La Cimbali M32 Dosatron problem with water

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by Paqo »

Hello everyone
Does anybody here can help me sorted out why my coffee machine spits the water through the valve when it is building pressure at some point?

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#2: Post by HB »

That looks like a vacuum breaker; see How are vacuum breaker valves supposed to work? and Can someone please explain false pressure? If the vacuum breaker closes once the steam boiler pressurizes, it's working as designed. If it continues to spit droplets, then it may have scale buildup preventing it from closely completely. When is the last time you descaled?
Dan Kehn

Paqo (original poster)

#3: Post by Paqo (original poster) »

That's a good question. I was repairing electronic board for the customer and was trying to get it back to live.
So you mean that the valve needs to be cleaned or changed? Or the whole system should be descaled?

So actually water drops are coming from the top of the valve where the screw is.

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#4: Post by HB »

Let's not overthink this: A vacuum breaker is a valve with a weighted piece that is pushed up by escaping steam when the steam boiler heats up. This lets air escape so the steam boiler is filled with saturated steam, not a mixture of steam/air. When the steam boiler cools, the weighted piece falls, opening the steam boiler to the atmosphere so it depressurizes; without this valve, the steam boiler would be under vacuum since the water volume decreases as it cools.

These simple valves may stick closed, leading to "false pressure", or they may fail to close completely, leading to drips/slowly escaping steam. Based on what you've described, your task is figuring out why it's not closing completely. Cleaning them with white vinegar usually resolves the problem, but the sealing surfaces can wear too, in which case it's a repair/replace situation.

There are hundreds of prior discussions if you need more guidance; search on "vacuum breaker" or "false pressure". Here's a handy photo of a vacuum breaker. It's not the same as your La Cimbali, but they all work on the same principle I explained above. The item labeled (1) is the weighted piece I described and it seals against the item labeled (3); the item labeled (2) screws into the boiler and is capped by the unlabeled item.

From Vacuum breaker - serviceable?

I asked about descaling because that's the most common cause of vacuum breaker (and other) failures. Here's an example of what can happen:

From Is there any way to (partially) descale a commercial espresso machine without pulling it apart?
Dan Kehn

Team HB

#5: Post by JRising »

In that type of sight-glass topped vacuum breaker you'll often get spitting while the boiler lets out its air. There is a tube from top of boiler to top of glass, another tube from bottom to bottom, of course. Because the water in the boiler is heavier than the air, of course most of the air/steam mixture is blowing out along the upper pipe and there's no movement in the lower. Thus, when a splash gets into that upper tube, the level in the glass is disturbed by the pressure change, the sight-glass water rises high enough to be caught by the air/steam flow of the upper tube and it spits out.

There's nothing wrong with the valve if it seals up once the boiler is fully boiling.
If the spitting is really bad, it may be that the boiler is over-filled, although if I'm seeing it correctly in the photo, it's fine.

Paqo (original poster)

#6: Post by Paqo (original poster) »

So I changed sealing and will test it soon as it seems to be pretty clean inside...

Paqo (original poster)

#7: Post by Paqo (original poster) »


Paqo (original poster)

#8: Post by Paqo (original poster) »

So it looks like machine is not leaking anymore but I have another issue.
Water is almost not coming (few drops) from both group heads

Please check video :