# HX behaviour



## rsnidjik (Nov 4, 2018)

I've just bought an eight-year-old Expobar Office Control and am learning to use it. My previous machine was a PID'd Silvia, so most of my learning curve has to do with getting used to an HX machine.

With the Expobar, I've noticed that the machine can take a very long time to put out water through the group head if it's been powered on but sitting idle for a while. *I'm guessing this is because the machine cycles cooler water through the group to cool it down to an optimal brewing temperature. Is this correct?*

*
*

Here's some data:

At initial warm-up in the morning, if I pull a shot right after the brew light first goes out, water comes out of the group head almost immediately when I hit the brew switch. The chart below shows the wait time for water to emerge at various times following the previous shot.

5 minutes after previous shot: 11 secs.

10 minutes after previous shot: 30 secs.

20 minutes after previous shot: 42 secs.

30 minutes after previous shot: 43 secs.

60 minutes after previous shot: 48 secs.

I ran this sequence a second time and got very similar timings.

Once the machine is initially warmed up, steam and hot water emerge from their respective outlets without a wait regardless of the time elapsed since previous shot.

*Question #1: Is this behavior normal for an HX machine?*



*
Question #2: Since it appears that the machine is doing its own cooling routine, should it be necessary for me to do a cooling flush prior to pulling a shot? I don't have a good way to check brew temperature right now. *

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Thanks!


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## DavecUK (Aug 6, 2013)

1. No it's not normal

2. No it's not special in any way your understanding of how the HX works is not correct. Use the link below which will lead you to other links on the Wiki that explain how it all works.

http://coffeetime.wikidot.com/heat-exchanger-machines-how-they-work

Probably why you thought I was talking crap when I said the Pulser based machines run very very hot is because yours isn't working right. The HX unit is running dry and of course this stops group keeping warm....So you think aha the shots are coming out nice and cool 9which they are, possibly too cool). How long do you warm it up for?


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## Jony (Sep 8, 2017)

Boom


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## rsnidjik (Nov 4, 2018)

DavecUK said:


> 1. No it's not normal
> 
> 2. No it's not special in any way your understanding of how the HX works is not correct. Use the link below which will lead you to other links on the Wiki that explain how it all works.
> 
> ...


Thanks for your comments. I didn't think you were talking crap. It's just that my experience didn't line up with your description of the machine (and I guess I was a little miffed that you dissed my new baby! But I'm over that now.







)

The coffee isn't nice and cool -- it's about right, I'd say. The temp as measured at the group head is a steady 94.5 - 95.0 degrees C without manual flushing. That's measured with a Thermopen thermometer held about a third of the way from the center to the edge of the shower screen, about 5 mm below the screen. I don't consider that technique optimal, but it's the best I can do with what I have on hand.

I'll read up on HX machines. I've done some already but clearly need to do more.


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## rsnidjik (Nov 4, 2018)

Jony said:


> Boom


Ha! Starting in about 1998, I survived eight years on alt.coffee on Usenet, where the daggers were always out for any unsuspecting noob. I deserved most of the abuse I suffered, though.


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## MildredM (Feb 13, 2017)

rsnidjik said:


> Ha! Starting in about 1998, I survived eight years on alt.coffee on Usenet, where the daggers were always out for any unsuspecting noob. I deserved most of the abuse I suffered, though.


Haha! You want to try being new, clueless AND female . . .


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## DavecUK (Aug 6, 2013)

rsnidjik said:


> Thanks for your comments. I didn't think you were talking crap. It's just that my experience didn't line up with your description of the machine (and I guess I was a little miffed that you dissed my new baby! But I'm over that now.
> 
> 
> 
> ...


If your machine is acting as you describe, it's unlikely the temps are right, but then with the old Pulsers they were rarely right anyway. I wasn't dissing your machine, just realistic about what is effectively a 15 year old design that wasn't great in the first place. A sort of broad hint, not to invest too much love and money on it and that if you really like your coffee a quick fix up, ebay out and upgrade might be well overdue. you will definitely taste the difference and find a more modern machine easier to use. Although I d0 think it's admirable not to landfill these old machines and that they are kept going and still giving service for decades.

Of course if the machine is new to you, once you get it working properly you will notice bigger cooling flushes (or you will get that black ring on the crema), but hopefully better performance and no doubt find it very agreeable to use compared to what you had before. The great thing is that in the future further investment will bring more noticeable benefits. So only good things to look forwards to.

I certainly wouldn't get upset though...because that's definitely not the way to learn more..


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## rsnidjik (Nov 4, 2018)

MildredM said:


> Haha! You want to try being new, clueless AND female . . .


You just sent my wife into near hysterics! She knows what these boy clubs are like.

I've got several things on you, though: I'm 62 years old, short, got a paunch -- and, worst of all, had to check myself from writing "HX behavior" instead of "HX behaviour" as the subject of my thread. Need I say more?


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## rsnidjik (Nov 4, 2018)

DavecUK said:


> If your machine is acting as you describe, it's unlikely the temps are right, but then with the old Pulsers they were rarely right anyway. I wasn't dissing your machine, just realistic about what is effectively a 15 year old design that wasn't great in the first place. A sort of broad hint, not to invest too much love and money on it and that if you really like your coffee a quick fix up, ebay out and upgrade might be well overdue. you will definitely taste the difference and find a more modern machine easier to use. Although I d0 think it's admirable not to landfill these old machines and that they are kept going and still giving service for decades.
> 
> Of course if the machine is new to you, once you get it working properly you will notice bigger cooling flushes (or you will get that black ring on the crema), but hopefully better performance and no doubt find it very agreeable to use compared to what you had before. The great thing is that in the future further investment will bring more noticeable benefits. So only good things to look forwards to.
> 
> I certainly wouldn't get upset though...because that's definitely not the way to learn more..


Nah, I'm not upset. I love my new-old machine even if it's gimpy. I'm living in North Africa, and, apart from some amazing espresso equipment in some of the swankier big-city cafés, what the rest of us have access to is stuff that Europeans have gotten tired of. People here are extremely resourceful about maintaining old machines and keeping them working acceptably well. For the most part, I don't mind being 10-15 years behind the cutting edge (except when I go to the dentist, that is). Regardless, it's a small price to pay for beautiful weather year-round and, as I type this, luscious pomegranates at the equivalent of 12p each.

But I do wish I could find freshly roasted beans a little more easily.


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## rsnidjik (Nov 4, 2018)

Update to the problem that I reported in my first post:

On a visit last week to the U.K., I got a replacement pump, OPV and pstat for my Expobar Office Control. (Excellent service from all four U.K. vendors, by the way. I got a bunch of other odds and ends, too.)

Yesterday I installed the pump and OPV, and the problem with the delay before water would emerge is now resolved. So DavecUK was right that things were not normal.

Now I'm dealing only with the standard HX problem of needing to flush the grouphead before pulling a shot. In the U.K., I ordered the itty-bitty teflon disk to use as a thermosyphon restrictor and I even have a nice new flare nut spanner, but I'm going to hold off on that mod until I get used to my machine's vastly improved behavior.

Thanks for everyone's input.


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## rsnidjik (Nov 4, 2018)

A further update:

With a new pump and OPV, my Expobar Office Control was operating pretty consistently. I was still having to flush 350 ml of water to get the brew temp in the right range, but at least the machine was consistent.

I was contemplating doing the thermosyphon restrictor mod but first decided to try the less invasive but possibly problematic method of adjusting the pstat downward. My Expobar is new enough (2010) to have the pstat that's adjustable with a little plastic dial. I was able to access the dial by removing only the front panel. I first tried a quarter-turn counterclockwise and got a lower idling temp, but it was still running hot (about 98º C.) and requiring a high-volume cooling flush.

A second quarter-turn did the trick, reducing the idling temp to about 95º. Best of all, the flush volume needed to get to a brew temp of about 93º is now 200 ml instead of 350 ml. That means far fewer refills of the tank and less time waiting for my coffee. Flushing 200 ml feels normal; flushing 350 ml each time felt dysfunctional and dominated my workflow.

I know the jury is still out on optimal brew temperature and that it's probably dependent on the bean as well as who knows how many other variables. In my case, I almost always get that nasty-looking dissipated crema when the temp is too high. I'm not getting that when I brew in the 93-94º range, and, more importantly, the taste is usually to my liking.

Brew temp appears to remain very steady throughout the time of extraction, at least according to my measurements. (I'm measuring brew temperature with a good digital thermometer [Thermopen] inserted through a small foil cup that nestles snugly into my bottomless portafilter.)

Steam pressure remains robust.

So, I'm content for now. Soon, though, I'll tweak things further until I really mess everything up. Then I'll come whimpering back here. Thanks in advance!


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