Rehabilitating the La Marzocco GS/3 vacuum breaker

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Peppersass
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#1: Post by Peppersass »

Other GS/3 owners may benefit from my recent experience rehabilitating the vacuum breaker on my GS/3 steam boiler:

A couple of weeks ago, I noticed a fair bit of hissing and sputtering coming from inside my GS/3. It sounded just like the sputtering that occurs before the vacuum breaker activates and closes off the steam boiler vent, so I was reasonably certain that the breaker was stuck in the open position. Removing the right side panel confirmed this: I could see where steam and moisture bubbling out of the breaker had coated a considerable portion of the inside of the rear cover with condensed water.

For reference, a photo of the vacuum breaker may be found at GS3cafe. The breaker is labeled "Q". The breaker in the photo doesn't have the rubber protective cap, which is now standard on the GS/3. The rubber cap prevents insulation and other debris from falling on the vacuum breaker stem, which can make it stick in the open position. In the photo, you can just see the top of the stem, which is fully retracted (i.e., in open position.)

Since the rubber guard cap prevents access to the breaker stem, I removed the rear panel by loosening the two phillips-head screws that secure it to the brain box and lifting the panel straight up. This allowed me to poke the stem with a long screw driver to reseat it (careful if you do this -- if the machine is on and warmed up, hot water and steam will surge out of the valve when you depress the stem.) After exercising the stem a few times, it seated properly and the hissing/sputtering stopped.

However, after a few days I heard occasional hissing and sputtering again, and by yesterday it was clear that the stem was starting to stick and would probably get worse. After consulting with the service department at Chris Coffee, I decided to remove and clean the vacuum breaker assembly.

First, I shut off the machine, let it cool, opened the steam valve to make sure any residual steam was purged, and removed the rear panel. I pulled off the vacuum breaker rubber cap and used a 17mm open-end wrench to unscrew the entire assembly (both the brass and plated hexagonal pieces shown in the photo.)

The vacuum breaker assembly is composed of a threaded brass cap with a hole for the stem, and a plated hollow barrel with threads at both ends. One end of the barrel threads to the steam boiler and one end threads to the brass cap. The two pieces were screwed very tightly together, so I had to put the brass cap into a vise in order to unscrew the barrel with a 17mm open-end wrench. Inside the hollow barrel are a plastic (delrin?) cylinder with a hole for the stem, the stem itself, and a rubber O-ring on the stem that fits into a depression in the plastic cylinder.

The cause of the problem was clear: there was a build-up of fine greenish residue inside the assembly. It appeared that the residue had partially coated the o-ring, keeping it from seating completely against the plastic seat. Residue on the stem and in the holes in the plastic cylinder and brass cap may also have caused the stem to hang up before fully seating.

Though only a very thin and dry coating, the residue looks suspiciously like the green "verdigris" found by Ken Fox and Shadowfax inside their GS/3 group heads. But since the steam and coffee systems are isolated from each other, I doubt that's where it came from. I think it may be the minerals that make up the alkalinity content of my cation-softened water (Ken has spoken of a fine powder left by his cation system.) I do wonder, however, if the greenish tint is caused by oxidation picked up from inside the tubes feeding the steam boiler. Conceivably, oxidation could have formed in the feed tubes while my "fire sale" machine sat in the Franke warehouse.

I took the valve assembly completely apart and soaked all the pieces in a solution of vinegar with a little salt. A few hours later the green stuff was gone. There was still a very thin coating inside the barrel and on the cap of the stem assembly, but I got most of that off with a combination of brushing and some copper cleaner. I thoroughly washed all the chemicals off the pieces before reassembly. I also put a very thin coat of food-grade lubricant on the O-ring and stem (and I mean very thin.)

After re-assembling the valve (used the vice again to make sure the two pieces were securely screwed together), I screwed it tightly back onto the steam boiler, closed up the machine and fired it up. After the machine came up temperature, there was no longer any hissing and sputtering.

I'll certainly keep an eye (or ear) on this and will report back if the valve clogs again.

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shadowfax

#2: Post by shadowfax »

Something to remember with vacuum breakers is that if you turn your machine off and on a lot, and that valve thus opens and closes a lot, you will likely clog the seal on the valve a lot more often, particularly with ion-exchange-softened water that has a high TDS. The reason, as I understand it, is simple: when the machine heats up, the water in the steam boiler starts to boil, and moisture accumulates all over the non-submerged parts of the boiler, in particular the vacuum breaker valve. As it tries to close, it sputters and spits—more water up there. And that water isn't sealed off inside the boiler. In fact, it's evaporated off as the boiler heats up. The water that is evaporated in this fashion leaves almost all its wonderful dissolved solids behind, right on the top of the breaker valve and all over the other areas that have exposure to the outside air.

Like water filling a crack in a rock slowly opens that crack as it freezes over and over again, gradually this arrangement makes the vacuum breaker valve seal take longer and longer to make as the machine heats up, and then eventually causes it to actively leak all the time. If you don't like it, you should consider either (a) switching to a filtration system that reduces TDS as well as hardness or (b) stop turning your machine off on a daily basis. If you don't do this, I think your fate is pretty much just pulling it on a regular basis (every few months) and rubbing the scale off. In any case, eventually you'll start having to replace the o-ring. I've heard silicon o-rings are the best to get.
Nicholas Lundgaard

DavidMLewis

#3: Post by DavidMLewis »

I'm actually rather surprised that the GS/3 has a vacuum breaker. When my Reneka Techno is heating up from cold, the firmware lets it partially heat (as determined by the temperature probe in the steam boiler), and then opens the steam valve as it's approaching boiling. I don't know whether it then closes the steam valve based on time or temperature, but it's open for roughly a minute, by memory. The system works well, and I would have thought it would be a common design in electronically controlled units like the GS/3.

Best,
David

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dsc

#4: Post by dsc »

Hi guys,

what if the valve doesn't open/close due to a fault? say it's a stuck relay or simply there's something wrong with the solenoid. Sure a vacuum breaker can fail, but it's dead simple and I think the probability of it failing is much less than what you've described.

Regards,
dsc.

DavidMLewis

#5: Post by DavidMLewis »

On the Techno, the steam valve is controlled electronically rather than by a mechanical valve. So the solenoid has to be there anyway, and eliminating the vacuum breaker removes another part and point of failure. And if the steam valve doesn't work, you really don't care whether the steam boiler has air in it, because you can't use it.

Best,
David

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Marshall

#6: Post by Marshall »

Peppersass wrote:First, I shut off the machine, let it cool, opened the steam valve to make sure any residual steam was purged, and removed the rear panel. I pulled off the vacuum breaker rubber cap and used a 17mm open-end wrench to unscrew the entire assembly (both the brass and plated hexagonal pieces shown in the photo.)
Thanks for the guidance, Dick. I replaced mine this evening. The hissing has stopped.
Marshall
Los Angeles

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civ

#7: Post by civ »

Hello Peppersass:

I had the same problem come up with my Cimbali D/1 after a few days' use, probably because it's previous owner had it sitting unused in a corner for a couple of years and it never saw any maintenance. Did the same as you and replaced the old 'o' ring with OEM issue acquired locally, although the original was still soft and supple. The problem came up again a few days later so I went through the procedure again but replaced the 'o' ring with a silicone one. It's been a few months without a hitch now.
shadowfax wrote: I've heard silicon o-rings are the best to get.
Indeed.
Paul Pratt did a test on the commercial machines he services and found that silicone 'o' rings are the ones that seal best and last longer. I'd risk that the 'o' rings in these valves are standard size and not hard to get from an industrial supplier, but you may have to buy a couple of dozen like I did.

Read here.

Now all the 'o' rings in use inside my Cimbali D/1 are silicone made.
I was also luicky to find a fellow who had the right molding to make me a set of silicone PF seals for it.

Cheers,

CIV

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JohnB.
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#8: Post by JohnB. »

The anti vacuum valve used on the Speedster comes standard with a silicon o'ring which seals against a teflon seat. As you can see in the photo below it is mounted remotely to keep it away from direct heat & normally there would be a drain line attached as on the steam boiler safety relief valve in the background.

Image


Even so it can still act up as mine did last week after draining the steam boiler to remove/descale the heating element. After both boilers were back up to temp I could hear the quiet gurgle of water entering the drain line. Traced it back to the a/v valve spitting out 1-2 drops of condensed steam every 3-4 seconds. Whatever was preventing the valve from sealing passed through by the next morning so I didn't have to open it up & clean it this time.
LMWDP 267

greedus

#9: Post by greedus »

civ wrote:Hello Peppersass:

I had the same problem come up with my Cimbali D/1 after a few days' use, probably because it's previous owner had it sitting unused in a corner for a couple of years and it never saw any maintenance. Did the same as you and replaced the old 'o' ring with OEM issue acquired locally, although the original was still soft and supple. The problem came up again a few days later so I went through the procedure again but replaced the 'o' ring with a silicone one. It's been a few months without a hitch now.



Indeed.
Paul Pratt did a test on the commercial machines he services and found that silicone 'o' rings are the ones that seal best and last longer. I'd risk that the 'o' rings in these valves are standard size and not hard to get from an industrial supplier, but you may have to buy a couple of dozen like I did.

Read here.

Now all the 'o' rings in use inside my Cimbali D/1 are silicone made.
I was also luicky to find a fellow who had the right molding to make me a set of silicone PF seals for it.

Cheers,

CIV
Any news on where to get a couple of these silicone O rings for the GS3?
Mine is hissing and needs replacement.

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erics
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#10: Post by erics »

Any news on where to get a couple of these silicone O rings for the GS3?
Yes.

McMaster-Carr P/N 9396K12 or $3 for a couple from me.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at rcn dot com