Author Topic: Blind OPV Adjustment  (Read 70269 times)

Offline D4F

  • Global Moderator
  • Grizzled GUG Veteran
  • *****
  • Posts: 1734
    • Gaggia Classic w PID
    • Baratza Forte-AP
Blind OPV Adjustment
« on: January 04, 2014, 12:16:59 AM »
Most owners of a Gaggia Classic will want to adjust the OPV.  The standard way to make the adjustment is with a pressure gauge on the PF.  The other common advised method is to turn the OPV counterclockwise 270 degrees.  Most who measured pressure found it about 12.5 bar from the factory and assuming good quality control on the OPV spring and components, then 270 degrees counterclockwise would give about the same reproducible result, a pressure of about 9 – 10 bar depending on whether static or dynamic pressure is considered.  That said, many make the adjustment blind, without measurement.  I am not really recommending that.

What to do with the OPV when buying a used machine??? If is it was actually used by a knowledgeable Gaggia geek it may be already adjusted.  Blind adjustment of a used machine should not be done unless the seller is sure that it has not been adjusted.


The OPV can be adjusted without a gauge and not completely blind.  It will be an approximation, but should get your machine into the right range of about 9 bar pressure.  Please note that the group is blocked and the measurement is of OPV return.

Remove the tank and put a full glass of water in place of the tank.
Place an empty measuring container under the OPV return line.
Use a blind basket or equivalent.
Run the machine for a known time, say 15 seconds or 30 seconds and measure the OPV output.  Measure volume or weigh.  The ULKA E5 pumps used in the
Gaggias will flow about 260 cc/min at 9 bar or about 130 ml in 30 seconds.

http://www.ulka.it/admin/moduli/m003_web/file/pag_ULKA_web.pdf  No longer active and updated below

update

http://www.ulka-ceme.co.uk/E_Models.html

Since the group is occluded, all of the outflow is back to the OPV container.  If set previously, it will be in that range and if close to 12 bar factory setting, then the flow will be more like 140 cc/min or about 70 in 30 seconds.

This is not a recommendation of adjustment without a gauge, rather a description of a method to avoid completely blind OPV adjustment.

It is best, most accurate, to use a gauge.


Edited for clarification of OPV output and to update the current source of the graph.





« Last Edit: April 06, 2017, 12:18:30 PM by D4F »

Offline gingerbean

  • Getting the Hang of It
  • **
  • Posts: 16
    • 2007 Classic (270 blind OPV mod)
    • Dualit 75015 grinder
Re: Blind OPV Adjustment
« Reply #1 on: January 04, 2014, 05:43:53 AM »
thinking this through...
I'm currently filling 2 espresso cups in about 20 seconds, so things are way off.

I definitely need a better grinder.

I can do a 'glass of water' OPV adjustment now to get me in the ballpark pressure-wise.

When I get my grinder (in say, 3 months), I must do a measured OPV fix before I start trying to dial in a new grind, otherwise I'm using 'random pressure' as a fixed part of the equation.

Does that sound like a good way to go for a newbie wanting to see results faster than my wallet will allow?

Offline IntrepidQ3

  • Grizzled GUG Veteran
  • *****
  • Posts: 350
    • Gaggia Classic with PID and Dimmer
    • HG-One
Re: Blind OPV Adjustment
« Reply #2 on: January 04, 2014, 08:38:23 AM »
I know the thread is about Blind OPV Adjustment, but I figured I would mention this, as it might be helpful.

For those resorting to a blind adjustment because they do not have a gauge (whether they do not want to buy one or make one) there is a loaner pressure gauge in the Lending Library. This maybe extremely helpful for those who have bought a used machine and do not know the machines history or previous owner.

Susan was kind enough to put her gauge there. I am not sure if the pressure gauge is able to be shipped outside of the U.S. or not, this is something Susan will have to address.
"As you know, an explorer's temperament requires two basic qualities: optimism in attempt, criticism in work." - Sigmund Freud

Offline SusanJoM

  • Administrator
  • Grizzled GUG Veteran
  • *****
  • Posts: 2410
    • Classic
    • Compak K-10
Re: Blind OPV Adjustment
« Reply #3 on: January 04, 2014, 01:08:40 PM »
Susan thinks adjusting the OPV without a gauge is a waste of time, but the gauge is not available for international shipping, sorry.
“Not everything that can be counted counts, and not everything that counts can be counted.”
Attribution in Dispute

Offline gingerbean

  • Getting the Hang of It
  • **
  • Posts: 16
    • 2007 Classic (270 blind OPV mod)
    • Dualit 75015 grinder
Re: Blind OPV Adjustment
« Reply #4 on: January 05, 2014, 12:14:43 PM »
Out of curiosity, and being decidedly untechnical, why doesn't the glass of water thing work?

If the idea of making espresso is to get a certain amount of liquid in a certain length of time (keeping coffee out of the equation for now), if I know the time and know the resulting volume (in the glass of water test) then doesn't that mean the pressure is correct by default ?

I know it assumes everything in the system is working efficiently, but doesn't any test of the system.

by the way, in the water test I consistently get around 80ml in 30 secs, working with a full system.

Offline D4F

  • Global Moderator
  • Grizzled GUG Veteran
  • *****
  • Posts: 1734
    • Gaggia Classic w PID
    • Baratza Forte-AP
Re: Blind OPV Adjustment
« Reply #5 on: January 05, 2014, 04:29:55 PM »
The method does work as described.  It is an approximation, better than nothing or not adjusting.  Factory setting is about 12 - 12.5 bar.  If you will look at the pressure vs flow for E5

http://www.ulka.it/admin/moduli/m003_web/file/pag_ULKA_web.pdf

You can see the blue line medium is about 150 ml/min at 12 bar. Your 80 ml/30 sec should be about 12 bar.  Now look at it the other way and say you have a flow of 80 ml/30 sec and go to the graph and depending on which line you; actually fall on, you have between 10 and 13 bar.  Likewise if you get 250 ml/min are you at 7 bar or 10.5 bar.  You get an approximation and could in fact be 9 bar on the blue line. 

I initially set mine before a gauge at 270 degrees counterclockwise, and then checked it with the method described and got 125 ml/30 seconds measuring time not with button push, but with actual start of flow which took a couple seconds.  When I got a gauge and checked it, pressure was close and I tweaked a little.

If no gauge is available I would use the above method, I did :)  Of course I always like to figure a "MacGyver" solution to things.

Offline gingerbean

  • Getting the Hang of It
  • **
  • Posts: 16
    • 2007 Classic (270 blind OPV mod)
    • Dualit 75015 grinder
Re: Blind OPV Adjustment
« Reply #6 on: January 05, 2014, 06:15:09 PM »
I see, thanks for going to the lengths you have in demonstrating it for me D4F. So it's an approximation that's a pretty good ballpark to be playing in until I get a gauge.

So, am I right in thinking that the actual pressure is the important thing that effects taste then, and not just flow, as any given flow measurement could be anywhere within a range of pressures?

One thing I don't get is how pressure can fluctuate so much for a given flow rate. Or am I looking at it wrong. Does that mean that once I set the pressure, I may still get a fluctuation in flow (anywhere from 200-350cc/min) and will that adversely effect consistency of results?

Or... is it the case that flow is irrelevant as once the system has filled up during a shot and the water has hit the coffee (i.e. resistance), it then proceeds at the set pressure and that's when we get consistency. Are the pressure/flow figures in fact meaningless unless we have coffee in the way!?

Sorry, I've never had to think like this before so I'm trying to get how it works. Am I over-complicating it, or more or less there...  :P

Offline D4F

  • Global Moderator
  • Grizzled GUG Veteran
  • *****
  • Posts: 1734
    • Gaggia Classic w PID
    • Baratza Forte-AP
Re: Blind OPV Adjustment
« Reply #7 on: January 05, 2014, 06:22:48 PM »
You can see that this is an opinion thread :)  I think that if you set by flow, you cannot be sure what the pressure is from the graph.  Perhaps a pump tolerance issue.  Flow will give you a range of pressures by looking at the graph, IMHO all probably better than the 12+ OEM setting, as long as you have an adequate grinder, fresh beans, and non-pressurized baskets.

Offline SusanJoM

  • Administrator
  • Grizzled GUG Veteran
  • *****
  • Posts: 2410
    • Classic
    • Compak K-10
Re: Blind OPV Adjustment
« Reply #8 on: January 06, 2014, 11:57:32 AM »
You can see that this is an opinion thread :)  I think that if you set by flow, you cannot be sure what the pressure is from the graph.  Perhaps a pump tolerance issue.  Flow will give you a range of pressures by looking at the graph, IMHO all probably better than the 12+ OEM setting, as long as you have an adequate grinder, fresh beans, and non-pressurized baskets.
The factor you are ignoring is the resistance of the puck, and that is very variable.
The grinder, the setting of the grinder, the beans, the roast level of the beans, the freshness, your tamp pressure, your dose in .1 grams will all determine the resistance.

For me the reason to adjust pressure is to nail down one of the variables in making espresso.  To adjust from one unknown to another was and is of no use to me in my journey.  Obviously opinions on what is close enough differ.  For me knowing the  actual pressure matters, and that requires a gauge.
“Not everything that can be counted counts, and not everything that counts can be counted.”
Attribution in Dispute

Offline gingerbean

  • Getting the Hang of It
  • **
  • Posts: 16
    • 2007 Classic (270 blind OPV mod)
    • Dualit 75015 grinder
Re: Blind OPV Adjustment
« Reply #9 on: January 06, 2014, 02:10:19 PM »
Points taken Susan, but where I'm at at the moment is trying to improve my rubbish coffee by:

Adjusting my cheap grinder to an unknown 'finest it will go but its nowhere near fine enough'

Turning the machine pressure 'down a bit' from the OEM setting that we all know is too high

Squish the not really fine enough coffee down with the plastic Gaggia tamper that is too small and lightweight to be any real use.

And you know what? My coffee tastes better than it did 3 weeks ago when I got my machine and was still using supermarket bags of ground coffee  ;D

I will buy a 'proper' grinder, I'll do a pressure gauge OPV adjustment and I will buy a better tamper. All in good time, but at least I'm drinking better coffee whilst I wait.

Being inquisitive (and impatient) I'll also keep trying lots of seemingly daft other little things, just in case they make a difference, and they will all be of use to me on my journey.

I do understand though, that you cannot recommend a blind OPV adjustment as a guaranteed solution - if only so that everyone on a forum like this is on the same page when trying to help each other. If I came back on here in 3 months with all the gear but still struggling, the first thing I'd expect to be told would be do a proper pressure gauge OPV adjustment".

Offline SusanJoM

  • Administrator
  • Grizzled GUG Veteran
  • *****
  • Posts: 2410
    • Classic
    • Compak K-10
Re: Blind OPV Adjustment
« Reply #10 on: January 07, 2014, 10:57:24 AM »
That sounds just fine to me.
Everyone gets to do it his or her way.
My only interest is in making sure you know as much as possible about what you can and can't expect to achieve.
Keep us posted
Susan
“Not everything that can be counted counts, and not everything that counts can be counted.”
Attribution in Dispute

Offline gingerbean

  • Getting the Hang of It
  • **
  • Posts: 16
    • 2007 Classic (270 blind OPV mod)
    • Dualit 75015 grinder
Re: Blind OPV Adjustment
« Reply #11 on: January 07, 2014, 04:56:49 PM »
And it's much appreciated.  :)

So the 270 degree tweak I made has improved my crema, reduced some of the sharpness (acidity?) in the shot and given me a bit more flavour. I'm using the same beans as a benchmark during this period so I can judge differences.

The timing has improved but it still feels fast despite tamping hard. That isn't going to change until I significantly upgrade my grinder and tamper, but I'm very happy with how it's turned out. Thanks guys

Offline D4F

  • Global Moderator
  • Grizzled GUG Veteran
  • *****
  • Posts: 1734
    • Gaggia Classic w PID
    • Baratza Forte-AP
Re: Blind OPV Adjustment
« Reply #12 on: January 07, 2014, 07:08:22 PM »
Great to hear, glad it worked ;)

Offline SusanJoM

  • Administrator
  • Grizzled GUG Veteran
  • *****
  • Posts: 2410
    • Classic
    • Compak K-10
Re: Blind OPV Adjustment
« Reply #13 on: January 08, 2014, 05:53:13 PM »
For the record, I would like to clarify my objection to going the blind adjustment route:  it may improve the cup that you are working on, but it will not improve and may in fact hamper your espresso skills.  Espresso needs to be brewed at 9 bar.

The purpose of adjusting your Gaggia to 9 bar is so you have fewer other variables to correct/adjust.  If your pressure is not at 9 bar, all of your adjustments of temperature, grind and dose will be based on an incorrect calibration.  Think about using a thermometer;  when you first use it you test it to be sure that it registers correctly for zero and for boiling;  otherwise the reading you get will be skewed.  The same goes for pressure.  To brew espresso, the machine needs to be tuned to 9 bar. 

Adjusting without a gauge (the blind leading the blind) is probably not a problem if you plan to use the same bean/roast for the rest of your espresso life.  You can probably find a combination of pressure/temp/dose/grind that will work and you can keep enjoying that cup for the rest of your espresso life.  And, if that is the full extent of your journey, then I can't see why you wouldn't just adjust it willy nilly and take what you get.

If, however, espresso itself is your interest, and not just getting your morning cuppa, I think you are setting the barr (pun intended) too low.

Lowering the pressure at all only makes sense if you want to tune your machine correctly and learn to pull shots correctly with the correct pressure.  Lots of people never adjust their OPV at all and they adjust their grind/tamp/dose  to make perfectly decent drinks with their Gaggias.  So, if you are not going to adjust it correctly, why bother adjusting it at all?  You can certainly compensate with temp/grind/dose for those few bar of extra pressure if you work at it a bit.  If you adjust to a lower (than what???) pressure, everything you teach yourself from there on in will be what you know for a machine set to some indeterminate pressure, and can't be shared with anyone whose pressure is set correctly or at another incorrect pressure. 

If we want to talk the same language, we need to know that we are (or are not) discussing a machine set to 9 bar.  If you are a haphazard user that is fine;  and it may satisfy you, which of course is what we want.  But if you want to do it right?  get/borrow/make a gauge and set  your pressure to 9 bar.  Everything else is just an approximation of espresso.

As an interim measure?  Sure....go for it, but realize that what you are learning with it at that interim setting is mostly....rubbish (I like that word, Gingerbean....:-))))  )

Susan
« Last Edit: January 08, 2014, 10:33:07 PM by SusanJoM »
“Not everything that can be counted counts, and not everything that counts can be counted.”
Attribution in Dispute

Offline D4F

  • Global Moderator
  • Grizzled GUG Veteran
  • *****
  • Posts: 1734
    • Gaggia Classic w PID
    • Baratza Forte-AP
Re: Blind OPV Adjustment
« Reply #14 on: January 09, 2014, 03:57:10 PM »
As noted this topic may elicit opinions, so a little more support for those who feel the need to adjust without a gauge.  If you wish espresso then you need to be at a pressure of 9 – 10 bar by SCAA definition.  Other definitions state 9 bar, but apparently 9 – 10 bar is the accepted Americanized standard noted in the link below.

http://coffeekind.com/reading-room/blog/what-espresso-and-what-shoot-when-you-first-start-pulling-shots

If you do not have a gauge then you can use the machine as is and be fairly sure that you are not getting “espresso” as OEM setting is about 12 bar.  If you feel the need to try to get in the accepted range of 9 – 10 bar then the non-blind, or modified blind technique of using OPV back flow may be tried as described.  Another thread describing the technique is below.  Note the the initial tone of the thread makes is seems like it is not feasible, but the response by Eric Svendson clarifies.  Eric S is a known name in espresso.  He explains pressure versus flow how the puck is affected in easily understood terms, and that the “majority of users who have measured ended up on the solid line” of the flow versus pressure diagram, right where needed.   

http://www.home-barista.com/espresso-machines/how-to-determine-brew-pressure-from-flow-rate-t23424.html

Note that the use of gauge is still the accepted method and for that matter, use of a gauge with flow regulator so that the pressure is dynamic and accurate.  Susan’s gauge is the loaner and has a flow valve.

Hope this helps to clarify and is not the blind leading the blind :)

 

LIBRARIES

Reference Library

Owners Manuals, Parts Diagrams, Wiring Diagrams, and How-To-Do-Stuff Articles.

 

+-Recent Topics

The Forum is Shutting Down, closing as of Jan 1, 2018 by SusanJoM
December 31, 2017, 08:39:24 PM

Coffee Deluxe by SusanJoM
December 31, 2017, 11:47:12 AM

(Questions) - Homemade pressure gauge for adjusting pressure by SusanJoM
December 29, 2017, 03:19:19 PM

Nice OWC restoration at HB by D4F
December 27, 2017, 04:27:49 PM

Pump leaking from plastic by wjm
December 24, 2017, 05:37:39 PM

Using Thermoblock as preheater by jerryseabridge
December 24, 2017, 11:00:25 AM

Use OWC OEM portafilter for DIY pressure and/or temp gauge? by rcfitz86
December 22, 2017, 03:02:00 PM

Classic, solenoid or pump issue - help needed! by DG Classic
December 15, 2017, 11:32:58 AM

Gaggia Classic Solenoid Spring Question by SusanJoM
December 15, 2017, 10:59:51 AM

Dosing on Gaggia Classic Stainless Steel boiler by benm
December 13, 2017, 06:15:59 AM

Powered by EzPortal