Hi

I have two issues on my LM Linea 1 Group AV (1996) which I can observe at the pressure gauge. I've bought the machine a couple of months ago of a private sale. Since then I'm running the Linea directly out of a 5 liter bottle without flojet or such a thing. The machine is generally in a very good condition but I've noticed a couple of spare parts, which are not original, but from Nuova Ricambi.

The first issue is that the needle of the pressure gauge is fluctuating. The intensity of the fluctuation varies according to the pressure on the grouphead. If I tamp really heavy or even use a blind basket the fluctuation is minimal. If there is no portafilter installed the fluctuation is maybe +/- 0.5 bar. I did already know of this issue when I bought the machine but I want to fix it now. Even though the previous owner said the pressure gauge is LM original, it looks like a spare part to me. Has someone an idea what the problem could be and how I could fix it?

The second issue is something I only noticed a couple of weeks ago. At once, the pressure gauge started to behave strange when I start the brewing. Before I start the brewing the gauge shows something between 9 and 12 bar. Now when I start the brewing the pressure should drop to 9 bar, but in my case the pressure drops to 3-5 bar, you can see a jerk going to the water tube which goes to the pump, and then the pressure rises to the 9 bar. This process takes about 0.5 seconds, but it is very good noticeable. This then happens all the time when I start the brewing until I remove the tube from the water bottle to clean/refill the bottle and some air gets into the tube. The next time when I start the brewing at one point the pressure gauge shakes heavily for a second, and then everything is fine... for a couple of days. Any idea? Could it have something to do that I don't have the 2-3 bar pressure from the plumbing?

Cheers and thanks for your ideas,

Mac

I'm the first to admit I'm no expert on this. But it sounds to me as though you are losing the prime from the water source to the pump. The pump pressure drops then recoups when water is drawn back to the pump when running. Most rotary pumps are not happy and do not work very well when trying to draft water from a source. That's why people use flojets and pressurized water sources. Some have one way or three way valves to combat pour over or plumbed in water supplies. I think most of your troubles would go away with a water source with a regulated pressure. Not much is needed but some. But don't mistake- those pressure gauges are telling you something and not that they are broken. Id put a pressurized water source on there and see where it takes you.

Mac,
Just for fun you should check the expansion valve to see if it is leaking. This is the component that limits pressure to ~12 bar. If it leaks before 12 bar then it needs cleaning. Also make sure there is a one way valve on the output of the pump.

About you pump and reservoir: All rotary vane pumps are differential pumps. Meaning that the pump is rated for a particular pressure with a stated inlet pressure (i.e. if inlet pressure is 2 bar and outlet pressure is 9 bar then the pump is creating 7 bar). The higher the inlet pressure the less the pump has to work (for a given pressure). These pumps can operate with a wide range of inlet pressures, even less than "0" or negative pressure. If the pressure is too negative then you will never be able to reach your desired pressure. In the case of La Marzocco machines, the motor/pump is external. If the pump is sitting on the same surface that the water reservoir is sitting, then you will almost always have "0" pressure or greater. For other machines some have the pump inside the machine. In this case the pump has to overcome the pressure due to the height difference from the inlet of the water hose to the inlet to the pump.
Most all LM machines at tradeshows are run with a 5 gallon water jug and I personally have one at my house that I have been using for several years. Additionally David Schomer uses water reservoirs in his bar to avoid the pressure changes in the city water lines. I think he has been doing this for 15+ years.


Bill C

Even though the previous owner said the pressure gauge is LM original, it looks like a spare part to me. Has someone an idea what the problem could be and how I could fix it?

If you take a look here - La Marzocco - Linea 2AV - Rebuild - you'll see a pic of an LM pressure gage partially undressed. If I remember correctly (and that's iffy), the little coiled spring serves to dampen out some fluctuations in the needle. Perhaps yours is broken. But, even if that be the case, there is little you can do about it short of taking the gage to a "fix it laboratory". These "fix it laboratories" are scarce nowadays but they could fix this and calibrate your gage in a very short time frame. Unfortunately, those $ equal or exceed the cost of a new gage.

Whether the existing gage is equivalent to that originally supplied on your Linea would be very tough to determine without an autopsy - maybe even multiple disassemblies. The gage in the pic I linked to does look pretty good.

What is the nameplate data on the pump you currently use? While I certainly agree with what has been posted re the pump taking suction from a bottle, you could always buy a simple plastic container, drill a hole through the side near the bottom, and rig it such that the pump always has some positive pressure on the suction side.

Billc wrote:Mac,
Just for fun you should check the expansion valve to see if it is leaking. This is the component that limits pressure to ~12 bar. If it leaks before 12 bar then it needs cleaning. Also make sure there is a one way valve on the output of the pump.
Bill C

I agree with Billc to start here and check the expansion valve, and clean it (soak in citric acid) replacing the rubber seat. (this may be nearly impossible to find as most places only sell the expansion valve as a unit, and not as parts) I had a similar issue with my HX machine (Quickmill Anita), and replacing the seat has been one of the two suggestions by service techs. If the unit is older, the pump may need to be cleaned, although they say descaling is not necessary because the water in the pump is not heated, I did find that mine was scaled over with something, so I sent it out to be rebuilt, for $45 including shipping, and less than a week's turn around.

I'm currently rebuilding a Linea (the link Eric sent you is my thread) If you need more photos of the broken gauge I can send them to you, but if there are issues with that, you are better off (in my mind) just buying a new one.

Just a few suggestions.
-Justin

Hi

Firstly I would like to thank your help and ideas. I had a very busy week and didn't have the chance to do any work at my Linea. But in the next week a friend will pass by and and properly plumb my Linea. The problem with the fluctuating gauge already existed when the machine was plumbed at the previous owner's home. So I guess it must be something wrong that has noting to do with my 0-pressure water tank I'm thinking of replacing the gauge. Justin, could you send me a close up photo of you new gauge? Is it the new LM gauge version or the old one?

The pump is a fluidotech PA01504 http://www.fluidotech.it/Pages/en_po_500_1000.aspx, the motor isn't important I guess!? I have my water tank ca. approx 10 cm above the pump, but the tube has to go up and out of the tank first before it goes down. Maybe that's the problem?

Cheers and thanks,

Marco

Mac18 wrote: Justin, could you send me a close up photo of you new gauge? Is it the new LM gauge version or the old one?

Sent you a PM.

Marco,
If the water reservoir is at or above the pump it is OK. Since the inlet hose goes from the pump up some amount and then down, presumably the same amount, then the pressure difference is about zero. The amount of water going up is about the same weight as the water going down so it averages to about zero.

Bill

Hi,

Last week I finally got my machine properly plumbed. First I thought, that the issue with the brew pressure shortly dropping to 3-5 bar when I start the brewing is fixed, but after a couple of shots it happened again So I'm not sure if it really has something to do with losing the prime from the water source to the pump. I only have around 2 bar pressure after the water filter but I guess that should do it? I also have a check valve installed between the water filter / pump. Any other ideas? I will do a short video and post it.

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?

Thanks for your help,

Marco