Posted Tue Oct 8, 2013, 7:50am 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.
Posted Tue Oct 8, 2013, 1:50pm 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.
Posted Wed Oct 9, 2013, 4:07am 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?
Posted Wed Oct 9, 2013, 8:01am 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.
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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