joey Senior Member Joined: 24 Dec 2002 Posts: 332 Location: madison, wi Expertise: I love coffee
Espresso: Oscar Grinder: Mazzer Mini Drip: Chemex Roaster: Behmor
Posted Wed Mar 28, 2012, 4:42pm Subject: 3 way valve works; just not during backflush
I just bought a used oscar that the owner took great care of. Ive had it for a couple weeks now and did my first backflush. Put half a tsp cafiza in blank disc, turned on 8 seconds, off and splash went the three way. Second time it was much quieter splash and shorter. Third time there was no discharge. Handle locked in tight i got it off with some spray from the group. I rinsed and did it with water a few times with the same results. Hoping it was a little buildup i did another round with cafiza and had the same issue. I did some pulsing of the brew button, opened steam wand, coudlnt get it to discharge. I just pulled a shot and the valve works fine. Has anyone ever had this issue? What do I have to do to fix it?
Posted Wed Mar 28, 2012, 5:58pm Subject: Re: 3 way valve works; just not during backflush
The difference between the two events is that after brewing the coffee will relieve some of the pressure through its permeability. My guess is that the 3-way is sticking because of the higher-then-normal pressure from the blind filter. Solution? I would think a removal of teh 3-way for inspection and possible external cleaning of that as well as the grouphead itself may be in order. But before taking out the tools, I would try a prolonged backflush-detergent soak. Try turning on the brew cycle as you normally would to backflush, but turn it off before the pump reaches full pressure, repeating that a few times, and see if that can get some detergent through the 3-way.
Posted Wed Mar 28, 2012, 11:06pm Subject: Re: 3 way valve works; just not during backflush
If I'm reading your description correctly, this sounds like the same thing that had me scratching my head once. When you lock a blind filter in (and it is empty) and then hit the pump, it creates "AIR pressure" as the water is pumped in and the air that was trapped in there has no place to go. So the first time you get a really big WHOOSH because all that compressed air blasted everything when the 3-way released the pressure. Now there is a lot of water left sitting in the blind filter so the second time you don't get quite as much WHOOSH and the third time it is almost all water (which doesn't really compress) so there isn't any WHOOSH at all.
That's what it sounds like to me --- and if so, it seems perfectly normal to me. You could test by just unlocking the PF and seeing how full the blind basket is - dump half of the water/detergent into a cup and then lock the half empty basket back in and backflush again and see if you get the whoosh.
joey Senior Member Joined: 24 Dec 2002 Posts: 332 Location: madison, wi Expertise: I love coffee
Espresso: Oscar Grinder: Mazzer Mini Drip: Chemex Roaster: Behmor
Posted Thu Mar 29, 2012, 3:57pm Subject: Re: 3 way valve works; just not during backflush
Andy, I see what you're saying, and it does make sense. But regardless of the pressure being from air or water, once i release the brew button, shouldnt the three way release the excess pressure into the drip tray? From what i've read and all the backflush videos i've seen, the three way should release the pressure once the brew button is released. And i see what you're saying about the sound, but its not just the sound, the problem is the fact that the three way is not releasing.
Posted Thu Mar 29, 2012, 4:04pm Subject: Re: 3 way valve works; just not during backflush
are you saying that when you unlock the portafilter with the blind basket then it spurts out all over the place? That is what would happen if there were pressure inside the blind basket that wasn't released by the 3-way valve.
If the blind basket comes out without any burst of pressure when you unlock the PF, then there was no pressure inside there that wasn't bled off by the 3-way when you turned off the brew switch. But if there is pressure trapped in there and it bursts out when you unlock the PF, then the 3-way valve isn't releasing the pressure (as you suspected) and you would continue troubleshooting it.
What happens now when you lock an empty blind filter in there and start the pump? Do you get a whoosh and a release when you stop the pump? (the first time you try - starting with an empty blind basket)
Water* can have pressure on it ... but air compresses and when you open the container, that compressed air quickly expands back to its original size (the whoosh and the force of the backflush back through the 3-way). Water doesn't really compress (water usually has tiny air bubbles though and those air bubbles can compress) so if there was nothing but water in the sealed container and it was under high pressure, when you open the container the amount of expansion would be very, very slight (because it didn't get much smaller from its original volume when you put it under pressure) so you wouldn't notice much in the way of liquid bursting out (and you also wouldn't hear the sound of the air whooshing back to its original volume because there wouldn't have been any air)
(* Note: liquid water I mean --- when water expands into steam, that steam can be compressed back into liquid water again)
joey Senior Member Joined: 24 Dec 2002 Posts: 332 Location: madison, wi Expertise: I love coffee
Espresso: Oscar Grinder: Mazzer Mini Drip: Chemex Roaster: Behmor
Posted Thu Mar 29, 2012, 4:53pm Subject: Re: 3 way valve works; just not during backflush
yes, when i unlock it water spurts out, but only after the third time i backflush for 8 seconds each time. if i backflush just once, it releases just fine, second flush and it releases some, third time no release. if i put a blind in and run it for 8 seconds, the three way releases just fine. the only time there is trouble with it is when i sequentially backflush. the three way works fine when i'm brewing espresso as well.
Posted Thu Mar 29, 2012, 5:13pm Subject: Re: 3 way valve works; just not during backflush
As a test, would you please try three backflushes in a row, but unlock and empty the blind filter in between each so each of the three backflushes start with an empty blind basket. Does it release all three times or does it get worse on the second again and no release on the third?
If it does release all three times ... the next test would be to fill the blind basket with water before you lock it in and notice if you get a release then.
Posted Thu Mar 29, 2012, 10:51pm Subject: Re: 3 way valve works; just not during backflush
sounds to me like it's working normally.
It is normal to not get much backflush when the blind basket is full of liquid - because the liquid cannot compress under pressure - if it doesn't compress under pressure then it will not expand when the pressure is released. But air does compress and will expand when you remove the pressure.
When you pull a shot, the coffee grinds can compress and expand (coffee grinds are light and fluffy, they are mostly air/co2 gas pockets left from when all the moisture was roasted out of the beans) and the co2 gas is extracting into the liquid (gas bubbles make the liquid foamy and that is compressible) so that's why you get the expected backflush of pressure releasing when you stop your shot. And there is probably some spring to the filter basket too that bounces back when the pressure is released.
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