Disassembled A Bosch Vp44 Injection Pump

[Jeeper Jimmy]

I apologize, Michael; this is going to look like another book, but~~~

 

First off:  I don't believe that I have read from any credible source that high feed pressure could rupture the diaphragm--just low feed pressure.  I think it's pretty well established that high feed pressure can cause hard starting of a warm engine.  I think this is caused by abnormal operation of the timing circuit causing it to not be in its retarded position during startup.  I guess the front seal is another possible problem area with high feed pressure, but I've never heard of one being damaged.

 

Do I believe the diaphragm that Mike is holding can Flex?

In a word~~yes!

 

Bear with me.  As the cam ring and followers squeeze fuel in the injection pump it pushes a volume of injection pressure fuel towards the port of the selected cylinder.  When the Pump Control Unit (PCU) decides that the delivery fuel is what it wanted, the valve between the feed chamber (bowl) to the injection opens.

 

The followers on the cam ring, however, have not reached the top so it is still pumping fuel.  When the valve opens back to the fuel chamber,a high-pressure spike is felt back in the chamber.  The pressure of this spike is at injection pressure value, but it is very small (probably a drop), but it has to be dealt with because when the cam follower starts to cause the injection pump to take on fuel again, it wants to be back at it's normal pressure.

 

Since the spill is being pumped back into a solid system and fuel cannot be compressed, there are a limited number of placed that can take up this extra volume.  One is back to the vane pump.  It, however, is a positive-displacement pump driven by the big Cummins engine so nothing is going to happen there--at least not in the time available.  Something has to give to dissipate this high-pressure spike.  In my humble opinion (as well as the VP44 Service Manual and the interactive training CD that I have), the diaphragm does flex.

 

Bear in mind, it only has to flex enough to compensate for the drop of high-pressure fuel that is been absorbed into a larger volume of fuel. Figuring the area of the diaphragm, the volume of the chamber, and the volume of the fuel drop, you probably could calculate how much the diaphragm has to flex to absorb this spike, but it's only a small fraction of a millimeter.  I think that calculation is beyond my capabilities (maybe I'll look into it later).  Realize that the pressure in the bowl needs to be ready for the next injection in a matter of milliseconds. This operation can occur upwards of 50 times a second).

 

Looks like a book doesn't it?  As far as the rupture of the diaphragm, I'm not sure why that happens (if it does), except that, apparently--in the early days of its use in the Cummins, the diaphragm would flex beyond it normal operating range with too little feed pump pressure.  Since the VP44 has been in use several years before that in other vehicles (Europe and possibly some tractors), any rupture must be peculiar to the 5.9 Cummins.  I think that rupture problem has been taken care of with later rebuilds of the VP, and, from Mike says, the diaphragm he has is much stronger.

 

I think the Bosch engineers must have been smoking some pretty good stuff when they engineered the VP44, but it is, after all, just a machine controlled by a computer.  There is nothing magical about it.  It's complicated but if operated with in it's design parameters, will be happy for a long time.

 

I believe one of the things that should be seriously considered in keeping it happy is keeping it lubricated and, to me, that means the use of two-cycle oil during every fillup (as recommended by Mike).  This design does date back to the days when diesel fuel had better lubricating qualities.

 

Once again, these are only my opinions, based on what I think I have learned over the last ten years.

And now~~back under my desk to Dodge the incoming flak.

Humbly,

jimmy

[diesel4life]

Actually, it & the 37 series (Virtually the same without computer) are very common in europe.

Ed

I have heard of a few vehicles in Europe with similar version of the VP44, but is it the same? Being their target emissions have always been different from the US...I guess my original question pertained more to the US anyhow, would be interesting to find it in another vehicle.

As far as tractors/equipment, that would be highly unlikely (but I'll never say impossible) as the sole reason of the replacement of the P7100 with the VP was to meet highway emissions. Construction/Ag equipment has always been several years behind highway emissions until recently. I have seen 12 valve engines with the P7100 stuffed in equipment as new as 03- 04, and from there they went right into the common rail fuel systems.

Again, this is just what I have seen and am not saying I know the VP44 doesn't exist in anything else here in the states except Dodge and the big brown trucks, I have been curious what else they are in, if any.

[Me78569]

Jimmy,

 

Great posts.  I am always willing to read and listen to someone that can form thoughts into meanful senstences. 

 

Nick

[Mopar1973Man]

Going with Jimmy idea of flexing. The piece I've got here is harden steel. I took out a scratch awl on my Leathermen and attempted to scratch the disc and can't. Can't mar it even. Roughly measuring the thickness of the disc the plastic is roughly 0.040 inches and the steel is 0.100 inches. This very very hard steel. Seriously doubt the flexing would be possible.

 

Then the other problem if it did flex or move then the o-rings might not seal as well being the one on the shaft relies on the snap ring to hold the disk down and the outer o-ring just the bit of plastic to hold it for the outside.

[Ilikeoldfords]

I am also not quite understanding how a steel plate could rupture?? Unless the early ones were in fact just plastic of some sort?

[Jeeper Jimmy]

Since nobody yelled at me very loud, I'll put my foot in my mouth one more time.

 

In the interest of keeping his thread alive, I did some calculations.  I won't bore you with these calculations, but if anybody really cares, I can post them.

 

First off~~we are not talking big numbers here; we're talking fractions of millimeters and cubic millimeters.

By my calculations, the diaphragm only has to flex (or move) about 0.12 millimeters (mm) (about the thickness of a piece of 20 weight copy paper) to absorb the high-pressure spill coming back into the feed bowl.  And that is assuming full volume of the injection pump pistons is spilled back to the  fuel bowl.  Any amount (about 50 cubic mm at max engine load or 4.5 cubic mm at idle) of fuel being injected into the engine will make this number smaller.

 

Again, this is a very small amount of fuel, but it's coming back at a bone-jarring pressure and the fuel bowl has to recover in a matter of milliseconds to get ready for the next operation.

 

I used Mike's pictures to give me a best guess at dimensions for the feed bowl.

  I used 3 inches for the diaphragm with 1.5 inch hole taken away.

  I used one inch for the bowl depth.

 

I took the plunger dimensions from the VP44 Service Manual.

  I used 7.4 mm for the plunger diameters (there are three).

  I used 3.5 mm for the plunger stroke.

 

I whole-heartily agree that it would be probably impossible to rupture a piece of one-tenth inch hardened steel.  I don't see that could possible happen.  I also think I agree that you're not going to flex that piece of steel much.  The  point I'm trying to make, I guess, is that when you put a high pressure spike of fuel back into closed system, something has to give.  And there isn't much time (may 100 milliseconds to fix it.)

 

I guess that's enough~~ Back under the desk

 

humbly,

jimmy

[Mopar1973Man]

So back to this picture...

 

 

Now Jimmy help me figure this out...

 

What the heck is this made of? What series of pumps was it used in? Because we have a picture of a part of pump (what series or model is unknown) but we have a picture of a rupture diaphragm out of a pump that is missing nearly 90* of the disc. The vane pump and timing piston look like its VP44 but that disc? What is it?

[TFaoro]

Since nobody yelled at me very loud, I'll put my foot in my mouth one more time.

 

In the interest of keeping his thread alive, I did some calculations.  I won't bore you with these calculations, but if anybody really cares, I can post them.

 

First off~~we are not talking big numbers here; we're talking fractions of millimeters and cubic millimeters.

By my calculations, the diaphragm only has to flex (or move) about 0.12 millimeters (mm) (about the thickness of a piece of 20 weight copy paper) to absorb the high-pressure spill coming back into the feed bowl.  And that is assuming full volume of the injection pump pistons is spilled back to the  fuel bowl.  Any amount (about 50 cubic mm at max engine load or 4.5 cubic mm at idle) of fuel being injected into the engine will make this number smaller.

 

Again, this is a very small amount of fuel, but it's coming back at a bone-jarring pressure and the fuel bowl has to recover in a matter of milliseconds to get ready for the next operation.

 

I used Mike's pictures to give me a best guess at dimensions for the feed bowl.

  I used 3 inches for the diaphragm with 1.5 inch hole taken away.

  I used one inch for the bowl depth.

 

I took the plunger dimensions from the VP44 Service Manual.

  I used 7.4 mm for the plunger diameters (there are three).

  I used 3.5 mm for the plunger stroke.

 

I whole-heartily agree that it would be probably impossible to rupture a piece of one-tenth inch hardened steel.  I don't see that could possible happen.  I also think I agree that you're not going to flex that piece of steel much.  The  point I'm trying to make, I guess, is that when you put a high pressure spike of fuel back into closed system, something has to give.  And there isn't much time (may 100 milliseconds to fix it.)

 

I guess that's enough~~ Back under the desk

 

humbly,

jimmy

 

So if this "diaphragm" does flex how is it going to break or rupture? As mike has stated, the metal part of it is extremely hard. So by your tiny amount of "flex" could this even break it?

[Jeeper Jimmy]

Mike,

That looks like somebody got mad at it and took a bite out of it.  If that round,black thingy were whole I would say it is a diaphragm. (as illustrated on Jasper's web site but not found in your breakdown).

 

That's a very strange combination of parts; looks like the hub of a vane pump, a beat up timing piston and a ruptured (or cut) diaphragm?  (Probably not ruptured, because it's too clean a cut) I think this is part of somebody's training aid, and maybe that the chunk has been deliberately cut out to show what it is made out for whatever reason I can't imagine.

 

Back to the piece you found:  How are the plastic and metal parts tied together?  Are they bonded or independent?  Is there anyway for pressure to get to the 'plastic' part?  Is the plastic part on the bowl side or the feed pump pressure side?  Also, is that snap ring the only thing that holds that piece you've got into the body?

The reason I ask is I've always been under the impression that low feed pressure can damage a diaphragm but high feed pressure cannot because the diaphragm had a strongback between it and the vane pump pressure to prevent high feed pump pressure from flexing the diaphragm in that direction (probably more folklore?). 

 

The mystery continues. 

[Mopar1973Man]

The plastic is moulded to the metal and the plastic side is inward towards the bowl. There is two sealing o-rings one smaller on the shaft and then the larger o-ring on the lip of the plastic. The only thing holding the plate in place is one snap ring.

[snowshoveler]

The plastic covered piece of steel with the bite out of it.

If the plastic bonded all over or just on the edges.

If just on the edges, its conceivable without actually having a personal look at it. That the plastic could move away from the metal during a low pressure moment and pust back toward the metal during a high pressure moment. Kind of like a air pillow but with the fuel itself being the cushion on both sides of the plastic.

Don't really have any idea , just throwing ideas out there.

 Chris

[Mopar1973Man]

More pictures. Like I said I still going to keep this ring on my desk for all the pictures anyone wants of it.

 

Inside plastic.

 

Outside harden steel face.

 

The damaged edge from prying it out.

 

Looking through the hub.

[snowshoveler]

That one looks like a seal of some sort.

Not the same as the one with the bite out of it?

Mike are you planning to repair this pump and do somthing with it.

From what I have seen of your pics so far, a man of your talents could machine a new piston and put in a few new seals / orings and be good to go.

Not pretty but should be good for at least a spare. 

Chris

[Mopar1973Man]

I wish... To many things are too damaged. The timing piston is so screwed up that you need to use a propane torch to heat up the body of the pump to even move the timing piston. I lost a few springs on the vane pump as they went flying across the shop as I pulled it apart. Then I broke the piston ring on the timing piston messing with it. The body of the pump is all beat to death from the previous owner.

 

[snowshoveler]

Thats a challenge my friend.

Build it and have fun while doing it.

There are many folks here on your forum that have the talents to help you.

Only real hard part is the o ring seal area in your last pic.

Even that can be repaired with a skilled welders help.

 Chris

[Yankneck696]

JB weld to the rescue !!!

 

Ed

[madog1969]

Could the term Diaphragm not be taken correctly? When I think of it my thoughts go to an accelerator pump on a carburetor. Maybe the steel ring sealed by an oring just separates two chambers??? Does it appear the steel ring floats? I cant really tell by the pics.

 

Just a thought

 

Also wonder if most of the 216s could be fixed by replacing just the piston on honing the hole out.

 

Again fyi...6 months ago I picked up a 216 and cold start dead pedal.....gone after 10minutes and key trick bla bla bla we all have heard of...then after reading the IAT fooler for fuel consumption, I saw where IAT adjust timing. Since doing the mod I can control my dead pedal....Its all coming together now with the stuck Piston

 

 

Matt

[snowshoveler]

I still think Mike could rebuild his pump. Machine a new piston, punch its hole out oversize and maybe put in a sleeve.

A bit of creative welding on the mounting boss and it would be good to go.

Once its able to run, then get creative with some mods. Open up that fuel return path and see how pressure responds. 

Heck, he might even have it on his truck by now.

More pics Mike or we are going to think you are holding out on us.

 Regards Chris

[Mopar1973Man]

Not holding out just been busy... Between working with Ed and fire fighter classes...

[Texas CTD]

Not holding out just been busy... Between working with Ed and fire fighter classes...

 

Squirrels are time-consuming animals...