Post By dlight
Post By dlight
VBM Replica Single Group (Commercial): 3 way valve doesn't exhaust at end of brew
I have an unusual machine - Vibiemme Replica Single Group. It uses standard VBM commercial parts. The group is identical to the Domobar range.
It is in spotless condition and I have recently descaled it. There was virtually no scale - descaling solution was relatively clean after a couple a hours of descaling.
The problem I have is that the machine doesn't exhaust through the 3 way valve at the end of a brew cycle. It maintains the pressure which slowly dissipates through the puck.
When I back-flush, the pressure doesn't get relieved - nothing from the exhaust port.
I've taken the group apart - looks very clean and all the parts appear to be in very good condition. Even the seals look okay.
Any ideas on what could be causing this? Happy to replace parts where required, but no obvious reason why it doesn't work. The exhaust port is opened manually when the brew cycle completes, so I don't understand why it doesn't release the pressure.
I've attached a few pictures of the machine.
Have you checked the springs, seals and that cam opens the exhaust valve? It's all mechanical so not much to go wrong. There is a video of a cut away group that might be handy for diagnosing.
Yep, done that. The exhaust spring is extremely strong, I suspect it might not be the correct part. I put an O ring with the Teflon washer to lengthen the exhaust, ie reduce the pressure applied by the spring. This has resulted in the exhaust port working more often than not. As I say, very puzzling, since you would think the mechanical action of the cam opens the port irrespective of the spring pressure.
I'll dismantle the exhaust port and attach pictures.
VBM e61 style groups use a non-standard infusion valve (longer part pictured above) that has a longer tail (triangular rod) than generic parts. I dont know what it should measure off the toppa my head, but suspect you have the standard one for some reason. They also omit the brass guide bushing that the infusion valve spring seats into on standard groups.
When you assemble the group and push the lever down you should feel the resistence increase at 45 degrees as the triangular pin of the infusion valve bottoms out on the top pin of the exhaust valve. If there's no change, the pins are not making contact.
Maybe try ECA in sydney and order a new set of VBM specific valve assemblies all round, just to be sure.
Oh, also, re. your first picture. You're assembling it with the thick spring UNDER the exhaust valve right?? Stating the bleeding obvious perhaps but the order shown in the photo is not correct.
Many thanks for your reply.
I don't feel a change in resistance when the lever is pushed down, so it looks like the infusion valve might be short. I'll get VBM replacements for the infusion valve and exhaust valve and I guess that should sort this out. I'll also replace the springs, for good measure.
Yes the picture is in the wrong sequence, however, it was/is correctly assembled.
All sorted now. Turns out that I hadn't tightened the infusion valve housing adequately. It was hand tightened only. Surprisingly, no leaks with this limited torque. When I used a spanner to tighten it, it screwed in a surprising amount, which has resulted in the exhaust port working as expected. I haven't over tightened it, so all good.
I did check the infusion valve length with another one from a VBM machine and it was the right part. And yes, it is longer than the standard infusion valve.
Many thanks to coffee_machinist, you really helped with resolving the issue.
It is worth noting that this machine makes a beautiful coffee.
My 'other machine' is a Breville double boiler (BES920). This is a great machine for home use - very quick warm up, exceptionally stable temperature, very easy to microfoam milk, no temperature surfing required,...
At the same dose and yield, with the same VST basket, the Vibiemme produces a noticeably better espresso. It brings out a sweetness in the coffee that the Breville just doesn't seem to be able to. And the flavour is, well, 'richer', more pronounced, distinctive with a lovely mouth feel.
And it is really enjoyable using an older machine that just performs beautifully. I smile every time I make a coffee, and find the ritual quite tranquil.