La Marzocco Linea Mini Slayer Mod - Page 3

#21: Post by **Ahmad H.** » January 13th, 2021, 11:13 pm

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...

Cheers!

- Jake

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).

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

.

#22: Post by **Jake_G** » January 14th, 2021, 7:11 am

Sorry. When I said the solenoid might be leaking by, i mean internally.

I haven't looked at your plumbing in detail yet, but i presume you have a solenoid valve that blocks the unrestricted flow when in pre brew and opens when in brew mode. Solenoid valves are directional, so if that valve is installed backwards, it will leak by in the closed position and allow some flow to bypass the needle valve.

You won't notice a thing when in brew mode, because the valve is open, so everything should be consistent, no matter the valve orientation.

Cheers!

- Jake

January 14th, 2021, 8:15 am

Hello everyone,
i am the developer of the kit.

After receiving photos from Ahmad, the mistake was quickly clear. He installed the needle valve the wrong way round, which leads to this weakness. So it was not a problem with the conversion but simply a carelessness during the installation.

But Jake is right. Another source of error would be incorrect installation of the solenoid valve. But this seems to be installed the right way round.

All best,
Torben