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JonEdwardsOffline
Post subject: Gaggia Classic OPV issues  PostPosted: Apr 17, 2008 - 11:26 AM



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I've been struggling for what seems like ages with really fast messy pours on my Classic (even with my Superjolly dialled down as fine as it will go).

I've been a bit slack with my maintenance and hadn't descaled in ages - the end result being that last week the thing pretty much ground to a halt. However as it did so, I got some *really* good shots, due to the restricted water flow. Anyway, descaled and I'm back to espresso all over the kitchen.

So this set me thinking about OPV pressures. Ab it of googling came up with the "how to" for a classic. A bit more came up with the pressure chart for my Invensys pump. Some faffing later and I'd determined that their wasn't enough water coming out of the return (running pump/steam together) I was getting 70ml in 30s, rather than the required 125ml (as I understnad it) for 8.5bar. A bit more faff and that's sorted.

The shot is neater, but still fast. Back off the OPV some more, then some more. Not a lot is changing. I don't think its helping that I've got some *very* fresh beans, so I'm ending up pouring half a cup of crema, and can't really get an idea of how much liquid volume I'm producing. (pour a dull espresso cup, leave it for 30secs and its losing about 1/3 its volume) The grinder is still dialled as tight as I dare go, and I'm now getting to the "too many variables to make sense" confusion point. (not helped by tasting FAR too many espresso shots last night Shocked Shocked )

So... does anyone have a portafilter mounted pressure gauge that will work with a gaggia classic coffee? That's the simple answer to getting the OPV set correctly for pressure at the p/f.

Is there anything *bad* that will happen if I carry on backing the OPV off? What I think I'm trying to achieve is to keep the grind/dose/tamp constant, but then get the opv set so that the balance between water going through the brewhead and water going through the return gives me the required 75ml in my cup in 27secs.

Any advice gratefully received!

Cheers,

Jon
 
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NarraOffline
Post subject: RE: Gaggia Classic OPV issues  PostPosted: Apr 17, 2008 - 05:44 PM



Joined: Jan 15, 2008
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My thoughts:

I think your after a flowrate out of your grouphead of about 60-90mL in 10 seconds. That is with no portafilter locked in.

Gaggia Classic pump produces 15 bar of pressure, Id imagine the OPV on that machine is pretty ordinary at best, thus not very adjustable and probably shouldnt be touched. The OPV probaly allows 11-12 bar through. I would leave it at its orginal position. If your getting too much water through the group head the seal on the OPV may be damaged or not seated properly. Tighten it back up, dont loosen it off.

You said your aim is for 75mL in 27 seconds, I always aim for 50mL in about 27 seconds.

All the best,
Paul
 
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knewmansOffline
Post subject: RE: Gaggia Classic OPV issues  PostPosted: Apr 17, 2008 - 11:15 PM



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If its the CP3 pump then with the steam valve shut and the steam button pressed ( so no water comes out of the group head) if you switch the pump on then you should get 125ml in 30sec out of the OPV at 9bar. This has nothing to do with how much water will go through the coffee when you are brewing. When brewing any excess will go out of the OPV.

Once you've got the 125ml in 30sec forget about the OPV - its ok. Now its all about adjusting dose and grind. My Classic always liked a dose of about 17g. Much less and I found it difficult to control. Maybe try that and adjust the grind from there.

Are you using the double or single basket?

The OPV is straightforward to adjust and pretty reliable. See here - http://tinyurl.com/3slj6j

Ken

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JonSOffline
Post subject:   PostPosted: Apr 18, 2008 - 09:27 AM



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I'd agree with what Ken said.

Don't keep backing off the OPV once you have the correct amount flowing from the return pipe, otherwise, eventually, it will likely start to behave badly.

It's been a while since I used my classic (probably too long) but I would tend to be looking at other factors for messy pours. Too fresh coffee which needs more time to degas isn't going to help you make sense of what you're seeing. In addition, like Ken, I've seen problems with the classics with too low doses. Pours starting off well enough, then falling apart badly with a huge cone and fast pour. Obviously too much will cause issues with the screen disrupting the puck on lock in. There's a sweet spot. I saw this the other night on a friends classic, mainly because he hadn't yet got himself a reliable way to dose the "right" amount repeatedly.

A Super Jolly ought to be able to easily choke a machine. Are you sure you have the zero point correctly identified ? If you are confident that you have, then I would really put my money on a dose size / distribution / tamp issue.

Although I don't use it so much now, I have an ex-demo Mazzer Mini which, in conjunction with a couple of different machines, was a beast to try and get a decent pour out of (I struggled for almost a year). After an accident requiring some new burrs, and a breaking in period, I can actually get far better pours from it than I ever thought possible. Though I'd actually bought a much better grinder in the end. So, did you pick up the SJ new or if not, are you sure that the burrs are up to scratch ?

Jon

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JonEdwardsOffline
Post subject:   PostPosted: Apr 18, 2008 - 10:26 AM



Joined: Nov 17, 2005
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Thanks for the replys...

Well coffee this morning was pretty good. Still a little fast. Tasted nice though. One issue on top of everything else I do have. First shot is always OK, second shot is always worse. I'm not aware of doing anything different between the shots in terms of dose & tamp, and i make sure the boiler has been properly refilled if I've steamed after the first shot (doesn't actually make any difference whether I have or not.)

The grinder was bought second hand, but was fitted with new burrs (now ~1yearold). I've had doubts before as to whether the burrs were sitting parallel to each other, but having had it to bits multiple times, I can't see anything wrong. If I spin the lower burr by hand there's a once-a-revolution tick, which is what I take as my zero point. (in terms of the numbers on the grind adjustment ring this is around 1.2, 1.3)

I dose to 17.5g, measured on a digital scale (0.1g accuracy). double basket.

I do put a lot of effort in to try and make the dose and distribution as even and repeatable as possible, likewise the tamp within the calibration (!) of my elbow. I am tamping pretty hard.

Pours do start off well, but then do degenerate into a huge cone. (that's a good pour!). Historically they've also been one sided -looking from above the machine biased towards 5'oclock (even if I turned the basket round in the filter handle after tamping). This seems to be less of an issue now. The machine is level (within the limits of my spirit level).

I think I've worked out a way to bodge a pressure gauge onto a blind basket, so i'll give that a try and adjust the OPV to give the right grouphead pressure. At least I know it'll be right then!

Thanks again!

Jon
 
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knewmansOffline
Post subject:   PostPosted: Apr 19, 2008 - 11:41 AM



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I found my Classic much easier if I double dosed. Dose half, tamp lightly, finish the dose and lightly tamp again. I was much more consistent like this. This was using the timer on my MC2 so not as accurately consistent as weighing but the shots were fine.

Ken

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JonEdwardsOffline
Post subject:   PostPosted: Apr 22, 2008 - 08:42 AM



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Right, progress report...

12 at plumbase and a raid of my box of leftover brassware produced enough oddments to let me bodge a pressure gauge onto the bottom of my blind basket with the guage dangling through the hole on the bottomless filterhandle. Sure enough pressure was now a bit low, so i tweaked that back up to an average of a bit under 9.0 bar (the vibe pump makes the needle vibrate by over a bar, but you can kinda see where the middle is!)

I then turned my attention to the grinder. As above, I've never tried winding the grind adjust any lower than the 1.2 mark as I thought that's where the burrs began touching and I didn't want to damage them. However this time I carried on going and discovered I could get down to about 0.4 before there was a *really obvious* metal on metal noise - not just a gentle tick, shortly followed by the lower burr locking up solid. Obviously this means I can now grind finer than I thought I could.

So what's the coffee like now? F'kin awesome! Repeatable, time after time, clean, controlled 26/27 second pours, as well as distinct difference in taste. I'm terrible at describing taste, but it all seemed much more open/distinct - I could identify different sensations with each sip and on differnt parts of my tounge.

I spent most of Saturday rattling off the walls from caffeine overload, but Sunday Monday and today have all resulted in top notch shots too. Happy days!

Thanks for all the advice!

Cheers

Jon
 
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JonSOffline
Post subject:   PostPosted: Apr 22, 2008 - 10:31 AM



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Oh nice, glad you got it sorted out Very Happy

Don't suppose you could post a couple of pics of your pressure gauge effort for reference, I'm sure it would be useful for other domestic Gaggia owners to see ?

Not that it really matters, but generally, you can dampen the pressure oscillations on the gauge, caused by the vibe pump, by using a coil of small bore copper piping to connect the gauge up. this is basically what's done in most machines that have integral gauges.

Jon

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Isomac Zaffiro w/PID | Isomac Gran Macinino | Mazzer Mini
Scace Thermofilter
Custom-built grinder timer
 
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knewmansOffline
Post subject:   PostPosted: Apr 22, 2008 - 08:34 PM



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Glad its sorted

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JonEdwardsOffline
Post subject:   PostPosted: Apr 23, 2008 - 08:35 AM



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OK, here ya go



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