Building an Espresso Machine version 2 - Page 2

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FotonDrv
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#11: Post by FotonDrv »

Interesting project! Kudos for attempting such a task :)
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TomC
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#12: Post by TomC »

I think what you're doing is so cool. Impressed by your speed of assembly too. I look forward to seeing you get it all together.
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pizzaman383
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#13: Post by pizzaman383 »

What did you decide to do for the boiler and temperature control?

The temperature of the water that reaches the group head in an E61 setup (or any setup that has two input lines feeding the group head coming from different locations in the boiler) is impacted by the proportion of water coming from the two boiler outputs. This usually means hotter water comes from the higher output and cooler water comes from the lower output to get mixed in the group head entry chamber.

The mixed water temperature feeding the group head can be adjusted by the amount of flow coming through each of the pipes. This can be adjusted by the placement of the boiler outputs, the diameter of the tubing (or a restrictor in one of the tubes), or the water flow pattern inside the boiler. From a mixed water temperature is a flow-weighted average temperature of the top and bottom temperatures.

If the top and bottom temperatures are steady throughout the shot, this averaging just impacts the offset between the boiler and the group head temperatures. If the difference between the top and bottom temperatures changes during the shot then the group head water temperature can be made to increase or decrease depending on the relative flow rates in the top and bottom tube. Tuning this turns out to be important for many espresso machine designs because the specific group head, tubing configuration, boiler exit points, source water injector, preheat (if any), and boiler water dynamics all play a role.

After playing with various group heads, temperature control methods, and boiler water dynamics this turned out to be the most surprising lesson I learned.
Curtis
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fancycoconut (original poster)
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#14: Post by fancycoconut (original poster) »

Hey thanks guys, it really has been fun! Unfortunately, I think work is going to come to a screeching halt in the next few days, as mid-terms are only a week or so away. But, the end of midterms means the beginning of my winter break which means TONS of time to work!
Curtis-
To be honest, I understood very little of what you just said :D . However, I can tell you a bit about my temp control. I've created a PID function for maintaining the boiler temp, and I have a temperature sensor in my boiler. Now, concerning the grouphead. I have a solenoid (just a 2-way) attached to my outlet (lower) port. When brewing, this closes, to direct the flow of water to the coffee. I will also using a temp sensor to monitor the temp of the grouphead. When this temp is no longer within the specified temp range (when idle of course), the machine will turn on the pump BUT keep this solenoid valve open, circulating hot water through the grouphead, effectively raising the temperature. Now, in ideal circumstances, I would have fabricated the boiler, and used a closed brew system, pressurizing the boiler to ~1.2 bar to allow for thermosyphoning, by diverting the flow around the pump when idle. But, I don't have access to the tools/materials/facilities required to construct a boiler like that.
Now, since this is my first time building an espresso machine, and I am certainly no expert, nothing is set in stone yet. Everything requires testing, testing and, oh yea, testing! But honestly, I think that's a big part of what makes it so much fun.
Ethan

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pizzaman383
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#15: Post by pizzaman383 »

Most of what I said only applies if you have two lines from the boiler to the group head plus a third feeding the boiler.

What you're doing is another approach to the problem which is worth trying. If you plumb the second group head port to a drain line through a solenoid in you could do short pulses while the three way valve is still closed to bring the group head up to temperature without cooling the boiler too much then go into regular pumping mode when you pull up the brew lever.
Curtis
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jonr
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#16: Post by jonr »

It looks like the gear pump can handle hot water if you have PEEK gears. I'd be concerned that an open system (perhaps 99C max) might not be hot enough by the time the water gets to the coffee. Maybe not - measurements are the key.

fancycoconut (original poster)
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#17: Post by fancycoconut (original poster) »

Yep, I have the PEEK gears, so I'm ok up to 120 C or 248 F.
Maintaining group temp is definitely one of those things that will require lots of testing to sort out. Getting the boiler plumbed in is next (when I have the time of course), and then I can begin testing.

jonr
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#18: Post by jonr »

Seems like there should be lots of old, small espresso boilers around. And almost all of them can run above atmospheric pressure.

fancycoconut (original poster)
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#19: Post by fancycoconut (original poster) »

So! Little update...
In 12 hours, exams will be in full swing (almost break!). Anyway, I've been doing some modeling to get an idea of the frame and how things will fit in it. I designed this simple yet very crucial plate that holds the brew pump, fill pump and boiler. I'll get it 3D printed out of ABS plastic. Here are some pictures;
The boiler is the rust looking thing, and the other part is the brew pump. The other cutout is for the fill pump (not modeled)






Ethan

fancycoconut (original poster)
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#20: Post by fancycoconut (original poster) »

Winter break is finally here! Plenty of time to work now.
I started/finished building the frame today. Working on the machine is so much easier now that the parts aren't completely spread out on my table.
I'm having a few electrical issues, which are probably due to the lack of organization in my wiring. I'll try to redo everything tomorrow, hopefully that will fix it.



Of course, this is not the final placement of the pump :D , just a convenient place for it at the moment. There are still a few pieces of the frame missing, but really only the parts around the drip tray.
Ethan