Diesel auto bleeding.

R

rogerthebodger

Well-Known Member
Joined
3 Nov 2001
Messages
14,330
Visit site
The discussion on water tank vent had a reference to an auto air bottle vent and wandered if that device could be used between the lift pump and the injector pump to auto bleed then fuel system of to prevent air getting into the injector pump and injectors

Any one considered it or done something this.

Robocal Automatic Air Bottle Vent
 
Rogershaw said:
The discussion on water tank vent had a reference to an auto air bottle vent and wandered if that device could be used between the lift pump and the injector pump to auto bleed then fuel system of to prevent air getting into the injector pump and injectors

Any one considered it or done something this.

Robocal Automatic Air Bottle Vent
Click to expand...
It would be another step down that long and unfortunate road allowing all sorts of unsuitable people to take up sailing. From roller reefing to hot water, from fridges to chartplotters all the skill and hardiness and mystery is being taken away. We need those difficult events to put people off and keep anchorages less crowded. The only truly helpful thing left is getting rid of loads of wannabe sailors the first time they feel a boat heeling over. We’d have even more people afloat if anyone could think up a way of making a sailing boat that didn’t heel.
 
RupertW said:
It would be another step down that long and unfortunate road allowing all sorts of unsuitable people to take up sailing. From roller reefing to hot water, from fridges to chartplotters all the skill and hardiness and mystery is being taken away. We need those difficult events to put people off and keep anchorages less crowded. The only truly helpful thing left is getting rid of loads of wannabe sailors the first time they feel a boat heeling over. We’d have even more people afloat if anyone could think up a way of making a sailing boat that didn’t heel.
Click to expand...
You'll have to ban multihulls now?
 
My Mitsubishi based engine is self-bleeding. Dunno how it works but after changing fuel filters etc, just crank the starter and off she goes. I suspect having an electric lift pump has got something to do with it.
 
RupertW said:
We’d have even more people afloat if anyone could think up a way of making a sailing boat that didn’t heel.
Click to expand...

They have they are called catamarans which have become very popular so the wife can come along and will not spill the tea.

Having had a very difficult to find fuel air leak that cause my engine to stop just as I was coming into my mooring on a windy day, I just wanted to stop the panic of all around me.
 
I have added a Facet copy - the patent has long expired - electric lift pump to my system. Under 20 quid from ebay.

My engine has no lift pump, it is incorporated into the injector pump.

5K Stirling for a replacement injector pump.

No brainer - and no bleeding required after filter changes.
 
rotrax said:
I have added a Facet copy - the patent has long expired - electric lift pump to my system. Under 20 quid from ebay.

My engine has no lift pump, it is incorporated into the injector pump.

5K Stirling for a replacement injector pump.

No brainer - and no bleeding required after filter changes.
Click to expand...


Is your engine a common rail diesel. Common rail diesels do not need bleeding but mechanical injector diesels do as any air the the injector line will prevent the mechanical injector opening.
 
Rogershaw said:
Is your engine a common rail diesel. Common rail diesels do not need bleeding but mechanical injector diesels do as any air the the injector line will prevent the mechanical injector opening.
Click to expand...

Sorry, but both of those statements are incorrect.

A great many modern, non common rail, engines do not need bleeding, or at worst minimal bleeding. It's unusual these days to have to crack injector lines. Those that need anything much n the way of bleeding, in a boat, are more often than not because of the tank position, the lift pumps struggle to suck fuel over a hill if the tank is low or the fuel liners rise and fall over, say, a bulkhead. Many boat engines will start without any bleeding, others may need the primary filter bleeding, in many, many cases, we bleed some air air to save over stressing the starter motor, but the engine would start without bleeding. There will, of course, be cases where they need bleeding and indeed some can be difficult.

Not all common rail engines will self bleed. Some have no electric lift pump, they very rarely need injector lines cracking (good job, as they are under great pressure), but some can be a real pain to bleed, when there is no electric lift pump especially.
 
My van is a Nissan import with a rare(ish) 'QD32' 4cyl 3.2 turbo diesel with an electronic fuel injection pump. As far as I understand it, it self bleeds because of having the electric injection pump. Even with the engine cranking, the pump is getting 'full power' from the 12v and thereby pumping enough fuel to eventually clear the air through. It does work, eventually, but sounds like a bag of spanners in the process, so I normally still pump the primer to give it a helping hand!

I plan to fit an electric lift pump to our Beta 50 at some point (mainly just 'because') and would be interested to see whether this will 'self bleed'. I reckon it sort of will, because of course the lift pump isn't doing the work of a fully-electric injection pump.
 
OK I have a Leyland 4/99 very old diesel engine in DistantShaws. I have both engine driven lift pump and also electric priming lift pumps which are Facet copy.

The injector pump is totally mechanical and so will feed an amount fuel to the injectors and once the pressure get to the injector opening pressure the fuel will squirt into the cylinder and ignite. If there is any air in the pipe from the injector pump to the injector the air being compressible in my case will not alloe the injector pump to squirt enough fuel to compress the air enough to open the injector thus no fuel to burn.

With electronic injectors the injectors are opened by an electrical signal from the control system.

with all your engines that don't need bleeding where does the air do that has got into the fuel system following a filter change.

My previous boat has a Perkins 4/236 and also with mechanical injectors and injector pump and also needed bleeding following a filter change.

The diesel in my Toyota 4 x 4 does not need bleeding at it has electronic injectors.
 
PaulRainbow said:
Sorry, but both of those statements are incorrect.
Click to expand...

Maybe so but both the boat diesel engines need bleeding hence my questions


PaulRainbow said:
A great many modern, non common rail, engines do not need bleeding, or at worst minimal bleeding

Not all common rail engines will self bleed. Some have no electric lift pump,
Click to expand...

Ok Paul I'm no disagreeing as my main experience is with petrol engine including mechanical fuel injection on my Triumph 2.5 PI.

So how do these self bleeding mechanical injector engines get rid of any air in the injector pipes.

I can understand just changing filter with a auto bleeding before the injector pump the engine could start with the fuel already in the injector and injector pump.

Again I would like to understand how this works.
 
Rogershaw said:
Maybe so but both the boat diesel engines need bleeding hence my questions




Ok Paul I'm no disagreeing as my main experience is with petrol engine including mechanical fuel injection on my Triumph 2.5 PI.

So how do these self bleeding mechanical injector engines get rid of any air in the injector pipes.

I can understand just changing filter with a auto bleeding before the injector pump the engine could start with the fuel already in the injector and injector pump.

Again I would like to understand how this works.
Click to expand...

I can help with this question:

Older diesel engines need bleeding as they don't pump enough fuel through the lines to purge out the air. As air is compressible, the bubble simply shrinks and expands, and subsequently fuel doesn't move through the injector line.
Modern diesels solved this in a number of ways:
  • Later mechanical injected diesels allow a greater volume of fuel to spill down the return line, they also usually link the return line to the loading port on the fuel injection pump. Rotary FIP's have a vane pump on the rear end that eliminates a great deal of air via the return connection, the rest is solved by simply pumping more fuel down the injection line than is needed, if the volume of fuel in the HP line is greater the the bubble volume, the air bubble will move along the line and be eliminated via the return connection. If you have ever heard a diesel engine start up on less than all cylinders after a service, you have experienced this.
  • Common rail diesel engines work very differently. Rather than the pump just supplying one 'dose' of fuel each time it's time for that cylinder to fire, all injectors are connected to a fuel chamber (the "rail") that is permanently pressured to between 4 and 6 bar. When it is time to fire, the injectors are done so electronically, a piezo nozzle in the injector itself delivers the dose. Because there is a much larger and constant volume of fuel being circulated through the fuel "rail" they often don't need bleeding as air is eliminated automatically by a nature of the process. Interesting fact - a modern common-rail injector can adjust the nozzle opening up to 8 times in a firing cycle, this is a large part of how they are so much cleaner burning.
Hope this helps, the short answer is it's all to do with volume of fuel.
 
Moodysailor said:
I can help with this question:

Older diesel engines need bleeding as they don't pump enough fuel through the lines to purge out the air. As air is compressible, the bubble simply shrinks and expands, and subsequently fuel doesn't move through the injector line.
Modern diesels solved this in a number of ways:
  • Later mechanical injected diesels allow a greater volume of fuel to spill down the return line, they also usually link the return line to the loading port on the fuel injection pump. Rotary FIP's have a vane pump on the rear end that eliminates a great deal of air via the return connection, the rest is solved by simply pumping more fuel down the injection line than is needed, if the volume of fuel in the HP line is greater the the bubble volume, the air bubble will move along the line and be eliminated via the return connection. If you have ever heard a diesel engine start up on less than all cylinders after a service, you have experienced this.
  • Common rail diesel engines work very differently. Rather than the pump just supplying one 'dose' of fuel each time it's time for that cylinder to fire, all injectors are connected to a fuel chamber (the "rail") that is permanently pressured to between 4 and 6 bar. When it is time to fire, the injectors are done so electronically, a piezo nozzle in the injector itself delivers the dose. Because there is a much larger and constant volume of fuel being circulated through the fuel "rail" they often don't need bleeding as air is eliminated automatically by a nature of the process. Interesting fact - a modern common-rail injector can adjust the nozzle opening up to 8 times in a firing cycle, this is a large part of how they are so much cleaner burning.
Hope this helps, the short answer is it's all to do with volume of fuel.
Click to expand...


Ok now that really clarifies the issues.

As both the boat diesel engines I have are very old it explains why they need bleeding if any air get into the fuel system.

Now any one know of a auto beading system to the old type diesel engines like mine.
 
Rogershaw said:
Ok now that really clarifies the issues.

As both the boat diesel engines I have are very old it explains why they need bleeding if any air get into the fuel system.

Now any one know of a auto beading system to the old type diesel engines like mine.
Click to expand...

Auto-bleeding, no. I would be reluctant to fit a valve of this type in the fuel inlet line as I would always be concerned about it failing. My preference is to have fuel lines sealed of from air ingress possibility, so I would rather engineer a solution that makes it easier to bleed the system.

I have fitted a number of electric priming pumps back in a former time - we would connect these inline (ideally in parallel in the fuel line so that they are not running constantly). After a service, open the bleed valve and run the pump until all air is removed. The small lift pumps on the older engines (we have a Perkins 6.354 so I know the problem) are not great at pulling air out of the fuel line if it's an tricky run or if the tanks are a bit empty.

Some engines and installations are a pain for getting air in the injector lines, in these cases it's just a matter of working with what you have.
 
Rogershaw said:
Ok now that really clarifies the issues.

As both the boat diesel engines I have are very old it explains why they need bleeding if any air get into the fuel system.

Now any one know of a auto beading system to the old type diesel engines like mine.
Click to expand...

Auto bleeding can't be possible with older engines, such as yours. No matter what you fit, you can't get over the fact that system cannot get rid of the air in the injector lines.

If you've only changed the filters and not allowed air into the injector pump/lines, then an electric pump will help, as mentioned. It might help if you fitted a tee in the supply line, just before the injector pump and connect the other end to the return line, after the injection pump, fit an isolation valve in it, before the pump. You could then open the valve and use an electric priming pump to clear the air from the system, up until the injector pump. Should make filter changes simpler.
 
Not the same idea but my Perkins set up takes the return flow into the top of the filter and then back to the tank. I guessed that this was some self bleeding concept. The effectiveness was demonstrated when we had a couple of blockages/stopages( we thought ) while sailing down the Rhone ( in flood). The first one was a bit scary but after bleeding all was well until it happened again a few days later.
A careful check of the whole system revealed a small air leak and we believe that given the very low revs we were running at due to the current the return flow was insufficient to clear the air away.
 
Ok no auto bleeding.

What I did do was to fit a small needle valve and quick connector on to the bleed point of my primary filters so I can connect a hose to the bleed point ,open the valve and pump fuel with a prime bulb dipping the hose in a jar like bleeding brakes. This make it easy a cleaner to bleed the primary filter.

May be I will do the same on my secondary filters and the bleed points on the injector pump. The injectors I will just have to do as I do now.
 
michael_w said:
My Mitsubishi based engine is self-bleeding. Dunno how it works but after changing fuel filters etc, just crank the starter and off she goes. I suspect having an electric lift pump has got something to do with it.
Click to expand...
So is my Isuzu 55 but the fuel pump needs to run for 5 minutes before starting to allow it to get the air out of the pipes.
 
You must log in or register to reply here.

Share this page

Top