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Installing an OPV in a Nuova Simonelli Oscar
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Discussions > Espresso > Machines > Installing an...  
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nixter
Senior Member


Joined: 29 Jan 2008
Posts: 162
Location: Vancouver
Expertise: I love coffee

Espresso: Giotto Evoluzione, Oscar Pro
Grinder: Baratza Vario
Posted Sat Jun 19, 2010, 1:52pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

I had an Oscar for the last 2 years and I did the cold water opv thing. I've concluded that there really is no need to do this mod. Brew pressure is self regulated by proper grind and dose. Dose/measure your grind to your preference, say 17g. Tamp and pull. Adjust the grind so that your extraction is in the golden window of 25-30 seconds and you will automatically have about 9bar brew pressure. Basically your grinder is the only opv you need. The vacuum breaker mod is a fantastic idea on the Oscar.
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amish_hooligan
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Joined: 12 Jun 2010
Posts: 7
Location: Colorado
Expertise: I love coffee

Posted Sat Jun 19, 2010, 2:13pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

Thanks.

Why do you like the vacuum breaker mod for the Oscar?  I thought all it did is save the trouble of opening the steam wand after turning the machine on.

Using grind and tamp to regulate brew pressure makes sense but my grind is so fine I am getting some in the cup.  If I coarsen the grind then I'll have to tamp extra hard.  I was hoping the cold water OPV  mod would make the "adjustment window" for grind and tamp larger.
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nixter
Senior Member


Joined: 29 Jan 2008
Posts: 162
Location: Vancouver
Expertise: I love coffee

Espresso: Giotto Evoluzione, Oscar Pro
Grinder: Baratza Vario
Posted Mon Jun 21, 2010, 1:38am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

amish_hooligan Said:

Thanks.

Why do you like the vacuum breaker mod for the Oscar?  I thought all it did is save the trouble of opening the steam wand after turning the machine on.

Using grind and tamp to regulate brew pressure makes sense but my grind is so fine I am getting some in the cup.  If I coarsen the grind then I'll have to tamp extra hard.  I was hoping the cold water OPV  mod would make the "adjustment window" for grind and tamp larger.

Posted June 19, 2010 link

Yes, cracking the wand works but then you must wait for the machine temp to stabilize again. Full stabilization can take a while. With a vacuum breaker you can put Oscar on a timer and she'll be all ready to go when you wake up.

Based on what you're saying, I don't think your problem is pump pressure. Most likely stale beans or poor grind quality. How long after the roast date are you brewing? What kind of grinder do you have?
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amish_hooligan
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Joined: 12 Jun 2010
Posts: 7
Location: Colorado
Expertise: I love coffee

Posted Mon Jun 21, 2010, 5:49am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

I have a 9 year old Nuova Simonelli MCF.  I get green beans from Sweet Marias and roast them weekly.

If I could just measure the brew pressure that would eliminate the guesswork.  But I don't have the tools and the OPV mod looks cheap and relatively easy.


I'm all for the vacuum breaker mod too.  It just didn't seem like my biggest problem at the moment.  When you say full stabilization can take a while, how long is that roughly?

Thanks
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nixter
Senior Member


Joined: 29 Jan 2008
Posts: 162
Location: Vancouver
Expertise: I love coffee

Espresso: Giotto Evoluzione, Oscar Pro
Grinder: Baratza Vario
Posted Mon Jun 21, 2010, 6:25pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

20 minutes give or take I'd say.

I know what you mean by "eliminating the guesswork" but you really need not worry about about the pressure. Get the grind/dose/tamp right and the pressure takes care of itself. Even with the opv the pressure it's a static 9bar. It would just be a maximum of 9bar. I did this mod and it didn't make life any easier. If anything it just created a couple extra points for potential leakage. The only real benefit of the mod is that re-routed cold water can go back to the tank instead of hot water going to the drip tray. This means more stable brew temps and less refilling. BUT! Again... in the real world if you have your grind and dose right then these benefits never materialize.
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eastbaysanfranman
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eastbaysanfranman
Joined: 29 Oct 2007
Posts: 186
Location: east bay area san francisco
Expertise: I live coffee

Espresso: Nueva Simmoneli Oscar
Grinder: Rancilio Rocky doserless
Vac Pot: Hario
Drip: Technivorm/Chemex/Espro...
Roaster: Behmor
Posted Sat Mar 1, 2014, 9:18am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

nixter Said:

I had an Oscar for the last 2 years and I did the cold water opv thing. I've concluded that there really is no need to do this mod. Brew pressure is self regulated by proper grind and dose. Dose/measure your grind to your preference, say 17g. Tamp and pull. Adjust the grind so that your extraction is in the golden window of 25-30 seconds and you will automatically have about 9bar brew pressure. Basically your grinder is the only opv you need. The vacuum breaker mod is a fantastic idea on the Oscar.

Posted June 19, 2010 link

Is this Ok, digging up old posts?

The OP stated in the first place that he read the pressure coming from the group head with a portafilter and a gauge and that it was 15 bar, way too high. It seems (I'm a newbie, mind you) that in order to conclude that what you are saying is true, that back pressure coming from the resistance of the puck is noted by the vibratory pump and it stops pushing so hard and not only this, it regulates itself, adjusting to 9 - 10 bar pressure. Is this how vibe pumps work? Are they really that smart?

Also I would like to note that the OP stated that his shots got better. It seems Nixter did not have the same experience.
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boar_d_laze
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Joined: 21 Nov 2006
Posts: 1,219
Location: Monrovia, CA
Expertise: I live coffee

Espresso: La Cimbali M21 DT/1 Junior...
Grinder: Ceado E92; "Bunnzilla"
Vac Pot: Royal Coffee Maker
Drip: Chemex + Kone; Espro Press
Roaster: USRC Sample Roaster
Posted Sat Mar 1, 2014, 11:03am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

eastbaysanfranman Said:

Is this Ok, digging up old posts?

Posted March 1, 2014 link

Who's to say no?  The problem is getting noticed by someone competent.  So far, you've only got me.

The OP stated in the first place that he read the pressure coming from the group head with a portafilter and a gauge and that it was 15 bar, way too high. It seems (I'm a newbie, mind you) that in order to conclude that what you are saying is true, that back pressure coming from the resistance of the puck is noted by the vibratory pump and it stops pushing so hard and not only this, it regulates itself, adjusting to 9 - 10 bar pressure. Is this how vibe pumps work?

No.

Are they really that smart?

Again, no.  But this time let me explain a little.  You've got it backwards.  The pump isn't smart at all.  Turn it on, it just keeps on pumping; turn it off, and it stops.  

The more "resistance" (aka "load"), the more pressure a vibratory pump will produce in the system -- up to the pump's OR the circuit's limit, whichever is lesser.  A good analogy is pumping air into a bicycle tire with a slow leak, as opposed to using the same pump to pump air into a sealed tire.  The air escaping from the leak limits the pressure, not the pump.      

An inexpensive and effective way of limiting pressure in an espresso machine's brew (liquid) circuit is installation of an OPV (over pressure valve) on the circuit to relieve it when pressure builds too high.  

Give Nixter his due.  It's true that a properly prepared puck will limit the load to "proper" pump pressure for a "proper" extraction, but an OPV is a worthwhile fail-safe.  A puck which is too dense will take longer to extract than it otherwise should, but won't get spoiled by too much pressure; not that slow flow rate and long extraction times don't pose their own problems.

Also I would like to note that the OP stated that his shots got better. It seems Nixter did not have the same experience.

Funny how things work. Worth noting also, espresso machine makers don't agree with Nixter either.  Other than the Oscar, all but the least expensive and most primitive machines have OPVs.  

To each his own.  There's no "right" in this game.  Just "whatever works."  

Rich
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eastbaysanfranman
Senior Member
eastbaysanfranman
Joined: 29 Oct 2007
Posts: 186
Location: east bay area san francisco
Expertise: I live coffee

Espresso: Nueva Simmoneli Oscar
Grinder: Rancilio Rocky doserless
Vac Pot: Hario
Drip: Technivorm/Chemex/Espro...
Roaster: Behmor
Posted Sat Mar 1, 2014, 11:40am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

Heard you loud and clear and that's what I suspected. I also concur that there's a LOT of grey area in the game of espresso as there is just way too many variables. What grinder you are using, how sharp the burrs are, what roast you're using, what water you're using, how hard you tamp, how consistent you tamp, whether your tamper has a curve or is flat, whether or not your tamper covers the entire area of the portafilter, is there calcium in the machine, the law that anything mechanical will eventually break down so perhaps some item in any machine is not working 100% or not even not working 100% but just working differently.

Who knows? Perhaps if we had experience with Nixter's machine we would conclude that the OPV didn't make a difference in the world.

An example from simpler brewing methods. I've been using my Rocky to grind my french press for a long time. I realize how important it is to upgrade and I plane on getting a smart grinder until I can save a little more btw. Well I bought an Espro press and I just love that dang thing! To the point where I had determined that Bodum presses are now garbage and useful for not much. I have realized since then that even though the extraction rate of the different size particles is not optimal, the reason I saw sooooo much of a difference is that the filter of the Espro does such a much more amazing job (it's much finer than Bodums filter) of filtering out solids, providing a much cleaner cup. If I had a proper brew grinder in the first place, I may have posted on the forum, yeah, I bought the Espro press and it's pretty and all, but definitely isn't worth $100 to upgrade over a Bodum.

As for me, Im definitely going to end up installing an OPV into my Oscar.
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eastbaysanfranman
Senior Member
eastbaysanfranman
Joined: 29 Oct 2007
Posts: 186
Location: east bay area san francisco
Expertise: I live coffee

Espresso: Nueva Simmoneli Oscar
Grinder: Rancilio Rocky doserless
Vac Pot: Hario
Drip: Technivorm/Chemex/Espro...
Roaster: Behmor
Posted Sat Mar 1, 2014, 12:00pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

Quick question, I still need to purchase different "accessories" for my Oscar. Is a gauge fitted onto a portafilter the standard way to gauge group pressure?
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Frost
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Frost
Joined: 26 Jul 2007
Posts: 2,092
Location: Sierra
Expertise: I love coffee

Espresso: Isomac Venus
Grinder: Lelit PL53
Roaster: Poppery I w/variac, MET, BT
Posted Sat Mar 1, 2014, 12:16pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

If you hunt down the Ulka pump spec sheet, it will be clear why using a OPV for brew pressure regulation is a good idea.  There is a graph in the pump spec that shows pressure vs. volume. (sorry I don't have time to hunt this down right now...) The higher the flow,  the lower the pressure. As output resistance/pressure builds, volume (cc/minute) decreases.  If you follow this chart to see the pump volume for a normal double, this will be around 11 bar.

The 15 bar spec you see is for a 'stalled' pump; zero flow.

If it makes a difference comes down to if you can taste differences between shots pulled at 11+ bar or 9 bar,  what those differences are, and if they are important to your shot taste.

My opinion is that espresso works much better at 9 bar than it does at 11 bar.


Edit; to add that some kind of OPV is required on all machines as a safety relief for (potentially explosive) thermal expansion in the boiler. Many are set much higher than brew pressure for the safety issue only. They have been 're-purposed'  for brew pressure control.


Ok it didn't take long to find a copy of the graph::

Click Here (www.home-barista.com)
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