Hi jake, thanks for the help. I already do a purge before taking a shot, as you suggest due to the built-in "pre wetting" the linea mini does. I don't think this is the issue though as the variance between a cold test and a later test is huge (can be up to 20g or more).Jake_G wrote:To measure the flow rate accurately, you need to understand the implications of the pump delay on the linea mini.
Purging before testing should always be done to ensure that the water screw and the tube feeding it are full prior to any tests and you should also wat 2-3s before you begin weighing and timing, since the solenoid opens and water begins flowing before the pump begins pumping. If you measure this "pre wetting" flow and time, you will get inconsistent results.
Had a mini to measure water debit, I would tare a cup, move the paddle to the brew (or pre brew) position and wait for the pump to start and then slide the cup under the group for 10s before sliding it back out from under the group and then weigh the results. See if this improves your accuracy.
Measuring the dead time introduces error, though the error you describe seems much larger than what pre wetting flow could introduce. It seems that perhaps your full-flow solenoid is leaking by...
There are no visible leaks in the machine as I've been checking the machine continuously while testing. it is tight and the seals are good. The idle pressure is good as well (around 10-12). Also the water debt in full brew mode is spot on, around 250g/30s every time. The issue happens only in pre-brew mode.
Do you think thermal expansion has something to do with it, it's affecting the needle itself? Like I mentioned, the flow gets faster the more I use the "pre brew" position, maybe heat plays a part?
Also I have the .6mm restrictor installed and I have the pressure down to 7 bars. Maybe there is a connection?
I'm new to modification such as this, so I'm not sure what causes it .