Fuel lines

[buggsy]

Hi,

 

In previous posts i have had problems with air getting into the diesel supply and i have found a faulty lift pump which once replaced temporarily cured the problem but it has returned and i think it is due to too many couplings in the suction line. I have decided to drain the tank and start again, the question I have is I will be having some new hose assemblies made as i have repositioned the pre filter is it acceptable to use iso7840 hose assemblies from the shut off valves to the prefilter in place of the normal solid copper pipe??

 

I am guessing this is not the normal procedure due to cost

 

 

cheers

 

Steve

[John Orentas]

Hi,

 

In previous posts i have had problems with air getting into the diesel supply and i have found a faulty lift pump which once replaced temporarily cured the problem but it has returned and i think it is due to too many couplings in the suction line. I have decided to drain the tank and start again, the question I have is I will be having some new hose assemblies made as i have repositioned the pre filter is it acceptable to use iso7840 hose assemblies from the shut off valves to the prefilter in place of the normal solid copper pipe??

 

I am guessing this is not the normal procedure due to cost

cheers

 

Steve

 

 

Hi Steve.

 

As long as your pre-filter is mounted on the hull and not the engine I would be inclined to make a permanent installation using copper pipe, you have obviously lost confidence in compression fittings but when done properly, which isn't difficult they are totally leak-proof and will last the life of your boat. Having said that you can do it using flexible pipe to the standard you suggest as long as it is not a very long distance, but the ends must be connected as per the Red Book BSS 2 12/13 and most examiners will want to see the appropriate codes marked on the pipe.

 

The lift pump diaphragm is about the only way air can get into the low pressure side other than the supply pipes and shut off valves.

 

Copper piping is not recommended on cost grounds but it is the best most reliable way to do it.

[Speedwell]

In previous posts i have had problems with air getting into the diesel supply and i have found a faulty lift pump which once replaced temporarily cured the problem but it has returned and i think it is due to too many couplings in the suction line.

It takes quite a lot of air to actually stop an engine as shown by the air bubbles that I have seen going through the plastic feed into my metro diesel - makes it go a bit lumpy but it soon clears. Are your couplings weeping diesel when the engine is not running ? Diesel is very searching stuff and, if none is coming out, it's unlikely that much air could get in.

Arthur

[John Orentas]

It takes quite a lot of air to actually stop an engine as shown by the air bubbles that I have seen going through the plastic feed into my metro diesel - makes it go a bit lumpy but it soon clears. Are your couplings weeping diesel when the engine is not running ? Diesel is very searching stuff and, if none is coming out, it's unlikely that much air could get in.

Arthur

 

 

Sorry Arthur.

 

But air getting sucked into the low pressure fuel supply is probably the most common thing that brings an engine to a juddering halt. When it then gets into the high pressure side, and it can build up gradually, the injector valve will never open and so will not pass any air through. Any faulty couplings on the low pressure would not always weep fuel when the pressure is reversed.

Edited December 3, 2005 by John Orentas

[Yamanx]

Have you checked the sediment/water trap? This can let air in if its not sealing properly and recently on a glass one I had a hair line crack which was sucking in air and causing all kinds of running problems. Took ages to find as well.

[Speedwell]

Sorry Arthur.

But air getting sucked into the low pressure fuel supply is probably the most common thing that brings an engine to a juddering halt. When it then gets into the high pressure side, and it can build up gradually, the injector valve will never open and so will not pass any air through. Any faulty couplings on the low pressure would not always weep fuel when the pressure is reversed.

Sorry John.

I find that very difficult to believe. Have you any first hand experience of this happening ? It surprised me when I saw the bubbles going through the metro fuel system but it didn't stop. Most of it must nave gone out through the return pipe. Also when you bleed after breaking down the fuel system, you only bleed 2 injectors, the other 2 soon join in.

Arthur

[John Orentas]

Sorry John.

I find that very difficult to believe. Have you any first hand experience of this happening ? It surprised me when I saw the bubbles going through the metro fuel system but it didn't stop. Most of it must nave gone out through the return pipe. Also when you bleed after breaking down the fuel system, you only bleed 2 injectors, the other 2 soon join in.

Arthur

 

 

Arthur.

 

I think we are talking about different things here, most boats and I assume cars have a low pressure self bleeding system, a constant flow back to the tank and generally speaking any small amounts of air may well simply return to the tank, surely a plastic pipe can only be fitted on the low pressure supply.

 

It is only when air gets into the injector pump and then into the high pressure injector lines that you have problems, an injector pulse will merely compress the air and will not open the injector valve.

 

When it comes to bleeding injectors some engines can be very difficult, others very easy. When I have done RYA maintenance courses on my boat I allow air into the h.p. system in order to demonstrate the procedure of bleeding, the engine always starts before I have time to do anything, making me look silly. Other engine you have to fiddle around for twenty minutes.

Edited December 4, 2005 by John Orentas

[ChrisPy]

When I have done RYA maintenance courses on my boat I allow air into the h.p. system in order to demonstrate the procedure of bleeding, the engine always starts before I have time to do anything, making me look silly. Other engine you have to fiddle around for twenty minutes.

reminds me of a 6cylinder Perkins that I bought after it had been round the world in a packing case and had not been used for 15 years. I had connected the fuel lines, etc. but had not bled it. Fishing boat craned into the water, then rotate the engine to check the shaft alignment. Just a short press on the starter to kick it a quarter turn. .......... the bloody thing started and scared the sh*t out of the fitter.

[Speedwell]

I think we are talking about different things here, most boats and I assume cars have a low pressure self bleeding system, a constant flow back to the tank and generally speaking any small amounts of air may well simply return to the tank, surely a plastic pipe can only be fitted on the low pressure supply.

It surprised me at the time but the plastic was on the feed side - no BSS on cars.

Another thought, if air were getting in without diesel weeping when the engine was not running, it should be possible to prevent the air getting in by coating each compression joint with grease - far less searching than diesel. Should be worth it even if only as a test.

Arthur

[buggsy]

Hi,

 

I thought it would be a good idea to update everyone on my prpgress.

 

I have repiped the fuel lines and moved the prefilter down to a position level with the engine ( on the counter if this is the correct term). The original engine must have had the lift pump on the same side as the diesel tank but the Perkins D3 that was fitted once i bought the boat the lift pump is on the opposite side to the diesel tank. I decided to improve the installation of the fuel lines with some decent brackets.

One thing i have learnt you can get fuel hose assemblies made up by local hydraulic hose companies with the correct hose for alot cheaper than the chandlery shops. By the way also make sure you have the correct sizes of fittings before you start !!!!!!!!!!!!

 

When we tried to bleed up the system we could not get the engine to run for more than about a minute. So obviously i still had air in the system. We cheked all the connections and finally on the suggestion of my father who has experience of plant equipment we changed the fuel filter. I must admit i thought this was a long shot but hey presto problem sorted and now the engine runs spot on and today we have been out for about 4 hours cruising.

 

Earlier this year I had problems with a weak lift pump which caused problems after a few hours cruising, I changed this and at the same time replaced the FRAM fuel filter with an equivalent MAHLE filter but never totally cured the problem any way after all this rambling when you compare the MAHLE filter to the MANN filter which i have just fitted the top lip which seals on the top rubber is a far better design than the MAHLE so this is how the air was getting into the system so hopefully i have now sorted the problem.

 

I will keep you all posted.

 

Steve

[DHutch]

Yeah, thanks for posting-back.

[David]

Hi

Just coincidence but just before christmas a chap on our mooring did his service during which he changed the fram fuel filter. Later the engine would not run for longer than a few seconds. After several bleeding sessions still no result so he took the filter off and found a slight lump in the new rubber seal, swapped it for the old one, and you guessed it, fired up imediatly.

To add to the thread above diesel is very invasive and can be difficult to seal if not done correctly, but John is correct air can and does get in with no trace of a diesel leak evident.

david