder.

[Jim Cate]

Originally Posted by RaymondR

OK, a slip on type connection.

I suspect that the shear strength of the two options (copper and silver based filler rods) would not be far apart but that the better wetting action you have found with the silver solder would result in a far stronger joint overall. I'd favour the silver solder.

Wottie, I agree with the above opinion. A good silver solder joint in such an application will be quite strong, not terribly prone to fatigue failures and in general be superior to a marginally stronger join with a greater probability of poor execution.

Besides, it's nice to have a touch of precious metal on the boat (besides the Harken hardware).

Jim