Trouble adjusting pressurestat of Nuova Simonelli Oscar

Postby espressoheadyvr on Wed Feb 13, 2008 11:04 am

...split from How to adjust an espresso machine pressurestat by moderator...


I think I messed up my MA-TER pressurestat.

First off when I first adjusted it (because my brew was not hot enough) - it "felt" like it had a stop lock in the thread. ( A point where I could not screw down anymore) - but I seem to made that stop lock disappear; possibly just old plastic or grime build up - I don't know if it's really relevant - but the screw is now totally "screwable" all the way down to the brass steam pressure release part and all the way out.

But after I turned the screw to maximum and then backed off a little (the machine was off) - I turned on the machine again. Looked good, ton o' steam pressure and the safety reset button was not being flipped on. So now the brew test. And here's the problem...

The flow of the water just flew through the portafilter. I was using same dose and same tamp before and was getting 25 secs. Now I was lucky to get 10 secs. I adjust my grind finer and tamped more - and I stretched the flow to about 20 secs but the coffee was the worst. Super bitter. So I did some reading and maybe I adjusted the p-stat too much and too much heat. Well since I adjusted it so much I failed to mark my starting point of adjustment and had to guess. I backed off and backed off the p-stat now about 5 times and I'm still getting fast flow. It's times like this I wish the Oscar had a pressure and temperature gauge and I grumble about engineers.

So now I have this great machine and I'm unsure what I did but I can't make it go back to the way it was because there is no "default" position of the adjustment screw on the p-stat.

Does anyone know how many 360 degree revolutions backwards from "all the way screwed down" to "default" is? I can remove the brass adjustment screw completely for what its worth. Or did I break my p-stat? And is it "normal" for a little bit of steam to be hissing/dripping from the brass pressure stat valve?

Any idea as always appreciated.





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Postby cannonfodder on Wed Feb 13, 2008 1:13 pm

Your pressurestat has nothing to do with the rate at which water flows through the portafilter. It simply adjusts the temperature of the boiler up and down. The OPV (Over Pressure Valve) adjusts brew pressure.

The pressurestat probably had some thread lock on it to prevent it from moving during shipping. No idea about the revolutions, however pressurestats are sensitive and over tightening them can break them. Does your machine have a boiler pressure gauge?
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Postby espressoheadyvr on Wed Feb 13, 2008 1:21 pm

no pressure gauge unfortunately...
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Postby erics on Wed Feb 13, 2008 10:11 pm

Then you will need to adapt a gage to your steam wand and measure boiler pressure with the steam valve cracked open. Post a close-up pic of your steam wand w and w/o the nozzle tip removed.

Can you measure the size of the threading?
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Postby barry on Thu Feb 14, 2008 7:33 pm

cannonfodder wrote:Your pressurestat has nothing to do with the rate at which water flows through the portafilter. It simply adjusts the temperature of the boiler up and down.



Well, yes and no. It sounds like he's talking about the rate at which the shots are brewing, not just the flow from the pf. Water which is too cool will flow through the coffee at a much faster rate than "proper" temp water, so my first hunch would be that the machine has been reset to a cooler brew temperature. The absence of a pressure gauge is troubling, as I wouldn't recommend anyone attempting to adjust a pstat w/o some sort of available pressure measurement device.
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Postby cannonfodder on Thu Feb 14, 2008 9:51 pm

You are going to have to retrofit a pressure gauge to the steam wand to get your boiler pressure. Until then you are shooting in the dark.

From his description is sounded like water was gushing through. If I am not mistaken, the hot water hydrates the grounds faster, swelling them and slowing the shot. I did not think a cold shot would make that drastic of a difference but I have never pulled a shot on a cold machine either, an off temperature shot yes but nothing that dramatic. His temperature must be way off.
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Postby barry on Thu Feb 14, 2008 10:34 pm

cannonfodder wrote:From his description is sounded like water was gushing through. If I am not mistaken, the hot water hydrates the grounds faster, swelling them and slowing the shot. I did not think a cold shot would make that drastic of a difference but I have never pulled a shot on a cold machine either, an off temperature shot yes but nothing that dramatic. His temperature must be way off.



oh yeah. i'm thinking it's down around 150F or so. that cool and it'll just piss through the coffee. he definitely needs some pressure measurement device to get things right.
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Postby espressoheadyvr on Fri Feb 15, 2008 11:18 am

erics wrote:Then you will need to adapt a gage to your steam wand and measure boiler pressure with the steam valve cracked open. Post a close-up pic of your steam wand w and w/o the nozzle tip removed.

Can you measure the size of the threading?


I measured it and it appears to be about 60mm or 5/16" wide (that's the narrow part of the steam wand - not the head)...Is there a quick cheap way to get a pressure attachment?

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Postby cannonfodder on Fri Feb 15, 2008 11:49 am

You would need a pressure gauge that reads up to 1.5 bar, two bar may be better, and a fitting or several fittings to adapt the threads on the gauge to the threads on the end of the steam wand. The threaded portion that part xxxxxx003 (bottom of page) screws onto. Then you can open the steam wand to see what your boiler pressure is. I do not know much about plumbing in Vancouver. If everything is BSP threaded you should not have a problem. If it is NPT thread, you will need to adapt between the two or use a generous wrapping of Teflon tape to seal the union. I believe most commercial machines use a 10mm thread on the steam tip.
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Postby erics on Fri Feb 15, 2008 12:22 pm

Is there a quick cheap way to get a pressure attachment?


Well, I suppose that depends on what you mean by cheap. This gage would be a good starting point:

http://www.gaugestore.com/prodinfo.asp?number=38206

Then you need a 1/4" NPT female to barb adaptor available at any good hardware store and about one foot of 1/4" ID hose suitable for the temp and pressure involved, possibly available from that same hardware store but more than likely from an industrial hose supplier.

Remove the tip from the steam wand, slip the hose onto the wand, add a hose clamp, and you should be good to go.

I'm thinking that the threading on the end of your wand is 8 mm (8mm x 1.0 mm pitch) and, finding an adaptor for that metric size is difficult. If it were 10 mm (which I don't think), an adaptor is available from here:

http://www.hoseandfittings.com/ and these guys can also sell you suitable hose and fittings to go with that gage I linked to.
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