Engine/Transmission (1998.5 - 2002) Cavitation is NOT your VP-44's friend!

[cap-n-cray]

I posted this about cavitation back in April 2005. I am still convinced that cavitation can lead to the lift pump failing.



There is a lot of information at the site link in my post.



Cary



Good video Gary.

 

[Gary - K7GLD]

Sorry, the first test is NOT cavitation. It is either the internal relief valve opening with a bad ball and or seat. Or, most likely, a bad Vane sticking under a load. You can not cavitate a pump by restricting the output. Look up what cavitation is. . One other thing when was there the most flow? When the gage was at 10psi or when it was at 15psi? A pump does NOT make pressure, restriction does, the pump just the volume.

You musta missed my quote that the pump used in my demo was operating perfectly when pulled at 50K miles - it was still holding perfect, steady normal operating PSI, and had NO issues of any kind while on the truck - I merely switched to a Walbro to test one of those in real life. Fact is, that same pump will operate flawlessly days on end at 13 PSI or so - the displayed situation ONLY occurs once the pump's cavitation threshold is crossed at about 15 PSI - and THAT is as repeatable and predictable as sunrise and sunset!



Fact is, I have another LP, used on my truck for a period of time to verify proper operation - and also used several years back for the same, identical test as seen in my above video - with EXACTLY the same results.



Deny it if you choose, but what I have shown *IS* cavitation - not a defect or failure in any part of the pump!

 

[NoSeeUm]

If the pump was Caveatting why did the motor speed up?



.....

Robert

Good discussion, thanks for the comment. It is not my aim to argumentive just for the sake of it, but the one thought sticking in my mind is "It is airbound". Why would it get airbound?



My thoughts:



It is hard for me to tell if the pump RPM goes higher or it just gets noisier. Depending upon a what type of DC motor it is, it could noticeably speed up when load is dropped from it. A vacuum cleaner is a good and poor example of this, but ussually uses an AC motor. The only true illustration of load on the motor would be amp draw or flow rate, providing nothing else internal is going wrong. Maybe Gary could do a two bucket pump (or some such) test also if the mood strikes him to check flow rate.



In reference, a pump will not ussually cavitate much when it is airbound, nor will it pump at all or very well. In the first example on the video IMO Gary illustrates the behavior of a pump very similiar to one becoming airbound or as BobV tried to explain something else is going wrong.



A pump cavitating can still pump very well.



The second example in Gary's video IMO is a good example of cavitation and what I expected to see happen before I watched the video. Hence my question, making me wonder what really is going on in the first part of the video, because I am unsure.



A vane type pump is not all that complex and as some one stated above, not that far from a centrifical type pump in many aspects in this application. It will have characteristics of a positive displacement pump as well as a centrifical type pump.



In the trueist sense a vane pump, as well as any positive displacement pump, will pump a set volume of liquid each revolution irregardless of the discharge pressure depending upon the displacement of the pump. It should only pump less than that volume if it is cavitating. Because it will pump to any (elevated) pressure is the reason the discharge pressure must be controlled.



So... .



If the internal bypass was opening and sticking wide open (or close to it), it would do so probably at a set maximum pressure. This pressure should be where it was designed to open and control pressure below that value. But is something going wrong?



In my mind, the way that the pressure goes to 15 psi then pops down almost instantly could be a very good example of this very thing happening. The discharge pressure drops because, the pump is sucking the fuel right back to it own suction. The pump itself is at maximum load, but no much fuel is headed towards the VP44.



I don't know for sure;

Sorry for the novel;

Jim

 

[Gary - K7GLD]

Main thing to keep in mind, is that ugly things CAN happen at about 15 PSI when these pumps are installed and operated in the OEM fashion - there ARE steps that can be taken to reduce or eliminate the potential problem, and many of us have used them - purpose of this thread was to more clearly demonstrate what typically is occuring deep in the inner recesses of these pumps...

 

[NoSeeUm]

The pump will speed up when it cavitates because it can do no work and the motor runs free. Put your hand over the suction side of a vacuum cleaner and it will speed up. These pumps are low level vane pumps and just a step above a centrifugal and cavitates from restriction on either side.

This is another good point here. Many have argued is it working harder or not as hard. Awnser it is not working at all because there is no air to move thats why it speeds up. This is why a lot of turbos fail when the air filter gets really plugged "We see lots of this at the coal mine I work at" it overspeeds the turbo and shafts break and wheels come apart.

What you say is true, but air is compressable.



Jim

 

[NoSeeUm]

Main thing to keep in mind, is that ugly things CAN happen at about 15 PSI when these pumps are installed and operated in the OEM fashion - there ARE steps that can be taken to reduce or eliminate the potential problem, and many of us have used them - purpose of this thread was to more clearly demonstrate what typically is occuring deep in the inner recesses of these pumps...

LOL



Well said Gary.



Jim

 

[Misenheimer]

I don't know what pump that you are refering to but tne one that I have has NO internal buypass. The 1998. 5 and up gen 2 pumps are the same.



Take the three studs out of the top plate and you will see only a passage about 3/4 around the outside for the screen



NO INTERNAL BUYPASS IN THIS PUMP





Oo.

 

[JKinney]

I just took a $64. 00 dead campaign pump apart and it has a bypass

 

[Misenheimer]

If I can figure out how to attach a picture I will. I have three of the stock pumps and I think that they are Carter. They are identical to the one in the video. If you remove the top, screen, vanes, and holder you can insert a wire through the pump from one side to the other,

NO BYPASS VALVE

 

[Sixpack]

This discribes all my lift pump failures, but one problem. With a new LP everything would be fine for 6-12 months. Then it will cavitate once, and perform exactly as you have shown until finally replaced again. Why will I get 6 -12 months before seeing any cavitation, if cavitation is the problem?

OK so we all have our opinions on the cavitation issue. How bout some thoughts on what MBowman asked. Inquiring minds want to know!

 

[klaybus]

This discribes all my lift pump failures, but one problem. With a new LP everything would be fine for 6-12 months. Then it will cavitate once, and perform exactly as you have shown until finally replaced again. Why will I get 6 -12 months before seeing any cavitation, if cavitation is the problem?

There's the million dollar question..... Every LP I've ever replaced had the same symtoms with the exception of the "campaign pumps". They never lasted as long as the $140 DC pumps. Appeared to be the same pump without the longevity of the $140 pumps.

Dodge pumps would go 3-12 months & then die the same death as the rest. One pump we took apart had all sorts of metal shavings inside & the assembly was anything but high tolerance for sure! Not sure if it was just that particular pump or if the'yre all not a very high tolerance pump.



Clay

 

[Gary - K7GLD]

If I can figure out how to attach a picture I will. I have three of the stock pumps and I think that they are Carter. They are identical to the one in the video. If you remove the top, screen, vanes, and holder you can insert a wire through the pump from one side to the other,

NO BYPASS VALVE

TRUE - but the actual bypass section is in a passageway in the roof of that passageway you inserted the wire thru - it's NOT in line with that passageway, it's runs upwards into the motor section, thru the motor section, then DOWN into the other side again...



Here's a pic of those passageways AND the ball and seat portion of the bypass valve as seen from from the motor side of the casting:



#ad

 

[Gary - K7GLD]

I don't know what pump that you are refering to but tne one that I have has NO internal buypass. The 1998. 5 and up gen 2 pumps are the same.



Take the three studs out of the top plate and you will see only a passage about 3/4 around the outside for the screen



NO INTERNAL BUYPASS IN THIS PUMP





Oo.

Check the above post! :-laf :-laf



You have to LOOK FOR the bypass passageways, they are NOT in line with the inlet/outlet passageways, or easy to see without looking - but run upwards from them INTO the motor section...

 

[Gary - K7GLD]

Originally Posted by MBowman

This discribes all my lift pump failures, but one problem. With a new LP everything would be fine for 6-12 months. Then it will cavitate once, and perform exactly as you have shown until finally replaced again. Why will I get 6 -12 months before seeing any cavitation, if cavitation is the problem?

WELL, I have a theory on that - but no proof... :-laf



I suspect that a new pump is tight, and neither the brushes OR pump vanes have fully seated for full operational efficiency - and resulting PSI possibly a bit less than the max it WILL eventually reach. Once everything loosens up, gets seated and in it's prime - THEN the problems start...



Just a theory...

 

[Gary - K7GLD]

IT seems lots of guys are confused, and still don't realize or accept that the fuel actually flows THRU the motor section of these fuel pumps as part of it's design - just as it does in the Walbro and in-tank pumps...



This is done for cooling of the pump, and lubrication of the armature bushings...



And NO, it won't set the fuel on fire or cause it to explode!

 

[Misenheimer]

Gary and others

Please accept my apology for being hard headed. The passages are there alright.



THERE IS A BYPASS



and I missed it

 

[GHolcomb]

WELL, I have a theory on that - but no proof... :-laf



I suspect that a new pump is tight, and neither the brushes OR pump vanes have fully seated for full operational efficiency - and resulting PSI possibly a bit less than the max it WILL eventually reach. Once everything loosens up, gets seated and in it's prime - THEN the problems start...



Just a theory...

I'm in a good position to test that theory. I have put a new LP on my truck and on my brother's truck within the last couple of months. Both pumps were at 12-13 psi after installation. It will be interesting to watch to see if they work their way up to the 15psi threshold and then go into the demonstrated failure mode.



By the way, I am one of the guys that didn't know that fuel ran through the motor housing and that the pump has a relief valve. Thanks for the picture!



Greg

 

[Gary - K7GLD]

Gary and others

Please accept my apology for being hard headed. The passages are there alright.



THERE IS A BYPASS



and I missed it

Don't give it a second thought - I made a mistake once myself - or at least thiught I had... :-laf :-laf

 

[Gary - K7GLD]

One pump we took apart had all sorts of metal shavings inside & the assembly was anything but high tolerance for sure! Not sure if it was just that particular pump or if the'yre all not a very high tolerance pump.



Clay

HMMmm - I've sure seen LOTS of crap from outside sources both residing at the bottom of fuel tanks, and circulated in the fuel stream. Sorta makes me wonder if conditions as you mention have ORIGINATED in the pump - or were sucked into the pump and then began destroying the pump internals.



In my own case, I was seeing LOTS of small metallic particles caught in my Frantz sub-micron fuel filter element:



#ad




I assumed they were cast off wear particles from my LP and pusher pump - but eventually my VP-44 started tossing codes, and after doing the replacement bit, sent the bad one off to Industrial Injection for a rebuild of ONLY the failed parts.



Turned out mine was one of the infamous Bosch mistakes, where they used a brass timing advance cylinder inside the VP-44 - and they inevitably wore and failed prematurely - what I had been seeing on my fuel filter was the small bits of cast off brass VP-44 particles circulating thru my fuel system until the finer Frantz caught them.



Now with the replacement VP-44, which uses a steel advance cylinder - no more particles on the fuel filter - a good thing they hadn't, at least to this point - damaged my LP and pusher...



Things aren't always what they seem - or what we automatically assume! :-laf

 

[rweis]

How about someone else than Gary take a pump other than a carter and see if it will cavitate the same as the carter.



We try this pump and that pump and get sometimes results sometimes not.



Walbro pumps seem to be the latest "thing". How about someone take a Walbro and do the same test / demo Gary did and see what happens.



Aeroquip 1000's are anothe of the "now" pumps. How about someone take a Aeroquip 1000 and do the same test / demo Gary did and see what happens.



FASS AIRDOG RASP same same.



Test the pumps FIRST, before recommending them. The only "testing" is "it works for me on my truck" which depends on how YOU drive etc. I am guilty of the "it works for me" syndrom as well. Test first, novel idea?



Bob Weis



Flow bypass valves are looking better and better.