Yep! I agree. Let's go drive our CTDs around now, regardless of the LP we have!
It is snowing again here today! And naturally, I drove the Ram to work!
Cheers,
-P

 

I wish it was a good debate but i haven't seen anything to make me think that yet! Look at these links below. Like my original post said, "25# of fuel pressure is good for giving you less fuel flow. Pressure is a measure of restriction" This was based on increasing the pressure with the current pump being used.

So, since you are fond of the walbro pump, if i look on the magical chart below, it says at 25psi the walbro flows 65gph, and at 0 psi (no restrictions) it flows 75gph (at 12v)? So it looks to me like it is flowing less fuel at more pressure. I am sure you are going to tell me something different, but I will have to quote you on this one, "this is not my opinion, it is fact"! If I look at the rest of the pumps below they all flow less fuel at more pressure, how could that be?

http://www.glacierdieselpower.com/pr...f_id=GSL%2D392

http://www.holley.com/12-802-1.asp

http://www.aeromotiveinc.com/ldetail.php?prod=7&th=2

 

My take on this is...

If you put your thumb on the end of a hose...you increase pressure inside the hose and you decrease flow.

The only way to increase pressure and flow if my thumb stays over the end of the hose would be to turn up the spigot.

The other way to increase flow would be to remove my thumb which is acting as a restriction.

So it seems that CTD Nut is saying you either turn up the spigot or remove your thumb. Higher pressure pump...or fewer restrictions (big line kit).


If I am wrong...I apologize for wasting everyone's time.
-Geoff

 

Sorry...I forgot to ask...at what pressure is damage done? And I gather that the regulator which returns fuel back to the tank would maintain 14 psi between the regulator and the VP44? So when the fuel demand increases from the pump, the pressure remains the same in the line...thus you don't lose flow?

I am in the process of re-plumbing my fuel system, and I am thinking of going this way.
-Geoff

 

Just as I enjoyed Superduty's input I have enjoyed yours as well. That includes everyone else that took the time to post. Remember even though Superduty could be a little strong in supporting his theory his knowledge was sound. I wish he were still around because the Walbro setup is a great economical and most of all dependable solution. I wonder what else he is working on that would be of benefit. It's easy to get caught up in the defense of our own opinions but for the sake of knowledge don't shoot the messengers because you either don't believe them or have your own theory to promote Just use all of it to stimulate your own research and then do what you decide is best.

 

Team,

You mean to say this isn't a good debate?!?! You are still posting aren't you?

Should I be offended?

You are absolutely correct when speaking of pump performance instead of fuel system restrictions and flow. When rating pump flow (Pump performance, ie flow vs pressure), the flow will go up as the resistance to flow goes down. I certainly don't need to click any links to understand that. For example, it takes one heck of a lot more power to flow 50 gph at 25 psi than it does at 0 psi (free flow).

Let's use 25 psi to illustrate my point. We will use this in context with the VP44 and lift pump performance. Lets say you would like to see 25 psi at WOT and your flow requirement is 50 gph....if you have a pump that is rated for 50 gph at 25 psi, you should see just that in theory. However, what if the pump cannot flow 50 gph at 25 psi? What happens to the pressure? Well, it drops, right? Why? Because if the demand is 50 gph, the pressure will have to drop to the point where the pump can flow 50 gph. But this isn't what was intended, right? No, the intent was to flow 50 gph at 25 psi. So, was the flow requirement less than 50 gph at 25 psi, than, say 20 psi? No, the flow requirement is fixed....

The problem with your analogy is that you are referring to 2 different relationships between pressure and flow. In one instance we are talking about the system restrictions and the effect they have on pressure and flow, and the other instance that you have now brought up is pump performance and the diminishing effect pressure has on flow as categorized by the performance of the pump itself which is also a measure of efficiency. Pumps that are very efficient have a much lower rate of diminishing return on flow as pressure increases. Leak down or the percentage of leak down categorizes how much volume the pump puts out in theory compared to reality. As the resistance to flow increases the percentage of leak down within the pump also increases....meaning, it leaks more as pressure goes up, thereby displacing less fluid per revolution which in turn results in a drop in volume (flow). Different styles of pumps have different capabilities of efficiency than others. One other factor is pump input hp. As pressure goes up, more input hp will be required to maintain the same flow. If there is no reserve hp as pressure increases, pump rpm will drop at which point it will obviously start to displace less fluid in the same amount of time so, flow will drop if the pump slows down!

So, to break it down it terms of pump efficiency, as pressure goes up, the pump leaks a higher percentage of it's displacement which directly results in a drop in flow....and as pressure goes up, so too, does the hp requirement...if input hp is fixed, pump rpm will drop which will result in a drop in flow. In theory, if there was a pump that had 0% leak down at any pressure, it would flow the same at all pressures - assuming there was an adequate amount of input hp for the pump to do this since more hp will be required as the pressure goes up to maintain a constant/fixed flow.

 

Close, what we want to do is flow more fuel up to the point of the highest restriction in the system....or rather, relocate the point of highest pressure to the VP inlet which is done by removing or minmizing restrictions upstream of the inlet. This seems to be the point where pressure and flow get muddled up. By flowing more up the inlet, we can realize a pressure increase since pressure is the resistance to flow. Flow more fuel leading up to the restriction and what happens to the pressure? Well, it goes up! Since pumps don't produce pressure (they only produce flow), the only way to increase the pressure at any given restriction is to flow more fuel to that restriction....with a small change in flow, we often see a very large change in pressure.

And you are not wasting anyones time for participating in a good debate so please don't think that way.

 

Am I a messenger or shooter? If I shoot myself, could I be both?

 

You are right CTD NUT I did learn something from you, you are always right.
Now we are talking about how much pump input horsepower is required to keep the same pressure and flow and the theoretical efficiency versus actual .
I bet you could tell me how the flux capacitor in back to the future works right? But you could have made it a little better because it wasn't as efficient as it could have been?
You are a master of your trade, I bow out to you now, because I am waist deep in what you are spewing and before long I wont be able to breathe!

 

O.K. I get it now...thanks! I will now re-engineer my plan here...I have some areas where I can remove restrictions...I'll focus on flow for now, and we'll see what pressure issues I have after that.

Y'all are the best.

 

I am lost....did I offend you?

It was you that changed the subject and brought up different pumps of which I was a willing participant to discuss the effects of different pumps.

I am truly sorry you feel you are waist deep in what I'm saying. I never attacked your character or integrity in debating this subject. Just because we don't agree doesn't mean we have a problem. How else could we have a good debate? What is the big deal? If you disagree, say so and explain why...this is the type of discussion that can bring lots of interesting info from all different points of view - without being hostile!

It appears as though I'm coming off as a self-proclaimed expert or "master of my trade". Yippee....call me on it and we can discuss why you don't agree.

At this point, I think I will stop posting in this thread if this is the way my posts are interpreted. I have no interest in creating unintentional hostility in a thread about which I perceive to be interesting discussion. This thread has steered well off course now anyway.....

I'm sorry you feel that way.....

Hillcountry,

If you are interested in discussing fuel system issues more, start your own thread, of which I will be a willing participant.

 

Ok let me throw my two cents in here. I have spent hours and hours reading all post concerning lift pumps. My original was replaced with an in tank and as we all know maybe they are ok or not I think the jury is still kinda out on that. So after my truck ran out of warranty I bought a campaign pump and put it back on the engine and was running both. Eric at Vulcan said if you want to do that put a DrawstrawII in the fuel tank. Now bear in mind at this time I was running 22psi with both and about 18psi at wot. Got gutty and did my first tank drop today. This is not hard at all as long as you have the correct tool to take the lines loose which I have as these are standard Mopar fittings. Eric's instructions are flawless he is a good man. Installed my DrawstrawII plumbed it in, now if one or the other pump goes I still got fuel, but hear is the funny part about flow restrictions etc. Now my pressure went down to 16psi but you can't make it move from that point regardless how hard I push it. I also plumbed it in in such a way so if the campaign pump goes, I got a place in the frame to mount and hook up a walbro unit. Thank I hope I am done with LPs for a while. Now I can save for when the IP dies LOL

 

scook6 - sound like you plumbed your two pumps in parallel. This is why your pressure is lower but more stable. In series, the last pump in line builds its pressure on top of the first pump's pressure. But the flow is limited by the lowest output pump. In parallel, you have combined flow capacity from both pumps. When the consumption goes up at WOT, there is ample supply from two pumps. But the pressure is lower because it will be only so much as the balanced pressure of the two pumps.
This situation is better: 16 psi is a great pressure, and clearly the combined flow is enough to maintain it as flow increases. Great job!
-P

 

Nope! You're doing fine... Keep up the good work. And if I ever get up to your part of Canada I want to see your jeep!!

 

This parallel pump arrangement sounds intriguing. I wonder if both pumps need a check valve installed in each supply line, otherwise if either pump fails, the working pump will push fuel through the path of least resistance--back to the tank through the dead LP instead of going to the VP44.