Over on TDR there is a very interesting video on what happens when the stock LP pressure reaches 15psi. Anybody interested in Lift Pump issues should definitely watch this video. If, what is demonstrated in the video is what is really going on with our LPs, then there is an astounding conclusion to be drawn and that is that Cummins goofed (we know that from the failures) in the way they used the Carter pump and,also, the CTD community has been taking the wrong approach in just mounting the LP by the tank and not doing anything about cavitation.

A few months ago I installed a fuel pressure regulator (Simflow, available from Wide Open Diesel for about 40$) to limit the output pressure from my Campaign Pump to 12psi) and, so far, it is working well. My intention, in adding the regulator, was to save the bypass valve but it looks like I might have prevented cavitation as well.

 

As I see it, the video is a crock.

The output is restricted so the pump cavitates, WRONG. When the output is restricted, the pump bypasses and because there is no where for the fuel to go in his "example", the pressure falls off. It is exactly the same as saying that your kitchen faucet is cavitating because when you turn it off, nothing comes out!

Change the "example" around and restrict the input to the pump and then it will cavitate. With the restriction, the pump basically sucks the line dry because it will suck more than the line will flow. That is cavitation.

The pump is basically set to bypass at 15 psi although they do vary considerably. My Carter lift pump and others that I know of will pump 18 psi at idle.

Biggest problem with the TDR is all the arm chair pilots on there that eat this crap up and suddenly every one thinks it's right because the TDR says so.

Don't believe everything you see on the TDR.

Jeff

 

"When the output is restricted, the pump bypasses "

Since the bypass is just a spring-loaded ball, the ball should seat itself once the pressure drops a couple of psi. In the video the pressure drops to 3psi( I think). Surely the spring would seat the ball at 3psi and the pressure would build back up. How do you explain that?

 

With the restriction, the pump basically sucks the line dry because it will suck more than the line will flow. That is cavitation.



BINGO.....

NCA

 

Yes, but here we are talking about a restriction on the output line, not on the input line. There is plenty of fuel available since there is no restriction on the input.

 

If I follow this thread correctly, the output of the lift pump is actually the inlet of the IP...so actually the LP is causing the restriction to the intake side of the IP

so actually your output is really a restricted input... confused? I am !

 

Do you have a link to the video, I can't seem to find it..

 

Here is a link to the video
http://media.putfile.com/Cavitation

In all the previous discussions, input and output refers to the LP, IP did not enter the picture at all. The video is a test of the LP by itself, there is no hookup to a IP.

 

Very interested in this. The video describes exactly what is happening to my truck, weird fluctuation in pressure for no reason. The answer in the video if I got that correct was to restrict the output to the "VP" to less than 13psi, my normal idle pressure is 16psi with a stock carter pump. Wish I had clear tube to actually see this but I don't. I also don't feel like spending $400+ on a new walbro or more on a FASS setup.

Now more confusion is the VP wants more pressure to cool, lube etc. How is that possible if the fix for the LP is to restrict the flow to the VP. Dead end, either the LP is happy or the VP is happy BUT in my case if it really is cavitating the VP isn't happy either.

Waiting for more educated people to respond, as I'm just confused now .

Thanks

 

There are two very important things to think about in this case. The first is pressure and is the only thing that this video focuses on. The other is flow. In this video the discharge is closed resulting in the pump spinning in a static liquid. This makes lots of heat resulting in flashing liquid and will cause the pump to cavitate. In the case of our lift pumps they always flow to the IP and the IP passes excess fuel back to the tank. This flow keeps the liquid cool and a liquid.

 

My view on this is its all about the draw from the vp44. If you are at idle, the pressure will build up because the vp doesn't need a large volume of fuel. Give a tap on the pedal and the vp wants more fuel causing the pressure to drop. the faster you go the more fuel you draw the lower the psi. with a clean fuel filter and a new stock lp I get 13 psi at idle 8-10 psi wot and about 11 psi cruising on the highway. even at idle I can never seem to get more than 13 psi so according to the video no problem! well we'll see i still think that some pumps are just born defective, just like some of us! lol... build a better mouse trap and someone will buy it! Until then cross your fingers..

 

I just watched the video again, again this is not proof by any stretch but it does act similar to alot of posts on this board.

Now if the restriction was on the output side of the LP leading to the VP, maybe the check valve in the VP, would cavitation happen at idle or WOT. According to the vid the more restricted the input or output flow the harder the LP has to work thus causing cavitation as your maxing out the pumps ability to flow, did I get that right? So in other words if there is a restriction in the line, pre or post LP, and the LP can't pull or push the fuel, it just spins pumping air and little fuel until the restriction is relieved correct??

So last question if I got everything correct above. My stock Carter LP pumps 16 psi idle and about 9~10 WOT, stock location engine mounted. Filters replaced every 2 oil changes etc. Would I be looking at the check valve at the VP or a restriction from the tank to the LP. Or is it more complicated than that. I just wish there was a way to bench test the pump while it's on the truck but unless I give it a WOT run the pump will always stay and 16psi idle but when it does cavitate (if it really is) it will idle then at 9psi and down to 2-3 psi maybe less WOT but that is just a short (less than 1 second) drop in FP until it's back up to about 10 PSI WOT as it's done cavitating.

Sorry for the long post just trying to figure all this out and not spend more money if I don't have too.

Thanks everyone.

 

I watched the video without comments, just turned the audio off. This helps to avoid any bias, and make your own conclusions. And all I saw was a demonstration of a bad pump performance with no evidence of any causes of such. Then I listened. The narrator simply states "cavitation", and you're supposed to believe it. Plus, I could not see the other c-clamp on the right for most of the experiment.
I am not going to tell you what to believe but to me it looks like the cheesy plate bulges under pressure just those few thousands that it takes to lose the efficiency in the rotor volume. And it drops the pressure. Just inadequate pump setup. Install a bypass valve on it and it will work much better. No need to think that bypass is only useful for 255 GPH Walbros and FASSes.
-P

 

"Now more confusion is the VP wants more pressure to cool, lube etc. How is that possible if the fix for the LP is to restrict the flow to the VP. Dead end, either the LP is happy or the VP is happy BUT in my case if it really is cavitating the VP isn't happy either."

12psi is more than adequate pressure to keep the VP internals lubed and cooled, I don't think higher pressure leads to any extra benefits. So, install a bypass regulator between the LP and the VP to keep the pressure at 12psi.

"In the case of our lift pumps they always flow to the IP and the IP passes excess fuel back to the tank. "

Not exactly. At idle there is very little flow thru the VP, the VP just ends up blocking most of the output of the LP, so you are dead-ending the output of the LP. Assuming that the pump in the video is not defective, what the video demonstrates if that once the pressure reaches 15psi some undesirable thing happens. Maybe it is not Cavitation, Gary,in the video, is hypothesizing that it is. Even if it is not cavitation the phenomenon is not something we can ignore and might be an explanation of the abysmal performance of the Carter pump in the CTD application.

"even at idle I can never seem to get more than 13 psi so according to the video no problem! "

In your case the "cavitation" phenomenon is not happening, so perhaps your pump will last a long time.

"Now if the restriction was on the output side of the LP leading to the VP, maybe the check valve in the VP, would cavitation happen at idle or WOT. According to the vid the more restricted the input or output flow the harder the LP has to work thus causing cavitation as your maxing out the pumps ability to flow, did I get that right? So in other words if there is a restriction in the line, pre or post LP, and the LP can't pull or push the fuel, it just spins pumping air and little fuel until the restriction is relieved correct??"

Correct.

"My stock Carter LP pumps 16 psi idle and about 9~10 WOT, stock location engine mounted. Filters replaced every 2 oil changes etc. Would I be looking at the check valve at the VP or a restriction from the tank to the LP."

16 and 10psi is not bad at all and you will only gain small increases in pressure by using larger lines and eliminating the banjos.

"unless I give it a WOT run the pump will always stay and 16psi idle but when it does cavitate (if it really is) it will idle then at 9psi and down to 2-3 psi maybe less WOT but that is just a short (less than 1 second) drop in FP until it's back up to about 10 PSI WOT as it's done cavitating."

This does not appear to be the 'cavitation' phenomenon, I think it is the pump just trying to catch up to the sudden increased demand at WOT if it is only lasting for a second and it is happening when you apply WOT.

" Install a bypass valve on it and it will work much better. No need to think that bypass is only useful for 255 GPH Walbros and FASSes."

That was pretty much the thrust of my original post, a bypass regulator seems essential for proper operation of the Carter pump. And,if it is, how did the Cummins engineers miss it and how did the entire CTD community miss it for so long? The wisdom at DTR,TDR, DieselRam and other forums has consistently been "mount the pump by the tank, eliminate the banjos, use larger lines". I mounted my pump by the tank and added prefiltering and larger lines years ago and it did not lead to increased LP life.

 

This is a very interesting thread. It's been a while since I've dealt with hydraulics so I'm going back and reviewing some info I have. I would like to see the test have used needle valves rather than simple clamps and the inlet and out let could have gone into a clear water jug so we could see the bubbles.

Somewhere above there was mention of the cover deflection. I just ran Cosmos stress analysis on an approxomation of the cover as I don't have a loose one for real dimentions. If someone can send me a sketch I'll run it again. Simply put deflection is not an issue.

We're looking at about .0003 in the middle worst case. I doubt the cover is even that flat to begin with.