Proper Adjustment for Oscar's Pressure Stat

[Greased Lightning]

I was on this forum a few months ago asking for help about an Oscar that would not heat up. It was lent to me by a friend who said that if I could get it working, I could use it until I got my own machine. Without a grinder, I didn't have much incentive to do anything with it and I let it be. Today, he also lent me his Pasquini Moka grinder, so I opened up the Oscar to see if I could do anything.

Thinking that I might have a pressure problem, I tweaked with the pressure stat. After doing a lot of twisting on the adjustment screw, I noticed that sometimes the heating element light would come on for only a split second, other times for a few seconds, and other times not at all. I tried doing various things like change the lead contact and opening the steam valve to see if there was false pressure. Finally, I ran the pump for a few seconds and then opened and closed the steam valve. Suddenly, after laying dormant for a year, the heating element came on and stayed on. Problem solved.

Now I have a new problem. There is no pressure gauge on the Oscar and I have no idea how to set the pressure stat back to where it should be. It is set WAY too high right now, as evidenced by the fact the overpressure relief valve blew before the heating element shut off.

My question is, what do I need to do to adjust the pressure stat to the correct setting? About the only thing I *think* I know is that I need to adjust the screw in the "-" (negative) direction. My thoughts are that I need to find a way to quickly and accurately measure the brew water temp at the portafilter. Or maybe there is some trick with watching the steam with the valve open. Perhaps other Oscar owners can tell me about how long it should take for the heating light to go out from a room temperature start. I don't even know how sensitive the adjustment screw is....I have turned it several times over. I'm looking for any and all advice you all have.

Thanks in advance! I'm looking forward to enjoying some fine coffee in the near future.

[HB]

My thoughts are that I need to find a way to quickly and accurately measure the brew water temp at the portafilter. Or maybe there is some trick with watching the steam with the valve open. Perhaps other Oscar owners can tell me about how long it should take for the heating light to go out from a room temperature start.

Measuring the brew temperature water won't give you an accurate indicator. Comparing the force and sound of the steam would give you a ballpark estimate of the boiler pressure. The boiler cycle time would give you a very rough guess too, but probably not within more than 0.3 bar, which is too wide a margin of error as a starting point for brewing espresso.

I don't even know how sensitive the adjustment screw is....I have turned it several times over.

Would you post a picture of the pressurestat? The newer Oscars come with a Sirai pressurestat. Those have lots of turns to the adjustment. The Mater/CEME type pressurestats are very sensitive and vendors have mentioned that over-torquing them is a major cause of failure (and not covered by the warranty).

It would be best to actually measure the boiler pressure with a gauge, but that of course assumes you're willing to pay a certified repairman to install one, or have necessary skills to install one yourself (please insert standard disclaimer about the risk of scalding, explosion, burns, fire, and death here).

[Greased Lightning]

I have the one on the left, the C.E.M.E. Assuming it's not broken, at this point I guess I'm looking for a very rough way to gauge the pressure I'm at. What should the pressure be at anyway, if I were able to measure it? What variance in the setting can I expect per 1/2 turn? I would like to get it into reasonable working condition (i.e. makes steam and temp is in coffee range) and then, if needed, do whatever would be most cost effective to get it set to where it should be. Maybe this means taking it to a service center. Or would just replacing the stat with a MA-TER be more cost effective in the long run? About $40 from Chris Coffee. Not sure what a service call would cost. Would a new stat be pre-set so I would not have to worry about it?

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[HB]

What variance in the setting can I expect per 1/2 turn?

I remember it being quite sensitive, around 1/8th turn per 0.1 bar. Of course I've never worried about it too much because all the machines I've adjusted had boiler pressure gauges. That said, I could probably guessimate the boiler pressure to less than 0.3 bar by watching the steam (the difference between 0.7, 1.0, and 1.3 bar is not at all subtle!). My recommendation to have it serviced / install a gauge is because you're not familiar with the machine; if you had lots of experience with it or other HXs, I would be inclined to "wing it" since you'd know by prior use when you were in the right zone. Attempting to learn how to use an espresso machine that's maladjusted would be a frustrating experience.

Would a new stat be pre-set so I would not have to worry about it?

Doubtful. Do you know anyone locally with an HX espresso machine with gauge? It'd be a strange request, but you could ask them to let you install your pressurestat to regulate it.

[Greased Lightning]

Well, the machine is back to what it had been doing before. I'm pretty sure I need a new pressure stat. I talked to my buddy this morning and told him about what happened (the overpressures situation) and he said that the machine had been doing that ever since he got it. He got it used from his dad who upgraded, and he said that if he left it on it would do that after about an hour.

[cannonfodder]

A half turn on a CEME (my Isomac uses one) is an ENORMOUS adjustment. I just re-tweaked my Pstat, touch it with a screwdriver, think about turning it and you just made a .1 bar adjustment. A half turn is easily 1 bar.

Which screw did you adjust? The larger Phillips head in that center recessed hole is the pressure adjustment. The tiny slotted screw in front of it is the deadband adjustment (don't adjust it).

Sounds like you need a new one.

[Greased Lightning]

I turned the center screw. I think I just need to buy another one. Maybe whoever I buy it from will be kind enough to adjust it for me since there is no pressure gauge on the machine.

[Reasnor]

I've had over-pressure problems with my Oscar for a couple of years now. The odd thing is that it seems to be random. Sometimes the heating element won't turn off...sometimes it will. Anyway, I talked to Roberto at Nuova Simonelli USA and he said right away to get it replaced with the commercial Sirai pressure-stat. It must be somewhat of a common problem.

Anyway, if you're willing to pay the freight there and back...they'll install it and probably be nice enough to check it out too. Not sure how much the whole kit is...somewhere in the neighborhood of $125 to $150. That seems high...but if I can get my machine fixed for that much, then I'm not spending $1800 on the "new machine that I want."

Nuova Simonelli USA

[TetOff]

Had the same sometimes-off, sometimes not problem that (eventually) became a never-off pressurestat. Switching out to the Sirai has completely changed that...have had absolutely no overpressure or overtemperature problem since then. That said, it's not a trivial job. You've got to carefully remove the old stat and T-connection and then somewhat replumb the Sirai into place (it's a lot bigger and only fits in the case in one orientation), checking for leaks in a setting in which "leaks" are scalding steam. Not a particularly hard task, but be aware of what you're getting into.

That said, the Sirai shows up at some random setting that will be way, way too low; it takes a lot of adjustment screw turning to get there. The styrofoam cup and thermometer method to measure water temperature at the group will get you a ballpark number, and is far easier than installing a gauge somewhere in the machine that would ultimately provide only an estimate of a different, but related ballpark.
Note that you have a built in upper bound, since the overtemp switch will pop if you adjust way too high, and the overpressure valve should be opening with some regularity by then too. These are events it sounds like you are already very familiar with...

[sheygetz]

Hi, as an Oscar owner, also with recent ps trouble I'll chip in.

The irregular on/off thing you describe indeed points to your Ceme being gone for good, unless it's the wiring, but I guess you checked that. As to the replacement, the Sirai certainly is the most robust ps commonly available. That being said it also is rather a tight fit in the Oscar's casing, as it originally was not intended to carry those big mothers, and actually to this day NS sells the machines with Cemes or Maters (the one with the attached microswitch, on the right side of the pic above) in Europe. Also it is rather expensive and its deadband is slightly larger (usually 3°C). If you just get yourself a Mater ps - 24€ here, ymmv - it should be rather a simple job given you can handle a wrench and some teflon tape. No bending or readjusting of tubes, as it will be the same size.

Why HB thinks measuring the temperature would be insufficient escapes me - though of course installing a boiler manometer is the easiest way to go, if you have the cash. Regulating temperature is what the ps is - albeit indirectly - all about. And should you start experimenting with different beans, you will soon be starting to accomodate temps to coffees. So, yes, that is what you want to measure. Get yourself a multimeter with a temp probe and a styrofoam cup which you cut off about 4 fingers from the bottom. Push the probe in as close to the bottom as you can get. Follow your usual flushing or whatever routine, but instead of inserting a pf into the group, stick the cup "into" it. I find personally, that a max of 90° and/ or 84°C after the first 5 secs provide a good starting point.

Sheygetz

[HB]

Why HB thinks measuring the temperature would be insufficient escapes me - though of course installing a boiler manometer is the easiest way to go, if you have the cash. Regulating temperature is what the ps is - albeit indirectly - all about.

The OP said the machine "was lent to me by a friend who said that if I could get it working, I could use it until I got my own machine." That indicated to me that he has no experience and why I said:

My recommendation to have it serviced / install a gauge is because you're not familiar with the machine; if you had lots of experience with it or other HXs, I would be inclined to "wing it" since you'd know by prior use when you were in the right zone. Attempting to learn how to use an espresso machine that's maladjusted would be a frustrating experience.

It boils down to a tradeoff of time / frustration versus money. Given that his friend reported the machine had been inoperable for awhile, having it serviced to confirm it's in good working order makes sense to me.

[Greased Lightning]

Thanks for all the replies. HB, you are correct in your assessment that I am a total newbie, but I'm also a do-it-yourselfer and I have a strong desire to learn, so I've decided to order a Mater from Chris'. I spoke with Jason the other day and he told me the factory set point should be pretty much where I need it since I am at sea level. I'll probably do the styrofoam cup method to check the temperature and adjust accordingly. I can't wait to eventually get my own machine. In a few years I hope to get something from Quick Mill like the Anita or Andreja Premium.

[erics]

Greased Lightning - Since you are a DIY person:

Here's a way to measure boiler pressure on a TEMPORARY basis, with the standard safety disclaimers:

Remove the steam tip, measure the size and pitch of the male threads on the steam arm.

Use teflon tape or teflon paste on all thread connections except use tape on the steam arm.

Screw a 1/4" NPT brass plug into a 1/4" brass coupling.

Drill & tap the 1/4" NPT brass pipe plug to match the threads on the steam arm.

Screw a 0-25 psig gage (that has 1/4 male threads into the coupling.

Warm up the machine and bleed off any trapped air in the boiler.

Trickle some water into the pressure adaptor assembly and then screw the assembly onto the steam arm.

Open the steam valve and you should be able to easily read boiler pressure with 1.0 bar = 14.5 psi. Its really 14.5038 but you don't need that accuracy for what you're doing.

Eric S.