Hi,

I just got a sweet deal (I hope) on a barely used Izzo Duetto II. I was expecting the brew pressure gauge to show me the pressure at the puck. I have only been into this for a year, but I thought a coarse grind would give me less pressure than a fine grind. On this machine it shows 9 bars no matter what grind I use. With an empty porta-filter I still get 9 bars. That seems odd to me. Can someone tell me where the pressure is measured and why it's not measured at the puck? I would thing that the pressure applied to the grounds would be significant information.

My previous machine was an old Breville single boiler with no gages, so I don't have a frame of reference.

Thanks,
Dave M.

The 9 bar is the output pressure of the rotary pump. If you grind finer, there'll be more resistance to flow, but the pressure won't exceed what you've set your OPV at. Coarser grind just reduces resistance. You're not measuring the resistance of the puck.

I'm only good at talking about roasting, so there'll be many others who can explain it better than I.

dmeeusen wrote:With an empty porta-filter I still get 9 bars. Can someone tell me where the pressure is measured...

Pressure gauge should be reading just after the pump as TomC mentioned, after gauge is likely a flow reducing jet. Because of the flow reducer, you will still see high pressure after the pump, but the dispersion block will take some amount of time to get up to pressure (once it's fully filled with water). Or even if it never fills with water, the high pressure line before the flow reducing jet should almost always be at pressure. Some systems I believe even never depressurize and so the gauge will always read very close to it's factory setting.

dmeeusen wrote:...and why it's not measured at the puck?

I would say it's not measured directly at the puck due to customer expectation. Generally the 9 bar being considered a "correct" number, so if it were to vary significantly while natural pre-infusion is taking place, many people would be wondering if their pump has a problem. The gauge is really just to give you an idea of the health of your pump and OPV system.

dmeeusen wrote:I would thing that the pressure applied to the grounds would be significant information.

This would be significant information if you could vary the pressure in some way, but since the pump is giving a constant pressure, I believe the manufacturer goes with this system as it looks more reliable. And in some ways is easy to diagnose problems with the hydraulic system over the phone, to know if a major repair is necessary, or if a simple part could be sent and replaced by the user.

These are just my impressions on why, it could be manufacturers have differing reasons as to the why. But I don't see it as much of a downside, unless you plan to try to modify your machine to control pump speed manually or automatically in the future, to try to pressure profile. In that case another pressure gauge should be added, which would give you more of an idea of what is happening during the pre-infusion stage when the line between the flow reducer and puck is filling with water.

Thanks for the info. Love the machine!