[Skulemate]

It doesn't quite work that way in a system with a resevior. That's because the resevior is open to the atmosphere, and hence, has no pressure relative to atmospheric. It's a simple matter to write Bernoulli's equation between the surface of the resevior feeding the pump and the pump inlet itself. For ease of calculation, suppose that I place my datum at the centreline of my pump intake (i.e. along the centreline of the impellor shaft). If one assumes that the flowrate is actually 150 GPH = 0.15773 L/s, and substituting the relevant values into the equation, one finds that the pressure term at the pump inlet is equal to:

p/gamma = 0.276m - losses (measured in m H2O)

This was simply calculated as ~0.29m water (the elevation head of the resevior) minus the velocity head of the fluid at the pump inlet. Now, given, I don't know the losses that occur through the short connection between the resevior and the pump, but I doubt that they equal more than ~0.276m H2O, given my flowrate and pipe diameter... I could be wrong, but I doubt it.

One other thing. If the pressure at the intake were negative, then the flowrate would be less than I predicted since the pump is using some of its head to lift the water to the intake. The flowrate from the pump would only be greater than I determined from the H-Q curve if the pressure at the intake head was positive (i.e. if the intake pressure is 1 psi, and the pressure at the pump discharge is 8.5 psi, the pump only imparted 7.5 psi to the water, not 8.5).