Pressure continues to rise after pulling shot on Vibiemme Domobar

[bdbayer]

Lately I have been seeing a decrease in pressure when pulling shots on the VBM. I tried to get a reading using the blind and found I was topping out a about 8 bars. Then, after the whoosh of the backflush, the pressure would rise to 12.

I tried playing with the OPV and found no matter how much I turned it, the pressure remained at 8. The only change was that the level to pull the shot became harder to move and the pressure rose to as high as 13 after the OPV change.

I did a complete descale using citric acid last night (by the way, you can get that stuff at an Arabic grocery if you have one in your area). The crud that came out wasn't much. I use filtered watered and a softener in the tank. After cleaning the pressure then would max out at 6 and still continue to rise after the shot.

I moved the OPV setting again and got it up to 10 with the blind, still going to 13 after the shot. This higher pressure remains until it lift the lever again. The lever is also much stiffer with the OPV set higher.

Any thoughts?

Thanks,
Barry B.

[Randy G.]

The first thing I would recommend to any VBM DS user having odd behavior in regards to brew pressure would be to check the OPV spring itself. Unscrew the pressure adjustment screw and examine the spring. Refer to the photo in my post on this page:
buyers-guide-to-vibiemme-domobar-super-t4019-100.html

If you have the correct, heavier spring, remove the piston in the bore of the OPV's body and clean the bore and use a little food-grade silicone grease when reassembling it. Examine the bore to be sure it is free of corrosion or any galling that might inhibit the piston's movement and be sure the piston moves smoothly in the bore before replacing the spring.

[cafeIKE]

The stock lube on the OPV valves becomes thicker over time.
Mark the position of the valve and remove the spring and piston.
Clean off all the grease from the piston and barrel.
Lube SPARINGLY with something like Lubrifilm from EspressoCare.

Use a dab of Lubrifilm on the steam tip threads weekly to keep it easy to remove.

While at EspressoCare or your favorite vendor, get a 8.5mm group gasket [~1 year life] and Anti-Vacuum valve [stock is ~1½ yr life]. Replace 'em before they go TU

[bdbayer]

Thank you for the tips. I was afraid that was where this would go.

I am real good at taking things apart, it's the back together part that get a bit sticky.

That said; do I need to remove the OPV from the machine before disassembly or just leave it in place and take the screw out?

Thanks again,
Barry B

[cafeIKE]

No need to remove from the machine.

Make sure the machine is stone cold.
Remove the hoses from the tank so you don't syphon the reservoir.
Mark the position of the slot and note how far in the adjuster is. [They vary]
Back out the screw and take out the spring and piston.
Clean, lube and reassemble

With ten thumbs, it's a 15 minute job.

[erics]

I second everything Randy and Ian said - after all Randy is the author of the manual that ships with the Vibiemme from (all?) US retail outlets and Ian has had his Vibiemme for several years.

The flushing flowrate from my loaner Vibiemme is 500 ml in 72 seconds or about 7 ml per second with no PF in place. The pressure gage reads 3.0 to 3.4 bar during this flush depending upon whether the heater is on or off.

"Flushing" with a blind filter in place yields a pressure of 10.1 to 10.2 bar, again depending on the heater status. This particular blind filter pressure results in a very accurate 9.0 bar (measured at the group with an independent gage) when using the Scace Thermofilter. I have made no adjustments to the OPV because (obviously) there has been no need.

Pressure gage readings when the machine is not pumping (lever down) mean nothing.

[cannonfodder]

Hold up boss. The reading after the shot means nothing. It is simply residual pressure in the closed system. The pressure will also rise simply because you have a closed circuit with cold water in it. As the cold water in the closed circuit heats, it expands and builds pressure. If you brew pressure is stable during the shot, minus the small dip in pressure when the heater kicks in, you are in good shape. When I do backflushes I get the same thing.

[cafeIKE]

Whoa, hoss. If the OPV is functioning properly, any pressure increase from cold water expansion will bleed off when it exceeds the OPV set point. Unless of course, the OPV is sticky.

[bdbayer]

Hold up boss. The reading after the shot means nothing. It is simply residual pressure in the closed system.

It's not the pressure that bothers me, it's the lever getting sooo tight, almost to the point of lock up. If I lift the lever again right after the shot to drop the pressure gage, it is fine. If I let that pressure build the lever gets really tight for the next pull. Changing the OPV setting make this different but not the pressure of the shot being pulled, even into the blank. Still 8 bars at max.

Thank you for all the input. I have done all that has been recommended here with no change. It does have the thinner spring. I have sent Jim at 1st Line an email, to which he replied very quickly (great service from a great company). He felt a descale should be done prior to changing the spring. Since that was already done and the OPV looked very clean while it was apart, I am back to square one. When it cools I will take it back apart and see if the piston has any new debri to clean off. The fact that it fell out when I tipped the machine up, though, makes me think it wasn't stuck.

I am waiting to hear from Jim again, but thought it would be good to keep the brain trust here at HB active on the problem as well. Maybe we can all learn something new?

Thanks,
Barry B

[Randy G.]

The stiff lever would make me disassemble the moving parts of the brewhead and take a look in there. Might as well have replacement gaskets and the proper lube on hand. It could be that the cam is worn or some such thing, but there is no way to tell without taking it apart. The two socket head screws on top of the group actually make it fairly easy to disassemble compared to other E-61 machines.

[bdbayer]

The stiff lever is only when the pressure gage is reading 12 or 13. When I turn down the OPV and it doesn't go up, no problem with sticky lever.

[erics]

Barry - Amongst other things, try this: After you brew your shot, draw some water from the hot water tap which will cause the boiler fill circuit to energize. As the boiler fill is taking place, the brew pressure gage should head towards ZERO. Actually it should read ABOUT whatever the boiler pressure is but these gages are not that good. How does the lever feel after you do this?

The brew pressure gage in the Vibiemme takes its reading UPSTREAM of a rather large check valve which itself is UPSTREAM of the OPV. So, any pressure build-up in the brew circuit is not seen by the gage because of the check valve but the OPV would relieve this pressure once it reached the OPV setpoint.

[bdbayer]

Barry - Amongst other things, try this: After you brew your shot, draw some water from the hot water tap which will cause the boiler fill circuit to energize. As the boiler fill is taking place, the brew pressure gage should head towards ZERO. Actually it should read ABOUT whatever the boiler pressure is but these gages are not that good. How does the lever feel after you do this?

The gage does indeed return to zero when the autofill kicks in. At this time the lever also returns to a normal ease of operation. Just prior to the autofill the lever is still very tight.

Am I getting a false reading on the gage?

[erics]

Am I getting a false reading on the gage?

No, the reading on the gage is just a couple of bar higher than what it should be. I would think that once you replace the OPV spring as Randy G. first mentioned, everything should be OK because, as he said, the incorrect spring raised havoc with Vibiemme pressure issues.

If you can, it would be helpful to others to take pics of your disassembly.

How old is your machine? Still under warranty?

[bdbayer]

No, warranty is up. It was purchased before they went to a 2 year and my one year was up in February.

Here are the pictures though. I'm not sure if the marks on the piston mean anything. They are not deep enough to feel. The other thing that I question is the red rubber that has a groove in it.

What do you all think?

[erics]

Nice pics Barry.

The red "rubber" and the "piston" it fits in are the valve part of the OPV assembly. The groove in the rubber is caused by the valve seat - no problem.

Its pretty obvious when comparing your spring to Randy's pics (referenced earlier) that you have the spring which has caused pressure problems with the Vibiemme. When you receive the new spring, be sure to apply a film of food grade lubricant to the o-ring on the adjustment screw.

Adjust the "new" OPV to produce 9.5 to 10.0 bar when using a blind filter. Whatever you adjust to should be the maximum pressure you ever see with the machine.

[cafeIKE]

Are those marks or grooves on the piston?

I've had my machine OPV apart 3x over two+ years, as well as two other Vibiemme, and the pistons had no marks or grooves.

[bdbayer]

Are those marks or grooves on the piston?

They are not grooves but marks. I went over them with my fingernail and felt no real depressions. It is just slightly scored (more rough than scored) on the finish, but I woudn't call them grooves.

Can someone help me understand the operation of the spring? Does the piston move back during a shot or what? I think the marks are there because the thing is screwed in, almost to the maximum point. If the spring allows the piston to move...well, I don't think it is. That could be what the marks are from. If the piston stays in a static position instead of having some travel.

I just completed a second descale, just in case I missed something on the last try. The water came out so clean you could drink it (if it weren't citric acid water). At the very last purge of the steam wand a small amount of a dark water came out though. Could I be breaking down a washer or something from descaling again so soon?

Anyway, after the 2nd descale the pressure problem still exists. So, I'll get in touch with 1st Line on Monday and try to get the spring.

Barry B

[mhoy]

Can someone help me understand the operation of the spring? Does the piston move back during a shot or what?

Yes, it continuously keeps the pressure at a constant setting when operating correctly. You might as well replace the OPV seat since it has a groove in it and they are inexpensive.

Mark

[cafeIKE]

A groove is present from new from the spring pressure. Yours looks a bit deeper than usual. If you do replace the seat, you may have to tweak the adjustment a couple of times as the seat beds in. It's a fraction of a bar, but it does drift slightly.