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Message: [QUOTE="TARM, post: 72563, member: 578"] That woudl all be true if there was something creating the restriction that would cause pressure. There is nothing other than the Dahl itself creating any pressure and the Dahl 150 is rated to only create 0.75 psi of pressure per 80gph flow and I believe that is with the 2 mic filter where I am using a 30 mic version. Beyond the filter you have a surge tank that has no pressure. It has lines going back to the main tank so there is no pressure build up in that tank. Because of this setup that Carter pump has no pressure against it. Well it likely has about 1 psi. So while the dahl may not be in a vacuum its not under any real pressure either. Another fact is the Dahl 150 is rated for up to 25 psi. BTW there is really no difference between the 6 psi 4600 and 16 psi 4601 Carter pumps other than what their internal reg is setup to. But per amount of pressure they flow the same amount and are the same pump itself. So no pressure on the Dahl in this setup. BTW I am using a 30 mic filter on the Dahl as I have a 3 for the final and want it staged. I could also use a 10 mic but for me wanted toe least effect to flow and wanted the best balance between filter changed of the two stages. Using the 2 mic they offer does not make much sense. In this setup I can still measure when filter changes are needed by instead of measuring vacuum I can measure pressure on the Dahl inlet. As the filter become clogged it will create more restriction and the pressure created from the flow of the Carter pump will increase. Why I chose to put the carter before and not after the Dahl is almost all the pumps used for fuel that are popular were designed to push not pull. As I want the max flow and there is no actual pressure against the pump even on the outlet side other than that created by the dahl it puts the least amount of stress on the pump. One of the goals of this setup is maximum duty life of the pumps so the least stress. This does that by using two pump stages and in positions they need to do the least work and get the most cooling and lubrication. [/QUOTE]