Like the title states, why does everyone worry about pressure. If the fuel is suppose to be cooling/lubricating, wouldn't flow rate be a better thing to measure. From what I understand pressure is just an indication of restriction. Would it not make more sense to say flow 100g/h at 5 psi with bigger lines and better fittings(less restriction). Then to flow 50g/h at 15 psi through the stock system?

 

that is interesting wonder what others will say

 

That is very true, and Dodge actually changed the diagnostic procedure to reflect it. I would rather have a lift pump that put out 5 PSI at idle and WOT than one that put out 15 PSI at idle and dropped to 2 PSI at WOT.

 

How do you plan on measuring flow at wide open throttle?

A fuel pressure guage is a cheap and reliable way of determining if the VP-44 has enough feed to work properly.

Yes, eliminating the banjo bolts, increasing line size and having a better pump are a huge help but we all know that already.

 

are you changing the pressure relief value on the return line at the VP?
I seem to remember that it opens at 14psi..so trying to feed lots of volume at low pressure might not work..change this a 5 psi and you have an interesting idea. just not easy to measure.

-dkenny

 

Yeah, it's true that we can't measure flow while we are driving down the road. Pressure is indeed the best indicator, as we know that if the pressure drops under high demand, flow isn't great enough.

 

I work with water pressures and sprinklers on the engineering side. I don't know how uch of this applies here, but here is what I can share.

Pressure is the requirement that sprinkler manufacturers are looking for to ensure proper performance of the sprinkler. Flow comes into play because the higher the flow, the greater the pressure loss due to friction. Elevation change also causes pressure loss. Also the general rule is to keep velocities under 5 ft/sec to avoid turbulance.

Let me give you a couple of examples. My brother in law has been running a hose out to his barn for a couple of years. It barely drips by the time the water get there from the hose bib at the house. The hose is 5/8" diameter. When we ran an 1 1/4 pvc line out there to install some permanent hydrants he couldn't believe the flow. This is big line kits increase pressure because the cause less friction.

The other example is calculating for booster pumps. The first thing that I do when I get a project is to call the water authority or district to determine the estimate water pressure for a particular address. They can determine the pressure by checking which pump or gravity tank feeds the line there and using the distance, size of pipe and elevation change into a pressure loss equation. The next step is a common misconception. I determine the flow requirements by the sprinklers themselves. Each sprinkler is rater for a particular flow. Even the little drippers have a specific flow. I add up the sprinklers and multiply by their flow. The same would be true for the injectors. I imagine that they have a specific flow each that would be used to determine the required flow of the system plus I assume there is a return volume for cooling the VP. The point is that volume will determine the system requirements for maintaining proper pressure, so it's safe to say just like the hose, because the pressure was low, the volume will also be low.

The last consideration when sizing booster pumps is that one of the design inputs is static pressure. Meaning how much pressure is in the system before the pump. In our case, how much is the lift pump providing. I don't know what the pump manufacturers change based on this information, but I know that it is something the require to be provided so that the bosster pump (think VP) will function properly.

At the end of the day, pressure reading is a fine figure for me to monitor the proper performance of my fuel system.

I know this is a lot of information that is not very organized, but its christmas eve and I have been writing for long enough. I'm sure there will be questions, and that this will take a few readings for some of these things to start sinking in.

 

Your restriction is remaining constant (VP44). How would you increase the volume while decreasing the pressure with the same restriction? Look at electricity, voltage is your pressure, current is your flow, resistance is the restriction. V=I*R. If R stays the same, to make the current (flow) go up, you must increase the voltage (pressure).