Vibiemme Domobar Super - sudden pressure drops / pump noise change during shots

#1: Post by **Bex** » May 27th, 2008, 9:46 am

Hi all.

I've been enjoying my VBM Domobar Super for several months now, but this weekend encountered a problem.

Sometimes during a shot the vibe pump's noise will drop dramatically and the pressure will drop from 10 bar to around 7.5. The shot continues to pour and looks normal.

This doesn't happen every time, but if I pull 3 shots, it's guaranteed that one of them will exhibit this behavior.

Any idea what's going wrong? I have no idea if it's related, but the hose that joins the top of the reservoir has started trying to slide out of its slot. When I open the lid to refill the reservoir, it's never snugly in its slot.

#2: Post by **Randy G.** » May 27th, 2008, 11:47 am

This can happen if there is an additional load on the electrical circuit such as a large light, refrigerator, heater, air conditioner, etc. or if an extension cord that is too long or of insufficient gage. Use a volt meter and monitor the line voltage so that when it happens you can check. Also watch to see if it happens only when the heating element comes on. In combination, the extra current draw will create this sort of situation.

#3: Post by **cafeIKE** » May 27th, 2008, 1:25 pm

If you're handy, UNPLUG the machine, pull off the side cover and check all connections, including the screw terminals to the Gicar. Give each Fast-On a good wiggle and make sure it is fully seated. Look for any overly brown insulators indicating high temperature from a bad crimp. Replace any connectors that look 'fried.'

Several months ago, when the machine was 18 months old, my Vibiemme started the same behavior. No bad connections were found, but the the problem vanished.

#4: Post by **another_jim** » May 27th, 2008, 2:45 pm

If it isn't electrical, it could be a valve not seated right, either in the OPV or in the pump. In the OPV case, loosening, then retightening the valve will probably fix it, in the pump's case, a disassembly, and cleaning the tiny little ball valve will do it.

There were pictures posted for doing this, but you'll have to look for them.

#5: Post by **cafeIKE** » May 27th, 2008, 2:51 pm

Repairing a ULKA vibratory pump

May 27th, 2008, 4:52 pm

Thanks, guys. I will take a look at these and see what I can diagnose.

#7: Post by **Grant** » May 27th, 2008, 6:45 pm

No one suggested the OPV spring replacement yet? Check for the heavy duty spring in the OPV.

#8: Post by HB » May 27th, 2008, 8:03 pm

Grant refers to the new over-pressure valve spring (l) versus old over-pressure valve spring (r) found in some early model Vibiemmes. The weaker spring had a very touchy adjustment and could provoke erratic brew pressure changes.

As reported by Randy G. here

#9: Post by **cannonfodder** » May 27th, 2008, 9:34 pm

Could it be as simple as your boiler fill solenoid is opening to top off the steam boiler while you are pulling the shot. Happens to me now and then on the Elektra and Domobar Super. There is a noticeable change in the pitch and a sudden drop in pressure, then the pressure will return to normal and the pump to its normal pitch.

#10: Post by **cafeIKE** » May 27th, 2008, 10:46 pm

The boiler fill is typically much less frequent than 1 out of 3. I can go weeks, other than when making milk drinks, without the boiler fill opening during espresso sessions.

OTOH, if the boiler AV valve were leaking, water could be boiling off and the fill valve opening to make up the loss. That would be indicated by a shorter than normal, say 120 to 150 seconds, pstat cycle.