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NS Oscar Question re: retaining valve
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Discussions > Espresso > Q and A > NS Oscar...  
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Lyndon_s
Senior Member


Joined: 7 Oct 2013
Posts: 14
Location: DC
Expertise: I love coffee

Espresso: NS Oscar
Grinder: Baratza Preciso
Roaster: Nesco
Posted Tue Oct 8, 2013, 8:50am
Subject: NS Oscar Question re: retaining valve
 

I have a used Oscar that I believe is having issues. Having worked to dial in my grinder (Baratza Preciso), I find that there is 10-15 secs between pushing the pump button, and the emergence of coffee. I have tried settings on the grinder from the finest (which chokes the Oscar) to more course settings where espresso rushes out. On the current setting, the pump 'tone' changes from a louder sound to what I imagine is the beginning of extraction at around that 10-15sec mark. The flow (even with fresh beans, 4-6days past the roasting date) is not smooth, but broken. I have tried various tamping pressures, which makes a difference to where within the 10-15secs the coffee starts pouring, but that initial wait still seems long. The flavor of the espresso is lacking the body and sweetness of the same beans on my Gaggia Classic.

Also, after three espresso's (with flushing in between each), my drip tray is almost full.

I contacted NS support, and the response came back: the retaining valve is leaking into the drip tray. I read on other forum about leaking retaining valves, but when I opened the top of my machine, I didn't see any indication of a leak, at least a leak into the body of the machine. So, what does it mean that the valve is leaking into the drip tray? Is this a pressure thing?

EDIT: After pulling a shot, I measured the water in the drip tray. It collected almost an entire cup (250ml) during one shot. With the top off, I watched water flow from part #3 (in the attached diagram) via the tube into the tray. Water began flowing very soon after I pushed the button to start the pump. It continued until I pushed the pump button again at the end of the shot.

Any help would be appreciated.

Lyndon_s: Oscar_Professional_WW_2.gif
(Click for larger image)
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Frost
Senior Member
Frost
Joined: 26 Jul 2007
Posts: 2,095
Location: Sierra
Expertise: I love coffee

Espresso: Isomac Venus
Grinder: Lelit PL53
Roaster: Poppery I w/variac, MET, BT
Posted Tue Oct 8, 2013, 2:50pm
Subject: Re: NS Oscar Question re: retaining valve
 

The valve in your diagram is leaking (3-way). It could be dirty with coffee residue and sticking. First thing is to try and clean it with a detergent flush using something like Cafiza. That may get it working, or it may need rebuild/replace.
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plindy
Senior Member
plindy
Joined: 27 Nov 2002
Posts: 73
Location: Seattle
Expertise: Just starting

Espresso: NS Oscar
Grinder: SJ Pharos Lido HG-One
Posted Wed Oct 9, 2013, 2:44am
Subject: Re: NS Oscar Question re: retaining valve
 

tip  
half way down the page
Too much water in the water drain plastic tank

careful there is little room in which to move wrenches
try not to strip the 4 threads in the group , or the 8 on the valve
support the outside  , turn the inside

could also be debris stuck between valve seat and spring loaded plunger

pics show new style neplex , yours  may look different  but react the same
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Lyndon_s
Senior Member


Joined: 7 Oct 2013
Posts: 14
Location: DC
Expertise: I love coffee

Espresso: NS Oscar
Grinder: Baratza Preciso
Roaster: Nesco
Posted Wed Oct 9, 2013, 5:07am
Subject: Re: NS Oscar Question re: retaining valve
 

Thanks.
I removed the expansion valve and cleaned it with urnex descaling. It seems to be in decent condition, though upon reinstall, it continued to express water during backflush and pulling a shot. I read that it's role is to release pressure from the brew head at a particular bar level.

So, I'm wondering, before I simply replace it, how much water should I expect when backflushing or brewing? And, how do I know if it's releasing  at the right pressure?

With much thanks,
Lyndon
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Frost
Senior Member
Frost
Joined: 26 Jul 2007
Posts: 2,095
Location: Sierra
Expertise: I love coffee

Espresso: Isomac Venus
Grinder: Lelit PL53
Roaster: Poppery I w/variac, MET, BT
Posted Wed Oct 9, 2013, 8:29am
Subject: Re: NS Oscar Question re: retaining valve
 

Your problem description points to the 3-way valve (the valve that relieves pressure in the portafilter after you complete the shot, dumping it into the drip tray)

It appears you serviced the OPV; Over Pressure Valve. This valve limits brew circuit pressure.

The  3 way needs to be cleaned with a detergent like Cafiza, not a descaler; you are cleaning coffee residue.


Edit;  I just re-read your last post,  appears the OPV is also implicated.....
Sounds like you need to set/adjust your OPV.
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Lyndon_s
Senior Member


Joined: 7 Oct 2013
Posts: 14
Location: DC
Expertise: I love coffee

Espresso: NS Oscar
Grinder: Baratza Preciso
Roaster: Nesco
Posted Wed Oct 9, 2013, 9:01am
Subject: Re: NS Oscar Question re: retaining valve
 

Thanks again. I have gone ahead and ordered a new OPV and 3-way valve. I couldn't get the current 3-way completely open (the screw was on very tight, and I dared not risk any damage to it), and the machine is one of the older models, so I think i'll start fresh and see if this improves things.

Also, I will remember to clean them with Cafiza!

Thanks for the help.
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plindy
Senior Member
plindy
Joined: 27 Nov 2002
Posts: 73
Location: Seattle
Expertise: Just starting

Espresso: NS Oscar
Grinder: SJ Pharos Lido HG-One
Posted Thu Oct 10, 2013, 1:27am
Subject: Re: NS Oscar Question re: retaining valve
 

valve  #3  open at 16 bar
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Lyndon_s
Senior Member


Joined: 7 Oct 2013
Posts: 14
Location: DC
Expertise: I love coffee

Espresso: NS Oscar
Grinder: Baratza Preciso
Roaster: Nesco
Posted Thu Oct 10, 2013, 8:20am
Subject: Re: NS Oscar Question re: retaining valve
 

plindy Said:

valve  #3  open at 16 bar

Posted October 10, 2013 link

Got it. I have a new valve coming from EspressoParts. If I understand correctly, the valve is pre-set to open at 16 bar though it can be 'adjusted' through tightening or loosing the screw (on the output side). I plan to leave it as-is.
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