I have been reading a lot from many sources to help me decide between E61 rotary pump or vibratory machine. The idea is that someday I will do a little project, adding a pressure adjustment capability similar to what nicholas did long time ago.

In his thread
'Pressure Profiling' With The Fluid-O-Tech TMFR Pump - Or, Wholesale Copying Greg Scace's Ideas

I don't understand why instead of doing modification around the available GS3 pump, he bought another pump and put it outside the box.
I have found that vibratory pump is easier for pressure profiling, not many mechanical works involved.

I agree that a vibe pump is easy to use for pressure/flow control. Manually or automated.

Thanks for the answer.

I'm still curious why all people seems to use the same method by adding/changing into Fluid-O-Tech TMFR Pump when doing pressure profiling upgrade. Why don't just working out the already available rotary pump? Isn't it just the same ac induction motor? which could be controlled in the same manner with a single phase inverter?

I think i've found my answer. Did some research apparently the rotary vane motor an espresso machine usually come with is a capacitor started motor which is very difficult / not suitable for speed modulation.

I think that flow rate is much more important than pressure. I mention this because it influences pump selection. For example, a fixed displacement (eg, a piston) pump with a variable speed brushless DC motor could make flow control easier.

I use a vibe pump with variable voltage and an electronic scale on the drip tray to measure and profile flow rate. I really don't care what the pressure is, as long as it peaks at anything close to 9 bars.