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Disassembled A Bosch Vp44 Injection Pump

Mopar1973Man
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rancherman

rancherman

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isn't the main reason that valve is there..  is  to help  maintain  'pressure'  within the   system,  after all,     no pressure  can be   'made'  unless there is  a  restriction.     Sure,   fuel is  there,  but unless there is  'flow'  which  equals   cooling,   then  we all know  what  happens  when  there is too much heat..

 

Pressure  doesn't necessarily mean there is  'flow'..   I've   thought  for years  the  true health of our  fuel system  should be measured  on the  downstream (overflow)  side of the pump..  volume  mainly.     If  there isn't  any or very little  overflow,  then   one shouldn't expect much cooling to take place.

 

Bosch  would  want  a  certain amount of  residual  pressure  within  their  pumps,   to ensure   all  components  are  adequately  supported  with  airless  fuel..  so  no  component is    never  starved  for  fuel.    Vane pumps,   rotor heads,  all are designed to fill  with  fuel  at a certain  level of  pressure.(ON THE BACKSIDE)   If  they are forced  to  'pull'  fuel,  then  other  problems  surface.    This is  where  the  15 psi   check ball comes in.

 

The  overflow  kinda   handles  both  issues,     keeps  a certain amount of  pressure  within  the  pump,  allows   the  rest to return to tank.     Plus,  it  keeps fuel from draining back after shut down. (yah, yan,  I know it  takes  air  to  break the  vacuum within a  liquid  to  cause it to drain back)..

This  still    is   all dependent   of  what  the  supply  can  deliver.   

Mike  really never answered  my question  a  few months ago,  when I asked if  the vane pump  has  ANY EFFECT of  the  PRESSURE  within the  pump itself..  ie  against the overflow valve...     Meaning  in effect,   as long as there is  volume to the  intake side of  the  vp,   will the vane pump  "do the  rest"  and  take care of  the  internal pressures  and  cooling  needs  as well???    Or is  all fuel  running through the  vane pump all directed  to the  rotor head.

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man4mopar

man4mopar

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1. Yes the port is completely open.

 

2. Yes there was 15+ PSI at the time of the video.

 

3. Fuel pressure is mechanical gauge (no sensor) so that is actual input pressure to the pump.

 

The problem is you got to start the flow of fuel from the front of the pump and work your way all the way back to the rear of the pump. So now the fuel has to pass through the vane pump, then all the galleys to the rotor and then when the rotor is done then the excess fuel is sent towards the overflow valve.

 

 Thanks for the information much appreciated. #3 I should have used the term pressure gauge port instead of sensor. Some put the port before a filter as a means to know when to change the filter. Wanted to make sure the psi I saw on your gauge was the actual restriction of the VP with the volume of fuel you send it not something else like a filter. You saved me some time in trial and will now regulate pressure before the VP.

 

Cheers and enjoy your day,

 

Josh

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KATOOM

KATOOM

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Or better yet.....  Is the "crack" even a problem or is it just merely the outer plastic.  Or.....does the plastic form some kinda diaphragm seal which whereby the "crack" is allowing fuel to bypass under pressure, thus the reason why when the diaphragm cracks the timing piston is soon to follow because of it beating itself up from improper fuel timing?

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KATOOM

KATOOM

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No, what I meant by "outer plastic" was that its a steel disc covered in plastic.  To the best of my understanding its always been plastic but the upgraded version became plastic over steel.  So that said, is the "plastic" serving as some sort of sealer?  Something about the diaphragm must be sealing because when the diaphragm fails, proper fuel timing is no longer achieved at the timing piston.

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Mopar1973Man

Mopar1973Man

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109882-182413-MARKPEDERSONIMAGE2.jpg

 

That's what I don't understand that disc is on the back of the rotor assembly. It has no connection with timing piston. Maybe hydraulic it might be connect dumping the pressure back in the body of the pump. I'd have to pull my pump off the shelf and pull it apart again. But the steel plate is held in by 1 snap ring and has 2 o-ring seals. The plastic can't flex with steel backing it. Like photo above I wonder about the crack like it was force or pried again from the center hub. Improper assembly? Because if you got a steel disc backing the plastic there is no way to flex the plastic. But being the crack is larger at the center hole going to the outer diameter this seem to me from prying out.

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Mopar1973Man

Mopar1973Man

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I think I found the answer on this. While taking my morning shower I was thinking about that plastic backing. We all assume there is pressure there because most of us use a fuel pressure gauge. Let's assume the owner doesn't have a fuel pressure gauge and a bad fuel filter. Now the only time that plastic will flex is under a VACUUM. The plastic is not glued to the steel. So if there is a vacuum present it would pull the hub inwards and crush against the inner o-ring till it deformed and cracked.

 

Sound about right?

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KATOOM

KATOOM

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Hmmm…..viable.  The way it was explained to me some years ago was that the VP has three levels of pressure within itself.  High, middle, and low.  I know “middle” isn’t the correct terminology but let’s not split the hairs just yet.  So the diaphragm is situated on the low pressure side of the VP but yet because of the rotor design, the mid pressure pulses are allowed to travel back through the low pressure side.  The only thing to stop or offset those mid level fluid pulses from traveling back through the low pressure side is the pressure from the fuel pump.  And when the fuel pump pressure is too low then the mid pressure pulses are the stronger of the two and the constant wave of mid to low, mid to low, pressure signals felt by the diaphragm are what causes it to “flex” and eventually fail.  Apparently it seems were not sure what the actual failure is or if the failure is what we think it is as this diaphragm seems pretty stout.  But nonetheless…..

Sometimes I feel like the VP holds mysterious secrets like the pyramids of Egypt.  You’d think after 16 years SOMEONE would have an accurate understanding about the mystical VP diaphragm.

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Mopar1973Man

Mopar1973Man

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You'd figure after 16 years someone would of fixed these mysteries. But why invest in a obsolete technology since common rail came out.

 

As for pressures the vane pump goes directly to the rotor in those ports IIRC. As for the body of the pump its at fuel pressure level. So that would be you middle pressure from the vane to the rotor head.

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KATOOM

KATOOM

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You'd figure after 16 years someone would of fixed these mysteries. But why invest in a obsolete technology since common rail came out.

 

Strangely though, Cummins is not the only engine to use the VP44.  Lots of people work on the VP but the true understanding of what’s going on inside it seems to be some highly guarded secret no one will divulge.

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rancherman

rancherman

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You'd figure after 16 years someone would of fixed these mysteries. But why invest in a obsolete technology since common rail came out.

 

As for pressures the vane pump goes directly to the rotor in those ports IIRC. As for the body of the pump its at fuel pressure level. So that would be you middle pressure from the vane to the rotor head.

LOL,   yah,  why  'fix' a   'cash cow'??   

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