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Orange Baby Gaggia restoration restored
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Discussions > Espresso > Espresso Mods > Orange Baby...  
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SJM
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Posted Tue Aug 28, 2007, 2:12pm
Subject: Re: Orange Baby Gaggia restoration restored
 

JR Said:

P:S.: Susan, sorry for the hijack, I'm trying to get educated here...

Posted August 28, 2007 link

NO Problem.
Me too !!!!

Susan
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CraigA
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CraigA
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Location: Rexdale, Toronto, Ontario, Canada.
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Posted Tue Aug 28, 2007, 2:13pm
Subject: Re: Orange Baby Gaggia restoration restored
 

Everyone please take a look at Tex's, or Dan K's, or ? pictorials/text on OPV's. I have pdf files in my Documents folder also on this, & also posted links to it/them on the other thread I'm pretty sure..

Here's the link: http://myweb.tiscali.co.uk/coffeetime/_sgt/m1m4_1.htm#top

Once there, please click on the link on the OPV's., it'll open the pdf.

 
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JR
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JR
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Posted Tue Aug 28, 2007, 2:45pm
Subject: Re: Orange Baby Gaggia restoration restored
 

CraigA Said:

Everyone please take a look at Tex's, or Dan K's, or ? pictorials/text on OPV's. I have pdf files in my Documents folder also on this, & also posted links to it/them on the other thread I'm pretty sure..

Here's the link: http://myweb.tiscali.co.uk/coffeetime/_sgt/m1m4_1.htm#top

Once there, please click on the link on the OPV's., it'll open the pdf.

Posted August 28, 2007 link

While his diagram is informative, IMO it is flawed.  It implies that the excess pressure of a 16-bar pump will get vented prior to moving on to the puck.  Not so.  In fact, a 16-bar pump does not produce 16 bars of pressure at all.  It is simply capable of producing this, if there is sufficient resistance.

The entire system from the pump to the puck is one "chamber".  You can pump in water, and the same pressure hits the puck as hits the OPV.  You can't vent off any pressure via the OPV PRIOR to its hitting the puck.  Pressure will simply follow the path of least resistance.  If that is the puck, the OPV does nothing at all.  If you have a blind filter in place, the path of least resistance would be the OPV, which should vent at whatever pressure it's set for.

Again, I'm creating this on the fly, so I'm perfectly willing to be edumacated if I'm wrong...

Jack

 
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Frost
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Frost
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Posted Tue Aug 28, 2007, 2:48pm
Subject: Re: Orange Baby Gaggia restoration restored
 

AIspent quite a few hours & days looking into this before I choose to use voltage regulation of the pump. ( I owe a special thanks to Jim Schulman for providing this idea) Anyway, the OPV appears designed in most machines to protect the pump and hardware from damage. It has been adapted for use in pressure regulation as most machines pump too much Volume of water at 9 bar .... so what to do with the excess volume of water? If you look at the Ulka Pump data sheets there is a curve (almost a straight line) where you will see that pressure & volume are related: the lower the pressure, the higher the volume. The idea is to get around 1 or 2 shots at around 9 bar in around 25-30 seconds. Most pumps put out substantially more.  Ok, here's what I have found,
(thanks to earlier work by Jim Schulman in profiling pump pressure using a variac): You can change the pump pressure/volume 'curve' by adjusting voltage. What I have found to be a curious coincedence on both the Gaggia pump and Venus pump is that a voltage of 110 is just about right for a double at 9 bar! Check your line voltage & if you are at 110volts you can likely set the OPV well above 9 bar and get 2oz in 25-30 seconds.
Anyway, I know that using the OPV is very common to relieve excess flow/pressure during brew, but I have exactly the same issues and concerns being raised here.  I will stay tuned for answers as well, but I also suggest to take a look at voltage as it will affect pump output regardless of OPV settings.
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Tex
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Tex
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Posted Tue Aug 28, 2007, 5:04pm
Subject: Re: Orange Baby Gaggia restoration restored
 

In a well-tuned espresso machine the pressure in the group has been adjusted to ~9bar (whether using an OPV or governing the pump is irrelevant) and the GRIND is adjusted to the pressure so that a pull of 30ml in 25 - 30 second occurs. Nothing other than the grind is ever adjusted from that point, until the next tuning session.

The reason for adjusting group pressure with a pressure gauge equipped with a valve is to simulate the exact conditions of a pull. So we use a needle valve adjusted to release 1ml per second. The ideal back pressure that builds up in the group is ~9 atmospheres. Pressure exceeding this level will force open the OPV, diverting excess pressure from the group. If pressure drops below that threshold the spring in the OPV will force it closed again and it will remain closed unless pressure exceeds 131psi again.

Setting group pressure is one way to limit the variables in producing espresso. This adjustment of pressure is what permits us to grind to ideal time & volume of a shot as established by Ernesto Illy.

Tex: OPV-PRV diagram.gif
(Click for larger image)

 
Tex
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CraigA
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CraigA
Joined: 19 Dec 2001
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Location: Rexdale, Toronto, Ontario, Canada.
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Espresso: PID/PressureMod 2001...
Grinder: BUNN FPG-2 DBC, Baratza...
Vac Pot: Bodum Santos manual, Yama 5...
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Posted Tue Aug 28, 2007, 5:13pm
Subject: Re: Orange Baby Gaggia restoration restored
 

Thanks Tex! What I couldn't quite put into words, but what I'm well aware of the understanding of .., too busy, too tired, flustered, whatver to get it proper here., & I just got back in & posted.

Lively debate yes, but I don't want to add to the confusion!{;-o {:-D

SJM Said:

Whoa, this has me totally confused.  I thought the purpose of the OPV was to temper the pressure coming out of the pump before it contacts the puck.  I have assumed***that we were trying to adjust the pressure ON the puck, not THROUGH the puck.  

Clarification requested.

Tex's explanation & my mine were right, but so it's not too difficult for you to adjust & fiddle with Susan., I'd just adjust the OPV to the blind pressure of 10 bar. Then you brew pressure will surely be a very close 9 bar.

 
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Frost
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Frost
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Posted Tue Aug 28, 2007, 5:42pm
Subject: Re: Orange Baby Gaggia restoration restored
 

A couple things about this scenario and diagram Tex:

On the diagram, incoming water from the pump will not exceed 9 bar.  Nit pick I know, OPV limits pressure to 9 bar.  (I think most vibe pumps stall pressure is around 16bar, no flow)

In order for this scenario to work properly ( in most machines) the brew pressure must achieve 9 bar (8.5 won't open the OPV and the pump will put out way more than 1-2ml/sec) and the excess flow at 9 bar must flow through the OPV.   ie: you can't pull a good shot under 9 bar.

Just clarifying here: obviously this method works well or so many would not be using it with success.
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SJM
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Joined: 17 Nov 2004
Posts: 1,721
Location: CA
Expertise: I love coffee

Espresso: SAMA (2), Maximatic, Cremina...
Grinder: K-10PB, Rancilio MD-50
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Roaster: HotTop   Huky en route
Posted Tue Aug 28, 2007, 5:57pm
Subject: Re: Orange Baby Gaggia restoration restored
 

Okay, so a lot of this stuff is just making my eyes get glassy, and I'm not sure I quite get the pressure/resistance concept, BUT I'm making progress doing it anyway.

With time out to take a limping dog to the vet, I have gotten the needle valve adjusted so that the pump puts out 10 ml in 10 seconds.

On to the next step;  I just have to scroll back a few pages to find out what that is....

Susan  

OMIGOSH.  It's at 134 PSI right now.....Amazing....

SJM: IMG_2512.JPG
(Click for larger image)
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CraigA
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CraigA
Joined: 19 Dec 2001
Posts: 11,255
Location: Rexdale, Toronto, Ontario, Canada.
Expertise: I live coffee

Espresso: PID/PressureMod 2001...
Grinder: BUNN FPG-2 DBC, Baratza...
Vac Pot: Bodum Santos manual, Yama 5...
Drip: Behmor BraZen, BUNN VPR-APS,...
Roaster: Refurb Behmor 1600, BBQ...
Posted Tue Aug 28, 2007, 6:26pm
Subject: Re: Orange Baby Gaggia restoration restored
 

And to add, my old unadjustable OPV valve on Silvia was putting a brew pressure of 170 psi or 11.56 bar. At that pressure my water debit was 120 -125 ml in a 10 second test.

After my installation of the new Silvia adjustable OPV & adjusted to 10 bar 147 psi static | 9 bar/132psi dynamic, my water debit was 100 - or 105 ml. The Silvia's water debit is fine anything over 90 - 100 ml is standard for Silvia in the 10 sec test.

I posted about my trial runs with the valve here, posted a link to my full test on alt.coffee, & that test was the 1st one that was submitted to EPNW as "write a review", although snipped for brevity.

P.S. For anyone that didn't read my alt.coffee link in my post above, or who don't like clicking on links., sorry, I can't help you there..!, but a lot of useful info can be gleaned from following links that are referred to. Here it is in its entirety:


Well, I just KNEW that there was gonna be a hell of a difference in the
shot quality of the Black Cat that I'm using. On my May 2001 Rancilio
Miss Silvia, the OPV valve pressure that I didn't know what is was till
Fri Feb 23/07 when I completed my portafilter pressure assembly with
needle bleed valve., is/was 170 psi! or 11.6 bars. So my readjusted
dynamic pressure is 135 - 140psi, a drop of 30 - 35psi or 2.04 -
2.38/2.4 bar. Quite significant IMO.

VERY MUCH sweeter tasting, smoother, no harshness, no blonding, & due to
the lower extraction pressure drop from 17.7% - 23.5%., & from my
previous grinder setting I had to go 3 notchs coarser or approx 30%.

The very first shot I forgot to readjust my grinder & pulled a very
sweet, intense ristretto 1oz with 16 - 17 grams of Black Cat., slightly
under dosed La Marzocco style (Ascaso of Spain) ridgeless double basket.
Second re-adjusted shot was right on the money, same basket., 18 grams
of BC & 1.8 - 2oz.

Brad Ford, the Canadian Intelligentsia rep for Canada recommends &
Chicago Intelly recommends running 199.5F/~93C at the grouphead for
Black Cat, roughly the same for KidO. They use a Cirqua system to get
the water close to SCAA spec and run the pumps dialed back to about 8.2
bar as well. That's what they were running at the Toronto HostEx show as
well on a brand spanking new La Spaziale Vivaldi S1.
http://www.hostexshow.com/

I was running 198 - 199F at the grouphead & a little more than 1 bar
more pressure (1.3bar more). I wanted to err a little on the high than
low pressure side.

I PID'd my machine on June 24th, & the new Rancilio OPV on Sun Feb 25th,
dam I WISH I had'a done., or had the money to do the pressure mod then!
Cheers,
Craig.

 
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Tex
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Tex
Joined: 27 Apr 2006
Posts: 840
Location: Texas - That's God's country to everyone else!
Expertise: Professional

Espresso: Bunn ES-1A (PID'd), Gaggia...
Grinder: Rancilio MD50
Vac Pot: Way too many vintage Silex...
Drip: Melitta Clarity
Roaster: TurboCrazy &...
Posted Tue Aug 28, 2007, 8:48pm
Subject: Re: Orange Baby Gaggia restoration restored
 

With time out to take a limping dog to the vet, I have gotten the needle valve adjusted so that the pump puts out 10 ml in 10 seconds.


Thought you'd stopped beating the dogs?

Tex: smiley face 03.gif

 
Tex
--
http://www.tinyurl.com/mb4uj - My coffee pages.

http://www.tinyurl.com/2tnv87 - My 'Guidelines For Newbies' page.

http://www.tinyurl.com/2cr3e2 - I sell things for friends & neighbors here. Can I list something for you?

http://www.tinyurl.com/235dfr - BUG is Bunn User's Group (espresso)
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