Posted Tue Feb 27, 2007, 1:29am Subject: Gaggia pressure problem and subsequent fix
I've been having trouble with my Gaggia Evolution, and just finally figured out how to fix it. I thought I'd share my experience, in case anyone else has a similar problem.
I recently connected a pressure gauge directly to my threaded portafilter and discovered that my gaggia was putting 14 bar to the group. From everything I've read on here, somewhere between 8 and 10 bar is ideal, and 14 bar is just way too much. I've been pretty dissatisfied with my shots lately. so...
I did some research and found out that I needed to adjust the over pressure / expansion valve (OPV). It's the T-shaped brass thing between the pump and the boiler, for anyone who's a bigger newbie than I. The screw was almost backed all the way out, but I topped it out fully and did another measurement. Still 14 bar! And not a single drop was being diverted by the valve.
I called wholelattelove tech support to order a new OPV, but they told me it's an emergency valve that doesn't regulate brew pressure, and that all gaggias put 12-13 bar to the group at the very minimum. If I wanted to change that, I would have to modify the pump itself, which they did not recommend. So I gave up.
Then I stumbled upon this article which actually explains how the valve physically works: Click Here (myweb.tiscali.co.uk)
So I decided the thing was stuck shut. I shoved a small allen key in the side opposite the adjustmend screw, and felt a satisfying pop as the piston broke free.
I screwed everything together, measured the pressure... 10 bar! w00t!
That was ten minutes ago, and the ristretto I'm enjoying right now is reminding me why I got into this espresso game in the first place.
Posted Tue Feb 27, 2007, 12:04pm Subject: Re: Gaggia pressure problem and subsequent fix
I've been getting some bad shots lately myself using the same Evolution machine. I might have to check into this, but basically all you did was fix the stuck valve not modify it right? I also just ordered a new Silvia that comes with the adjustable OPV so I'll have to also buy the parts to measure the pressure. Interesting stuff. That article was really helpful and had nice pictures to show just how they work.
Posted Tue Feb 27, 2007, 12:54pm Subject: Re: Gaggia pressure problem and subsequent fix
Jeff_K Said:
I've been getting some bad shots lately myself using the same Evolution machine. I might have to check into this, but basically all you did was fix the stuck valve not modify it right? I also just ordered a new Silvia that comes with the adjustable OPV so I'll have to also buy the parts to measure the pressure. Interesting stuff. That article was really helpful and had nice pictures to show just how they work.
Hey Jeff, you can order a cheap & dirty one from EspressopartsNW for $43.67. I can't say how well it'll perform as the gauge looks to be a "dry" gauge, not a "wet" one/glycerin filled to dampen the pulses from the vibe pump.
Dunno if Terry Z's techs use this one, but I'm sure Terry wouldn't sell one if the gauge swing/oscillation was too great., but that's why I built my one.., to be on the safe side.
Posted Tue Feb 27, 2007, 2:25pm Subject: Re: Gaggia pressure problem and subsequent fix
That one's very similar to what I was thinking of using, but honestly I didn't even think of what you were mentioning with the oscillation. Maybe I'll have to do some investigating into all the options, but it's definitely nice that the new Silvias already have the adjustable OPV. The OPV/pressure adjustment information is really new to me but it's interesting as I really like to learn how things work and then "tinker" with them. I wouldn't know half this stuff without this site - it's really a great resource especially with the people here that know all kinds of things like yourself. Thanks for the info.
Posted Tue Feb 27, 2007, 2:52pm Subject: Re: Gaggia pressure problem and subsequent fix
Yep, with a dry Bourdon tube gauge & without a "snubber" to dampen the pulses & resultant oscillations, that style of gauge can be unreadable due to the wild range of swing/oscillations of the needle hand. That type of mechanical vibration/oscillation abuse will destroy a gauge in short order, it'll literally shake itself apart!
I've done my research/homework into this, & thanks., you're welcome! {;-)
Posted Tue Feb 27, 2007, 4:43pm Subject: Re: Gaggia pressure problem and subsequent fix
The old style stock Rancilio Portafilter with "V" notch, hence the extra work modifying the blind backflush insert. If a person used the other configuration of fittings I mention below, & a brew basket instead of the bind one in the old Silvia PF, the water/coffee will go between the interface of the outside wall of the brew basket & the portafilter body & spray/leak like crazy through the V notch!
I believe this was Rancilio's way of controling a shot that was too fine (stalling/choking) the machine for too long & the possibility of burning out the Ulka 41 watt vibe pump.
I didn't want the added expense of buying a 2nd Commercial Rancilio portafilter, but with that you won't have the problem mentioned in the 2nd paragraph. If anyone goes that route, you just use a coffee basket in the portafilter & no blind insert to worry about., but a slightly different configuration of fittings that will simply screw onto the bottom theads of the commercial portafilter.
Posted Tue Feb 27, 2007, 4:43pm Subject: Re: Gaggia pressure problem and subsequent fix
Assembled OPV pressure measuring assembly. The far right hand side fits to the bottom of the copper tube coming out through the bottom of the old style Rancilio PF head with a brass compression ferrule.
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