Can leaving the brew lever of E61 grouphead in the middle position cause damage in a single boiler espresso machine?

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Derryisreal
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#1: Post by Derryisreal »

I found this warning on a British coffee forum (Coffeetime) and it caused me some concern:
Now this next bit is important: There is no middle position for the lever that is meant to do anything, and you absolutely don't want to use it with a single boiler machine like Puristika. This type of machine has no way of knowing if water is low in the boiler, plus it introduces air in the system, that stuff we were talking about. If one day you forget and leave it in the so called preinfusion (middle position), you stand an excellent chance of a failed heating element on your return, if you are gone long enough....and don't for a second think the limit stats will always save the heating element....they most likely won't. This is because it's not water overtemperature, but the top of the heating element becoming exposed and going bang.
This is from the forum's administrator, a very knowledgeable man, who also helped ECM correct their thermosyphon issue on the Puristika. Not quite sure what he meant though, I leave the lever in the middle position while I backflush with chemical, according to instructions from ECM themselves:
What if you bump the lever to the middle position, while the machine is off and leave it there, would it be any danger when you start the machine?
Not really sure what to make of it?
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another_jim
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#2: Post by another_jim »

You block the thermosyphon and open up the brew path when you raise the lever. So don't. I have no clue whether it will damage the machine; but it will mess up any shots you do subsequently.

As to your what if worries -- what of you leave the gas running, or your car, etc. These are questions for a shrink, not a forum.
Jim Schulman

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Derryisreal (original poster)
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#3: Post by Derryisreal (original poster) »

another_jim wrote:As to your what if worries -- what of you leave the gas running, or your car, etc. These are questions for a shrink, not a forum.
Wow, you are rather blunt, if I didn't have the respect I do for you, I would reply accordingly.
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Nunas
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#4: Post by Nunas »

I'm no expert, but I've messed with a few e61 groups. I perhaps can't answer definitively, but I can at least give you my opinion and some understanding about how the e61 works.

When the lever is down, the exhaust valve is open and the brew valve is closed.
When the lever is in the middle, all valves are closed.
When the lever is in the top position, the brew valve is open and the exhaust valve is closed.
The pump switch should be set so that the pump comes on only when the lever approaches its topmost position.
Neither of these two positions (down and middle) should disrupt the thermosiphon or introduce air.
The middle position is not a preinfusion position; preinfusion only happens when the lever is cracked open a tad above the middle position. This is true for both plumbed and reservoir machines.
The middle position does have a purpose. Once some pressure has been established, via the mains by cracking the lever just above the middle position (plumbed) or via the reservoir by briefly raising the lever to the top position, moving the lever to the middle position provides a soak function, preinfusion, if you wish to call it that. I doubt that many people use this function.
In the down and the middle positions, the thermosiphon is unaffected.

So, what does this all mean? I posit that leaving the lever in either the down or middle position will do nothing to harm your machine, although, one would normally leave it in the down position. As for running out of water on an SBDU with the machine left on a long time, I suppose that this might theoretically happen, but I think it would take a very long time, and I don't see how it has anything to do with having the lever in the middle position.

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Derryisreal (original poster)
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#5: Post by Derryisreal (original poster) »

Fantastic explanation, Nunas, thanks! You cleared plenty of my confusion about the E61 group. I rather like the design for its simplicity (well, once you grasp how it works) and ingenuity.
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HB
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#6: Post by HB »

Derryisreal wrote:What if you bump the lever to the middle position, while the machine is off and leave it there, would it be any danger when you start the machine?
First, a quick review:

E61 groupheads may look alike, but there are slight differences. The middle "detent" position for some does nothing (no valves open); for some it cracks opens the upper valve to the brew chamber ever so slightly, allowing water to flow from the boiler. It's easy to tell which you have in front of you: If it's the former, nothing will happen in the middle position -- the pump doesn't start, water doesn't flow, the pump pressure remains unchanged. For the latter, the pump will not start, water will drip from the grouphead, and the pump pressure will drop from its normal idle pressure (2-4 bar) to zero.

The ECM Puristika is the latter type - in the middle position, the brew pathway is open, water drips slowly, and the pump pressure gauge drops to zero. Now, onto the espresso imponderable.

How might the E61 lever middle position present a problem?

Let's say you left the brew lever of the ECM Puristika in the middle position for hours and hours. From a hydraulics point of view, this would be the same as if you had disconnected the pump's power and lifted the lever to the brew position - the pathway from boiler to grouphead is open. As the boiler reheats, some water vapor would escape. Why? The brew boiler temperature is above the boiling point of water because there's a temperature drop between it and the grouphead. Consequently, the heat-boil-cool-heat cycle would force out a tiny bit of water vapor each time.

If the brew lever was in the middle position long enough, presumably the boiler would eventually boil off enough water to expose the heating element. I have no idea how long it would take, other than "a long time".

References:

Is there a purpose for the E61 middle brew lever position? and quite a few other threads plumb the mystery of the brew middle position. Internals of an E61 Brew Head is a step-by-step video overview by Bill Crossland.
Dan Kehn

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Derryisreal (original poster)
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#7: Post by Derryisreal (original poster) »

Thanks for taking the time to respond, Dan, very informative, appreciate it!
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Randy G.

#8: Post by Randy G. »

For more info on how the E-61 works, consult pages 5 through 8 in the Vibiemme Domobar Double owners manual, (PDF download). (DISCLAIMER: I created the manual but the download is free, hosted on Stefano's website, Espressocare.com). The diagrams on those pages illustrate exactly how a manual E61 group works.
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JRising

#9: Post by JRising »

Do remember that that warning post was for the Puristika, a SBDU machine. That's not a HX, there's an element in that boiler and no boiler-fill logic to make sure that element isn't heated dry. Leaving the lever for a long period of time in middle position has the cam resting against the brew valve, possibly holding it open a crack depending on the strength of the springs in the head. Given enough time, the boiler will evaporate dry.

The time it sits neutral while backflushing isn't a problem, firstly, it's not long and secondly, the blind disk has the evaporation route closed off, anyway. In HX machines it's only going to evaporate the HX dry, it won't damage anything. Anyone with a leaking brew valve has experienced the "It takes more than 30 seconds to get first drops" when the HX has been allowed to evaporate.

Of course, on a 2 boiler machine, it's as bad for the heating element as it would be for the SBDU.

There, I'm done, I'll shut up now. Sorry.

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Derryisreal (original poster)
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#10: Post by Derryisreal (original poster) »

Thanks guys, I am amazed at the depth of knowledge and the willingness to help on this forum. Very grateful for all the replies!
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