A month ago I upgraded to a breville dual boiler from a Bambino. I have a specialita grinder. I was getting decent shots from my bambino. But I had it for 2 years and I enjoy this hobby so I decided to upgrade. I have a lot of variables I can play with compared to the bambino and it's a little overwhelming. But my shots have been ok so far.

One thing I keep seeing that seems strange is the pressure gage during a shot. I have pre infusion set to factory settings for now. When I start the shot using manual button, it stays in pre infusion for the 7 seconds and the gage never rises from zero. Then full pressure comes on and it goes to around 9 bar. I start seeing drips about 10 seconds in. But the pressure starts dropping fairly quick. When I get to my desired yield of around 40 grams from my 20 gram dose, the pressure is now down to around 6 bars. This takes about 35 seconds total. If I go finer the shot takes even longer but the pressure drop is slightly less . If I go coarser, I see more dropping. But a shorter shot time.

When I watch videos of the dual boiler in action, the shots seem to stay at 9 bars and only drop maybe 1 bar max. I can't replicate that. I'm using fresh coffee from George Howell. The shots don't taste bad, but I don't know why the pressure doesn't hold . Thanks for any advice.

The pressure is a function of the puck resistance so as it flows through the pressure drops. Nothing wrong with the machine.

I assume you know that both the pre-infusion duration (Pd07) and the pre-infusion power (PP60) can be adjusted.

Thanks for the responses. I know that I have full control of the pre infusion settings and I plan to play with them as I learn more about how they change the extraction. So I guess what you are saying is that the pressure dropping must be coming from the puck eroding or channeling? I get that will happen. I'm just curious how I see shots being pulled by some online and the pressure gage really doesn't move from 9 bars the whole duration. Sounds like I might need to work on my puck prep. I wdt and use a bottomless pf and see no obvious channeling. I have ims, vst and stock baskets. All have similar results with the pressure dropping. The machine holds right at 9 bars with the backflush disk so it does seem as if machine is performing normally.