Expobar Pulser - How to adjust pressurestat cause too hot

[jjue]

Hi,

I've been reading a little about the expobar and how it usually runs hot. I tested mine using the styrofoam/steam thermometer and my machine was slightly over 210F! I would like to turn the temperature down. From what I've read, I can do this by adjusting the pressurestat down. Where can I find the pressurestat on my machine and how much should I turn it down?

Assuming that most Expobars ship at 12bar, does anyone know how much to turn the pressurestat to achieve 9bar? Like, 2 turns counter clockwise or something like that. Do I have to get some complicated pressure gauge?

Thanks a lot.

Jason

[HB]

The Expobars do run hot, but if you're willing to flush more water, it's manageable.

The Expobar Lever I tried out had a large flush (6-8 ounces) and very fast rebound (only 15 seconds, IIRC), but I quickly adapted to its preferred flush-n-go technique (see Jon's Water flushing and "knowing" your HX machine for details). Apart from the large volume flushes, the only other "drawback" of the flush-n-go technique (compared to the flush-rebound documented in HX Love) is that your margin of error is smaller. Flush an ounce too much or delay 10 seconds too much and your temperatures are off. That's why some refer to flush-n-go as the "pro's method", i.e., because it's the requisite technique for commercial HX machines, which recover in seconds, not the leisurely pace of semi-commercials we're discussing.

If I've not convinced you to adapt your technique and put off adjusting the pressurestat, see the picture below:


Yellow cap and two wires exiting near top of boiler
(red dot is paint blob covering the adjustment screw)

As you might guess from the semi-permanent seal, the manufacturer is suggesting you don't touch. You'll need a pressure gauge. I've read accounts of using an ordinary tire pressure gauge, a length of rubber brake tubing, and a couple clamps over the steam arm to measure. Make certain the tubing can take the heat! I think the Expobar is typically set to around 1.0 bar and I've heard of owners turning it way-y-y down to 0.7 bar. That may be acceptable if you don't mind wimpy steam.

Regulating the brew pressure is slightly more complicated without the convenience of a portafilter pressure gauge. First, this is the Expobar's expansion valve (OPV):



Jim Schulman's Adjusting vibe pump pressure on HX machines explains the mechanics, including the diagram below:

(reproduced with permission)

You can guesstimate using his runoff technique, or build a pressure gauge. A setting of around 9 bar is a good start.

[luca]

Just to add a few things to Dan's post:

In Australia, some people have reported the same problem with their expobars. The importer has rectified it by putting a smaller diameter restrictor into the thermosyphon to lower the group temperature. (Basically, the flow of hot water through the group head is restricted, which makes it cooler so that you can get a cooler temperature at the grouphead for a given pstat setting, as well as avoiding having to flush such a huge amount) Perhaps you could talk to the guys that you bought your machine from.

Dan didn't explicitly say it, but just to make sure that you're not needlessly turning the wrong thing, note that the pstat controls the boiler pressure (ie. temperature) and the OPV controls brew pressure (ie. pressure at which the water is forced through the puck). Last weekend we dialled an Expobar Brewtus down from 13 bar brew pressure to 9. From memory, I think that it took about a revolution and a half anticlockwise, but the adjustment wasn't linear. We used a portafilter with a pressure gauge mounted on it and, like Dan said, I would strongly urge you to get your hands on one if you're going to be adjusting your brew pressure ... for all that you know, you could be at 15 bar or 10! Again, probably worth talking to the guys that sold your machine.

Hope that helps,

Luca

[jjue]

Thanks for the prompt responses and all the useful information. I will try flushing the machine first before messing with any of the default settings. I'm surprised that it's a requisite to flush on commercial machines because I assumed pro grade machines would be more tuned. You would think an expensive machine would be able to set and hold a constant temperature.

What is the disadvantage of changing the setting of the pstat so that one wouldn't require flushing? Why don't the pros just tune their machines so they don't require flushing?

Thanks!

Jason

[HB]

Most espresso machines require some initial flushing, even dual boilers, whose grouphead tends to cool when idle. Jim's $10 Method for Temperature Tuning an HX Machine explains the HX dynamics for continuous use and the effects of pressurestat changes. The tricky part is intermittent use. Your Expobar will hold a very stable temperature - once it has gotten started.