Flow Control HIgh Flow Rate Issue aka Loss of Graduation

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#1: Post by rbax238 »

Recently I found my Flow Control behaving oddly, and the only posts I've found anywhere that appear to addressing the same issue is "Flow Control Issue with ECM Synchronika" thread here (now closed for comments). I think I've found what's behind the issue on my machine and thought I should share it.

Here's how the FC always worked previously: turning the control (which is a screw-like mechanism) to fully closed completely cuts off all water flow. Opening the control gradually increases the flow, and the pressure (shown on the brewhead manometer).

Here's how the behaviour changed: closing the control fully STILL COMPLETELY shuts off all water flow. This is NOT an issue with the control handle slipping and the control not fully cutting off the flow. However, turning open the control - even a crack - instantly allows a large flow rate and pressure to return to max (OPV) level. There's just no graduation in between full off and full on. !@#$

I've put up with this for a while as I didn't have time to deal with it. However, much to my surprise it completely "fixed" itself when I started using the new bag of beans - which are a lot more gassy. Sure, the last bag was getting old - I think it was getting into the 4th week.

I'm thinking that the gassiness of the coffee is the distinction here. I haven't modified the machine in anyway other than changing the beans. I did lower the temperature (these are different beans) but I think I did that AFTER noting the difference in the FC behaviour.

Has anyone else out there suffered this "loss of graduation" of their FC? Have they tried varying the gassiness of their beans?


#2: Post by daviddecristoforo »

Pull the mushroom and check the bottom o ring. I'm betting it's effed up. If so, install a new one and be sure to lube it well before you reinstall the mushroom.

rbax238 (original poster)

#3: Post by rbax238 (original poster) »

Interesting. I'm going to save this idea. For some reason, with the new bag of beans, things have returned to normal. I'm on a new 340g bag. Just bought another 5lb bag and so will see as it ages if the problem returns.


#4: Post by JRising »

Remember that it's a flow control device. Its effect on pressure is only because it functions as one of the two major restrictions in the brew circuit.
If your puck prep is fine and solid, that puck will be the more significant resistance to flow unless your needle valve is almost completely closed off. (As with a blind disk in, pressure drop across the blind disk will eventually be max pressure regardless of needle/gicleur). This is how the FC device is beneficial, allowing you to cut the flow off to nearly zero so that the puck will have a moment to bloom without pressure messing up the prep, then be able to ramp the flow up so that there's no sudden change.

And, of course, the opposite is also true, if your puck prep is weak and coarse, the puck won't be a significant resistance to flow except perhaps with the FC wide open, gaping more than a stock 0.8mm gicleur. In this case, the flow difference controlled by the FC would have far less effect on the pressure drop across the puck simply because the puck is no longer a significant resistance to flow.

So with the change in the beans used (Or with the aging of an open bag of beans to some smaller degree) or with any changes to the grind and prep, there will be a considerable change to the flow control device's actual effect on pressure drop (ie. graduation) across the coffee puck.

rbax238 (original poster)

#5: Post by rbax238 (original poster) »

Well, I bought the machine Oct'2021 and have never seen this behaviour before. I've bought 3 5lb bags of this medium roast coffee so far and not seen this behaviour until the bottom of the 3rd bag (I share the beans with my wife's pour-overs).

People seem to fixate on the Pressure but I don't think it is the independent variable. All it is, is the "back pressure" caused by forcing the water flow thru the resistance of the puck. That is, we have two independent variables (Water Flow Rate and Puck Resistance) and one dependent variable (Back Pressure) and the Pressure drop across the puck = Flow Rate x Resistance (with use of suitable units).

Of course, there is some resistance before the puck - in fact I'd model the Total Resistance as "Some Resistance Before the Flow Control" + "Resistance of Flow Control" + "Puck Resistance". I'm going to make the assumption that the resistance before the FC is small and just ignore it.

However, if the screw opens in a graduated way, then the resistance will also decrease in a graduated way.

I should add that not only the back pressure went from 0 to OPV almost immediately after starting-to-open the FC (which it never did before) but I observed the Flow Rate of the espresso (actually the SIZE of the stream) to be large. It's like the graduation was lost. I think we'd agree that this means that the Puck Resistance was VERY HIGH so the effect of the FC was reduced to "no-flow" followed by "flow, but almost all the pressure being dropped across the puck".

If the FC was working correctly and causing half of the flow due to its restriction, then half of the pressure should fall across the FC and half across the puck. It appeared to open and allow full flow and full pressure without having to unscrew it any significant amount of the possible 2.25 turns available.

I think you're saying that "the difference is accounted for in the difference in the beans and in the difference in puck preparation." I'm unaware of any difference in the preparation. I used the machine for 2 (or 3) shots a day for more than a week. I figured something broke but I hadn't had time to do anything about it. Because we were at the end of the bag I picked up a 340 bag to tide us over until the regular arrived (by mail). With the new beans, the FC changed back to its old behaviour immediately. Hmmm... now that I think of it, I do recall that the "failure" wasn't immediate, but "got worse" over a period of days. This fits with "blaming it all on the beans".

I do wonder, though, why I've never seen this behaviour before. I did change roasters 3 bags ago but we've used about 1 5lb bag a month since October, and that's 7+ bags of coffee.

BTW the previous thread was talking about a possible problem with the screen internal to the mushroom, and I was hoping to read of any further development on this idea. I couldn't reply to that thread (it's closed) though. Before I could get around to making up this thread I got the new beans and the whole thing appears to be "this is how it works" instead of "something broke, need warranty help."

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#6: Post by Nunas »

I recall an issue with early Biancas where one could close the FCD all the way, get the needle stuck in the seat, then unscrew the stuck on seat when opening the valve.

rbax238 (original poster)

#7: Post by rbax238 (original poster) »

Yeah, I saw that claim in a video a while ago and it really bothered me because I've not seen that said of my FC. Further, I watched Mark of WWL show/talk about shutting the FC off completely for some extended preinfusion.

The previous thread that I alluded to above raised that question as well - do we really believe that it is ok to run the machine with the FC completely closed? So far, the answer in the videos is "yes, but not for a long time at one go - but long enough for a pour". Me? I dunno what to think. I'm just happy it appears to work again.

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#8: Post by PIXIllate »

Here is my experience (with photos) servicing my flow control. It's worked flawlessly ever since and I now use it in every shot.

Profitec Pro 600 - No Pressure/Water from Group

rbax238 (original poster)

#9: Post by rbax238 (original poster) »

Awesome, thx!

As my machine is 7 months old, this concerns me some. How old was your machine when you did this fix?

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#10: Post by PIXIllate » replying to rbax238 »

It's about 2 years old now. Owning an espresso machine means learning how to service plumbing. It's oddly satisfying.