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Installing an OPV in a Nuova Simonelli Oscar
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tpowells
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Joined: 13 May 2008
Posts: 46
Location: Northern California
Expertise: I love coffee

Posted Sun Mar 22, 2009, 9:38pm
Subject: Installing an OPV in a Nuova Simonelli Oscar
 

The NS Oscar is a nice compact HX machine, with a big boiler and huge steam power.  However, it lacks a proper overpressure valve (OPV), so it is not possible to control the brew pressure.  It does have a pressure relief valve in the brewhead, which is not really meant to be adjustable, and even if you do adjust it for proper pressure, it's on the wrong side of the heat exchanger (the hot side).  I wanted to add an OPV to the Oscar and, after doing some reading, decided to do it a bit differently than the other descriptions on CG and HB.  I thought I'd post a description and some pictures for anyone else who wants to do it.  My Oscar is the newer model with the Sirai pressurestat.  The OPV is from Chris Coffee, and is a very nice unit.  With a portafilter-mounted pressure gauge, this modification makes it easy to dial in the pressure and has made a major difference in the quality of shots over the stock machine, which runs at the full pressure of the vibe pump (about 15 bar - much too high).  

I spliced the OPV into the plastic line coming from the pump.  This is accessible by removing the top of the machine, then removing the front panel.  A 1/4" T fitting was added to the line, with a new line going up the front of the frame to the OPV, which is zip-tied to the frame.  I added a 1/4" compression fitting to the bottom of the OPV to connect it to the line:

tpowells: oscar_opv.jpg
(Click for larger image)
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tpowells
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Joined: 13 May 2008
Posts: 46
Location: Northern California
Expertise: I love coffee

Posted Sun Mar 22, 2009, 9:43pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

continued...

The return hose from the top of the OPV was snaked to the back of the machine where it fits through a very convenient square cut-out in the top, near the water tank:

tpowells: oscar_opv_2.jpg
(Click for larger image)
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calblacksmith
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calblacksmith
Joined: 25 Nov 2007
Posts: 7,853
Location: Riverside, Ca, U.S.A.
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Espresso: ECM Vene. A1, La Cimbali M32
Grinder: Azkoyen Capriccio, Major
Vac Pot: 40s era Silex
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Roaster: gave it a try, decided no
Posted Tue Mar 24, 2009, 6:10am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

I had an Oscar for over a year and never felt the need to install an OPV. I did install an vacuum breaker so I could put the Oscar on a timer but that was the extent of any mods I felt it needed. Congrats on the install, I am sure you will have several hours of tweaking ahead, ENJOY!

 
In real life, my name is
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Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!

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tpowells
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Joined: 13 May 2008
Posts: 46
Location: Northern California
Expertise: I love coffee

Posted Tue Mar 24, 2009, 9:02am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

calblacksmith Said:

I had an Oscar for over a year and never felt the need to install an OPV...

Posted March 24, 2009 link

I think many Oscar owners would agree with you, but my experience has been that too high brew pressure is probably the main cause of people getting frustrated with pulling good shots from their machine.  High pressure makes for a very narrow window of workable grind, dosing and distribution, whereas the proper pressure is much more forgiving - all revealed with a naked portafilter.  Think of all of those Gaggias pumping through the puck at 15 bar...   On the other extreme, my Astra Pro came from the factory set for a very low brew pressure (about 5 bar), presumably to allow it to work better without tamping, a "feature" they advertise.  Bringing it up to 9 bar made it behave more like a standard machine.
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olph4rt
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olph4rt
Joined: 16 Jul 2007
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Posted Tue Mar 24, 2009, 11:20am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

I just ordered one.  You have no leaks with the 1/4 compression fittings?  I remember a leak when I installed my gauge, which I rectified by switching from 1/4" tube to 6mm tube fittings.  This was with 6mm teflon hose, mind you, which is like a rock.  So will I need a 1/4"npt female to 6mm tube tee?  I am doing this to hopefully rectify fluctuations in my extractions like this.
Oh, and very nice work BTW!

 
|| http://thoughtcompile.blogspot.com/ | + | It takes an average of 42 beans to make a shot.  Douglas Adams wrote in the Hitch Hiker's Guide to the Galaxy, that 42 is the meaning of life...coincidence?
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tpowells
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Joined: 13 May 2008
Posts: 46
Location: Northern California
Expertise: I love coffee

Posted Tue Mar 24, 2009, 1:21pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

No leaks, with appropriately sized brass inserts for the ends of the plastic tubing and delrin compression rings.  I did have one leak when I first brought it up to pressure, but that was at the joint of the OPV and the 1/4" female adaptor, which is a teflon-tape-requiring joint, and I didn't use enough tape.  The 6 mm tubing sounds like a better choice than the 1/4" polypropylene I used, which has a recommended working max. PSI of 140 at 70C, right at the edge in an espresso machine.
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caeffe
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Joined: 30 Aug 2007
Posts: 271
Location: socal
Expertise: I love coffee

Espresso: NS Oscar & Pavoni...
Grinder: Mazzer Major / PeDe Moka
Vac Pot: eSantos / Yama tabletop
Drip: Krups Moka Brew / Bodum Kona
Roaster: I-Roast 1
Posted Tue Mar 24, 2009, 1:41pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

tpowells Said:

The NS Oscar is a nice compact HX machine, with a big boiler and huge steam power.  However, it lacks a proper overpressure valve (OPV), so it is not possible to control the brew pressure.  It does have a pressure relief valve in the brewhead, which is not really meant to be adjustable, and even if you do adjust it for proper pressure, it's on the wrong side of the heat exchanger (the hot side).  I wanted to add an OPV to the Oscar and, after doing some reading, decided to do it a bit differently than the other descriptions on CG and HB.  I thought I'd post a description and some pictures for anyone else who wants to do it.  My Oscar is the newer model with the Sirai pressurestat.  The OPV is from Chris Coffee, and is a very nice unit.  With a portafilter-mounted pressure gauge, this modification makes it easy to dial in the pressure and has made a major difference in the quality of shots over the stock machine, which runs at the full pressure of the vibe pump (about 15 bar - much too high).  

I spliced the OPV into the plastic line coming from the pump.  This is accessible by removing the top of the machine, then removing the front panel.  A 1/4" T fitting was added to the line, with a new line going up the front of the frame to the OPV, which is zip-tied to the frame.  I added a 1/4" compression fitting to the bottom of the OPV to connect it to the line:

Posted March 22, 2009 link

That's an awesome idea and install!  I'll have to think about doing this.  I've adjusted my Pressure Relief Valve so that the brew head pressure is ~ 10 bar but the problem with this is that you lose a lot of water into the drip tray.  For my 2-3 shots daily this isn't that big a problem but when ever I become the party barista this could become an issue.

In the HB thread about doing something similar it mentions installing a fitting to take a temp reading of the brew water - before I do this mod I'm consider doing something to allow measurement of the brew temp directly also.
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Vicroamer
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Vicroamer
Joined: 3 Nov 2007
Posts: 31
Location: Australia
Expertise: I like coffee

Espresso: Aurora single group HX lever
Grinder: Mazzer SJ
Posted Sat Mar 28, 2009, 6:06pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

Oscar's look to be popular over in Germany, a Vienna dealer offers the mod as part of their Vienna Pro upgrade. German forum Kaffee-netz has several posts on this mod which is generally well received but a question has been raised suggesting the Oscar HX is designed for hot water flow through the fitted expansion valve, fitting a OPV on the cold water side will lead to reduced flow and results in a hotter brew temp, some feel this can be compensated by turning the pressure stat down. Keep in mind it is the higher voltage euro variant with a different pressurestat. Anyway I don't have a Oscar, I just keep up with the Oscar stuff, considering it as a possible Silvia replacement. Hope Oscar users find this of interest.
Babelfish link is here if you fancy wading through it.
Click Here (babelfish.yahoo.com)
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tpowells
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Joined: 13 May 2008
Posts: 46
Location: Northern California
Expertise: I love coffee

Posted Sat Mar 28, 2009, 10:54pm
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

Vicroamer Said:

...but a question has been raised suggesting the Oscar HX is designed for hot water flow through the fitted expansion valve, fitting a OPV on the cold water side will lead to reduced flow and results in a hotter brew temp, some feel this can be compensated by turning the pressure stat down...

Posted March 28, 2009 link

Thanks, that is interesting, although some of the Babelfish translation is hilarious!  I think they're mistaken (hard to say though with the language difference) about the existing expansion valve on the hot side.  At least on the US version that valve is cranked down so that it doesn't open during normal use.  It is possible to loosen it up, so that it does open although it's clearly not intended to be adjustable, and it sends large amounts of water to the drip tray if adjusted for 9 bar.  Note that there are at least two versions of this valve on US machines, and I'm only familiar with the earlier one.  Putting an OPV on the cold side makes the Oscar like almost every other available HX machine, and it is easy to adjust the brew temperature by adjusting the flush timing.
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Vicroamer
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Vicroamer
Joined: 3 Nov 2007
Posts: 31
Location: Australia
Expertise: I like coffee

Espresso: Aurora single group HX lever
Grinder: Mazzer SJ
Posted Sun Mar 29, 2009, 1:06am
Subject: Re: Installing an OPV in a Nuova Simonelli Oscar
 

At least on the US version that valve is cranked down so that it doesn't open during normal use

I think I saw a post on there about incorrectly specced valves( pressure to high) but I don't fancy wading through babelfish looking for it. I have to admit posting the link to stimulate debate amongst English speaking Oscar users.
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