Faulty pump pressure gauge?

#1: Post by **misterpieter** » April 16th, 2012, 9:41 am

my pump pressure gauge always goes to the max (which i manually did with the OPV): (10 bar)
-> before it was 12+ bar

when i put the machine on (after 10 sec): 10 bar
when it is idle: 10 bar and it slowly goes to 0
when i pull a shot just water, (no pressure) it drops to 0 bar
when i pull a shot it depends on the pressure: max 10 bar (= 9 bar on the puck)

so when i pull shots, it works fine: it gives me rating of pressure
but when it is idle, it says the pressure is at its max and slowly drops..

any ideas?

#2: Post by HB » April 16th, 2012, 9:54 am

misterpieter wrote:so when i pull shots, it works fine: it gives me rating of pressure...

That's all that matters. 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.

April 16th, 2012, 10:00 am

thanx