Repairing a ULKA vibratory pump

Equipment doesn't work? Troubleshooting? If you're handy, members can help.
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#1: Post by DVL »

First off, first time post here--but always lurking around CG or some espresso related site.

My problem today is...

ULKA pumps, how many wires. I just pulled apart a Gaggia Baby that I ebayed and noticed it had some backyard mechanics going on inside. Ugly connections, speaker wire spliced in, lose wires...not what I would call pretty. More what I would call a fire hazard. The one thing I noticed is that instead of the two blades for connections, like the other machines I have rooted through, this has one blade(ground?) and a connection with two wires coming off of it? Looks like a blade connection but doesn't pull off.

Any ideas? Please steer me in the right direction.


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Jerome a Nantes
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#2: Post by Jerome a Nantes »

Perhaps you'll find some help from an article about the ulka pump on my site : ... g=fr&pg=36

There is two blades on ulka pump for connecting to the power (AC current : order is not important)
One wire pass thru the thermal fuse who have a logement in the ulka pump next to the two blades.

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#3: Post by HB »

Wow, the images alone make for an excellent internals tutorial on vibration pumps. Nice work Jerome! I hope you don't mind this direct link to show an example:


Also see this video:
Dan Kehn

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#4: Post by HB »

Someone contacted me offline asking if it's possible to repair an espresso machine's vibe pump. It took awhile to relocate this very helpful how-to due to its obscure title: I ended up with a free Starbuck. I'll add this to the Resources page for future reference.

Below is another great schematic from Eric:

From Pump? OPV? Check Valves? Wit's end!
Dan Kehn

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Team HB
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#5: Post by another_jim »

My thanks for these links and to their authors. My Semi OPV adventures earned me a small piece of grit in the little spring valve at the output end of the pump. These instructions allowed me to get the Semi back to its ridiculously overpressured lovely self in very short order.

BTW, the Ulka is a very well thought out gizmo; simply put together and easy to work on.
Jim Schulman

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#6: Post by EspressoForge »

Was just searching for this for a friend, sorry for the resurrection, but some topics are timeless!

Good links btw, thanks. :)

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#7: Post by JimG »

Great stuff! Thanks for resurrecting the thread.

Is there similar information available for the electrical side of these pumps? In particular, I would like to confirm/deny the rumored presence of rectifier diode(s) on the AC supply.


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Randy G.
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#8: Post by Randy G. »

JimG wrote: In particular, I would like to confirm/deny the rumored presence of rectifier diode(s) on the AC supply.
Just disconnect it and put an ohm meter across the feed wires to the pump, +/- and then -/+ and you can easily verify that. - 2000-2023 - a good run, its time is done

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#9: Post by mini »

Based on everything I have read, the pump uses simple half-wave rectification to pulse current into the solenoid. I haven't checked myself, but I would bet money there is a diode. It sounds like it's oscillating around 60Hz too.

Read through some of these links. I did a lot of research into Ulka pumps at one point, but I don't have the time to pull out specifics for you.
Repair of a Breville machine (w/ Ulka pump) including a schematic
CoffeeGeek thread on using voltage control
CoffeeSnobs thread with claims of rectifying diode

I don't know how the schematic in my first link was created, but FWIW, it does show a diode in line with the pump.

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#10: Post by erics »

The rectifying diode is internal to the pump's coil wiring and is so indicated on the few Ulka housings (near the electrical connection terminals) I have seen.

And then of course, there is a thermal diode (typically called a Klixon or mfg by them) that is installed as an external add-on to lots of Ulka pump installations but not necessarily all.

Eric S.
E-mail: erics at rcn dot com