Fuel pipe banjo unions

[StefanSG]

Hi following my ongoing issues with air in the fuel filter I am looking to have new copper lines made and need a source for the banjo unions on the leak-off pipe. They require the fitting (nipple ?) for brazing the pipes on. Any suppliers or pointers gratefully received. Engine is a VP MD11C

SSG

Picture for reference:

 

[rotrax]

Remove the old ones and use them.

 

[Ian_Edwards]

That's what I did, I think that they are just soldered on, or it could have been brazed on.
But they came off with a torch on a small Campingaz cylinder, not too difficult, just hold the banjo in a vice and using a mole grip (hand vice) to pull the tube out.
Be careful you don't mark the faces of the banjo, I used aluminium jaw covers to protect the banjos. The tube is scrap, so you don't have to be careful with that.
I also used copper pipe for the new ones and soldered them into the banjos.
Soldered melts at around 300C, and copper is a lot easier to bend and a lot more corrison resistant then steel.
They were still serviceable years later when I sold the boat.

 

[PCUK]

You wont get air in the leak-off pipe as it is pressurised.

 

[RunAgroundHard]

Try these:-

Metric Type 9081 Weld on Metric Banjo Soldered or Brazed
Imperial Banjo Unions | Flexolite

 

[StefanSG]

You wont get air in the leak-off pipe as it is pressurised.

So fuel not being sucked down the pipe by the high pressure pump ? That means air can only be introduced from upstream of the secondary filter ?

 

[RunAgroundHard]

So fuel not being sucked down the pipe by the high pressure pump ? That means air can only be introduced from upstream of the secondary filter ?

On most boats the injection pump overspill line is open ended into the tank i.e. not sealed from the atmosphere.

Usually on a small boat fuel system air is introduced between the fuel tank fuel outlet, and suction fuel pump inlet. Typical flow path:

Suction Side: tank, external filters, pipes / hoses to lift pump inlet.
Pressured Side: from lift pump outlet, pipes from lift pump, engine fuel filter, injection pumps, injection lines, overspill lines venting back to tank. It should be noted that some overspill lines do not go back to the tank but tie into the top of the engine fuel filter.

As can be noted, air can be sucked in between the tank and lift pump inlet, or fuel can be sprayed out, from the lift pump outlet to the injection pump, HP fuel lines, injectors and overspill line.

The injection pump does not suck fuel, it is fed by fuel slightly pressurised by the lift pump. There are installations with fuel tanks above engine elevation that can gravity feed fuel to the injection pump if the set up is sized correctly. Injection pumps need a minimum head of pressure to operate as they can't lift fuel from a lower elevation by themselves.

That is my understanding, happy to be corrected by others.

How to service your marine diesel engine - Practical Boat Owner

 

[StefanSG]

edited

 

[StefanSG]

On most boats the injection pump overspill line is open ended into the tank i.e. not sealed from the atmosphere.

Usually on a small boat fuel system air is introduced between the fuel tank fuel outlet, and suction fuel pump inlet. Typical flow path:

Suction Side: tank, external filters, pipes / hoses to lift pump inlet.
Pressured Side: from lift pump outlet, pipes from lift pump, engine fuel filter, injection pumps, injection lines, overspill lines venting back to tank. It should be noted that some overspill lines do not go back to the tank but tie into the top of the engine fuel filter.

As can be noted, air can be sucked in between the tank and lift pump inlet, or fuel can be sprayed out, from the lift pump outlet to the injection pump, HP fuel lines, injectors and overspill line.

The injection pump does not suck fuel, it is fed by fuel slightly pressurised by the lift pump. There are installations with fuel tanks above engine elevation that can gravity feed fuel to the injection pump if the set up is sized correctly. Injection pumps need a minimum head of pressure to operate as they can't lift fuel from a lower elevation by themselves.

That is my understanding, happy to be corrected by others.

How to service your marine diesel engine - Practical Boat Owner

thanks RunAgroundHard yes that makes sense. Mine is the old type where the leak-off runs back to the secondary fuel filter

 

[rogerthebodger]

I had air leaking in the suction side of the feed from the tank before the lift pump

I Reolaced the banjo copper washers with Dowty washers' problem solved.

Never had air leaking in the injector blead off pipes as there's are not under a vacuum