Low brewing pressure (rotary pump?)

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by rorikk »

Hi all,

I'm new to the forum, but already spent quite some time here learning from the wisdom of the crowd :)

We recently bought a secondhand Vibiemme Replica 2 group unit. Everything seems to be working fine except for one thing.. The brewing pressure will not exceed 4.2 - 4.3 bar. I tested several things already to troubleshoot what's happening.

Some basics that seem to be in good shape
- flow of water is good from both groups
- Machine looks good everywhere I have inspected, no signs of bad scaling, the previous owner has always used the machine with a water softener and had it serviced professionally on a regular basis
- Inlet pressure is fine (2.1 bar)
- The machine warms up properly (although I would assume that does not have anything to do with brewing pressure)
- There is no water leaking anywhere when running with a blind filter

What I tried to change the pressure:
- Directly plumb without water softener (didn't make any difference)
- Adjusting the pressure relief screw on the pump assembly (zero difference, regardless of screwing it in or out)
- Letting it run on both groups for a while without portafilter to eliminate trapped air as much as possible

What I think could (not) be related to the issue:
- Something in the pump, either worn or something else. It does seem to be somewhat loud, but not extremely if I compare it to examples of the sound of worn pumps.
- I do not think blockage in the pump could be the issue, as water flow is very good?
- some other part that needs adjustment? I do not think these machines have an OPV, but maybe I'm mistaken?

The machine does by the way brew espressos, even on some finer grinds, but there is almost no crema developed and the coffee seems to come out somewhat diluted in my opinion.

Hope to get some answers or direction on what to look for! If I need to provide additional info, glad to provide it :)

Team HB

#2: Post by JRising »

There has to be an OPV somewhere performing the role of expansion valve. Without an expansion valve the brew boiler or heat exchanger would blow out its fittings. Make sure that expansion valve's set higher than 11Bar so that you can set the pump's pressure in the 9 or 9.5 bar range without the expansion valve interfering. I can't tell you where you'll find it unless you post pictures, but it will have to have it, perhaps on a tee fitting between pump and boiler, or perhaps it is itself a t fitting... It will probably have a silicone hose leading away from it.

rorikk (original poster)

#3: Post by rorikk (original poster) »

Thanks for replying. I will post some pictures later for reference, however this morning I troubleshooted a bit further and found the issue and its solution. Maybe good for someone in the future:

- Removed the pump from the motor (really easy job on this machine)
- Ran the motor without pump (perfectly silent)
- twisted the pump, felt not smooth
- I exchanged the pump for a spare I could loan from a friend and pressure is now good again! Also, it did make quite some noise if I compare them now ;)

I'm going to let my old pump sit in some citric acid to see if it's really worn, or just a bit gunked up with scale. If it is worn I'm looking into refurbishing it, but that's going to be a nice summer project :).