At first i thought it was a very useful video with the familiar debate about "mid position" etc in the following posts.

However, on closer viewing i noticed that the commentator completely wrongly described the function of the lower "pre infusion" chamber and valve, infact ignoring the automatic PI function ( a key feature of the E61) and passing it off as "just a way of diluting the outflow stream" !

The "mid position" PI debate may well continue, but there is no debate as to the correct function of the lower. I do feel that that video should have a addendum added such that new viewers are aware of the incorrect nature of some of its content.

How would you describe it?
BillC

Just as HB quoted with the diagrams from lino.
It acts as a pressure reducer valve during the initial feed of brew water to the group head.
IE to "automatically" effect reduced pressure pre infusion of the puck.
A fundamental to the design of the E61.
but the video is so misleading for anyone who wants a good understanding of the way the group works.
The issue regarding "mid lever position" is also so controversial, it should not be presented as factual either, since it does not actually work on many E61's, unless the operator manually holds the lever slightly off the mid position detent.
If the designers had intended it to function that way, the cam profiles would be sufficiently different to ensure the brew valve positively opens before the pump engages, on all groups

The way the Group is designed today vs the way it was originally designed is somewhat different. Especially concerning tolerances of parts. Most of my information came from the Dalla Corte family. Additionally I worked with the company in Italy that casts and machines the parts for about 70-80% of the E61 groups coming out of Italy. This company also allows the customer to specify the dimensions for each internal part. After more then 50 years the original design intent is not necessarily clear unless you speak the the man who actually designed it. There are many out there who claim to know exactly what something was design for based upon the use of the product. Do all current "E-61" groups function the same way, not at all. Do they all have similar features, absolutely.
There will always be some features that are debated throughout history, that is one of the most interesting areas of the coffee industry.


BillC

I had written a theory about the function of that valve and chamber. I discussed it with Stefano and he discussed it with the VBM factory. I made them aware of some of the physics that govern the valve's action which they had not thought of. My main point was that once the pressure in the infusion chamber was equal to or greater than the pressure in the brew chamber, the valve would have to be closed. It is more complicated than that because the force of the infusion spring has to be taken into account, but basically my main point was that the infusion valve is not always open during the extraction.

And my point here is that just because a company makes a device, that does not mean that they are totally aware of all its properties and functions.

Top valve = brew valve, middle valve = preinfusion valve with weaker spring designed to open at 4 bar. Lower valve is vent valve designed to open at 12 to 12.5 bar.

There is a little slack, by design between the preinfusion valve and vent valve to allow the preinfusion valve enough room to open slightly during the extraction. The preinfusion at 4 bar is longer with a Vibe pump and pretty short with a Rotary pump.

The middle position of the E61 is purely an accident, it should as other posters have said leave both valves closed. it is also a position that allows the cam to be easily withdrawn for lubrication purposes. As there should not be any pressure on each valves cam follower.

You can get the little black washers on the valves (I have some), but the manufacturers usually use a dab of threadlocker on the cam followers, so when you try to unscrew them to release the small black washers, the threaded portion on the valve snaps like a carrot. You can also buy just the cam followers as well...I have a (small pack of those). it means that unless you are quite fortunate, you have to buy the valves.

The different group manufacturers do indeed make the groups and valves to slightly different tolerances, but normally generic parts work well enough on most groups. One of the tricks is to actually unscrew a cam follower slightly to adapt it to slightly differently cast groups, you can get about 0.5mm adjustment quite easily, which is usually enough. You have to do this when the valve is new, otherwise the heat/corrosion weakens things and the threadlocker normally causes the thread to snap (e.g you can't do it after a year in the machine).

I've been working on a project recently where I have had to ask a manufacturer for the valves to be modified and the cam recut to cope with situations that an E61 would not usually be subjected to.

Yeah, I also found the description of the lower chamber confusing. I remember reading the original E-61 patent a while ago that was linked from another thread:

http://patft.uspto.gov/netacgi/nph-Pars ... /3,230,974

The lower chamber is explicitly there to provide a preinfusion at a lower pressure, which is why the upper exhaust spring is weaker than the lower one. In fact, while the E-61 gets a lot of credit for its thermal stability, the main claim in its patent relates to the preinfusion chamber.

In any case, I thought the cutaway was fantastic and really cool. Thanks very much for posting this.

My Anita was modified for plumb-in and I have the switch adjusted so the pump kicks in when the lever is about 10 degrees above level. Watching the erics thermometer, you can see the temp start to rise and/or fall when the lever reaches the 'pre infuse' state. So it seems that it has some sort of effect. It also appears that there's not enough pressure at this point to start the extraction process, as that doesn't start until the pump is engaged. Watching the thermometer, you can kick the mule right when the target is reached.

cuppajoe wrote:My Anita was modified for plumb-in and I have the switch adjusted so the pump kicks in when the lever is about 10 degrees above level. Watching the erics thermometer, you can see the temp start to rise and/or fall . So it seems that it has some sort of effect. It also appears that there's not enough pressure at this point to start the extraction process, as that doesn't start until the pump is engaged. Watching the thermometer, you can kick the mule right when the target is reached.

By.. "when the lever reaches the 'pre infuse' state".. i guess you mean the "mid position" ?
As has been said, some groups do not exhibit this effect, and it is likely that the amount of "lift" of the brew valve is variable on those groups that do appear to "infuse" , it is only logical to conclude that the flow rate and effectiveness of this "mid position pre-infusion" effect is highly variable and unpredictable from group to group.
Again i suggest, if the designers had wanted this manual control of pre-infusion , they could have simply re arranged the timing of the pump switch cam to be in the "top" detent lever location. That would ensure the brew valve is fully open to the un pumped line pressure for a predictable flow.

It should be remembered also, that when the pump does eventually start, the lower pre-infusion chamber will still function as designed, thus adding further PI time to the brew process.

Actually, when the lever is a bit above perpendicular. The pump switch is adjustable, so there is quite a bit of leeway as to when the pump engages in relation to the position of the lever. My adjustment is just seat of the pants, based on past references that pre infusion is possible..

The design engineers specified this switch, so it would seem that adjustability is designed in. My guess is there is an initial gap spec set during assembly, and just what that actually is depends on who put it together. And there's always the possibility that it gets readjusted along the way. I'm probably the third or fourth owner of this Anita. Then there's the fact that the E61 has undergone variations of design and construction among several manufacturers. Some of whom seem to indicate that pre infusion is designed in and some who don't.

And don't forget Monday/Friday syndrome...