Nuova Simonelli Oscar - how to lower the brew pressure?

[sdelgran]

Thanks for the great forum which I have been reading for months now. Writing my first post because... I have a question.

I have a Nuova Simonelli Oscar Professional (not plumbed at the moment but used to be). I have assessed with portafilter brew pressure gauge that it delivers around 13 bars brew pressure, if not more (my spout-gauge still leaks a lot). I did check the brew pressure because I felt the coffee was sour (compared to my Livia).

I understand the Oscar has an expansion valve. But does one know whether I can adjust this valve or not (I saw pictures on the forum of the expansion valve of a Giotto that you could open and adjust)? Is this even normal to get such a high pressure with the expansion valve or does it reveal that it is not working properly?

Thanks!

[HB]

I understand the Oscar has an expansion valve. But does one know whether I can adjust this valve or not (I saw pictures on the forum of the expansion valve of a Giotto that you could open and adjust)? Is this even normal to get such a high pressure with the expansion valve or does it reveal that it is not working properly?

The brew pressure should measure somewhere around 8.5 to 10 bar, depending on the machine and your preference. Below is a general diagram that shows how OPV / expansion valves work with vibratory pumps:



The maximum brew pressure is thus gated by the over-pressure valve (OPV). Following the (exhaust) tubing from the water tank will lead to the OPV. I don't recall the type employed with Oscar and how it adjusts. Would you post a picture of it?

[sdelgran]

Sorry for the delay...

I have been able to open the Oscar quickly. I could not find the expansion valve. I could only see one pipe going to the tank. I must be blind...



It could still be under there where the pump seems to be:



The manufacturer Website has this hydraulic schematic:



I will try to open some more and see if there is a t-pipe there with the expansion valve.

[sdelgran]

Here is a picture of the pump. Only one pipe to the tank... Still no clue where the expansion valve is.

[jesawdy]

I think it might be at the top arrow in the picture below, can we get a closer look at this two things?



Look for something that has a water supply line and a return line that should either go to the pour over tank or goes to the drip tray. The over pressure water has to go somewhere.

[HB]

The manufacturer's diagram doesn't show an expansion valve / OPV. Not all espresso machines have one (e.g., Salvatore), the reasoning being that the brew pressure will be correct at espresso flow rates. That is, a vibe pump's pressure is inversely related to the flow rate, so all is good in the world if the curve works out such that the brew pressure is ~9 bar when the flow rate is ~2 ounces in 25 seconds. Of course if your machine doesn't have an OPV and you like ristrettos...

It's hard to judge from the photos, but this looks like an expansion valve:

[jesawdy]

Yes, I think Dan found it.... that is a somewhat unusual placement right there at the group.

[sdelgran]

Absolutely correct! Thanks...

So I checked again now that I knew what to monitor exactly. With a blind filter and about 10 sec after full pressure has been built up, nothing comes out the expansion valve.

I took the valve off. It released pressure like mad (the machine was off, of course)! I opened the valve. Here is how it looks:





No adjustment as far as I can tell. Do you think there is one?

It has a lot of limescale. On the picture, it does not show very well inside, but I hope this is what kept it stuck...

It is now soaking in citric acid. Let's see...

[jesawdy]

The OPV you have does not look to be adjustable. You might could get it to be somewhat adjustable by using teflon tape/gaskets/spacers to increase/decrease the spring tension to raise/lower the pressure setting, respectively. The trick will be keeping a good seal in the process.

Hopefully it is just scale, but make sure the valve seat on the end of the spring is facing the brew path, not the outlet.

[sdelgran]

After a few hours of descaling I put everything back together and... it works great!

I will check how much pressure I get now on the portafilter but it will sure help.

Thanks a lot for your support!

[kitt]

Hi, my nuova simonelli ellimatic (model before oscar) has the same opv in the same location, it's called the neplay valve in the schematics. Not sure why they put it after the boiler therefore dumping excess hot water back to resovoir? I had a feeling mine was set a little high, so simply unscrewed the bronze nut that houses the spring, therefore lessening the pressure keeping the valve closed. As long as you don't loosen it off too far and expose the sealing o-ring it should be ok. Mike

[sdelgran]

Hey, that's a good idea... I will try. I also have an Ellimatic apart from the Oscar.