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Water volume variations
Recently the espresso output of one of our machines (La Cimbali M39 Dosatron) are varying considerably. What could this indicate? A partially faulty flow sensor?
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14 Replies
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It could be several things. Water system pressure, solenoid valve, Timer circuit, and of course the big and common one, The user. Grind and tamp have to be dialed in for every new roast. And with the global problem getting beans of a consistent quality, don’t rule out that that may be your problem. All Roasters have had to drop back on their bean standards to just be able to supply the market. The growers have a heat and water problem. The buyers and shippers can’t get containers to ship or load due to Covid. One supplier actually bought a bulk ship and is shipping their beans bulk. So you can bet everyone is cleaning out the corners to fill demand.
Wire a visual indicator to the valve and check with a stop watch for variation of the time. Watch the pressure gauge of the pull. And if using multiple grinders and roasted beans, each has to be dialed in . Make sure to check the burrs to see if they are worn out and not giving a consistent grind.
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Water pressure is very high in the building. I’ve already ordered a reduction valve. Is 3 bar ok, or should I set it lower?
Solenoid valves (various 24V and 230V) also ordered. Would the valve you’re talking about be pn 533-795-510 on page 9 or pn 533-893-300 on page 8 in the attached document?
I’ll hook up a data logger to the solenoid and record for a full business day, and see if I see any fluctuations.
Timer circuit would be the pcb(?), so hopefully it’s ok.
New burrs are also ordered. We only have one grinder for this machine, but the baristas aren’t confident adjusting the grinder. I tried to school them many times, but they are scared of messing up 🙁
70062-M39.pdf 3 MB PDF - Click to view Options Copy Download Link
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Generally when you set up one of these machines there is a filter setup for the machine. The filter could be in need of replacement.
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We don’t have a filter (very soft and pure water in Norway).
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I did a small bit of research on this machine since I’ve never seen one. I don’t know what configuration yours is, since they can add Bluetooth, grinder dosing, payment systems to it, but it does have a dosing meter. DV on the hydraulic chart. They can be very fussy if any particles get into it. They are usually like a water meter that turns inside and counts the pulses. Not sure if it’s cleanable on yours, or if it has to be replaced. But I believe that’s where your going to find the problem.
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It’s totally cleanable. Top lid goes off, impeller goes out and all that’s is the chamber.
I’ve also ordered a few extra dosing lids (which contains the electronics/hall sensor), since these are one of the parts of any coffee machine which is totally un-serviceable. I try to keep a few of every part that I can’t MacGyver back to life (until a replacement arrives).
I think the dosing meter counts pulses relatively good (I’ve made a few coffees with the machine, and it outputs fairly the same each time.). But perhaps the impeller magnet is getting weak, hall sensor is getting old or there is debris inside the dosing chamber, they could all mess up readings, but perhaps not every time. I’ll acid treat and steel wool (finest 0000) the chamber and see if that helps. Perhaps also clean the pcb with isopropaol (in case dust along with humidity creates some creepage).
I have to say, I’m very grateful for the help I’m getting and this excellent forum.
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The place to look for interference is the bearing and the side clearances. Especially if they have any plastic that can warp.
You have a data logger! sweet! That means you can determine if it’s a solenoid or flow meter with certainty.
The specs I found on it say less than 6 bar for supply. Because of the sudden stop that solenoid valves do, water hammer becomes a concern. That means line size and velocity has to be looked at. Something to be aware of. I actually added a tee on the inside of one and a stand pipe due to the hammer. If you just lightly feel the line through a cycle, You’ll know if it hammers.
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From the attachment I sent, which is the solenoid I should be looking at?
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I personally would not replace anything until I was certain of the problem.
Now for me to have a feeling of what you have I need more information.
How many heads do you have?
Early or late Dositron?
Is the problem with one head or all heads?
What is the boiler temperature and pressure?
Does the boiler level rise beyond normal or pressure drop during a shot pull?
Does it only happen after the machine sets idle for a bit of time?
The reason I ask all this is because there are many variables that can cause a deviation of shot. Like if the boiler is a bit on the high side, the heat exchanger behind the head may get hot enough the flash steam during venting. Causing a steam pocket that is compressible inside the heat exchanger. Metering I believe is done on the supply side of the heat exchanger. The line that feeds the head just displaces the brew water in the heat exchanger. Each head has it’s own heat exchanger and a dip tube to pull from the bottom.
Now they use a common pump for all functions. and a diverter valve to either send water to the head or boiler. Boiler should have priority. If boiler pressure drops or level rises more than normal, I would check the diverter valve. The other thing I see is the bypass needle valve. Have you ever had to clean any of them?
Let me know what you find.
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3 heads.
Late version i think, since ours have digital pressure sensor (the old have pressostat).
I’m not sure – i’ll ask the operators (and it’s a good question, since if it’s on all heads, it wouldn’t indicate a dosing meter, since each head has individual meters).
I think I saw 1.2 or 1.3 bar pressure.
Boiler level – I need to ask the operators again, or pull some shots myself and observe everything you ask for.
Idle or not – I need to ask them this too.
In januar 2020, I disassembled almost all pipes, valves, boiler, etc and did a thorough acid treatment. But I didn’t touch the pump head or valves close to the pump.
Where in the parts diagram do I find the bypass needle valve? And diverter valve? Then I can say if I remember cleaning them.
I meant which solenoid I should put my data logger to monitor? Not to replace it, until I know it’s faulty.
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Your going to want to monitor the group head solenoid first. Then the diverter valve. ( ie the valve that sends water to the boiler or the flow meter lines) You also have a double line from the flow meter to the group head. on that line is a flow control you set with a screw driver and a pressure restrictor valve that opens when the mixing valve resistance is to high. I believe it is to lower the shot temp to ideal temp for you blend of coffee for a flavor adjustment. it injects a small amount or water at the head solenoid and the the injector valve supplies the heat exchanger tube.
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Ok. I’ll do that.
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oh, do you have a tech card to insert for troubleshooting?
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I don’t. But I read some time ago, that card is the same as flipping one of the dip switches on the pcb (to access setup meny, define number of heads, steam system, heating element power, etc).
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