Lift Pump Questions

[LBZ]

So I have been thinking of going with another KD lift pump. My question is this- Would it be more of a benefit to run two pumps in parallel sharing a common suction (SoCal P/U) and then going back into the single OEM fuel rail, as opposed to just putting both pumps in series with each other?

My thoughts on why the series set-up may not be the best, is that if the pump closest to the tank does not put out as much as the 2nd pump, it may work against what we are trying to achieve with two pumps. Especially if positive displacement pumps like the PPE and FASS are used as you cannot draw any fuel through them correct?
In parallel it wouldn't matter-as long as the suction side of the pumps could keep up with the demand from two pumps.

I know to fully take advantage of a dual lift pump-parallel setup it would be best to run each on it's own fuel line on both the suction and discharge-but that is not what I am trying to achieve-at least not right now.

The reason this came into my head is with the new higher rpm's that we can get with the LBZ's, I'm wondering if we may have a harder time maintaining the supply to the CP3 at these higher rpm's. It wasn't an issue when it defueled at 3300rpm!! This may also be helpful thinking for those running dual CP3's.

I'm just looking for your thoughts here and let me know if I am out to lunch on this thinking!

Thanks to all!!
Dale

 

[sweetdiesel]

I think for the KD pumps,series is best.
One pump prechages the other, if you run in parellel you risk loosing prime to the pump easier by over drawing the pump 3-4 psi will draw down to 0 psi easier than 7-8 psi ( starts to cavitate ) and then you still have a T where these meet causing a agument of to who is first into the T and then they fight! and the stonger pump and less restrictive line will do most of the work.

But, I could be way off base here! believe it or not it happens from time to time

 

[LBZ]

I agree with your precharge comment,if the first pump inline was bigger-but it's not. Your not precharging it if both pumps put out the same. If anything, your risking cavitation between the two aren't you??

Also how would you lose prime? Your still discharging into the same size line to the CP3 meaning you aren't going to be moving a whole lot more fuel, you should just get more pressure!
The only difference I see, is that you may get a more even flow and a more stable, higher pressure. The two pumps fighting each other would only be because you are supplying MORE than enough fuel right? However, one flaw I didn't factor in, is if one pump quit, it may just circulate back through the other pump to the suction side again. But it shouldn't if the CP3 is still drawing fuel.

I smell another test that needs to be done Simon. You have the duels in series now and gauges. If you can fit in your busy schedule when I get home, maybe we need to try it out.

 

[LBZ]

To explain it in oilfield talk, think of a C-Pump system on a cementer or acid buggy-which is basically what the KD's are. If you put two c-pumps inline and you drop the rpm on the first pump to less than that of the second or stop the first pump-you create a restriction. Once the restriction gets too high, you lose prime. I've done it!!

That is the only reason I started this thread. Something about running two KD's in series kind of bothered me. Unless I'm wrong about them not being positive displacement. But then what regulates their pressure then??

Sorry-I'm rambling.

 

[sweetdiesel]

I agree with your precharge comment,if the first pump inline was bigger-but it's not. Your not precharging it if both pumps put out the same. If anything, your risking cavitation between the two aren't you??

Also how would you lose prime? Your still discharging into the same size line to the CP3 meaning you aren't going to be moving a whole lot more fuel, you should just get more pressure!
The only difference I see, is that you may get a more even flow and a more stable, higher pressure. The two pumps fighting each other would only be because you are supplying MORE than enough fuel right? However, one flaw I didn't factor in, is if one pump quit, it may just circulate back through the other pump to the suction side again. But it shouldn't if the CP3 is still drawing fuel.

I smell another test that needs to be done Simon. You have the duels in series now and gauges. If you can fit in your busy schedule when I get home, maybe we need to try it out.

test it sure! thats how we prove it, right? it will go backwards why do you think i put the check valves in my setup
if it drops below zero pressure dale it wont regain its discharge pressure untill you let off the go pedal. Now its sucking! and that sucks.

 

[Kat]

I moved this in here :hug:

 

[JoshH]

The pumps Kennedy uses are draw through pumps. If one of them quits you aren't going to hurt anything. My pumps are the exact same as the pumps Kennedy uses and they are plumbed in series. I can easily hold 26k psi of rail pressure with 2800 uS of duration. Even with duration out to 3000 uS it was holding almost 25k psi. One other problem I see with running parallel is if one pump dies you will run the risk of fuel wanting to go back through the dead pump. You would have to put a checkvalve there and that would potentially reduce the efficiency. Like Simon said, you won't know until you try it.

 

[kodydog]

Lift Pump

Kennedy also has a great wiring harness that works with an oil pressure switch.

 

[sweetdiesel]

You would have to put a checkvalve there and that would potentially reduce the efficiency. Like Simon said, you won't know until you try it.

i see what your saying on a potential restriction,However i did NOT notice a difference,they are a 1" valve and atleast 1/2" inards

Not saying i did not reduce some flow,I just never seen any


And as far as the oil pressure switch it looks nice but not needed IMO

 

[kodydog]

Oil pressure switch is nice when you have the key turned on and the pumps are not sitting there running.

 

[LBZ]

test it sure! thats how we prove it, right? it will go backwards why do you think i put the check valves in my setup
if it drops below zero pressure dale it wont regain its discharge pressure untill you let off the go pedal. Now its sucking! and that sucks.

Ok, that's exactly the same as a C-Pump then. If you over draw them they too will lose prime.

So check valves are in order for the parallel set-up-like I suspected. But I still don't see how in series we are doing any good with two pumps.

FYI I run a single KD and I too have no problem keeping excellent rail pressure. So why put in a second one?? Would that in any way help us at all if the end result is the same? Simon you didn't see much of a gain in fuel pressure when you added the KD did you? When at wot I recall that your gauges dropping about 7psi!!

Your right Simon. IMO we do need to test this!!

 

[sweetdiesel]

to be honest i loose rail pressure no matter what i do,unless i add the duel cp3
however as you have seen dale the precharge pressure ( liftpump) drops like a mofo when i install it,but the rail doesnt!:cool2: yet i still dont like the precharge dropping like it does,Actually i hate and hindsight i wont ever go with kennedy pumps again!my cheap ass carter pump flows more than both kennedys and has lasted just as long!

KD pumps are quiet and flow through and so far very reliable but just dont keep the pressure,just on a 100ish hp tune it drops to 3 psi this is with a Socal pickup , I thought it was due to the raycor filter but if i turn on the carter and run it by its self i have 8-9PSI constantly! untill i add the duel cp3 then it drops to 5psi but no less

another thing dale you do have the new upgraded version of the KD pumps maybe they are better....simply put when you get home we will do some testing!

 

[sweetdiesel]

FYI I run a single KD and I too have no problem keeping excellent rail pressure.

we also need to work on that!

 

[sweetdiesel]

Oil pressure switch is nice when you have the key turned on and the pumps are not sitting there running.

a 2 dollar toggle switch will do the same thing

 

[LBZ]

A new pump is going to be ordered then at the end of the month so I can test this out.
What kind of check valve did you use Simon? A spring or flapper style?
Yes you may be right about the newer version Simon-maybe you should put those KD's on the Can-Am!!

 

[sweetdiesel]

What kind of check valve did you use Simon?

spring,but very low downstream pressure needed to open it! less than 1 psi,actually hydrostatic should open it!

i would prefer flapper, but tough to find! in that size
1" is the smallest ive found and wieghs a mere 12 pounds

 

[LBZ]

I can get 3/4" ones and they aren't near that heavy!!

 

[sweetdiesel]

well bring em home! how heavy is the flapper? and they are metal correct?
metal and long term use doesnt sound good to me?

 

[LBZ]

Brass actually and we have them at the shop in RD. They are quite light!
They are used on our N2 pressure build coil returns!

 

[Killerbee]

if it seems you are running into volume limitations of the lift pump, then parallel. I am not familiar with the different pumps, so i don't know if that could be the case. But in series, you won't benefit flow rate much typically (IMO), just the end pressure.