Cavitation Video and Lift Pumps.
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Joined: Feb 2006
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From: Austin, TX
I am by no means an expert in liquid propulsion...Take what I say for what you will...
Cavitation happens when you create a low pressure zone on the inlet side of a pump. On a boat if the propeller is not matched to the boat and the prop pushes the water faster than the boat can move, it will create such a low pressure zone immediately on the bow side of the propeller that it causes air bubbles in the water. This is similar to an inlet restriction. Therefore the propeller churns through airated water and is inefficient.
It stands to reason, that in any test with any pump...if you have a restriction on both the inlet and outlet of a pump (like in the video)...you won't have cavitation because the flow is within the range of the pump. If you remove the outlet restriction and not the inlet restriction you are creating the ideal environment for cavitation. Flow out is easy---flow in is restricted. So that video sets up the pump to cavitate. Any pump would do that.
So it tells me nothing really except if I start so see symptoms on my gauge like what I see on the video I need to clean the prefilter in the tank.
It also tells me that removing restrictions in a fuel line on both sides of the LP is important.
Cavitation happens when you create a low pressure zone on the inlet side of a pump. On a boat if the propeller is not matched to the boat and the prop pushes the water faster than the boat can move, it will create such a low pressure zone immediately on the bow side of the propeller that it causes air bubbles in the water. This is similar to an inlet restriction. Therefore the propeller churns through airated water and is inefficient.
It stands to reason, that in any test with any pump...if you have a restriction on both the inlet and outlet of a pump (like in the video)...you won't have cavitation because the flow is within the range of the pump. If you remove the outlet restriction and not the inlet restriction you are creating the ideal environment for cavitation. Flow out is easy---flow in is restricted. So that video sets up the pump to cavitate. Any pump would do that.
So it tells me nothing really except if I start so see symptoms on my gauge like what I see on the video I need to clean the prefilter in the tank.
It also tells me that removing restrictions in a fuel line on both sides of the LP is important.
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Joined: Apr 2004
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From: St.Paul , MN
In order not to confuse things, I need some info before I add my $0.02 tothe original thread.
I got my truck in '02 with about 50k on the clock. I already knew about the lift pump issues so I installed a simple full time gage right away. I had right at 13-14 psi after the filter up to about 102k when it began falling rapidly. I installed a new one purchased from a diesel service center in Nashville. New pressure was 14-15 after a new filter where it is now at 175k. Lucky maybe.
Now the question. I took the old pump apart as far as I could without cutting up the motor case. Inside there was a ball check valve and spring. The ball seat, what remained of it was large enough for the spring to go thru and get cut up by the pump rotor vanes. The ball was worn flat and really chewed up and the spring was I'd guess 1/2 of its' original length. The screen was almost gone..just enough that I could recognize it. The vanes had a perfect arc worn in them where the ball had contacted them and gradually worn a nice groove the size of the ball. About 1/4 inch. The reason for the falling pressure. The filter housing had a large amount of very fine metal particles in it some magnetic and some not. This indicating that the ball, housing and vane particles had been caught by the filter. Lucky me. Anyway I reassembled the pump but missing the spring, ball and screen to see if it would work. It actually pumped quite a flood but not with any pressure at all so it was dead. Now the question is...whew..was this a 'campaign' pump this long ago?? The reason I ask is there was a thread on another form called anatomy of a pump and there was no relief valve shown in the pictures.
I since have taken 3 other dead pumps apart all from the 2001 era or earlier and they all had spring, ball, and screens like mine. In other words a built in check valve. One had the shaft coupler sheared other wise the failure was exactly like mine. IE ball seat wallowed out entirely.
So the bottom line is that these pumps have some kind of relief valve built in which makes sense as you would not want to dead head them or something will break or at least stall. (and shear the coupler) It could be designed so there would be a flow thru in event of a lock up which is what I think the 'campaign pumps have but I have not seen the insides of one.
Sorry for the long post but I needed some clarification before I go and shoot off the keyboard on something without facts or knowledge.
thanks
I got my truck in '02 with about 50k on the clock. I already knew about the lift pump issues so I installed a simple full time gage right away. I had right at 13-14 psi after the filter up to about 102k when it began falling rapidly. I installed a new one purchased from a diesel service center in Nashville. New pressure was 14-15 after a new filter where it is now at 175k. Lucky maybe.
Now the question. I took the old pump apart as far as I could without cutting up the motor case. Inside there was a ball check valve and spring. The ball seat, what remained of it was large enough for the spring to go thru and get cut up by the pump rotor vanes. The ball was worn flat and really chewed up and the spring was I'd guess 1/2 of its' original length. The screen was almost gone..just enough that I could recognize it. The vanes had a perfect arc worn in them where the ball had contacted them and gradually worn a nice groove the size of the ball. About 1/4 inch. The reason for the falling pressure. The filter housing had a large amount of very fine metal particles in it some magnetic and some not. This indicating that the ball, housing and vane particles had been caught by the filter. Lucky me. Anyway I reassembled the pump but missing the spring, ball and screen to see if it would work. It actually pumped quite a flood but not with any pressure at all so it was dead. Now the question is...whew..was this a 'campaign' pump this long ago?? The reason I ask is there was a thread on another form called anatomy of a pump and there was no relief valve shown in the pictures.
I since have taken 3 other dead pumps apart all from the 2001 era or earlier and they all had spring, ball, and screens like mine. In other words a built in check valve. One had the shaft coupler sheared other wise the failure was exactly like mine. IE ball seat wallowed out entirely.
So the bottom line is that these pumps have some kind of relief valve built in which makes sense as you would not want to dead head them or something will break or at least stall. (and shear the coupler) It could be designed so there would be a flow thru in event of a lock up which is what I think the 'campaign pumps have but I have not seen the insides of one.
Sorry for the long post but I needed some clarification before I go and shoot off the keyboard on something without facts or knowledge.
thanks
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From: Toronto, Canada
"Flow out is easy---flow in is restricted. So that video sets up the pump to cavitate"
In the video it is the outlet that is restricted, not the inlet.
" The reason I ask is there was a thread on another form called anatomy of a pump and there was no relief valve shown in the pictures."
All the pumps, OE and Campaign pumps, have the internal relief. This thread on another forum that you mention must have been in error.
In the video it is the outlet that is restricted, not the inlet.
" The reason I ask is there was a thread on another form called anatomy of a pump and there was no relief valve shown in the pictures."
All the pumps, OE and Campaign pumps, have the internal relief. This thread on another forum that you mention must have been in error.
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From: St.Paul , MN
Ok, That's what I suspected as it looks like the lift pump but there was no pocket for relief valve. Maybe it was the low pressure Carter. Still it looked like the Dodge connector. So discount that thread as not right. I won't post the picture without the author's permission so leave it at that.
thanks
thanks
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From: Colorado Springs
"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."
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."
Would cavitation happen at idle or WOT?
Second your reply that it does not appear to be cavitation but rather a sudden increased demand for fuel if that were true wouldn't the pressure return on it's own to the normal 16psi? In my case I have to make a quick WOT to get the pressure back. Again the same WOT run will drop the pressure and it will stay that way until another WOT run. (see where my mileage is going here?)
Third, a bypass valve before the VP. So after the LP and before the VP and tap into the return line?
Thanks again.
Thread Starter
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From: Toronto, Canada
"Would cavitation happen at idle or WOT?'
The 'cavitation' phenomenon(if,in fact, that is what is going on in the video) is unlikely to happen at WOT because, with the high demand for fuel, the Carter pump is not able to generate 15+psi. It could happen at idle because of the low demand for fuel. In your case I am not sure what is going on, perhaps it is a worn out internal pressure relief valve that is acting up.
"Third, a bypass valve before the VP. So after the LP and before the VP and tap into the return line?"
That is exactly the way I have it set up on my truck. It has only been on for four months and, so far, it is working well with a constant pressure of 13psi ; only time will tell if it increases the longevity of the LP.
The regulator is only 40$ and it is not difficult to install. I was planning to switch to Walbro because, even after taking the steps that has been prescribed in this forum(and others) to help the LP, my LPs were barely lasting a year. The Walbro needs a regulator, so I installed the regulator as a first step in my changeover to a Walbro. Now I am going to wait and see how long my Campaign pump lasts with the regulator installed and limiting its maximum pressure.
The 'cavitation' phenomenon(if,in fact, that is what is going on in the video) is unlikely to happen at WOT because, with the high demand for fuel, the Carter pump is not able to generate 15+psi. It could happen at idle because of the low demand for fuel. In your case I am not sure what is going on, perhaps it is a worn out internal pressure relief valve that is acting up.
"Third, a bypass valve before the VP. So after the LP and before the VP and tap into the return line?"
That is exactly the way I have it set up on my truck. It has only been on for four months and, so far, it is working well with a constant pressure of 13psi ; only time will tell if it increases the longevity of the LP.
The regulator is only 40$ and it is not difficult to install. I was planning to switch to Walbro because, even after taking the steps that has been prescribed in this forum(and others) to help the LP, my LPs were barely lasting a year. The Walbro needs a regulator, so I installed the regulator as a first step in my changeover to a Walbro. Now I am going to wait and see how long my Campaign pump lasts with the regulator installed and limiting its maximum pressure.
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Joined: Nov 2002
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From: Az
If there was no restriction on the outlet side and no restriction on the inlet side. then there would be less than 0 psig on the gauge( Bernoulli's principle). There has to be some resistance to develop presure. Now, as in the video, if you slow the output to a point where the pump "backs up", then yes, it will cavitate or stall just like a turbo will do when the motor slows. As stated before, this test is setup for failure. If this is happening in a running truck, I would be looking at the IP check valve for either a sticking open or stuck shut situation..
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From: NE Pa.
Thank you for your answers, but I didn't get answers or maybe I did and I just missed them.
Would cavitation happen at idle or WOT?
Second your reply that it does not appear to be cavitation but rather a sudden increased demand for fuel if that were true wouldn't the pressure return on it's own to the normal 16psi? In my case I have to make a quick WOT to get the pressure back. Again the same WOT run will drop the pressure and it will stay that way until another WOT run. (see where my mileage is going here?)
Third, a bypass valve before the VP. So after the LP and before the VP and tap into the return line?
Thanks again.
Would cavitation happen at idle or WOT?
Second your reply that it does not appear to be cavitation but rather a sudden increased demand for fuel if that were true wouldn't the pressure return on it's own to the normal 16psi? In my case I have to make a quick WOT to get the pressure back. Again the same WOT run will drop the pressure and it will stay that way until another WOT run. (see where my mileage is going here?)
Third, a bypass valve before the VP. So after the LP and before the VP and tap into the return line?
Thanks again.
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Joined: Jul 2005
Posts: 1,008
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From: Colorado Springs
"Would cavitation happen at idle or WOT?'
The 'cavitation' phenomenon(if,in fact, that is what is going on in the video) is unlikely to happen at WOT because, with the high demand for fuel, the Carter pump is not able to generate 15+psi. It could happen at idle because of the low demand for fuel. In your case I am not sure what is going on, perhaps it is a worn out internal pressure relief valve that is acting up.
"Third, a bypass valve before the VP. So after the LP and before the VP and tap into the return line?"
That is exactly the way I have it set up on my truck. It has only been on for four months and, so far, it is working well with a constant pressure of 13psi ; only time will tell if it increases the longevity of the LP.
The regulator is only 40$ and it is not difficult to install. I was planning to switch to Walbro because, even after taking the steps that has been prescribed in this forum(and others) to help the LP, my LPs were barely lasting a year. The Walbro needs a regulator, so I installed the regulator as a first step in my changeover to a Walbro. Now I am going to wait and see how long my Campaign pump lasts with the regulator installed and limiting its maximum pressure.
The 'cavitation' phenomenon(if,in fact, that is what is going on in the video) is unlikely to happen at WOT because, with the high demand for fuel, the Carter pump is not able to generate 15+psi. It could happen at idle because of the low demand for fuel. In your case I am not sure what is going on, perhaps it is a worn out internal pressure relief valve that is acting up.
"Third, a bypass valve before the VP. So after the LP and before the VP and tap into the return line?"
That is exactly the way I have it set up on my truck. It has only been on for four months and, so far, it is working well with a constant pressure of 13psi ; only time will tell if it increases the longevity of the LP.
The regulator is only 40$ and it is not difficult to install. I was planning to switch to Walbro because, even after taking the steps that has been prescribed in this forum(and others) to help the LP, my LPs were barely lasting a year. The Walbro needs a regulator, so I installed the regulator as a first step in my changeover to a Walbro. Now I am going to wait and see how long my Campaign pump lasts with the regulator installed and limiting its maximum pressure.
Cavitation is only going to happen with a restriction on the inlet side. What you see in the video is the bypass in the pump working. IMO the reason the pumps not coming back to pressure is because the spring is weak and the ball and seat are worn. From what I read, the pump in the video has over 50,000 miles on it.
Slim I've been told the LP is bad so many times I'm beginning to believe it myself but will not replace it with a stock carter again. I'm just stumped with the good pressure idle and then not so good 9psi. Again all related to a WOT run. But your explanation of the ball and seat being worn is making sense to my thick skull. $40 now and a test for a regulator and then $400 later for a new pump Walbro if that doesn't fix it.
Great post everyone.
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From: Toronto, Canada
"As stated before, this test is setup for failure. If this is happening in a running truck, I would be looking at the IP check valve for either a sticking open or stuck shut situation.."
You are assuming that the VP lets the fuel flow freely thru it. At idle there is very little flow thru the VP(I think, someone correct me if I am wrong).
"IMO the reason the pumps not coming back to pressure is because the spring is weak and the ball and seat are worn."
Perhaps, but if the spring was weak and the ball and seat worn, I don't see the pump developing 15 psi at all, the spring would have compressed at a lower pressure, and the leakage past a worn ball and seat would prevent 15 psi from being developed. Also, Gary stated in the video that the pump was a well functioning pump and I have no reason to doubt it.
"George do you have a link or pics for your setup? Also was your fuel pressure wacko like mine was? Thanks."
Sorry, I do not have a digital camera. Yes, my fuel pressure was jumpimg up and down. Since you plan on mounting a Walbro, the regulator is needed, so consider the mounting of the regulator as the first step in the installation of the Walbro.
You are assuming that the VP lets the fuel flow freely thru it. At idle there is very little flow thru the VP(I think, someone correct me if I am wrong).
"IMO the reason the pumps not coming back to pressure is because the spring is weak and the ball and seat are worn."
Perhaps, but if the spring was weak and the ball and seat worn, I don't see the pump developing 15 psi at all, the spring would have compressed at a lower pressure, and the leakage past a worn ball and seat would prevent 15 psi from being developed. Also, Gary stated in the video that the pump was a well functioning pump and I have no reason to doubt it.
"George do you have a link or pics for your setup? Also was your fuel pressure wacko like mine was? Thanks."
Sorry, I do not have a digital camera. Yes, my fuel pressure was jumpimg up and down. Since you plan on mounting a Walbro, the regulator is needed, so consider the mounting of the regulator as the first step in the installation of the Walbro.
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From: House Springs, MO
my $0.02
from reading different posts & my experience...
i don't see many guys seeing this cavitation occuring... by this, i mean the fluctuation in pressure on a guage... most people are seeing a fall off in pressure between the LP & IP... this would lead me to believe that the cavitation is NOT what is causing most of the LP failures... as others have alluded to, cavitation would occur when a large build up of pressure on the outlet or starving the LP on the inlet...
again just my $0.02... i'm only a mechanical engineer
i don't see many guys seeing this cavitation occuring... by this, i mean the fluctuation in pressure on a guage... most people are seeing a fall off in pressure between the LP & IP... this would lead me to believe that the cavitation is NOT what is causing most of the LP failures... as others have alluded to, cavitation would occur when a large build up of pressure on the outlet or starving the LP on the inlet...
again just my $0.02... i'm only a mechanical engineer
Thread Starter
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From: Toronto, Canada
2500RAM. Didn't mean to mislead you but I think I did. My pressure was fluctuating with the old LP and I replaced it with a new LP. A month later I installed the regulator. So I do not know at all if installing a regulator will make your existing LP work properly.
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From: Colorado Springs
Thanks again everyone.
Glacier Diesel here I come. Now I just need $400 for the kit.
http://www.glacierdieselpower.com/pr...?pf_id=3929852
Oh heck I just ordered the Walbro kit. I need this truck running for camping season.
Wish me luck.
Glacier Diesel here I come. Now I just need $400 for the kit.
http://www.glacierdieselpower.com/pr...?pf_id=3929852
Oh heck I just ordered the Walbro kit. I need this truck running for camping season.
Wish me luck.
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from reading different posts & my experience...
i don't see many guys seeing this cavitation occuring... by this, i mean the fluctuation in pressure on a guage... most people are seeing a fall off in pressure between the LP & IP... this would lead me to believe that the cavitation is NOT what is causing most of the LP failures... as others have alluded to, cavitation would occur when a large build up of pressure on the outlet or starving the LP on the inlet...
again just my $0.02... i'm only a mechanical engineer
i don't see many guys seeing this cavitation occuring... by this, i mean the fluctuation in pressure on a guage... most people are seeing a fall off in pressure between the LP & IP... this would lead me to believe that the cavitation is NOT what is causing most of the LP failures... as others have alluded to, cavitation would occur when a large build up of pressure on the outlet or starving the LP on the inlet...
again just my $0.02... i'm only a mechanical engineer
My truck exhibited the exact characteristics of the pressure dropping just like the first part of the first video. For the first two LP's. You will see in the second video it is a none issue.
I think had Gary, not said or typed "cavitation" the focus of the video what have been more warmly welcomed outright, without discussion, as simply a pump characteristic vice whether it was cavitation or whatever.
Jim
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