La Marzocco GS3 MP Pre infusion pressure

[Ben_S]

Just plumbed in a LM GS3 MP with a C150 kit from Bombora. The kit has a PLV of 350KPA before the water filter. When I go through the pre-infusion process, the brew pressure reading is at about 5bar. From the reading I have done, this should normally be at aout 3-3.5bar. I have adjusted brew pressure to 9bar, but cannot find a reference to adjust pre-infusion pressure.

I was thinking of needing to reduce line pressure, but got given the steer that pressure going to the brewhead is from the boiler rather than the line (which made sense to me as it is heated).

Any bright ideas / direction? Or is 5bar ok?

thanks
Ben

[tucrazy]

Perhaps try tasting the coffee when pre-infused from the reservoir (should be about 2 bar from steam boiler) vs line pressure. Ideally, I think the pre-infusion pressure should be around 4 bar, but think 5 bar would be OK.

[Ben_S]

I had it running off boiler pressure for a couple weeks (about 1-2 bar). I changed a number of parameters at the same time, so difficult to compare changes in taste without significant effort. More interested in being able to adjust pressure as a brew parameter. I know there are various theories on pre infusion vs. taste impact, however I am keen to get the setup right in terms of recommendations that I have read.

[Ben_S]

Spoke to someone who repairs LMs and his view that the boiler pressure / preinfusion pressure comes from the line. So, I figured out that the PLV in the kit I bought was faulty. Went to Bunnings and bought a PLV with John Guest Fittings. Plugged it all in. Preinfusion pressure has dropped to 3.5bar. Looking forward to seeing if this influences taste tomorrow, but the bigger issue is the brewhead was leaking even when the machine was off. Will be interesting to say what the supplier has to say

[brendogs]

You may have a faulty brew solenoid which is letting pressure thru from the line pressure. Sometimes you can just replace the plungers depending on the condition of the seals.

[Ben_S]

don't think it is brew solenoid (but could be wrong) just think seals are shot from being under pressure for too long. Only been on line pressure for a month, so a bit frustrated, but will get to the bottom of it.