In this section of the website, /downloads/ , there are Linea manuals that would be worth your time to download & read. Specifically, have you adjusted the expansion valve as previously advised?

The 2.0 bar inlet pressure is fine as long as it is a reasonably regulated pressure. Why did you install a check valve between the filter and the pump? There should be a check valve on the discharge side of the pump - that is sufficient. It would also be nice to have a readily accessible shutoff valve (ball-valve) right where the water line connects to the machine.

If you simply flush water through the group, the brew pressure gage should indicate 9.0 bar or wherever you have it adjusted to on the pump.

I also have observed the behaviour of the pressure gauge while in "idle" state. After switching the machine and heating on the pressure goes up to 12.5 bar. After a short time it drops back to around 2.5 bar. This takes around 1 min. Then at a certain point it raises up to 12.5 again pretty fast (around 20 sec) where it stays for a couple of min before it starts dropping again. Is this normal for a LM Linea?

Under machine idle conditions, we are dealing with the thermal expansion of an incompressible fluid (water) in a closed system. Pressure gage readings are essentially meaningless. However, what is important is that the expansion valve be adjusted according to the manuals I previously linked to.

Mac18 wrote:I only have around 2 bar pressure after the water filter but I guess that should do it?

Have you considered bypassing the water filter and seeing if that isolates the problem?
Could be that your water filter isn't providing enough flow (regardless of pressure). If that fixes the issue, then concentrate on getting a beefier water filter that can provide better flow.

Hi

I have made a video of the strange brew pressure dropping which you can find here: http://vimeo.com/28583588

If you listen carefully, you can also hear the strange squeaking noise. Does someone have an idea?

And sorry, of course my check valve is before the water filter. After the pump is another check valve. The expansion valve is properly set to around 12 bar. It starts leaking at around 12 bar and the pressure sometimes rises a bit over 12 bar, maybe 13. I don't think that is a problem.

The water filter is new and I had this problem before. I have another manometer before the water filter and it also only shows 2 bar. But I live on the 3th floor of an old house. Guess that's normal.

Thanks,

Marco

Bar does not equal flow.
you can have a 2 bar inlet which gets you 1 tsp in a minute, or one that gets you gallons. A flow restriction, such as a filter, may not reduce pressure but may reduce the flow.

What happens if you bypass the filter?

Hi Allon

The water filter is relatively new and I had the exact same issues without the filter. But at this time, I also had no inlet because I ran the machine out of a bottle. So I'll maybe give it a try.

I have measured the flow rate at the group head:

In 10 sec I get 125 ml (4.22 oz) with the pump on. In pre-infusion mode (solenoid valve open and only inlet pressure, no pump) I get 57 ml (1.93 oz) in 10 sec. Are those figures ok?

Cheers,

Marco

The gage installed on the Linea reads brew boiler pressure not brew pressure but . . . they differ by only a couple of tenths during actual brewing. The drop in pressure you see on the gage is normal. The "screeching" sound you hear on pump startup is not. I would suggest you remove the checkvalve that is on the suction side of the pump.

Your freeflow is high - ~750 ml/min - seems like you have a larger gicleur than most. I am not aware of any standard size for LM Linea but GS3's have 0.60 mm and their flow is ~ 500 ml/min. According to their parts catalog, gicleurs range from 0.60 to 0.80 mm and it is always possible that you have something else or nothing.

Is the preinfusion mod something you did - I thought 1 groups did not have that option?

I was considering that the flow from the filter might not be enough to keep the pump fed, but that appears not to be the case, I guess. You hadn't mentioned that you had the same problem without the filter before.

Seems a little fast; There's a great thread here:

Flow rate of a rotary pump espresso machine

Hi Erics

By suction side you mean the "input" side of the pump? Hmm, I don't have a check vale on this side of the pump (well actually there is one before the water filter, but the problem started before I put it there), only on the "output" side. I will remove this one and try to clean it. Hopefully it helps.

I have changed the gicleur to a 0.6,mm a couple of weeks ago. Before I had the original gicleur in place and the flowrate was even higher  Could that indicate a problem with the pump or the pump motor?

Yes, I added something like a manual preinfusion mod switch which basically allows you to break the power circuit to the pump motor. So I can open the solenoid valve without starting the pump.

If the "problem" (the "screech") also occurred prior to the installation of the check valve (before the water filter) then, well, OK . . .. DO NOT remove the check valve on the output side of the pump - well, to clean & reinstall is certainly OK.

I believe your "screech" problem will be cured with removal of the check valve before the water filter - realizing what you have said .

Could that indicate a problem with the pump or the pump motor?

I don't believe this to be the case but I would be interested in the nameplate data on your pump and motor.

In the link that Allon referred to, you will see that measuring a 10 second flow is not favorable to me - I prefer something more like 30 seconds and jot this value down in the manual and date it. 0.60 mm gicleurs are not always 0.60 mm and small differences here can change the flow by a large amount. I do not have the personal experience to say "use a x mm gicleur on the Linea" but going even smaller is certainly an inexpensive trial.