What is normal pump pressure at idle?

Need help with equipment usage or want to share your latest discovery?
edschlukebir

#1: Post by edschlukebir »

I have an ecm michelangelo 2 group. What should the pressure gauge show at idle. Until recently, I think it was right around 3 bar, and 9 bar with the pump engaged.

This morning I noticed it had jumped up to about 6 bar at idle, and 11bar when engaged. What would account for the change?

User avatar
HB
Admin

#2: Post by HB »

A general comment from Faulty pump pressure gauge?
HB wrote:The pressure reading when the machine is idle isn't important.

To elaborate, pulling a shot introduces cooler water into a closed system, but then you suddenly close off the main exit at the end of the extraction. As the water in the boiler warms up, it expands and the pressure rises. The expansion valve is typically set to open around 12 bar for rotary pump espresso machines since they have their own bypass valve to regulate brew pressure. For vibratory pump espresso machines, the expansion valve (traditionally called an over-pressure valve in this context) is set to open at the desired maximum brew pressure, usually around 9 bar. This valve vents water into the driptray to avoid subjecting the hydraulic system to excessive pressure. It only needs to let a few drops of water escape to reduce the pressure sufficiently.
To your specific question, your espresso machine is probably plumbed in, so the gauge will show the inlet pressure, at least until the water heats in the system and expands. If the idle pressure increased at the same time as the brew pressure (3 -> 6 and 9 -> 11), I would check the inlet pressure as it appears to have increased by ~3 bar.
Dan Kehn

edschlukebir

#3: Post by edschlukebir »

thanks Dan,
that's kind of what I figured, since there isn't much going on before the pump. I just went out there again, and it has dropped back down some. Not sure what would account for an increase in pressure at the inlet though.

User avatar
HB
Admin

#4: Post by HB »

It could be a sign of a sticky pressure regulator, either at the inlet or for the building itself. Or even variations in the street pressure. If you're at a commercial location, the water pressure could vary more dramatically than a residential area since your "neighbors" may install equipment capable of drawing a lot more water at once than a typical home appliance. I've read reports of some cafes having to install a static tank and independent pump to eliminate inlet pressure variation.
Dan Kehn