What the heck is a gicleur-jet for?!?

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NinjaTech

#1: Post by NinjaTech »

So.. Here is my question, what is this thing even for? I know my Astoria machine has one, i had it out and cleaned it during its rebuild, and i understand that it acts as a calibrated restriction point, but why do we even use them is my question? I guess I don't understand why we would want to restrict water flow too the group head? If our pump is set at the correct pressure, and our coffee grind is proper, it should act as the only restriction we need correct?

I was doing a lot of reading on here this morning about measuring group head pressure, and several times it was mentioned the difference between what the 'gauge' pressure on the machine is reading (it seems most machines gauges are hooked up between the gicleur and the pump), and the actual brew head pressure that is between the coffee and the gicleur. From what I am reading most people say there can sometimes be a bar or more pressure difference here. (gauge pressure 9bar for example, actual group pressure 8 bar for example) So why not remove the gicleur, and the restriction it would cause? In my mind that would do two things, it would subject the coffee to the actual set pressure that the OPV valve on your pump is set too instead of a pressure that is gicleur restriction/flow rate dependent, and also make your machines gauge read actual group pressure.

The only reason I can see for a Gicleur to even exist is to prevent messes in the case of coffee ground way too coarse? Is it really just a handicap for improper coffee grinding, or am i missing something?

Has anyone tried running their machines WITHOUT it installed by chance?

Thanks,
Patrick

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HB
Admin

#2: Post by HB »

Pressure profiles, preinfusion and the forgiveness factor explains that a gicleur (orifice) slows the pressurization and thereby increases the barista's margin of error. Once the system is fully pressurized, the gicleur impact on the pressure reading is very small (from my measurements, somewhere between 0 and 0.5 bar).
Dan Kehn

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Peppersass
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#3: Post by Peppersass »

+1

On an LM machine, the gicleur is what makes the preinfusion gentle, and therefore makes the machine more forgiving.

NinjaTech

#4: Post by NinjaTech »

That makes perfect sense actually.

One other question.. Do you know if there is any particular reason they have the pressure gauge plumbed in between the gicleur and pump, and not between the group and gicleur?

I know, I have lots of questions.. I just am always eager to know exactly how and why something works the way it does.

Thanks,
Patrick

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HB
Admin

#5: Post by HB »

I assume most espresso machines locate the pressure gauge between the pump and gicleur as a matter of manfacturing/repair convenience. There's intentionally minimal distance between the boiler and grouphead since more distance traveled = more temperature drop. The La Marzocco Strada, for example, has the brew pressure gauge atop the grouphead to measure the actual pressure on the puck's surface. It has a hole tapped through the valve riser; obviously that's a bit more complicated design than a tee immediately after the pump exit.

For what it's worth, I don't worry much about the actual brew pressure value. Judging by taste/texture, I adjust it up/down 1 bar and declare victory.
Dan Kehn

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another_jim
Team HB

#6: Post by another_jim »

The gicleur is usually inside the group, downstream of most possible pressure gauge locations.

Old fashioned groups, with lots of air in them, like lever groups and E61s, do not need a gicleur, since the time it takes for the air spaces to fill with water provides a gentle ramp up in pressure.

There are other gicleurs in HX/Thermosyphon machines; but these are not for pressure management, but for temperature management. They control the flow rates of the water circulating through and around the heat exchanger during idle periods and at the start of the shot. The techniques for tuning these are still very much proprietary; and machine manufacturers like Cimbali and Nuova Simonelli, who are very good at fine tuning HX systems, aren't sharing their know how

If you want to experiment with pressure ramp-ups, you can install a a manually adjustable needle valve at the pump head. Andy Schechter, a legendary coffee amateur, did this and was able to stretch out the shot's initial ramp to full pressure to 20 seconds. However, he found that the ramp up time made little difference in the quality of the shot. It just had to be long enough so the puck wasn't destroyed by too rapid a pressurization; if you get five seconds or more before seeing any flow, you will usually be fine in this department.
Jim Schulman

NinjaTech

#7: Post by NinjaTech »

Fair enough, taste is more important than where a needle on a gauge is pointing anyway.


Thanks!

Beenbag

#8: Post by Beenbag »

.. Do you know if there is any particular reason they have the pressure gauge plumbed in between the gicleur and pump, and not between the group and gicleur?
Most likely because its easy and simple to plumb it that way inside the m/c casing.
Tapping off a pressure gauge after the gicleur inside the group, is much more complex.
..Old fashioned groups, with lots of air in them, like lever groups and E61s, do not need a gicleur, since the time it takes for the air spaces to fill with water provides a gentle ramp up in pressure.
Jim...I thought E61 groups have gicleur's in them...to control the pre-infusion. ?

NinjaTech

#9: Post by NinjaTech »

You all seem quite knowledgeable about the internal workings of these things, in my area our static water pressure is a hair over 8 bar and right now, so i had to run the OPV valve on my pump almost all the way out to keep brew pressure under 9 bar. You can't see any reason why that would be a issue do you? I wouldn't think a vane pump would care if its only having to raise the pressure by one bar, but thought i would ask.

Incidental when I first got the machine back together I forgot to actually plug the pump in so for the first few shots it was running on line pressure only, and working surprisingly well. I just figured the pump was THAT quiet until i realized it wasn't even running.

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erics
Supporter ★

#10: Post by erics »

. . . in my area our static water pressure is a hair over 8 bar . . .
As far as I'm concerned, that borders on being criminal. Your plumbing fixtures, including the espresso machine, would benefit greatly from pressure regulation down to ~50 psi for the house and ~35 psi for the espresso machine and other solenoid equipped items such as an ice maker in a fridge.
I wouldn't think a vane pump would care if its only having to raise the pressure by one bar, . . .
From a control stability standpoint, I would say you are "at the edge". To prove or disprove this, I would need a time machine to get back in the classroom - neither of which are happening anytime soon.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com