Help Troubleshooting VBM Junior

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tniccum
Posts: 3
Joined: November 14th, 2017

Postby tniccum » Nov 14, 2017, 5:52 pm

Hi all... I've tried searching for this problem - but I probably don't have the right terminology down... If there's a solution out there, please point me in that direction.

In the meantime I'll do my best to describe my symptoms (If it would help, I can even upload a video of the behavior).

So...

My machine tends to work normally first thing after heating up in the AM. However, after sitting for an hour or longer after that first cup of the day, I get the following...

After loading the portafilter and locking in, I turn on the pump and the pressure ramps up to about 10-11 bar. Sometimes, not always, it will then drop to zero. Sometimes it will pump normally, sometimes it will hover around 10-11 bar but jerkily. Occasionally it will drop to zero and turning the pump on/off will not restart it...

After a shot is pulled and the lever is returned to the off position, the pump pressure gauge will go back up to 9-10 bar... no pumping is going on. If I move to the midway lever position the gauge will return to normal (atmospheric) pressure. Steam usually comes out of the head... or hot water will dribble out.

I brought the machine in to a repair place in Minneapolis, where I was staying for 6 weeks while on the move and the repair person said it was all fixed, he replaced the OPV and gaskets in the head. Nothing changed at all.. It exhibited exactly the same behavior.

He did mention that he saw signs of arcing on one of the electrical connections which he cleaned up.

Some other notes:
1. If I run an empty portafilter it flows water just fine, around 4 bar
2. If I run a blank portafilter to backflush, it runs about 10 bar, and will sit there all day
3. It's only when I'm pushing through coffee that it seems to act weird.



Any thoughts that would guide me?

Thanks in advance!

pallen
Posts: 39
Joined: February 13th, 2008

Postby pallen » Nov 14, 2017, 10:02 pm

EDIT: Nevermind. My brain was on steam pressure, not brew pressure...

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erics
Posts: 6023
Joined: August 9th, 2005

Postby erics » Nov 14, 2017, 10:54 pm

If I run an empty portafilter it flows water just fine, around 4 bar

That is a correct reading.

The brew pressure gauge reading other than really brewing is not relevant.

Sounds like you need a replacement pump.
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at erols dot com

tniccum
Posts: 3
Joined: November 14th, 2017

Postby tniccum » Nov 15, 2017, 12:34 pm

erics wrote:That is a correct reading.

The brew pressure gauge reading other than really brewing is not relevant.

Sounds like you need a replacement pump.


Wouldn't be surprising - the only thing that throws me off is that is seems to get worse as the unit sits and gets hotter... experimenting, I think that a lot of flushing seems to help... but it's not consistent. I hate these intermittent problems :)

Anyway... A pump isn't that expensive so probably a decent guess to try. Thanks.

T

Flitzgordon
Posts: 54
Joined: May 7th, 2014

Postby Flitzgordon » Nov 15, 2017, 1:03 pm

If the gauge has a stable reading with a blind filter, maybe everything is good.

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erics
Posts: 6023
Joined: August 9th, 2005

Postby erics » Nov 15, 2017, 1:37 pm

If the gauge has a stable reading with a blind filter, maybe everything is good.

Not necessarily because when a blind basket is inserted, all flow from the pump is returned to the reservoir from the OPV relief port.

So, the brew pressure gage will simply read what the OPV is set to. It would be nice to measure that flow and see if it is steady or somewhat pulsating. It should be around 260 ml/min.

Image
Skål,

Eric S.
http://users.rcn.com/erics/
E-mail: erics at erols dot com

pallen
Posts: 39
Joined: February 13th, 2008

Postby pallen » Nov 15, 2017, 8:55 pm

Here's a good video on measuring flow rate. Its for an Expobar, but should be similar for others. Just find the return line off the OPV or measure from the line going from the OPV to the drip tray for plumbed in.
http://www.youtube.com/watch?v=kEl-uNOC1P4

tniccum
Posts: 3
Joined: November 14th, 2017

Postby tniccum » Nov 17, 2017, 8:56 pm

Thanks for the directions...

Ran experiment as outlined in the video... my results were a bit strange.

With blank basket, it was hitting 11 bar. The return line back to the tank put out 100ml in 1 minute. But I noticed that there was water going into the drip tray. I collected that and it was also 100ml... so the combination of return line water plus drip tray water was close to 200ml for 1 minute.

Based on the curve, at 11 bar that seems pretty low. It didn't seem jerky, but that's an intermittent problem... the performance ranges from pump starting and being jerky, to starting, and then stopping, but sometimes operating semi-normally.

Clearly - at this point the pump isn't putting out enough fluid, it seems.

 
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