Standardized parts and service.
Affordable.
Consumer demand.

Yeah... it's not the best option. It's not optimized for DB usage. But manufacturers can sell more for more profits if they use it. So be it.

As for the DC... suffice it to say that there are "mixed reviews" of this machine.

Marshall wrote:Cheaply? Without line pressure? The manufacturers who are actually in the business and controlling their costs seem to prefer the E61.

With no line pressure how exactly do pour over E61 machines preinfuse?

It relies on the spring-loaded chamber that hangs below the brewhead.

I think is is a very interesting discussion. According to my belief a well balanced e61 HX should bring the group at optimal brew temperature in idle status. The thermosyphon should be balanced in this way. If the grouphead is warmer or hotter than optimal brew temperature, the thermosyphon is not balanced and you need to do a "cooling flush" or a "warming flush" to get the group in right temperature. For a balanced thermosyphon you just do a "flush" which is flushing the superheated thermosyphon-water out from the pipes but you are not trying to change the group temperature by flushing for a long time.

OK, is there a lot of non balanced e61 HX out there?

I think, Yes.

Why? My personal thoughts is that the concept HX-e61 does not work to 100% when it is run as a HX-e61 with vibe pump and water tank.

First. When the water pressure in the thermosyphon is lower than the boiler pressure (as for vibe-water tank HX-e61) the water in the thermosyphon can start to boil and you get blend of steam and water in thermosyphon. My feeling is that it is very hard to design a well balanced thermosyphon when the water may start to boil. A plumbed in machine with rotary pump will pressurize the thermosyphon with a higher pressure than the boiler pressure and therefore the water in the thermosyphon will stay liquid and the heating of the group head will be more easy to control.

The second thing with water tank HX-e61 machines is that I think the variation in tank water temperature is too high in order to get stable brew temperature. The HX is designed to heat the incoming water to a temperature very near optimal brew temperature, the final adjustment is made in the brew head. The boiler temperature is quite stable for this purpose probable only varying a few percent up and down. The water flow is constant, set by restrictor and pump. The heat transfer physics in the HX is constant and does not change much. The inlet HX temperature is directly influencing the out-temperature of the HX. In a plumbed machine the inlet temperature will vary from summer to winter, in many cases this is only some 5F up and down. For a water tank machine the water tank temperature will vary from room temperature 70F (when starting the machine) to maybe 140F (when the machine has been running for some hours). This variation will directly affect the out-temperature of the HX and add another complexity to the brew heat control. This is very interesting when you study the Izzo Duetto where you can choose plumped in or water tank operation - is the HX designed for 55F inlet temperature or 140F inlet temperature? It can not be designed for both temperatures I would say...

Since most of the HX-e61 out there is vibe-water tank the general conclusions has become:

1. The group head on HX will always be too hot
2. I need to cool down the group head with a cooling flush

I think this is a result of above stated problems with the vibe-water tank design and is, to a large extent, avoided on a plumped in machine with rotary pump. I think a HX-e61 should be plumbed in with rotary pump in order to get best out of the HX-e61 concept. I also think that a PID saturated brew head design is better than the HX-e61 design, but the HX-e61 is far more fascinating piece of engineering.

I have no proof of this and all above stated can be totally wrong.

Stadler wrote: For a balanced thermosyphon you just do a "flush" which is flushing the superheated thermosyphon-water out from the pipes but you are not trying to change the group temperature by flushing for a long time.

In my experience (which relates to an Elektra A3), it seems that flushing the superheated water overheats the grouphead which in turns needs to be cooled down.
I have like many others a thermocouple placed in the grouphead inside one of the tiny holes of the diffuser where it regularly shows 90C when the machine has been idle for a while. Flushing the water until the end of the "water dance" the temperature will jump to about 104C and stay there. I need to keep flushing for several seconds more for the temperature to drop back to whatever value I want before pulling the shot.

Stadler wrote:When the water pressure in the thermosyphon is lower than the boiler pressure (as for vibe-water tank HX-e61) the water in the thermosyphon can start to boil and you get blend of steam and water in thermosyphon.

No, this is incorrect. The thermsyphon is a closed system with no steam, otherwise the thermosyphon would stall.

Stadler wrote:The second thing with water tank HX-e61 machines is that I think the variation in tank water temperature is too high in order to get stable brew temperature.

The brew temperature of any espresso machine will suffer if the incoming water temperature varies from one moment to the next unless it has a mega-huge boiler. Most prosumer/semi-commercial single boilers are less than a liter. It doesn't take a lot of 70F or 140F water to throw the brew temperature off. That said, I agree HX espresso machines are more vulnerable to inlet water temperature variation.

Stadler wrote:1. The group head on HX will always be too hot and 2. I need to cool down the group head with a cooling flush

If only it were only so simple.

Stadler wrote:I have no proof of this and all above stated can be totally wrong.

I was about to write that I don't agree with your assertions, but more precisely, I don't agree with arguing specifications. Your conclusion, to paraphrase the form, is essentially "I think result A is, to a large extent, avoided by B. I think C should be done in order to get best out of D. I also think that design E is better than the design F." I cannot judge which, if any, of these claims are backed by actual experience.

In my opinion, there is no substitute for hands-on experience. Arguing the superiority of one design over another based on specifications and abstract measures is pointless (Pressure profiles, preinfusion and the forgiveness factor documents one such "ah ha" experience).

erics wrote:I do concur that it was not originally designed for that specific purpose....

If I remember correctly, the original Faema E61 patent listed pre infusion as the reason for the design, not temperature stability. The expansion chamber in the group allowed a slow pressure ramp to pre infuse the puck before full pressure was reached.

HB wrote:The brew temperature of any espresso machine will suffer if the incoming water temperature varies from one moment to the next unless it has a mega-huge boiler.

Or if it has pre-heating of some type (Mistral, GS3, etc).

Group design is still much more art than science; and it pays manufacturers to imitate what works.

The classic counter example: The "obvious to engineers" brew boiler, saturated group design of the LM has required endless tweaking to perform as an ultra stable machine. It is hard to pull off and hard to engineer, so it has only been used by local secessionist manufacturers like Synesso. In any case, nobody knows what sort of temperature profile is best.

The other classic counter example: The spring loaded cylinder preinfusion of the E61 is another "perfect" designs that nobody imitated. Instead, subsequent groups use jets and fill up cavities to get a slow ramp in pressure (e.g. not even the "auto E61" aka E66, used a spring loaded cylinder). Unlike the LM group, the E61 as a whole is public domain and easy to fit on different machines, so it is widely used; but this particular element of its design is as dead as a dinosaur.

Here are some group design features that, once invented, have been widely imitated because they work so well:
-- thermosyphons and their associated jetting (Faema inventor) for thermal stability.
-- solenoid operated three way valves (? inventor) which are much easier to engineer and much more flexible than the manual levetta ones,
-- one piece HX/group designs with their associated water injection tweaks (Cimbali inventor) for thermal stability.
-- removable group bell assemblies (Brasilia inventor) including the screen, group gasket, PF mount, and dispersion blocks, which makes maintenance easier and provides a straight down water path, no matter how the water originally comes into the group.

There's a lot to be said for a group that uses these proven design elements sensibly rather than one using the latest in unproven technology, even when the later is theoretically better, and designed by somebody very competent.