I noticed that this has been subject to discussion in various forms on HB but never in the sense I will elaborate now and without an answer that may have covered my specific curiosity.

So, to describe the behavior I am seeing, I will start from the beginning, meaning heat-up.
When I start the machine (both boiler or only the brew boiler doesn't make any difference) the brew pressure gauge rises to 4 bars and then slowly drops to 0 until the unit is at brewing temperature.
The pressure gauge will remain at 0 until extraction or flushing.
When flushing, the pressure will rise to 2 bars (after a second or 5) and when closing the lever the pressure will drop to 0.
When brewing, the pressure will rise to 2 bars, then after 11 seconds from the pump start, it will rise to 9-9,5 (according to the OPV setting) and then slowly drops to 0 over 30 seconds after the pulling the shot has finished like in this vid
I will not argue that this will affect the quality of the shot in any way, the only reason that I've open this topic is to understand why mine behaved* like that and why other Brewtus IV machines usually rise in pressure at heat-up and/or remain at brew pressure after the shot was pulled.

* I said behaved because the described behavior has been true for my machine for the first 5 days of usage. After that, out of the blue, my Brewtus decided to go with the flow and act like the majority of other Brewtuses. Now when heating up the pressure gauge oscillates slowly between max pressure (according to the OPV setting) and 4-5 bars and after brewing a shot or using a blind portafilter for the backflush the pressure remains high.

A snapshot of it after brewing


I appreciate any insight on this "issue" as to what determined it to lose pressure.

The brew pressure gauge's reading when idle is largely irrelevant; I elaborate on this point in High brew pressure reading, excerpted below:

HB wrote:The pressure reading when the machine is idle isn't important.

To elaborate, pulling a shot introduces cooler water into a closed system, but then you suddenly close off the main exit at the end of the extraction. As the water in the boiler warms up, it expands and the pressure rises. The expansion valve is typically set to open around 12 bar for rotary pump espresso machines since they have their own bypass valve to regulate brew pressure. For vibratory pump espresso machines, the expansion valve (traditionally called an over-pressure valve in this context) is set to open at the desired maximum brew pressure, usually around 9 bar. This valve vents water into the driptray to avoid subjecting the hydraulic system to excessive pressure. It only needs to let a few drops of water escape to reduce the pressure sufficiently.

If the brew reading rises above 12 bar when the machine is idle, you should adjust the expansion valve such that it allows water to escape. Otherwise the brew pressure gauge's reading doesn't matter unless you're pulling a shot.

Dear Dan,

I read your exact same response on this issue on another topic and that is why I mentioned that I was not considering this to be a problem that may affect the shot. I was purely curious about why mine in contrast to other machines doesn't suffer from "High brew pressure reading" when idle and was dropping to 0 after the shot and during heat-up.

When comparing the youtube video to the photo you can clearly see the difference I was speaking of. Both, the video and the photo, capture the pressure behavior after brewing.

Regards

The slow drop in pressure after the lever is lowered could be due to the upper valve failing to seal completely:


See the yellow valve above the orange cam

If the machine is old enough, the rubber seal could be dried out or the pin worn. A water drop or two won't matter, but if water continues to drip-drip-drip out of the E61 exit, a bubble will eventually form and a thermosyphon stall will occur. The telltale symptom is an E61 grouphead that goes cold after idling for awhile. Constant dripping from E61 grouphead describes this problem and suggests a rebuild kit from EspressoCare.com for ECM, Quickmill, etc. (not sure if it's the same for Expobar; Stefano would know for certain).

Thank you Dan for your explanation. It makes sense because I was seeing some drops from the bottom of the E61 group dripping when losing pressure during the heat-up process but the group stayed hot.

Although the machine is new, and this "issue" lasted for only 5 days would it be possible that the valve you mentioned wasn't sitting properly or is there another explanation that may fit the bill?

It's possible that the valve seat is simply dirty, scaled, or slightly malformed; that could cause it to seal 100% sometimes and allow a few drops to squeak by other times. But I wouldn't worry about it until you see a consistent drip-drip-drip or the grouphead inexplicably goes cold.

Thanks for the explanation. I will not put more thought into it unless it starts affecting the brewing process.