La Marzocco succession of vaccum breaker valves

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

#1: Post by Frenchman »

SInce I m researching how to rebuild my very old L193 valve, I found some info about the different variations that I thought may be useful to post. I also link to a few parts catalogs showing the internals of the valves whenever possible.

The L193 valve that many of us may have (it has a hex cap that really looks like a cap on one's head) is discontinued, and can be replaced using one or two options .Those options are documented in TB174. This technical bulletin discusses both the L192 breaker (a new swivel design), as well as their new B.2.029 SMA valve.

The swivel L192 is a plunger design with the same internals as the L192 it replacs, and the L193 before that. From what I can see in parts service manuals, it looks like LM has a complex L193 design (see Linea Mini V1.1 (2015/10) and V1.2 (2019/01) manuals, pp. 10-11, where it's actually called L192.01, but L193.01 on pp. 20-21). They then replaced it with a simpler one under a versioned L193.02 name (as seen in the GS/3 V3.3 (2019/10) and GS/3 V3.4 (2020/03) parts catalogs). The Linea Mini keeps the dual L192.02 and L193.02 naming (as seen in the Linea Mini V1.5 (2019/04) and Linea Mini V1.6 (2020/03) parts catalogs, pp. 10-11 and 20-21). And then they redesigned the L192 one more time (the L192.03), and changing thread size on the Mini. You know, just to make our life easier... (Especially given that they don't have the same clearance in the GS/3 for example; use the B.2.029 SMA valve or rebuild instead). The .01, .02, .03 suffixes are not always used by retailers, and even LM makes misakes. Also note that they kept the same names with different thread sizes (example).

All the L193 and L192 valves can be rebuilt. You can get the parts, order a kit (from LM presumably, and for ~$15 from Clive Coffee at the time of this writing for the plunger, Teflon seat, and O-ring), or simply replace the O-ring if the other parts aren't worn out.

The SMA valve seems to be a Fluid-o-tech thermostatic antivaccum valve. It doesn't seem to be that much less subject to failures than its predecessors, sadly. It seems to all be about the O-ring. Apparently there is an official and expensive rebuild kit but I couldn't locate it. It does it seem to be that someone documented the right replacement O-ring so far. And the black cap is reportedly fragile (it may get brittle with the heat inside the machine?).

The Linea Mini V1.1 and V1.2 parts catalogs (and older GS/3 ones, like the GS/3 V2.1 (2012/11)) show the oldest version of the L193 valve, the one with a cap. See e.g., pp. 10-11 of either version for an exploded view (with internals and references and names for everything). This thread and the 1997 repair thread it links to are good references for replacement/rebuild.

The GS/3 part catalogs, as well as the later Linea Mini (V1.5 and V1.6) ones, show exploded views of the now-obsolete L192 (under the names L193 and L192, depending). The GS/3 V3.4 part catalog shows the B.2.029 (pp. 36-37), albeit not in an exploded view.

Hope this helps someone in the future...
LMWDP #712
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#2: Post by Peppersass »

Great post. Thank you for doing the research and clearing up potential confusion about the different vacuum breakers LM has offered over the years.

I finally got around to trying the SMA breaker valve in my circa 2008 GS/3 AV. I've had an SMA breaker sitting in a drawer for about 2 1/2 years, waiting for my L193.02 vacuum breaker to fail once again. It hasn't failed in a long time - until recently, when the O-ring started to fail. I think it had been 3-5 years since I'd replaced the O-ring, plunger and Teflon seat, longest I can remember. I attribute this to keeping my cation softener charged.

Installation of the SMA breaker was pretty easy, though, as always, I had to remove the rear panel to get a wrench on the old breaker and tighten the new one. My GS/3 is quite old - the chassis supports are turned 90-degrees from the the way they're oriented in newer GS/3s (see photos below.) I don't know if this leaves more or less clearance for the breaker. It's always been a tight fit on my machine, especially after I noticed the screw holding the flow rate meter had come loose and retightened it. Anyway, there was plenty of room for the tubing to make a gradual arc and drop down to the Tee fitting that connects to the OPV tube and exhaust fitting over the drain box. Here's how it looked after installation:

Unfortunately, I was a little disappointed with the performance of the $100 SMA breaker compared with the $30 L193.02 (the internal parts of which can be replaced for a couple of bucks.) When I fired up my machine, the steam boiler pressure rose about 0.25 BAR above my selected idle pressure of 1.5 BAR. After cycling the steam valve once, the idle pressure dropped to 1.5 BAR and stayed there. I'll defer to the experts here, but I think this means not all of the air was evacuated from the boiler before the SMA valve closed.

I don't think this is a safety issue because there wasn't a big pop or blast when I first cycled the steam valve. It just seemed like normal steam operation. Also, as others have noted, about an hour or so after turning off the machine, there was a noticeable noise that I'm pretty sure was the sound of air rushing into the boiler when the SMA breaker opened. So the "vacuum breaker" function seems to be working.

I believe there's air in the boiler after warmup because the SMA valve is adjusted to close at too low a temperature. The specs on the Fluid-O-Tech site say it's open below 203F and closed above 210F, which seems low to me. I was able to confirm this by mounting the SMA breaker on the boiler using the A.5.003 L bracket used with the L193.02 breaker:

Sure enough, when mounted this way, with the SMA removed from direct contact with the boiler body, the pressure rose only 0.1 BAR above my set point after warmup. I'd like it to be zero, but I doubt that's possible with the SMA breaker. I can live with it.

I got the mounting idea from regold's post:

La Marzocco GS3, another way of assembling the SMA vacuum breaker

(Thanks, Rainer!)

One thing I like about this way of mounting the SMA breaker is that it's more accessible for service: it can be removed without removing the rear panel.

My version is oriented a little differently. Rainer's SMA points up, while mine points down. I did it that way so any water wouldn't have to travel uphill, possibly falling back into the SMA breaker or the A.5.003. Probably doesn't make much difference. I didn't shorten the tubing because if the SMA fails often, or if replacement parts aren't available when it does, I'll try the new swivel L192 version, for which I'll need the longer tube. That said, it's not clear whether the new elbow fitting will have sufficient clearance in my GS/3 (though the tube looks bendable), or whether the hex screws can be accessed and the swivel removed for service without removing the rear panel.


#3: Post by Corny »

Just got thought replacing the black plastic vacuum breaker on my micra.
LaMarzocco seemed to think they are only good for 6-9months. And don't recommend rebuilding them.
My micra is 10month old, and one of the internals spring was bent.


#4: Post by acatespresso »

hey peppersass, I'm trying to replace my SMA breaker now too. Did you have to disconnect the black housing with the tube to get to the SMA breaker? I'm unsure what to do after loosening the brass bolt connected to the black tubing.... turning it seems to twist the plastic tube in concerning angles