Brew pressure drop during shot

#1: Post by **rennix** » April 18th, 2012, 10:43 am

I noticed the manometer for the OPV slowly decreases about a bar during a shot, and sometimes it makes that terrible vibration noise intermittently. Does this mean I need a new OPV?

(Vibiemme DB Jr.)

#2: Post by HB » April 18th, 2012, 10:53 am

Try with a blind basket; if the brew pressure reading is steady, then the pressure drop you're noting during an extraction is due to channeling. For the longer explanation of why, see I still don't get it: Why adjust the OPV?

April 18th, 2012, 12:43 pm

It was constant. With a little twitch here and there. First go the OPV was noisy the whole time.

#4: Post by HB » April 18th, 2012, 12:50 pm

I've read reports of over-pressure valve chatter before (e.g., Strange noise coming from my Andreja Premium). The general consensus was that it's just a harmonic and a slight adjustment to the OPV should fix it, though some ended up replacing the OPV expansion seal.

April 23rd, 2012, 6:55 pm

Another random issue. If I leave the machine on for a while, maybe an hour, occasionally it will make a boom. Sounds like someone hit the sheet metal casing.

#6: Post by **cannonfodder** » April 23rd, 2012, 11:23 pm

Generally, booms are bad. No idea on that one. Only thing I can think of is the metal in the case expanding as the machine heats. It may be expanding, then when the stress hits a point it flexes/bows and makes that pop/bang. My drip tray will make a resounding bang when I flush the group and the stainless rapidly heats/expands then bows from the thermal expansion.

#7: Post by HB » April 23rd, 2012, 11:44 pm

The Strada driptray makes the same pop/bang sometimes due to heat expansion. In the Expobar's case, my money is on the cup warming tray above the boiler (or maybe the panel between the boiler and reservoir). Warming it up without the cover in place would support/refute this assertion.

April 26th, 2012, 5:40 pm

Ok, thanks.