Questions about dimmer mod and the pump in Gaggia Classic Pro

Equipment doesn't work? Troubleshooting? If you're handy, members can help.

#1: Post by showmak »

Hi guys, this is my first topic and looking forward for your help.

I know the wattage of the ULKA Pump in my EU GCP is 48 watts. if I for example fix a dimmer rated 100 or 2000 watts, and turn the dimmer to max, does it overpower the pump? or will the pump operates at 48 watts?

The other question, if I don't have a pressure gauge, is it possible to know at which bar the water flows every time I turn the pump up or down? For example, how would I know when I am on 2 bar, 4 bar or 7 bar?

Team HB

#2: Post by JRising »

The pump will operate at up to 48 watts. The dimmer can not actually generate more power than what is available, it can only "dim" the power. It's 1000 watts rating is what the dimmer itself can handle without being damaged.
For example tires rated to 300 miles an hour can not make the car go 300 miles an hour, but the tires themselves should be able to survive being operated at that speed.

I don't think I understand the second question. If you don't have a gauge, how would you measure the pressure?
There are rough ways to make reasonable guesses... If you can stop the flow with your thumb over the steam tip, then the pressure is less than 8 bar, at higher than 8 bar it becomes difficult to stop (assuming normal sized steam tip holes).
If it is brewing great espresso, the pressure at the top of the brew chamber is probably higher than 7 bar.

showmak (original poster)

#3: Post by showmak (original poster) »

Thank you for your reply, it's clear for me now, and yes your understanding was correct for the second question.


#4: Post by randytsuch »

Thinking outside the box, you could make a portafilter mounted pressure gauge.

Then you could kind of calibrate the dimmer against the pressure gauge, and see how the pressure changes as you adjust the dimmer. Could even make marks for different pressure settings.

For this to work, I think your portafilter gauge would need a valve so you would have some flow when doing this.

My version from many years ago ... auge.html

I never tried this, just thought of it reading your post.



#5: Post by Mad_Beans_9bar »

I am in a similar situation, trying to dimmer my EU GCP. Got the dimmer, found a decent knob and I m about to go fiddling for a smooth pressure variation. My side objective here is to reduce pump noise and eliminate syncing during extraction. gcp will eventually land in my office.

I ll start with the original pump but also thinking about replacing it with an invensys/ars, just for the sake of trying it ;p standard ulka comes in 48w but I see cp3 and cp4 from ARS which are 65 and 70 watts and supposedly quieter.

In theory, OPV will still go off at 9 bar so its just me controlling the flow to get variable pack pressure. Will use a pressure gauge to mark sweet spots and additional rubber to eliminate vibration.

So my question is ulka ex4, ex5 or ARS cp3, cp4? Do you see any issues with the 70watts?

Hope it doesn't blow:}