A Basic Injector Pump Question

[Henro]

Simple question: Are injector pumps positive displacement pumps? I mean the older type, and not what might be used on common rail setups. I imagine they must be since they meter fuel to the cylinders.

Reason I am asking is I read somewhere that it is advised to crack the lines at the injectors, if one needs to bleed air from the system. Makes sense to me.

BUT what I also read was the reason to do it this way, was that the air will compress and the net pressure felt by the injector will not be enough to cause it to open and inject fuel into the cylinder.

So now I am wondering why that would be, if the injector pump was a positive displacement type. Wouldn't more and more fuel be pushed into the line, until the air collapsed to whatever volume it needed to reduce to, until the injector finally opened, and the air was pushed with the oil into the cylinder, and out of the line feeding the injector?

Now, if somehow things are set up so the pressure in the line, between the pump and injector, goes back to a very low pressure, between the time the pumps for the cylinder takes place, I can see the air in the line acting as a shock absorber, and pressure never reaching the trip point of the injector.

So how do the injector pumps on older tractors without common rail systems actually work might be my question.

Is there some kind of bleed off mechanism, that drops pressure in the lines to the injectors between pumps? Otherwise why wouldn't the air in the line just keep getting compressed more until pressure reached the trip point of the injector?

If there was air in there to begin with, of course...

 

[hagrid]

I think there used to be a check valve on either side of the pump piston.

 

[North Idaho Wolfman]

Older injection pumps delivery valves will:
1: Seal diesel rather well, air not so much.
2: The amount of air moved is rather small.
3: It takes a lot more time and energy to get air to 3000psi.

Note: You don't crack the Injector lines at the pump to blead them, that really doesn't do any good, you crack them at the injector side, but cracking them at the injector side doesn't harm or damage anything in the pump.
This is unless on some model pumps you loosen the delivery valve holders and allow the pistons to spin (that's very unusual) or you leave the delivery valves loose.

This is exactly how an older Kubota diesel injection pump works.

 

[Henro]

Older injection pumps delivery valves will:
1: Seal diesel rather well, air not so much.
2: The amount of air moved is rather small.
3: It takes a lot more time and energy to get air to 3000psi.

Note: You don't crack the Injector lines at the pump to blead them, that really doesn't do any good, you crack them at the injector side, but cracking them at the injector side doesn't harm or damage anything in the pump.
This is unless on some model pumps you loosen the delivery valve holders and allow the pistons to spin (that's very unusual) or you leave the delivery valves loose.

This is exactly how an older Kubota diesel injection pump works.

View attachment 76193

Just a question. Am I wrong in remembering that at least on some injector pumps if you loosen the lines at the pump side you can cause something to shift internally in the pump, which requires sending the pump out for repairs?

This is what I have come to believe after reading posts here at OTT, but have no basis to know if it is fact or fiction.

 

[North Idaho Wolfman]

Just a question. Am I wrong in remembering that at least on some injector pumps if you loosen the lines at the pump side you can cause something to shift internally in the pump, which requires sending the pump out for repairs?

This is what I have come to believe after reading posts here at OTT, but have no basis to know if it is fact or fiction.

There is a group of Injection pumps that have Security torx screws that is you loosen those it will change the settings.
Other pumps just have delivery valve holders, and some have locks on them to keep them from turning.
A loose delivery valve holder can effect timing and fuel amount, and because of the small amounts of fuel being moved, little mal adjustments have a drastic effect.
Just loosening the injection lines does not effect the pump.
Loosing the delivery valves or the delivery valve holders can effect the pump.

I've worked on quite a few pumps that someone has removed the delivery valves, and reinserted them in the wrong location, tightened them down and sheared off the pins that align them, it only requires a slight shift in rotation to cause this, and ruins both the pump body and delivery valve when this happens.

 

[Henro]

There is a group of Injection pumps that have Security torx screws that is you loosen those it will change the settings.
Other pumps just have delivery valve holders, and some have locks on them to keep them from turning.
A loose delivery valve holder can effect timing and fuel amount, and because of the small amounts of fuel being moved, little mal adjustments have a drastic effect.
Just loosening the injection lines does not effect the pump.
Loosing the delivery valves or the delivery valve holders can effect the pump.

I've worked on quite a few pumps that someone has removed the delivery valves, and reinserted them in the wrong location, tightened them down and sheared off the pins that align them, it only requires a slight shift in rotation to cause this, and ruins both the pump body and delivery valve when this happens.

Thank you for the reply Wolfman.

I guess I have/had the impression that loosening the line connections at the pump end might be dangerous.

So it seems from your reply that this is unlikely? I am pretty sure this is what you are saying, and that I misunderstood previous posts.

So it is unlikely that loosening the fuel line connections at the injector pump would be an issue right? IF it is just the nut that holds the line to the pump that is loosened.

Not sure why one would try to bleed the system at that point, but at least it sounds like if they would, it should cause no harm.

Just trying to understand and correct my misconceptions...

Kind of a read-something, think you understand it, but in reality you miss the point kind of thing...on my part I mean...

 

[North Idaho Wolfman]

So it is unlikely that loosening the fuel line connections at the injector pump would be an issue right? IF it is just the nut that holds the line to the pump that is loosened.

Yes that is right.

 

[RalphVa]

Think there's a return line off the primary pump that vents off any air in the lines when you change out the fuel filter. Still, the engine often starts and stalls once or twice before it bleeds off all the air.

Don't think it's necessary to ever crack a line to the injectors.

 

[Henro]

Yes that is right.

That is good to know. I will readjust my thinking...

 

[North Idaho Wolfman]

Don't think it's necessary to ever crack a line to the injectors.

That only works on newer models.
My L3450 with V1902 DI and My Bobcat with and V2203 DI, but will not work on my B7100 with a D850 IDI
The D850 will not self bleed, you have to bleed the air out of the injector line as no matter of cranking will burp it.

 

[Russell King]

Henro you are recalling the conversations mostly correct...
Someone bleeding air from system and then tractor runs poorly

Question is how they bled lines and they mention at top of the pump.
On the top of my injection pump are two nuts one large and one small per injection line, the large one has something to do with the delivery valve.

If the small nut is corroded to the large nut then they both turn when trying to loosen the injector line at the top of the pump

 

[Henro]

Henro you are recalling the conversations mostly correct...
Someone bleeding air from system and then tractor runs poorly

Question is how they bled lines and they mention at top of the pump.
On the top of my injection pump are two nuts one large and one small per injection line, the large one has something to do with the delivery valve.

If the small nut is corroded to the large nut then they both turn when trying to loosen the injector line at the top of the pump

I appreciate all the answers to my question.

At least I got one thing right, if bleeding is needed do it at the connection to the injectors, and not at the injector pump.

It is great to be able to get in touch with so many knowledgeable Kubota guys!

Thanks again!