E61: manometer stays at 9 bar after pulling shot

#1: Post by **Chris@R** » April 16th, 2014, 3:20 am

Ok, I think this is not a big deal, but I kind of want to understand what is happening here. After pulling a shot on my e61 double-boiler (Rocket r58), the manometer which indicates group head pressure stays at 9 bar after the shot has been pulled. It stays there for about a minute or two, and then very slowly begins to come down until it's eventually at zero again. In total this takes about 5 minutes.

Everything else is working just fine. Solenoid valve releasing water, nice dry puck, ok shots.

Can anyone explain to me what is causing this? My gut feeling is that it's nothing to worry about. But I could be wrong.

Chris

#2: Post by **Mouldy** » April 16th, 2014, 4:11 am

Hi there.

Not familiar with the exact configuration of the R58; however what you describe is the same as on my vintage Faema E61. It relates to the group design whereby with the lever in the fully down position, neither valve is open. This is described in a post by cafeIKE on page two of this thread;

Is there a purpose for the E61 middle brew lever position?

#3: Post by HB » April 16th, 2014, 7:26 am

From my previous reply to Brew Pressure at Rest:

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.

If the brew reading rises above 12 bar when the machine is idle, you should adjust the expansion valve such that it allows water to escape. Otherwise the brew pressure gauge's reading doesn't matter unless you're pulling a shot.

#4: Post by **rjamadagni** » April 16th, 2014, 3:14 pm

I see this (similar) behavior on my cellini as well, however it stays between 11-12 bar after shot is stopped. Normally I lift up the lever a little bit as if I am about to pull a shot and bring it down again without taking it up fully. This drops the manometer to almost 0 again.

I had asked this question to my vendor (WLL) and was told it isn't a big issue, a flip of lever would correct it.

#5: Post by **Beenbag** » April 16th, 2014, 8:18 pm

This simply highlights the fact that most of these "brew pressure" gauge set ups dont actually reflect the real brew pressure at the group (puck ).
Even during extraction, the gauge is only reading the pressure in the line between the boiler and the group before the gicleur restrictor ....which alter the pressure at the group.
Other than for initial setting of the OPV, i do wonder at the point of some of these brew gauges.

#6: Post by **Randy G.** » April 16th, 2014, 8:30 pm

I have a plumbed Vibiemme dual boiler E-61. I would be worried if the gauge didn't stay up after a shot. The brew side is a sealed system with the inlet being the pump supply and the outlet being a pressure relief valve or the group during a brew cycle. When my machine is on the pressure rises after an extraction as the water in the boiler is heated and expands. When the machine is cold the gauge reads the inlet pressure from the water supply line. If the pressure drops it means either they have the pressure gauge set up to read somewhere outside of the thermosyphon loop OR there is a leak in the brew side allowing the pressure to drop. I don't know the Rocket so am just applying what I know from the VBM. No charge for ignoring me.. I'll just make believe you're my wife.

http://users.rcn.com/erics/ · #7: Post by **erics** » April 16th, 2014, 9:53 pm

Normally I lift up the lever a little bit as if I am about to pull a shot and bring it down again without taking it up fully. This drops the manometer to almost 0 again.

That can, potentially, do more harm than good. The brewing hydraulics become a closed system once the lever is lowered to the "off" position and the thermosyphon system is enabled. Lifting the brew lever, for the purposes of taking a gage reading down, upsets the thermosyphon system.

This simply highlights the fact that most of these "brew pressure" gauge set ups don't actually reflect the real brew pressure at the group (puck ).

Aside from gage inaccuracy, it is pretty close. Of course there is a pressure loss across the system (primarily the ~0.70 mm gicleur), but this loss is in the order of 0.15 to 0.25 bar because the flow rates are so minimal.

#8: Post by **Randy G.** » April 17th, 2014, 1:01 am

rjamadagni wrote:I see this (similar) behavior on my cellini as well, however it stays between 11-12 bar after shot is stopped. Normally I lift up the lever a little bit as if I am about to pull a shot and bring it down again without taking it up fully. This drops the manometer to almost 0 again.

Besides what Eric stated, if enough pressure builds in the "mid position" and then the lever is dropped, the 3-way opens and can cause enough of a vacuum effect as the water exits the brewing area to dislodge the puck from the portafilter enough to ruin the extraction.

April 17th, 2014, 3:02 am

Alright, thanks guys - it's starting to make some sense now. I do indeed see that if I raise the lever to the middle position, the pressure is released - you get a little flush of water and the manometer drops to zero. I discussed it with the vendor yesterday, who also said that it's nothing to worry about - his own machine (an expo bar brewtus iv) also does this sometimes, although not all the time.

I do wonder what the manometer's actual use is, though. Even if I pull a blank shot, with just an empty portafilter and no coffee, it goes up to 9 bar. So in what way is the information it gives every going to make you change what you're doing? It seems to be just saying '9 bar', '9 bar' no matter what I do.

Chris

#10: Post by **Nate42** » April 17th, 2014, 7:32 am

Your machine has a rotary pump, which can generate enough pressure at any reasonable flow rate that you should expect it to always read 9bar, or whatever its set for. A vibe pump will show more variation since they can only generate full pressure at low flow rates. Other than confirmation that your pressure is set where you want it, it really doesn't provide you with any information you need during a shot. If you want confirmation that it works, with your machine off and cold it should read near zero. You will use it if you ever decide to readjust your pressure, and you might give it an occasional glance to make sure nothing has changed (if it starts behaving strangely it can be a sign things have gone wrong) but other than that you can pretty much ignore it.