Just for illustration purposes - the first diagram illustrates the position of the current "OPV".
You can see it is hot water side of the boiler. It drains into the drip tray.




This diagram shows the approximate location of the Izzo Vivi OPV I retrofitted to my Oscar. It is on the cold side of the boiler and drains into the reservoir.

Great diagram. I definitely understand the logic of placing the opv between the pump and boiler. Where did you get your opv from? Did you need to source any extra bits?

nik

2d : Since every part is a part that can fail, why not remove the post boiler OPV and move it to where it belongs? The fittings are likely British Standard Pipe.

Document everything, take lots of photos and post a thread once you're all done.

Do it right. Do it once.

Good plan. Can anyone confirm if in fact the whole opv unit will unscrew from the solenoid housing so that I can move it?

n

Actually I wouldn't move the existing OPV.

1. Its not adjustable.
2. It will leave a gap that needs to be filled by something.

Instead I would re-tighten that OPV to the point where it lets no water through and leave it where it is and forget about it.

I got this OPV (comes with a T joint)

http://www.bellabarista.co.uk/bel....asp?ProductID=278

That's a UK company, but I'm sure the major US retailers will do similar stuff.

I had to get some other bits of brass jointing just to connect the t, and various bits of 1/8 to 1/4 or 1/8 to 3/8 connectors etc. I can't recall off-hand the exact bits required but it is easily measured.

This diagram shows the standard configuration:



This diagram shows the setup of my machine:



Note that I had to trim the middle of the three teflon / plastic tubes to accommodate the OPV. Also note, from the photos posted previously that on Greg Irwin's machine chriscoffee fitted some copper pipe and left the full length of the teflon / plastic tube.

Hope this helps.

Don't understand the not adjustable part. Nixter adjustment was the source of his woes.

Filling the hole in the group should be easy enough with a male plug of the same thread as the OPV, no?
[ I could be talking through my hat as I've never had an Oscar apart ]
The manual lists it as 73012002 EXPANSIONE VALVE 1/8", probably BSPT

Maybe there is some sort of adjustment on the US OPV that's not on the EU one. Either way, it might be as easy to get a kick ass OPV that is easy to calibrate. I'll leave it up to nixter's judgment.

But in theory yes a male plug end should do the job.

The "OPV" on the NS Oscar is more properly termed an expansion valve. Its sole purpose is to relieve (drips) as the machine warms up from a cold state to brew state (45-60 minutes). The water in the hx circuit will naturally expand as it heats up and this expansion valve prevents any damage. This has been brought up by Dan before but I am not the best at remembering just where. As ONE example, expansion valves on La Marzocco brew boilers are typically set at 13 bar.

The manufacturers of the pumps used in our espresso machines all publish pump performance curves. These provide the AVERAGE pump flow at a particular discharge pressure AS MEASURED DIRECTLY AT THE PUMP OUTLET. The difference between this pressure and the pressure as would be measured "at the coffee" are different with the numerous machines discussed herein. It could very well be different between NS Oscars in North America and those like David's in Ireland. All it would take is a small orifice or other restriction installed in the brew path. As Greg Scace as pointed out (post reference not readily available), he has measured up to a 4 bar differential between pressures measured at no flow (blind filter) and those measured with acceptable brew flow.

Why not return the expansion valve to its original setting, let the machine warm up for 45-60 minutes, do a "water dance flush" and brew away?

The reason I'm unable to do a water dance flush and brew away is because I can't zero in on any predictable flush routine that gives me repeatable brew temps. I spent 2.5 hours last friday with the styrofoam cup and thermometer, flushing and waiting for all kinds of various intervals. I couldn't find a repeatable pattern. My temps were all over the place. I will be returning my "opv" to it's original position as I am picking up a proper opv and vacuum breaker this weekend.

My ultimate goal is "no brainer, walk-up espresso" Maybe the Oscar wasn't the best choice for this given that it's an HX and designed with steaming in mind. I drink straight espresso and make the odd latte for the girlfriend. The espresso is the important part though. I would gladly sacrifice some of the Oscar's awesome steam power for repeatable brew temps. If I can't get this sorted soon I see 2 options, PID or sell and get something else.

n

erics wrote:The "OPV" on the NS Oscar is more properly termed an expansion valve. Its sole purpose is to relieve (drips) as the machine warms up from a cold state to brew state (45-60 minutes). The water in the hx circuit will naturally expand as it heats up and this expansion valve prevents any damage. This has been brought up by Dan before but I am not the best at remembering just where. As ONE example, expansion valves on La Marzocco brew boilers are typically set at 13 bar.

Am I extra dense today or doesn't an OPV anywhere in the brew circuit relieve pressure built up by heating?