Well, hit a bit of a snag today. When heating up I'm getting some hissing. There's no obvious leak and OPV seems to be doing it's job, but I'm thinking based on how it echos a bit, it's likely the connection to the group. I'm using the factory group connection pipe, but maybe I'll have to make or buy a different connector that will be more reliable. I'm guessing the factory tube may not have been made for this application, but rather I'm guessing they assume the group will be sealed to a flange with the o-ring groove, the tube then just being for sucking up water.

I find that I need to start with a fake shot to warm the group up from idle temp or the first shot is much cooler and more sour than following shots. A flush doesn't work as well because the heating pattern is different due to the faster flow in the flush.

Got the new part in today...It lives!

Just pulled a shot and left the machine on for a while, here's the new steady state temp at 230f set point.



Will get more graphs this week and try some other set points.

I'm thinking about adding the cartridge elements too just so that I can reduce the temp offset from boiler, and likely have better control over the output profile.

I feel the current config will work, but my goal with this project is to allow the set point to change faster, so that changing coffees between shots is possible and practical.

Progress looks great!

Here's a cold start warmup to 230F, then a flush, then a real shot



I'll try 240F and see how it goes, that shot tasted a bit sour on a light roast.

I also reconfigured my pressure gauge on my regulator so that the check valve is before the assembly, this lets me see the pressure as the machine warms up, and during the shot to know when it's fully pre-infused. I have it set to 2 bar, and warmup takes it just under 3 bar (flush will kick it back down). Then up to 4 bar after a shot.

I'd like to get a better adjustable OPV, mine right now is at the minimum, and while I know it does bleed pressure in the past, I'm not sure at what pressure yet.

Just had a great shot with a dark roasted Yemen, lower group temp, higher TB temp (240F). To me when I tried a shot of this at 230F but warmer group temp it didn't seem as good. I'm thinking once I get some Scace data, I may try to calculate a shot temp, so you could pull one with a lower group temp, or you could adjust TB temp once the machine is more warmed up. Obviously the temp curve would be more falling or more stable depending on how far apart the temps are. But I think this would get me to the result I'm looking for.

Here first 3m are cut off, then a quick flush, then the shot:

If you had the cartridge heaters (and since you aren't using the TB for steam), couldn't you run the group and TB at the same temp? Is a 200 degree group temp possible?

Very nice progress Andre! Ought to post more videos on the shot. Scace data will definitely be interesting to look at as well.

What is group temp anyway? It could vary as much as 10 degree Celsius depending on which spot you're measuring. Apparently, the metal heat conduction isn't that effective/instantaneous such that the heat isn't uniformly distributed. The group is essentially a metal block with a temperature gradient when measured at steady state (that's what I see on my lever group head anyway).

Oh, I just came across some pictures of Faema Mercurio yesterday. With a metal sheet or two, it seems you can easily pretty up the OS lever. Probably you have seen this anyway...





A look inside the Faema Mercurio

FJ60Cam wrote:If you had the cartridge heaters (and since you aren't using the TB for steam), couldn't you run the group and TB at the same temp? Is a 200 degree group temp possible?

My DIY Dipper Lever has separate temperature control of the boiler water and the group head (via a heated plate to which the group head mounts). For my usage, I need to be able to pull three shots in a row all at the same temperature without too much waiting between shots for temperatures to stabilize. I have tried lowering the boiler water temp below 240 but I haven't been able to find a combination of plate/group head temperature and boiler water temperature under 240 that produces good shots (meaning a brew temperature near 190 degrees F).