ethom Senior Member Joined: 24 Nov 2012 Posts: 63 Location: Pittsburgh Expertise: I like coffee
Espresso: NS Oscar, Silvia broken :o( Grinder: Vario Drip: Bosch
Posted Thu Jan 10, 2013, 3:55pm Subject: Re: NS Oscar..Microfoam..Group head temperature..
Markarian Said:
Wow, this sounds familiar! I recently had a faulty neplax valve on the group that I had to replace. A good way to see if it is faulty is to take the cover off and see if water is flowing through the tube on the left of the group when you pull a shot or backflush. If it does, chances are you could benefit from NS' upgraded neplax valve as I did (my machine was made in 2004-2005, I think).
OK, I have the cover off and I can see down inside the machine. However, I don't think I'll be able to see water coming from left tube from the top. The tubes are red rubber, so any water inside is hidden and I can't see very well down to the drip tray because of other piping and parts. In the photo, you can see the red tube sort of disappear toward the bottom.
Now, if I leave the drip tray out, I'll be able to tell from the bottom, but will it make a mess or do damage without the tray?
ethom Senior Member Joined: 24 Nov 2012 Posts: 63 Location: Pittsburgh Expertise: I like coffee
Espresso: NS Oscar, Silvia broken :o( Grinder: Vario Drip: Bosch
Posted Thu Jan 10, 2013, 5:03pm Subject: Re: NS Oscar..Microfoam..Group head temperature..
I realized nothing could go too wrong with a clean water backflush, the drip tray removed, and a rag ready to sop up water. Here is what I found:
With the brew button pushed for 2-3 seconds, no water comes from the left tube. A sharp spurt does come from the right upon button shut off.
After having the brew button on longer, say 5 seconds or more, water will start to dribble from the left hand tube (looking at the machine front). Leaving the brew button pushed, water will keep dribbling.
Is the Neplax valve OK or suspect?
Is there any way to mechaincally adjust the Oscar for brew pressure (other than tamp weight and grind fineness)?
Markarian Senior Member Joined: 27 Jun 2012 Posts: 474 Location: Seattle Area Expertise: I love coffee
Espresso: Modded Nuova Simonelli Oscar Grinder: Vario-W, Mazzer Super Jolly Drip: Moka, Aeropress, Melitta 102 Roaster: Wear-Ever Popcorn Pumper
Posted Thu Jan 10, 2013, 10:53pm Subject: Re: NS Oscar..Microfoam..Group head temperature..
Ethom, you're having the exact same problem I was. You shouldn't be getting a dribble out of the Neplax (LEFT side, facing the machine) valve during backflushing. I see you have the older neplax valve, which is known to have problems and open around 9 bar. The newer ones are rated to 16. Ever since I replaced mine, I've had better shots and had to flush a lot less. I'm not saying the Neplax is your magic bullet, but if it's opening during only 5 seconds of backflushing, it's probably wearing out.
Now a word of caution: The Neplax looks ridiculously easy to replace and it is, in theory. However, it is so INSANELY easy to strip the brass threads on these valves that a velvet touch is called for. Only change it when the machine is cold, and make sure you use a proper 14mm wrench to do the job. Call Nuova Distribution in Ferndale to order the part, it's about $20 plus shipping. I stripped my old valve, AND my new one, AND partially my group head. Only a mountain of plumber's tape and a prayer keeps my group together. Luckily, I'm confident the seal will hold until I drive the machine into the ground.
I see you have the older neplax valve, which is known to have problems and open around 9 bar. The newer ones are rated to 16. Ever since I replaced mine, I've had better shots and had to flush a lot less. I'm not saying the Neplax is your magic bullet, but if it's opening during only 5 seconds of back flushing, it's probably wearing out.
Here is where my newbie-ness causes confusion. I've learned (at least read many times) that optimum brew head pressure is about 9.5 bar and people adjust their machines, install, or replace OPVs to reduce higher factory pressure down.
Now, if the old Neplax opens at about 9 bar wouldn't that be preferable to one that opens at 16 bar which I understand to be too high for good brewing? What am I not understanding?
Would a device like the one pictured help me determine where the brew head pressure is now? I've read there is a difference between static pressure and dynamic (flowing water) pressure as the puck actually encounters it. I don’t see how this gauge could measure pressure with water flowing but have found many people using ones like it.
Markarian, with your new Neplax valve, is your brew pressure 16 bar or is it limited somehow? Can you help me understand how the higher pressure valve improves your shots? Being an engineer, I like the physics aspect of these toys.
Finally, with my Neplax likely wearing out, what happens when it fails? Am I bound for Starbucks for a while ;o(
Markarian Senior Member Joined: 27 Jun 2012 Posts: 474 Location: Seattle Area Expertise: I love coffee
Espresso: Modded Nuova Simonelli Oscar Grinder: Vario-W, Mazzer Super Jolly Drip: Moka, Aeropress, Melitta 102 Roaster: Wear-Ever Popcorn Pumper
Posted Fri Jan 11, 2013, 1:41pm Subject: Re: NS Oscar..Microfoam..Group head temperature..
...and here's where you run into the limitations of being an Oscar owner.
The Neplax valve is purely for safety, NOT for controlling optimum brew pressure. The Oscar does NOT have an OPV. OPV's are for controlling brew pressure and need to be installed on the other side of the heat exchanger with a return hose that feeds back into the tank. Some have modified the Oscar to include one of these, as well as a vacuum breaker (another bit of baffling oversight on Simonelli's part). Also, just because the old neplax valve is designed to open at 9 bar or so doesn't mean it's not opening at less pressure.
The new neplax valve helped me with my shots because of two things: One, the valve was opening halfway through my shots as it encountered resistance from the puck. When it actually failed, I saw the coffee stream stop and suddenly suck back against the basket as if the three way valve had been triggered, even though the brew cycle was still going. Two, the valve was opening in its idle state, purely from the pressure of the HX, and its seal was failing where it met the group head; it was actually causing the heat exchanger to leak into the drip tray. This caused air to enter the HX through the group head and I would get sputtering and only an intermittent stream, rather than an immediate flow of water when I turned it on. This caused inconsistent brew temperatures and screwed up my flush routine. And, according to NS themselves, the old neplax valves just suck and have have reached the end of their lifespan. It's simply a calibrated spring with a silicone nipple at the end, nothing fancy. I'm not a tech, and I'm certainly not an engineer, but I'm sure someone on here can explain better why I'm so much more of a happy camper with the 16 bar valve. My understanding is that it should only open if there's imminent risk of a catastrophic failure, not as a means to control brew pressure.
There are only two ways an Oscar owner can control brew pressure--Install an OPV deep in the machine, or like Noobie's doing soon, install pressure-altering gicleurs in the HX. Let me know if all this info helps!
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