Hello everyone, I have a Rancilio Nancy (same internals as Silvia). The pump I have is an Ulka EK.
The problem I have with this machine is that, no-matter the distribution, tamping or dosage I use, shots blond early (at second 20 from pressing the brew button). I have tried a lots of types of different coffees and grinds and it doesn't seem to help. I have also tried pulling less ml of fluid to see what happened, but nothing seem to matter, shots blond at second 20. Simple or double basket, shots blonde at second 20.
So my guess is that I have a pressure-related problem, but I don't know if it is an over-pressure problem, or an under-pressure problem. My first guess is that it is an under-pressure problem, because with a rather coarse grind I get a rather short shots.
My second guess is that it is more a pressure-along-brew problem. Sometimes I get the feeling that pressure is not sustained through the pull.
And a third hypothesis is that the coil in the pump is not powerful enough to sustain pressure.
I also have electric problems in my house: for some reason pump seems to have much more power on some moments of the day. It's not a under-voltage problem, but rather some kind of pollution on the sinusoidal wave of electricity that I'm getting.

Self-Answer:

I think why it is. I believe it is because the pump has a higher flow than the original one, and because the OPV is a little over 9 bar. Let me explain: The first thing together with the second result in more cold water entering the boiler thus decreasing the boiler's water temperature faster than usual: this make overall water temp decrease too fast (and the high-pressure makes the puck extraction faster) which blondes the shots earlier. Please correct me if I'm wrong. I will post results when putting another washer to the OPV.

A few observations from my point of view:

• The pump is very tolerant of "dirty" sine wave mains power. I think that as long as the RMS voltage and the frequency are reasonably steady, the pump doesn't care too much about the shape of the signal.
• Despite the mixing of cold water inside the boiler, the measured shot temps on a Silvia still have a tendency to rise toward the end of 25 seconds. So I do not think cooling toward the end of the shot is the likely villain.

Could be that your OPV is set too high, so it will be interesting to hear if the extra washer helps. But I would bet on the root cause being the grinder or the coffee.

Jim

Yes, it is true that the pump you have installed has ABOUT 40% more flow at the same pressure as the typical Ulka EX pump BUT that excess flow goes out the OPV and NOT through the boiler.

You would do yourself a big favor by constructing a PF pressure gage (the results of a search on this site would keep you up several nights) and sanding that second copper washer until you had 9.0 bar with a pressure gage equipped blind filter. Be sure to use an oil filled 0-300 psi gage (typically glycerin).

And then there is the grinder and the coffee as Jim said.

JimG wrote:A few observations from my point of view:

• The pump is very tolerant of "dirty" sine wave mains power. I think that as long as the RMS voltage and the frequency are reasonably steady, the pump doesn't care too much about the shape of the signal.
• Despite the mixing of cold water inside the boiler, the measured shot temps on a Silvia still have a tendency to rise toward the end of 25 seconds. So I do not think cooling toward the end of the shot is the likely villain.

Could be that your OPV is set too high, so it will be interesting to hear if the extra washer helps. But I would bet on the root cause being the grinder or the coffee.

Jim

hmmm, see, great!, so I will use an RMS tester to measure changes on real AC power. ¿what would it be the appropiate tool for measuring incoming hz?
I'll watch the OPV too. Thanks a lot.

erics wrote:Yes, it is true that the pump you have installed has ABOUT 40% more flow at the same pressure as the typical Ulka EX pump BUT that excess flow goes out the OPV and NOT through the boiler.

You would do yourself a big favor by constructing a PF pressure gage (the results of a search on this site would keep you up several nights) and sanding that second copper washer until you had 9.0 bar with a pressure gage equipped blind filter. Be sure to use an oil filled 0-300 psi gage (typically glycerin).

And then there is the grinder and the coffee as Jim said.

Yes, I know, I should construct the pressure gage PF, but over here it's hard to get the parts. ¿what's the difference between a pressure gage PF to a manometer after the pump?
Thanks a lot for your answer

theCoffer wrote:so I will use an RMS tester to measure changes on real AC power. ¿what would it be the appropiate tool for measuring incoming hz?

Good digital multimeters (DMM's) will read both RMS voltage and frequency. I am most familiar with Fluke brand, but there are many other choices.

I still kind of doubt you will find power to the pump to be the main problem. The grinder and the beans would be the usual suspects.

Jim

. . . over here it's hard to get the parts. What's the difference between a pressure gage PF to a manometer after the pump?

Measuring the pressure at the pump is certainly possible but those parts would be equally difficult if not more so than those required for a PF pressure gage. It's much more involved and requires modifications to the internal plumbing whereas the PF pressure gage does not.

Under blind filter tests the pressure at the pump will be higher by about 0.1 bar, if that. When pulling a typical shot, the pressures will be ABOUT 0.5 bar lower than those measured with a blind filter. With Silvia or Nancy, the easiest course of action is adjust for 9.0 bar as previously described.