Modification of an anti vacuum valve to make it splatter free

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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#1: Post by legrunt »

So I have just experienced the (apparently) common issue of a hissing anti vacuum valve. After going through the usual opening and cleaning/o-ring replacement, I was taking a good hard look at the workings and intent of this valve.

Correct me if I am wrong, but the main and only function of this valve is to allow the build up of pressure within the boiler when heating up, while also to allow the boiler to cool down completely when shutting down without causing any implosion damage due to vacuum being created when all the steam condenses back into water.

With that in mind, looking at the way they work, the plunger/pin/piston is freely floating in the chamber below the sealing surfaces, and pressure building up below the piston needs to reach a certain speed before it is able to lift the piston pushing the two sealing surfaces together, right? And it is during this build up of velocity/pressure where the spitting/splattering happens.

So, why doesn't someone just put a light spring below the piston, such that any and all flow out of the valve is stopped during the heating up process, while allowing the slight vacuum created during cooling down to suck air in, preventing vacuum related damage?
This essentially makes this a one way valve.

Alternatively, use a U shaped copper tube coming off the top of the boiler to mount the valve upside down, essentially using gravity in place of a spring?

The only reason not to do this, as far as I can think, is that somehow during the splattering/spitting phase, air is being allowed to leave the chamber, ensuring that the volume is filled only with steam, but I think that the steam wand purge that everyone practices before steaming milk would be enough to purge any remaining air in the boiler?


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#2: Post by Jeff »

Another function is to let the air in the boiler be replaced with steam. If you don't bleed off the air, you can end up with "false pressure" impacting your boiler temperature.

One of the ways that I've dealt with the sputtering is with a version that has a barb for some (silicone) hose that I can run somewhere safe, like the drip tray or reservoir. I put a small hole in it somewhere if it is going to sit in water so that the vacuum doesn't draw it back into the boiler as it cools. It might be OK in the reservoir. I wouldn't be happy drawing up water from the drip tray.

Here's one that Chris' Coffee sells. It may not be the right one for your machine, but at least it gives a visual.

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#3: Post by Mike-R »

Jeff's answer is spot on. Note that many higher end machines come stock as Jeff described. As far as I know they all go to the drip tray or drain, not the reservoir, for reasons that Jeff explained.

You can mod as Jeff suggested, but it's not strictly necessary. When the sputtering occurs, the boiler will be hot enough prevent steam vapor from condensing and will quickly evaporate any water droplets that come out. So there shouldn't be any concern that it could promote corrosion. And the water droplets are condensed steam (i.e., distilled water), so they shouldn't cause any mineral buildup on top of the boiler. I'm not trying to talk you out of the mod, just letting you know that your machine doesn't have a design flaw.

If you do the U-bend mod and purge with the steam wand, you will just have to wait a bit longer for the temperature to come up before using the steam for drinks. But I suspect there may be a problem when you cool down the machine. The U-bend may trap some condensed water while the machine is cooling down. Then when the boiler pressure starts to pull a vacuum, it may allow the water to drain out onto the boiler. Since the boiler isn't that hot any more, it may not evaporate very quickly. It might be fine, but why take a chance with corrosion.

legrunt (original poster)
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#4: Post by legrunt (original poster) »

Ok, thanks for the insights.

I've ordered some barbs with female ends that i hope will be able to replace the top half of the anti vacuum valve... Some tubing, and some t joints. If all fits, I'll splice into where the pressure vents from the 3 way into the drip tray.

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#5: Post by stefano65 »

There are now days on the market several options for anti-vacuum valves more splatter free friendly compared to the "old" traditional one,
we cover few of them on one of our youtube videos,
the silicone barbe is logically the best as long as you have a "tee" or "Whee" fitting to attached the drain to or,,,,,,,,,,,, places the tube higher to create a level so water/splatter swill not go all over the places,
some have as well lesser splatters with different designs and one with a little guard,
the other consideration:
the "traditional old" one is very shallow, the barb is quite taller and to consider is the additional curving of the silicone tube, some are in between sizes.
Stefano Cremonesi
Stefano's Espresso Care
Repairs & sales from Oregon.