Suction tube or sump kit

[AH64ID]

34 minutes ago, Mopar1973Man said:

The only thing I want to note here is pressure stability is the difference between demand volume and supply volume. So if you demand volume is lower than supply volume then pressure will be stable. Now if you demand volume is higher than supply volume then pressure will fall accordingly.

 

Yes, mostly. The AD pumps are not of variable output and this is why they have their own dedicated return. The pump are always operating at a fixed rpm (which varies based on pump flow specs). The internal pressure regulator only pushes enough fuel thru the 2nd filter an out to the motor as needed to maintain the set pressure. If the change in flow is small enough the drop in pressure at the VP/CP3/psi gauge may not be noticed at the AD due to restrictions in the line in the form of fittings/additional filters/etc. Now if we get into a situation where the AD senses the output pressure drop and increases flow to the output (decreasing return flow) then yes a pressure drop means supply cannon meet demand, but only at that pressure. The demand is met with a lower pressure which is how the AD/FASS pumps work with a constant rpm pump.

So if your pressure drops and you had more than a small increase in demand it is safe to say the flow required to maintain 16psi worth of resistance isn't available but the volume of fuel is being met just at a lower resistance. The bottom line is filter are rated in flow not in pressure and flow is what we need to worry about when talking filtration efficiency.

It's been a while since I saw an AD or FASS flow vs pressure chart but one of those could better indicate how much one might be outflowing both of their filters by. As I mentioned the 1st filter is being out flowed on most, if not all, AD 150+ out there. The highest rated f/w sep filter I am aware of that fits the AD150 is only rated at 120 GPH.

With variable demand and flow (output, not input) it's hard to quantify a flow change with a pressure change. As the demand for flow increases the resistance changes and we see a pressure drop, but flow may be increasing due to the variable output from the AD even with a pressure drop. A 10% increase in demand from the injection pump may drop the resistance enough to require a 20% increase in lift pump flow for the same pressure.

34 minutes ago, Mopar1973Man said:

So pressure falling out during WOT is a sign your demand volume is exceeding the supply volume.

This is true if pressure is your #1 concern, but it's not with a filter. 100 GPH at 10 psi is the same volume of fuel as 100 GPH at 4 psi. Since I am talking filtration efficiency it doesn't matter if you are at 4, 10, 16, or 20 psi if you are flowing 100 GPH on a 60 GPH filter you are outflowing what the filter was designed for. There are filters listed for the AD150 that are only rated at 20GPH...