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Why I think the Expobars run hot...
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Lefty69
Senior Member


Joined: 14 Apr 2004
Posts: 282
Location: Elkridge, MD
Expertise: I live coffee

Espresso: Expobar Pulser
Grinder: Mazzer Mini, Capresso...
Vac Pot: B&D Infuze
Drip: Melitta Clarity,
Roaster: GG/SC Combo, Behmor
Posted Mon Oct 11, 2004, 6:41pm
Subject: Why I think the Expobars run hot...
 

I have been trying to dial in my Expobar.  Temps out of the box, after a proper warm-up of 1+hours yielded temps that were 205+.  

Tried turning the pstat down.  I was able to get temp down to a reasonable range, but at the expense of good steam pressure.  

Next I replaced the autofill probe with the probe from a pasquini.  The pasquini probe was 2.375 inches longer than the stock expobar.  Burying the probe in the boiler yielded only a very small temperature change, probably about 1.5 degrees.  This allowed me to take the pstat up from about 0.7 to about 0.8.  Steam was better but not great.  Also the water level in the boiler was probably only about 0.5L out of 1.7L boiler.  This must be outside the operating range of the boiler.

The words to follow are simply conjecture....So I started thinking about the origin of the machine.  The machine is supposed to be a light commercial machine.  I know the one Marcuzzi I have seen, manufactured about 3 years ago, IIRC, could be plumbed.  Was the machine engineered as a plumbed in machine?

Specifically when they tuned the boiler, and engineered the heat exchanger , they needed to assume a water inlet temp.  for a plumbed machine, that would be room temp or maybe even cooler, lets call it 72F.  I am running from a reservoir inside the case of the machine.  After about 2.5 hours of warm-up, the water temp in my reservoir was about 86F, about 14 degrees higher than room temp.

I think that the inlet temp has a great deal to do with why expobar is running hot.  Lets say 86F water is heating to 205F, if the inlet stream has a lower temp 72F, the outlet temp should be lower, probably not by 14 degrees, but maybe 6 or 7 degrees (HX should run more efficiently with a higher delta T, so with a higher delta, better heat transfer...better than 119 degrees...maybe 125 degrees).  Depends on the heat transfer coefficient of the HX.

My point is that I think I need to run the Pulser with a reservoir outside of the case or plumbed.  With the reservoir inside the case the water temp is not static during warm-up, and so the HX performs differently at different points of the warmup.  Just to give you another data point after about 45 minutes of warmup, the reservoir water was about 78F.  Tap was about 72F.  2.5 hours water was 86F.  This looks like a huge variable.

I will try this out this weekend...any thoughts?

Eric
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mike01
Senior Member


Joined: 21 Jan 2004
Posts: 372
Location: SE Michigan
Expertise: I love coffee

Espresso: Izzo Alex
Grinder: Mazzer SJ, Vario-W
Vac Pot: Yama Stovetop
Drip: Bunn Trifecta
Roaster: Hottop
Posted Thu Oct 14, 2004, 1:23pm
Subject: Re: Why I think the Expobars run hot...
 

I have actually wondered the same thing and have been having similar problems.  My expobar shipped with a boiler pressure setting of 1.2 bar and I was getting 210 degree temps at the group even after extensive group flushing (the temp stability of the e61 is truly amazing).   My pressurestat is currently set to 0.5 bar to get a 200 degree temp, which I what I have found works best with my current blend.  However, the steam pressure is less than I would like it to be.  I talked to Todd at WLL and he was saying that the machines were originally designed to be run at lower boiler pressures like this as the expobar was designed for the european market, which drinks fewer milk drinks than the north american market.   If you figure anything out, please let us know, as I am greatly interested.
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gscace
Senior Member


Joined: 19 Dec 2001
Posts: 237
Location: Laytonsville, MD USA
Expertise: I live coffee

Espresso: La Marzocco Linea 2AV, Astra...
Grinder: 3 Mazzers Robur, Kony,...
Vac Pot: Cona D, Hario Nouveau
Drip: Technivorm
Roaster: Has Garanti 1kg. electric
Posted Thu Oct 14, 2004, 6:06pm
Subject: Re: Why I think the Expobars run hot...
 

Hi:

I learned a very interesting trick for cooling e-61 machines that run too hot, from the designer of the Astra machines, which is to lengthen the water delivery pipe from the hx to the top of the group.  Water in the hx is too hot for brewing, as you prolly already know.  It cools on the way to the group as it passes thru the delivery line.  By lengthening this line the residence time in the line increases and the machine runs cooler for the same boiler pressure.  Soft copper refrigeration tubing in 1/4 diameter works well.  You can easily bend it into several coils to conserve space.  You will have to silver solder the tubing into British parallel pipe fittings.  I think Farmington Engineering still sells them (Farmingtonengineering.com or somethig like that).   I felt that my Astra ran pretty hot for the blends that i was using as I was looking for around 195 F at the top of the coffee cake for Barry Jarrett's Decatur Street Blend.  At the same time, I wanted to keep my boiler pressure above 1 bar when steaming.  I lengthened my delivery pipe by about 9 inches (3 coils 3 inches in diameter) and it worked like a champ.  

I noticed Dan Kehn's graph of three different e-61 machines showed that all of them ran around 201 F(or more?).  I think that is too hot for a lot of coffees and that these machines could use some cooling down, particularly since steam performance goes to hell when the pressure falls below 1 bar.  

-Greg
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Lefty69
Senior Member


Joined: 14 Apr 2004
Posts: 282
Location: Elkridge, MD
Expertise: I live coffee

Espresso: Expobar Pulser
Grinder: Mazzer Mini, Capresso...
Vac Pot: B&D Infuze
Drip: Melitta Clarity,
Roaster: GG/SC Combo, Behmor
Posted Thu Oct 14, 2004, 7:59pm
Subject: Re: Why I think the Expobars run hot...
 

Greg,

Any measurement on the temperature drop at a static pressure by adding the additional length?  

Any comments on my water inlet temperature theory?

I just noticed that you are only a hop skip and a jump away from me...Interested in meeting at Jay's shop(see: US East Forum)

Mike,

I have not tried an external water source.  After talking with Todd some more, I sent my Expobar back this morning.  He called me later today to tell me he overnighted a new machine to me, should arrive tomorrow.  Todd was ver helpful and certainly was willing to go out of the way to try and solve my issues, including replacing the autofill probe.  Hopefully the new machine won't require som much tuning.

Thanks,

Eric
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HB
Senior Member


Joined: 3 Apr 2003
Posts: 2,913
Location: Cary, NC
Posted Thu Oct 14, 2004, 8:10pm
Subject: Re: Why I think the Expobars run hot...
 

gscace Said:

I felt that my Astra ran pretty hot for the blends that i was using as I was looking for around 195 F at the top of the coffee cake for Barry Jarrett's Decatur Street Blend.  At the same time, I wanted to keep my boiler pressure above 1 bar when steaming.  I lengthened my delivery pipe by about 9 inches (3 coils 3 inches in diameter) and it worked like a champ.

Posted October 14, 2004 link

Neat idea!  According to what I've read, the Astra Gourmet boiler is 4.2 liters.  That's almost 2.5x larger than the boilers of the machines I evaluated and it's likely that the Astra has a bigger HX too.  I found that the temperature of "small HX" machines could be neatly reduced by increasing the flush amount, but that trick didn't work for a "big HX" machine like the Cimbali Junior.  I had to tweak Junior's pressurestat setting with considerable care to reliably hit the target temperature.  In the case of the Expobar, which I've yet to work with, my suspicion is that it will behave like other prosumer HXs, not your commercial HX, and thus a mechanical modification is unnecessary.  This is just a hunch.

I noticed Dan Kehn's graph of three different e-61 machines showed that all of them ran around 201 F(or more?).  I think that is too hot for a lot of coffees and that these machines could use some cooling down, particularly since steam performance goes to hell when the pressure falls below 1 bar.

The target temperature that I chose for the charts in "How I Stopped Worrying and Learned to Love HXs" was sort of arbitrary.  I'm not slavishly committed to a given temperature, although my own tastes run 198-201F for most blends, and maybe a tad hotter for brighter blends.  La Valentina is regulated to 0.9 bar, but that's mostly to slow the overheating between shots, not dial in a particular temperature.  I would push the setting up if I habitually served a big crowd.

-- Dan

 
www.home-barista.com
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mike01
Senior Member


Joined: 21 Jan 2004
Posts: 372
Location: SE Michigan
Expertise: I love coffee

Espresso: Izzo Alex
Grinder: Mazzer SJ, Vario-W
Vac Pot: Yama Stovetop
Drip: Bunn Trifecta
Roaster: Hottop
Posted Thu Oct 14, 2004, 8:26pm
Subject: Re: Why I think the Expobars run hot...
 

Lefty69 Said:

Mike,

I have not tried an external water source.  After talking with Todd some more, I sent my Expobar back this morning.  He called me later today to tell me he overnighted a new machine to me, should arrive tomorrow.  Todd was ver helpful and certainly was willing to go out of the way to try and solve my issues, including replacing the autofill probe.  Hopefully the new machine won't require som much tuning.

Posted October 14, 2004 link

I experimented with the overheated resivior theory a bit earlier, but I don't think that is the problem.  I put a bunch of ice cubes into the resivoir and measured the resivoir water temp at around 50 degrees.  This did make a small decrease in the initial water temp after a long flush, but the hx was able to quickly rebound to my normal temps in less than a minute.  Let me know how the new machine works out for you.  Perhaps we both have defective machines in which case I will have to give Todd another call.
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mike01
Senior Member


Joined: 21 Jan 2004
Posts: 372
Location: SE Michigan
Expertise: I love coffee

Espresso: Izzo Alex
Grinder: Mazzer SJ, Vario-W
Vac Pot: Yama Stovetop
Drip: Bunn Trifecta
Roaster: Hottop
Posted Sun Oct 17, 2004, 5:16pm
Subject: Re: Why I think the Expobars run hot...
 

How long should I be waiting after I do the cooling flush before pulling the shots?  Also typically, how fast will the hx overheat again after the cooling flush?  BTW, how's the new machine working out for you, Eric?
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Lefty69
Senior Member


Joined: 14 Apr 2004
Posts: 282
Location: Elkridge, MD
Expertise: I live coffee

Espresso: Expobar Pulser
Grinder: Mazzer Mini, Capresso...
Vac Pot: B&D Infuze
Drip: Melitta Clarity,
Roaster: GG/SC Combo, Behmor
Posted Sun Oct 17, 2004, 5:46pm
Subject: Re: Why I think the Expobars run hot...
 

mike01 Said:

How long should I be waiting after I do the cooling flush before pulling the shots?  Also typically, how fast will the hx overheat again after the cooling flush?  BTW, how's the new machine working out for you, Eric?

Posted October 17, 2004 link

I typically wait until the top of the boiler cycle.  That is where I measure my temp while adjusting.  Therfore, I know its at my target.

The new machine was damaged during shipping.  Todd, did dhip it overnight, which was very nice, but it is going back due to damage.  They are sending me another "Brand New" machine, instead of a "Next to New".  Gotta give WLL kudos for the customer service effort.  I should have my new machine on wednesday, which is when I will be back from Dallas.

I did fire up the machine, and after running quite a bit of water through it, I determined that without touching the pstat, I could reliably get 201F by flushing about 6 oz of water.  I also took the brew pressure down from 12 bar on the guage to 8.75 on the guage...tring to hit Schomers 8.2...I pulled some very good shots with some very unevenly roasted RSB.  I went to tweak the temp down just a smidge, but was roadblocked by a pstat I had never seen before.  So I let it go, since I was not keeping the machine anyways.  By the way, the boiler was set to about 1.15 to 1.2 bar at the top of the cycle.  Very good steam, but I wonder, even at 1.1 to 1.2 bar in boiler, if the steam tip hole diameter is a little large.  I think the hole should be a little smaller to get a bit more steam velocity.

So no machine for me until Wed.  Which is fine since I am out of town for 3 days.  But the damaged machine seem to work pretty well, doesn't it figure.

Eric
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mike01
Senior Member


Joined: 21 Jan 2004
Posts: 372
Location: SE Michigan
Expertise: I love coffee

Espresso: Izzo Alex
Grinder: Mazzer SJ, Vario-W
Vac Pot: Yama Stovetop
Drip: Bunn Trifecta
Roaster: Hottop
Posted Sun Oct 17, 2004, 6:05pm
Subject: Re: Why I think the Expobars run hot...
 

Well, I'm mangaged to get 202 temps 20 seconds after after doing a 8oz cooling flush, after increasing my boiler pressure to 0.8 bar.  However, the machine quickly overheats to 206 degrees after a 60 second rest.  The steam is better, but still not what I would call superb.  It sounds like my machine is suffering from similar problems to the your first one.  What could cause a problem such as this?
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Lefty69
Senior Member


Joined: 14 Apr 2004
Posts: 282
Location: Elkridge, MD
Expertise: I live coffee

Espresso: Expobar Pulser
Grinder: Mazzer Mini, Capresso...
Vac Pot: B&D Infuze
Drip: Melitta Clarity,
Roaster: GG/SC Combo, Behmor
Posted Sun Oct 17, 2004, 6:16pm
Subject: Re: Why I think the Expobars run hot...
 

I still think there is an issue withe the HX design on some of these.  If the HX is too long then it will be in the boiler longer and so the water will be hotter.  It could also have to do with the group being too hot due to thermosiphon.  I am not sure how this works, but sort of the smae concept, there is too much surface area for heat transfer between the group and the thermosiphon water line.  This would cause the group to recover quickly....all pure speculation.  Have you tried lowering your brew pressure.  I think this will go a long way towards reducing the bitterness in your shot.  I beleive the relationship allows you to brew at a higher temp if your brew pressure is lower...

In any case, your machine does seem to have an over temp issue>  i would call and talk to todd some more>

Eric
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