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Vacuum breaker not sealing: one-off events


viveur
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I've now had this happen twice. Machine (Expobar Leva DB) bought in 2017, first event in 2018, second event in 2020:

Steam boiler is heated on startup, vacuum breaker does not seal hence there's continuous venting of steam from the top, machine keeps heating until steam boiler pressure reaches 1.6 bar, safety valve triggers (I run to the kitchen and turn off the steam boiler). Some time later, I returned and turned on the steam boiler, and it works as expected (i.e. vacuum breaker seals, pressure stabilises in the usual range). Next day and thereafter, machine continues to work as expected.

This seems to be an issue with the vacuum breaker. Probably mostly random (if it happened twice), but maybe worth disassembling and cleaning*? Has anyone else seen something like this? Once is unlucky, twice is... a sign?

The pressurestat is configured for approx 1.1-1.2 bar - which is why I don't understand how the steam boiler could even reach 1.6 bar. HOWEVER the pressurestat and vacuum breaker are attached to one steam boiler outlet (so if the vacuum breaker is venting, perhaps the pressurestat sees a lower pressure), the safety valve is on a separate outlet that is also connected to pressure gauge and steam wand (hence sees the full boiler pressure). [Internal diagrams are online at: https://wiki.wholelattelove.com/images/3/39/OFFICE_LEVER_Parts_Diagram.pdf ]

 

* I'm planning to replace the vacuum breaker with one sporting a barb anyway: the current design distributes water all over the insides of my machine (during the time period that the breaker vents), and I figure the barb+pipe method from this thread might be sensible: https://www.home-barista.com/espresso-machines/vacuum-breaker-valve-causing-rust-in-my-machine-t41547.html

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This must be incredibly frustrating. I do sympathise with you: My La Pavoni had a similar issue: The anti-vac valve was stuck shut (sealed off) so the machine was not fully heating up - yes, you could open the steam wand and bleed it. I then replaced it with a brand new one, just to find out that every 2-3 months, it would not shut off properly and steam would escape. Thankfully on the La Pavoni things are rather exposed so giving it a knock with a wooden spoon always did the trick. 

How hard is your water? Have you taken the valve off to inspect and see if there aren't any calcification / dirt in there? 

Current: Lelit Elizabeth / Niche Zero / VST baskets / Distilled water + 100mg NaCO3/L

Previous: Gaggia Classic | Eureka Mignon | Rocket Cellini Evo | Profitec 700 | Profitec T-64 | Gene Cafe CBR-101 | Kinu M68 | Feldgrind 2 | La Pavoni Europiccola 2012

Also at: CoffeeTime Forum & Niche Zero Owners Group

 

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From what you say/ explain, the anti vac valve must close at some point or the pressure could not open the safety valve.

AS said above, disassemble the anti vac valve and check for scale , seat damage or seal damage ( not just a cursory look).

When / have you adjusted the P/stat ?  After a time they can take a set and not move freely / sufficiently. 

Take a note of the position of the adjuster screw ( in centre) . With the M/ch off gently wind adjuster screw backwards and forwards a few times, reset to original position and try M/ch. You will probably need to fine tune the setting to correct pressure.

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  • 4 weeks later...

Thanks for the advice everyone!

- Regarding water: I mix my own to approximately SCAA standard (i.e. I mix mostly RO with some tap water to get the right consistency). That said, I sometimes forget to purge the steam boiler (I don't use water from the steam boiler, so I have to rememember to purge it), meaning I might occasionally have quite a hard mixture inside the steam boiler. I do at least try to ensure the boiler gets filled with RO water after a purging (in other words: I turn off the machine, purge the steam boiler, put only RO water in the tank, let that fill the steam boiler) - but I don't really do that enough.

- Regarding cleaning the valve: I've just replaced it with the barbed variant, and had a look at the old valve: it does seem to have quite a lot of blackening on the boiler side, which doesn't bode well - it also smells a bit rubbery (I'm pretty sure I haven't gotten milk into the boiler - I also had a look at water coming out of the steam boiler: it looks and smells fine, but has a slight rubbery/plasticky taste). Left side is closest to steam boiler, I managed to cut off the top of the valve on the right:

IMG-5299.thumb.jpg.eca20af76ee310db7f45ddc590dd3607.jpg

There's no real use in cleaning this valve since it's no longer in use, but I'm worried what the inside of the steam boiler might be like if there's blackening like this - have others seen similar things? I'm wondering if I should do a larger scale strip down to see what the inside of the steam boiler is really like?

- Regarding PStat: it does seem to work fine - it regulated the pressure correctly the next time I turned on the machine, but I will monitor it closely in case it's actually just an early sign of impending failure.

 

And I'm now on the next adventure: like I said I replaced the vacuum breaker with a barbed variant (pipe leading to the drip tray, to avoid steam+water splattering over the insides). I can now hear a very faint hiss from the vacuum breaker area - very very faint - which seems to be at the joint between the vacuum breaker and the fitting it's attached to (the vacuum breaker is on a T-piece, which in turn sits on the steam boiler). I'm guessing I need to add some thread sealant, or teflon tape - or am I likely to have messed something up when fitting the new vacuum breaker? [I've only verified by putting a spanner over the joint, haven't tried the pipe-from-your-ear or mirror tricks yet.]

Edited by viveur
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If you are using the steam boiler you should run water from it regularly, failure to do this concentrates the minerals in the water . Not good.

 HISS. Just release the joint (s) wipe clean and apply 4 / 5 turns of P T F E tape . Keep it away from the very end of the fitting, you do not want any getting inside the pipe /valve.

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Thanks very much: 4.5 turns of the tape did the trick (first time round I thought I'd be clever and try 2 - which I soon discovered wasn't quite enough: there was still a tiny bit of hissing from one edge).

Now I've discovered that the safety valve is also hissing (I think that's new, I'm pretty sure it was only the vacuum breaker attachment that was hissing yesterday - but I might be mistaken). That should be a fairly easy replacement though - and probably not too surprising given I've had the machine for 3 years?

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