I'd be curious (it's a question for Xylem I suppose) then what the value is of a vibe pump in the Flojet versus a rotary/impeller style pump. I assume there's a reason they choose that when most of what they make are impeller style pumps. Yet it also seems to be the largest complaint about them...

Aquatec pumps are diaphragm pumps, not vane rotary pumps like used in commercial espresso machines. They can have very high flowrates at pressure and are available in a wide range of applications. Depending on the model, an accumulator tank should be used, both to even out the pulses from the pump and to extend the life of the pump. A check valve isn't necessary, as a diaphragm pump doesn't free flow like a vane rotary pump. The variable speed pumps (5800 and 550 series) don't need an accumulator tank, but they might also be overkill for a home setup. Aquatec makes other accessories like flood detectors/ leak shut off valves.

@Ciaran. Why do some of the pumps need accumulation tanks and others don't?

Well, for one the variable speed pumps are controlled by a pressure transducer. They have a smooth on and off cycle, and the pressure is nearly constant. As soon as line pressure deviates from the set point, the motor starts and runs relative to the output to maintain constant pressure.

The single speed pumps are controlled by a pressure switch, the line pressure has to drop below the low set point before the pump kicks on. For a 60psi pump, the cut in pressure is probably 40psi. So you have a 20psi swing in line pressure that is fairly abrupt, and can sound like water hammer in piping. Depending on the amount of line volume between the pump and the output, or connection to the espresso machine in this case, the single speed pump may cycle more frequently. An accumulator tank evens this cycling out as there is a "reserve" of pressure in the line. And the accumulator is basically an air spring in the line to absorb the shock.

How does its operation differ from a Flojet bottle pump, then?