Hi,

Besides the practical reasons for having a plumped in machine with rotary pump, the strongest reason for me to have a rotary pump is that the thermosyphon will be pressurized (in idle mode) with the inlet water pressure. If the water in the thermosyphon has a lower pressure than the boiler pressure the water in the thermosyphon may start to boil and cause negative effects for the group head heating. If you get steam the first few seconds when you flush your HX you probable have a vibe pump with water tank or a inlet pressure lower that the bolier pressure on a roto pump machine. I have no proof that this can cause big problems but for me it does not feel right to not have the thermosyphon pressurized. Many manufacturer recommend a lowest inlet water pressure of about 2 bar (like for Elektra A3), I can not see any reason for this apart from the theory above, or do anyone know why?

/Tomas

MCM wrote:Have narrowed down new espresso maker to the Vibiemme Double Domobar (with vibratory motor) vs the Izzy Alex Duetto II - which has a rotary motor.
[...] but want to know if there is a difference is
1) durability
2) espresso quality

Elsewhere in this forum it was mentioned (re 1) the vibe pump is self-priming and does not easily break in case of running dry. Convenient if you have a pour-over machine. I.e. lower TCO.
(Re 2) it was discussed vibe pumps have softer pressure ramp up resulting in a better cup (structure, complexity).

MDL wrote:I own a rotary, plumbed in machine and love it.
No reservoir to fill, clean or run down.
Much less noise than the rotary pump machine that I had before.

You do not reference durability, nor espresso quality.
I own a vibe and would have preferred a rotary if for the noise. That said, I will stick with it as it is simply good enough. I still need to open Andreja and reroute a few wires and tubes to get it as silent as Quick Mill's head of engineering got it in the factory, again.

MDL wrote:Fantastic brew temperature control (not a PID by the way).
Ability to make as many drinks (milk or not) as I have ever needed without loss of steam or temperature.
Ability to save energy by turning the steam boiler off when it is not needed.

Not referenceing durability, nor espresso quality. Brew temperature control ~ pump type?

MDL wrote:I would also say that an HX machine is not the best choice for a catering situation. In that case you would want a double boiler so that you don't have to worry about temperature surfing as you make coffee, tea and milk drinks.

Please remember where espresso machines were invented, how long ago, further developed and to what purpose. Famed FAEMA E/61 - HX. La Cimbali - HX. Kees van der Westen - HX. Listen to Kees in the Speedster MkII movie on YouTube, if you understand Dutch. Kees explains he prefers HX for quality of espresso. Why did he do Speedster as DB? Because there is a demand. But now he must go to great length to implement pressure profile in order not to get flat coffees. I would add the profiling is complicated by line pressure (plumbed in) and rotary pump with no ramp up.
Oh yes, those classic machines were not designed to do Americano's or triples, or whatever supersized beverage you could think of.
Also, elsewhere you'll find a debate on DB v. HX explaining why/how you'll need to flush both.

Regards
Peter