TECH NOTE: It is not necessary to read these highlighted sections
1 "Pads" of pressurized nitrogen gas are applied to the supply tans, as soon as the pressure falls below the pressure at which the pad saturated the liquid, the gas comes back out of solution, and simulates cavitation so unless you provide a suction boost pump as well, every suction stroke begins with a loss of volume into the pump and a potential fall in output.

RESULTS
In less than 2 weeks, & under $600
1) The constant velocity caused in the supply line, enables a pipe size reduction, which reduces time in the pipe & so reduces the warming even further.
2) Metering accuracy increase - 9% deviation down to 1/2%, consistent foam, and save excess blowing agent.
3) Stopped "finger pointing" at pump, & didn't need a new one.

The root cause of the problems was that because there was an "adequate" difference between NPSHA and NPSHR to cover flow friction, is was assumed that the pump would fill.
The NPSH approach assumed that the pump was centrifugal, positive displacement pumps are not centrifugal; reciprocating pumps need to avoid mass acceleration pressure loss for every stroke. A general term for this is "mass acceleration head" meaning pressure difference required to overcome the inertia of weight of the liquid in the pipe. This weight is obtained from the cross sectional area of the flow path, times length, to find volume times the specific gravity / density of the liquid = mass. Rate of acceleration time mass, gives the force = Delta P.
High Hz. = Comments Liquid Dynamics Intentional by - "Pulse-Doctor" Analytical, Diagnostic and Software services