Vibiemme Domobar Super - Small Fluctuations in Brew Pressure

#1: Post by **drmikenz** » May 10th, 2014, 5:27 pm

Hi everyone,

I've just recently bought a VBM domobar super, about 4-5 years old. Initially brew pressure with a blind basket was around 13 bar, so I adjusted the OPV until it sat at 10bar. However I notice when I pull a shot or with the blind basket in the maximum pressure fluctuates during a pull, for example it will hit 10 bar, then drop to 9.5 then back to 10 and down to around 9 then back to 10 and so on. There is slight changes in pump noise during this time as well. I just wanted to check if these small fluctuations were normal or if there was perhaps an issue with my OPV ?

thanks
M

#2: Post by **Randy G.** » May 10th, 2014, 5:56 pm

4 years old and possibly an unknown history, but in any case, there is no harm in disassembling the OPV (remove screw, remove spring, pull out piston, inspect and clean valve's bore, lube, and reassemble). If you have a voltmeter and can connect it to the outlet where the VBM is powered, you could also check for varying voltage which could have the same effect.

May 11th, 2014, 1:58 am

Thanks Randy, machine last had a 'service' in Feburary according to the tag but that doesn't really mean much since I don't know what they did.

Tried to disassemble the OPV but the screw is pretty much stuck and can't be removed without burring. So that looks suspicious. is it safe to use something like WD40 on it and then try again to disassemble ? I have always got other people to service my machines in the past so DIY is a new thing for me

#4: Post by **cannonfodder** » May 11th, 2014, 11:00 am

No. No WD40. That will leach into the works and you will end up with oil in your machine. The OPV should be easy to adjust. Excerpt from Buyer's Guide to the Vibiemme Domobar Super

The OPV (Over Pressure Valve) is located in rear of the machine. For those of you new to the espresso machine world, the OPV controls brew pressure by venting excess pressure from the pump and returning the water back to the water reservoir. The Vibiemme has one of the heaviest OPV's I have seen. Once the outer shell is removed, you can access the adjusting screw through an opening under the water reservoir. The angle is a bit awkward but still usable. It would be easier to access if the opening was cut a half inch lower. To adjust the OPV, turn the screw counterclockwise to lower and clockwise to increase.

Line voltage will cause you issues as well. Next time you pull a shot or backflush watch your heater light. Does the pressure drop coincide with the heater turning off/on? if so you are under voltage.

May 11th, 2014, 6:19 pm

Thanks, thats the picture I was using as a reference. I'm definitely adjusting the correct screw however it is anything but easy to adjust. We have the same machine at work and I adjusted the brew pressure yesterday and had no issues with the screw being stuck, just a small turn and the pressure dialled in at 10 bar. Any suggestions for 'unsticking' the screw ?

I've checked for any correlation with the heater light but unfortunately that seems to act normally and isn't related to any changes in pump sound or the fluctuations in brew pressure.

#6: Post by **Randy G.** » May 11th, 2014, 6:41 pm

There is an O-ring on that large screw. If it is that stuck you should either buy or make a screwdriver bit to fit the slot as closely as possible. Try tightening it maybe 1/4 to 1/2 turn, then loosening it. There is nothing designed to lock it in place so do what you need to to get it out. Probably the O-ring is stuck in the bore and may need replacing. The fact that it is difficult to remove may indicate that it needs servicing.