How does self bleeding work?

[chris95040]

My Westerbeke is "self-bleeding", but I have no idea how it works. Where does the air go?

As I think about this, I realize I never understood why (on my old yanmar) you needed to bleed the fuel lines on the _output_ side of the high pressure pump, wouldn't the problem just take care of itself? Maybe when air is in that leg, the pressure never builds up to the point where the injector opens, so it just sits there unless you let it out manually...

[zboss]

Westerbekes are "self-priming" not "self-bleeding". It uses an electric fuel pump... when you turn the key it energizes the pump and off you go.

I have found that you still need to crack the injectors to let the air bleed but you do not need to hand pump the fuel.

[chris95040]

Hmmm Westerbeke calls it self-bleeding, and I've had situations that would have normally required bleeding "take care of themselves" with this engine, so I'm not so sure.

Follow on question, why's an electric lift pump able to be "self priming" but a mechanically driven one isn't? Just no way to get that kind of suction from it?

[boatman61]

Sharp knife across the wrist is effective I believe..

[SkiprJohn]

Originally Posted by chris95040

My Westerbeke is "self-bleeding", but I have no idea how it works. Where does the air go?

As I think about this, I realize I never understood why (on my old yanmar) you needed to bleed the fuel lines on the _output_ side of the high pressure pump, wouldn't the problem just take care of itself? Maybe when air is in that leg, the pressure never builds up to the point where the injector opens, so it just sits there unless you let it out manually...

I'm watching your thread to see if there is some very knowledgeable folks who have experience with your engine will respond.

I too don't think it can be self-bleeding if the air is in the lines between injector pump and injector. Might be wrong about that though. Will air pop the injector enough to bleed through the injector nozzle?

[Tayana42]

Originally Posted by boatman61

Sharp knife across the wrist is effective I believe..

Sounds like frustration with hydrolic steering!


S/V B'Shert

[roverhi]

Originally Posted by boatman61

Sharp knife across the wrist is effective I believe..

You get some really bad advice on this site. If you are really serious about ending it, slice up, not across the wrist. You'll open a much larger area of the artery and will bleed out faster.

[glenn.225]

Not a lot of westerbeke experience but the only diesel I know of that could be called self bleeding is the Detroit 2stroke. They use an "unit injector" located in the head. that controls fuel delivery and rate and do not need to be bled. A mechanical and/or electrical pump will supply fuel through the filters, these may have to be bled depending on setup.

[Yeti]

I have recently installed a M25XPB and as I understand it the engine is self bleeding up to the something like the injector pump. The idea being that the electric pump runs way more fuel than the engine needs and will flush air bubbles through back to the tank via the fuel return line. This also more or less helps "polish" the fuel as well.

I'm not 100% sure off the top of my head if the electric pump will clear the injector pump. Probably doesn't, but when I installed mine I had no issues.

When you hit the "preheat" button the electric fuel pump starts. I believe the manual says to hold the preheat button for around 10 seconds at a time several times with breaks to let the glow plugs cool down if you need to clear some air.

[osirissail]

Be it air or diesel when the pressure delivered to the injectors reaches the proper amount the injector will open and let the air or fuel into the cylinder.

However, as other have said, having an electrical fuel pump instead of a manual lift pump you can deliver fuel or air to the injection pump. I would think that the manufacturer's use of "self-bleeding" or "self Priming" is there to indicate that the injection high pressure pump and handle a load of air and pass it through to the injectors. There are injection high pressure pumps that cannot process air so these would not be referred to a "self-priming" or "self-bleeding."

Having that feature would make life a lot easier as you would not have to open the bleeding ports on the high pressure pump or loosen the fuel line to the injector. You would just use the starter to rotate the engine and any air would be processed through the pump and the injectors and the engine would start running.

[Stu Jackson]

We have a Universal M25 engine.

It is NOT self bleeding.

It DOES HAVE an electric fuel pump.

One has nothing to do with the other.

I have to turn a knob on the top of my injector housing to bleed the air out of the fuel lines.

Later Universal diesel engines, the M35s, are self-bleeding. Whether or not they have fuel lift pumps. No manual intervention is required to get the air out of the fuel lines all the way back to the tank.

I am not an expert on just how the mechanics of the self-bleeding work, but it's odd that confusion appears about the engine's bleeding and a lift pump. The pump just makes bleeding easier - without trying to run the engine you can get the air out without having to push the ridiculous finger pump on so many filter housings.

[zboss]

I HAVE a westerbeke 46. They may call it self bleeding but it really is just self priming. Ask me how I know. During a normal change of the fuel filters it will self bleed just fine but if you run out of fuel you will need to bleed the injectors... and that takes quite a while.

A mechanical fuel pump will do the same thing but you need to pump that little sucker on top of the fuel filter about 3 billion times to get the fuel through the system.

[Jd1]

If you have air in the high pressure lines then your injectors will not fire. Air is compressible, diesel isn't - you can not build sufficient pressure to fire the injectors with air in the lines as the amount of diesel pumped by the injector pump is small. The pressure goes up a bit but the air compresses and acts as a cushion. The pressure can't get high enough to fire the injector.
Man this is difficult to explain considering how simple the concept really is!
As far as self bleeding, I can only speculate that the high pressure pump is fed by the electrical lift pump and will pump it's tiny volume as long as there is fuel on the pump input. The output pressure will be too low to fire the injectors but fuel flows through the fuel return system back into the tank which flushes air out of the system. Once sufficient air is removed the injectors fire.

[hpeer]

Originally Posted by roverhi

You get some really bad advice on this site. If you are really serious about ending it, slice up, not across the wrist. You'll open a much larger area of the artery and will bleed out faster.

I dunno, maybe I just a sick jerk, but this interchange gave me the best laugh I've had in days!

Thanks guys!

[Wotname]

Jdi, your explantion is quite correct however let me add one more comment.

The HP pump (injector pump) can only deliver a very small VOLUME of fuel into the injector line thus if this line mostly full of air which is compressible, the pressure created by adding a small amount of fuel into the line into the line remains low.

Only when the line is full of fuel, can the HP pump deliver the required pressure by adding a small amount of fuel into the already full line of uncompressible fuel.

OPPS...
EDIT...

Just re-read your post above and see that you have already covered this aspect in full .
Sorry and please disregard my waffling on...