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gaggia pressure gauge placement help?
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AndyPanda
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Posted Sun Mar 11, 2012, 10:10am
Subject: Re: gaggia pressure gauge placement help?
 

tegee Said:

Andy......
While we are on the topic, does the Gaggia Classic really need to have its OPV adjust to 10 bars static (9 bars brew) or is it all overhyped on adjust it on a Classic?  I have read and heard pros and cons

Posted March 10, 2012 link

Well ... there is a lot of opinions out there.  In the end, all that matters is if it works better/tastes better to you.

I found that my very old classic was pretty close to 9 bars static already, just a little high so I lowered it.  I have experimented by taking it back up to 10 bars and 11 bars and then back down to 9 and I prefer 9 bars static.  I don't really buy into the idea that 10 bars static gives 9 bars brew - but enough well respected folks have said it that I have to wonder.

If you didn't have a gauge at all, you could simply pull a few shots and notice how they taste and how they flow and the mouth feel (assuming you can grind/dose/tamp several shots in a row exactly the same - it's not easy to do).  Then adjust your OPV by 1/2 turn at a time and repeat.  I suspect the main difference you would notice is mouthfeel but it would be an interesting experiment to find the best pressure based on the quality of the pull (without using a gauge) and then put a gauge on there to find out what pressure you liked the best.

I have found that it isn't always what you might expect - lowering the pressure can sometimes increase the flow for example.
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tegee
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Posted Sun Mar 11, 2012, 5:12pm
Subject: Re: gaggia pressure gauge placement help?
 

AndyPanda Said:

Well ... there is a lot of opinions out there.  In the end, all that matters is if it works better/tastes better to you.

I found that my very old classic was pretty close to 9 bars static already, just a little high so I lowered it.  I have experimented by taking it back up to 10 bars and 11 bars and then back down to 9 and I prefer 9 bars static.  I don't really buy into the idea that 10 bars static gives 9 bars brew - but enough well respected folks have said it that I have to wonder.

If you didn't have a gauge at all, you could simply pull a few shots and notice how they taste and how they flow and the mouth feel (assuming you can grind/dose/tamp several shots in a row exactly the same - it's not easy to do).  Then adjust your OPV by 1/2 turn at a time and repeat.  I suspect the main difference you would notice is mouthfeel but it would be an interesting experiment to find the best pressure based on the quality of the pull (without using a gauge) and then put a gauge on there to find out what pressure you liked the best.

I have found that it isn't always what you might expect - lowering the pressure can sometimes increase the flow for example.

Posted March 11, 2012 link


Thanks Andy for your explanation.

I do have a liquid filled bar gauge and I have the OPV adjust to 10 bars static.  Don't know eiether if it equates to 9 bars brewed???  It was 12.5 bars (182 psi) out of the box and I tuned it down to 10 bars (145 psi).

Again...I don't know how it help?  I am a bit of a newbie with the Classic and I am struggling a bit with my new Baratza Virtuoso grinder.  I am wondering of I should up to the Virtuoso Preciso?

Anyway...enjoy the input and I am that much closer to dialing the Classic in.
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AndyPanda
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Posted Sun Mar 11, 2012, 11:17pm
Subject: Re: gaggia pressure gauge placement help?
 

I have never been nearly as fussy with the grinder setting as other people seem to be.  I don't own a virtuoso or preciso - but if I were buying one, I'd probably be happy with the virtuoso.  For me, that is because I find that I experiment more with raising/lowering the dose by very small amounts rather than changing my grind setting.

I have a mazzer major - and I've left the grind setting pretty much in the same place for months now.  I'll occasionally pull out the aeropress and set the grind coarser - and I also have one espresso machine with smaller portafilter (53mm) but straight walls and really big surface area where the filter holes are.  That espresso machine requires a finer grind or it really pours fast.  Before the Mazzer I used a Fiorenzato (still have it) that has notched settings - I found that I was totally happy with one click or the next click and did not need the super fine settings between - and found that .5 gram difference in dose had more affect - though the changes you get by up/down dosing are different from the changes you would see by slightly finer/coarser grind.  I'm not so sophisticated to discern that yet - I'm just going by what I read.    

Anyway ... my point (but I'm not in the mainstream at all - so I don't want to lead you astray) is that I could be perfectly happy with a grinder with great burrs but no microfine adjustment. (EDIT: I have since read many, many posts of people saying they bought a Virtuoso and wished they had gotten the preciso instead.  I don't own either so please don't use my opinion here to influence which model you buy)

Re: pressure - My suspicion is that low pressure would extract easy but might lack in flavor and that higher pressure might channel easier and might have more frothy looking crema that is actually thinner and might fade faster.  I've heard people say 8.5 bars is the sweet spot for them - I find 9 or 9.5 to be the sweet spot for me - that's where the crema feels really thick, it's the mouthfeel that I notice and the espresso is almost like letting a piece of chocolate melt under your tongue in terms of mouthfeel - thick and gooey. But I'd be very interested to hear what you find as you try different pressure settings.
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AndyPanda
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Posted Sun Mar 11, 2012, 11:32pm
Subject: Re: gaggia pressure gauge placement help?
 

Just thought of one other thing you might want to experiment with (regarding the lack of fine adjustment on your Virtuoso).  The specific basket you use makes a big difference.  I use a micro-fine basket that doesn't seem to be available any longer (the current ones have a shape I don't like as much). The holes are much smaller and more precise than the stock Gaggia basket and I find that I grind a bit more coarse for that basket and that I really don't need to fuss with fine adjustments on the grind as my coffee ages from 3 days post roast to a week or so.

I am very interested in getting the new VST baskets.  The reviews discuss how with such precise baskets, the pull can run longer without becoming bitter.  And this is what I found with my basket (which isn't as nice as the VST but it's in the similar ballpark) - if my grind is a bit too fine (or I overdosed a little) I can let the shot run 30-35 even 40 seconds and it still tastes great to me.  Though I still aim for a 25 second shot.  But I suspect that a small investment in a VST basket might give you more forgiveness for not having micro adjustments on your grinder.
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Posted Wed Mar 14, 2012, 6:55am
Subject: Re: gaggia pressure gauge placement help?
 

Figured I'd throw in some info about brew pressure on my modified Baby Class - My static pressure and brew pressure were about 2/3 bar off of each other. I've read a few times they would be about 1/2 off but for me it was slightly more. I haven't read of anyone that had it 1 full bar off but I'm sure they are out there.

I attached a pressure gauge to mine (internal, tee'd off the pump, it stays on the machine), and ran it with a blocked brew basket (took a pod basket I wasn't going to use ever and filled it with epoxy, LOL). Then I opened up the steam valve just slightly and tweaked it until I got about 2oz of water (measured in a shot glass) over a 25 second period. Those were the #'s I chose, yours may vary but likely will be close to that. I figured that the very slight opening in the steam valve that gave me that flow volume over that time was similar enough to a portafilter full of coffee grounds that I desired to yield the same flow / time results.

Anyhow, with the OPV set at a point that gave me a pressure of 135psi (close enough to 9 bar) when flowing 2 oz / 25 sec, it gave me 145 psi (10psi or 2/3 bar difference) when the steam valve was closed and no water was flowing at all.

This might give you an idea on how to do something similar with yours to imitate the flow rate you want when you do have espresso being made?

PS - while I had the top of the machine off I disconnected the wires to the boiler, so that I could just get water flowing during this testing and not deal with it trying to steam up on me.
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AndyPanda
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AndyPanda
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Vac Pot: vintage Corey
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Posted Wed Mar 14, 2012, 7:55am
Subject: Re: gaggia pressure gauge placement help?
 

This has me really curious.  

When I said I don't buy into static being higher than brew, I meant that when I use my PF mounted (gauge on a machine with a 3-way), I get the same pressure whether I am flowing the equivalent of a double or not flowing anything at all.  The exception being that if I were to flow so much that the OPV doesn't bleed anything off then of course the pressure drops - but as long as the OPV is bleeding off some flow, I get the same reading on my PF gauge whether locked tight or flowing 2oz.

But you are getting 2/3 bar difference with your gauge mounted between the pump and the boiler.  I would have thought it would give the same results as I get with the PF mounted gauge.  

I'm going to have to test this again - I hadn't tried the steam knob to regulate the flow - I've just been allowing 2oz to run from the PF.  I'm going to see if I get a different result using the steam wand for the 2oz.

=======================
OK ... I'm back.  I just tested and for a slow trickle from the steam wand (2-3oz in 25 sec) I get absolutely no drop in pressure from my PF mounted gauge.  But if I open up the steam wand a bit more - then of course I start to see the pressure drop but that is for the equivalent of a gusher, sink shot.

Perhaps it is different for gauges mounted before the boiler - but this is why I resist the idea of setting the pressure higher than desired (when using a PF mounted gauge) - my tests confirm for me that on a 3-way machine I can simply set the OPV with the PF gauge not flowing anything and that is the same pressure I will get for normal brew.
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Posted Wed Mar 14, 2012, 11:44am
Subject: Re: gaggia pressure gauge placement help?
 

Hmm. Doesn't make sense, does it?

The OPV bleeds off pressure. It will bleed off varying amounts depending on what is input to it, but when it's doing it's job (and fed a pressure higher than it's set for) it should hold that water path at a constant pressure (let's say 9 bars).

If you make espresso, or crack open the steam wand a tiny bit, you do open the line up and release water. If there was no OPV, you would see a pressure drop as the line is opened. But we have an OPV, and we believe our pump is able to put out a higher pressure than 9 bars ( more like 12+). So even with that little opening in the line flowing water, the OPV should simply bleed off a little less water of it's own but it should continue to hold the line at that same 9 bars.

The only thing I can see causing this is if the pump itself, while capable of putting out 12+ bars with a line completely closed, falls flat once there's some flow and doesn't even hit the pressure level that the OPV is set for.

I don't buy that though; 1) I see some water returning from the OPV, 2) I saw the line pressure change when I changed the OPV setting (I kept my grind and tamp the same throughout and the pressure changed predicatably higher / lower as the OPV was turned clockwise / counter-clockwise).

I saw this but have convinced myself I couldn't have.

I may have some time this weekend to try it again. I'm also curious, after some email conversations, to find out how much water I flow through my OPV while I make my 2oz shot of espresso. Maybe I can do both tests.
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AndyPanda
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AndyPanda
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Posted Wed Mar 14, 2012, 12:45pm
Subject: Re: gaggia pressure gauge placement help?
 

Yeah ... I'm really interested in this subject (can you tell?  hehe)  So it's interesting to hear what you find.

Lots of people don't use a gauge at all and set their OPV based on the volume of water being bled off from the OPV.  This would work if every pump were identical - but I have several of the identical model pump and they all put out completely different volumes and pressures (wear and tear - also mfg tolerances - etc)  so I go by the PF gauge.

It would be interesting to put a PF gauge on your machine and see if your internal gauge matches the PF gauge - and then open the steam valve a little and see if they diverge.

How large is the feed pipe to your gauge?  I know some of the built in gauges use a really thin tube (capillary)
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Posted Thu Mar 15, 2012, 7:07am
Subject: Re: gaggia pressure gauge placement help?
 

Agreed, measuring what is bled off by the OPV would only work if all pumps were exactly the same, which they aren't. Not much of a method there.

My gauge is attached to a Tee just before the boiler inlet, so it's not picking up any losses incurred by the 3-way solenoid or the boiler. I have to doubt there's much of a loss through them though, they will cause some but with the size of the boiler and the small flow rate it's probably a really small amount, almost negligible. That and I don't have the fittings for a PF gauge and probably won't bother to get some (I've bought too many useless fittings already as I kept changing my layout!).

I've got a 3/16" ID line running to my guage, which is less than a foot away. I also made sure the line was filled with water and not air. Assuming the gauge itself is reasonably accurate it should be making a good measurement.
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AndyPanda
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AndyPanda
Joined: 12 Jul 2010
Posts: 769
Location: San Francisco Bay Area
Expertise: I love coffee

Espresso: Olympia Cremina, Various...
Grinder: Mazzer Major, Fiorenzato,...
Vac Pot: vintage Corey
Drip: AeroPress
Roaster: BreadMachine/HeatGun
Posted Thu Mar 15, 2012, 8:11am
Subject: Re: gaggia pressure gauge placement help?
 

Hey ... I think I just realized why there could be a difference between static and brew.

The OPV is a spring loaded device - when there is no simulated flow (static) the spring in the OPV is compressed more because it has to flow the entire output of the pump back to the tank.   But when you are flowing a simulated shot (brew) the OPV spring is compressed less.  

So this would account for the difference between brew and static pressure setting and this is something I had been completely ignoring in my thinking about it before.

So thanks for making me think about this some more - I really enjoy when someone makes me think and I learn something.   It's looking like from your results, the 10 bar static for 9 bar brew could be true (though I'm very happy with the shots I get setting mine to 9-9.5 static - but I pull ristrettos)


I started to read this and suddenly realized what I had been overlooking about the spring in the OPV ... if you're interested, this looks like a heated argument over this very topic:
Click Here (www.home-barista.com)
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