Gaggia Classic water flow delay

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bean74

#1: Post by bean74 »

Maybe everyone on earth already knows this, but I had been blind to it, prior to installing a pressure gauge on my Classic's boiler. The Classic can have an enormously-variable delay in the time from switching on the pump, until water actually comes out of the group head. The delay is proportional to the time since the last shot, possibly due to water between the 3-way valve and group head evaporating.

Purging the machine with a few seconds of water flow, prior to installing the loaded portafilter, appears to resolve the variability. If you don't do this, expect your shot timing to vary by more than 5 seconds, due to no water in the first several seconds.

GDM528

#2: Post by GDM528 »

Have you correlated this with the audible shift in the pump sounds as the pressure builds up? It's very distinct on my machine, which I can use to start the timer from, rather than the switch.

JRising
Team HB

#3: Post by JRising »

While your machine's external elements are less vulnerable to self-desctruction from heating a dry boiler than immersion elements, you should definitely find and repair your boiler's leak. An idle boiler shouldn't be losing any water, all valves should be closed.

bean74 (original poster)

#4: Post by bean74 (original poster) »

JRising wrote:While your machine's external elements are less vulnerable to self-desctruction from heating a dry boiler than immersion elements, you should definitely find and repair your boiler's leak. An idle boiler shouldn't be losing any water, all valves should be closed.
Thanks for the replies, guys. I do not believe there's any boiler leak. It builds pressure as it heats, and holds the same pressure an hour at a time.

After further consideration, I believe the delay may be the result of water draining from the siphon tube between pump and reservoir. The delay could just be the siphon and pump re-priming itself.

I will look to prove or disprove this, over the next few days.
GDM528 wrote:Have you correlated this with the audible shift in the pump sounds as the pressure builds up? It's very distinct on my machine, which I can use to start the timer from, rather than the switch.
I will pay attention to this, tomorrow. Yes, I have noted the change in pitch, but usually always with the portafilter and coffee installed, I haven't experimented to see if it correlates with water flow to group head.

vit

#5: Post by vit »

My cheap DeLonghi SBDU machine was also doing this. As it turned out, it was caused by some amount of water returning from boiler into reservoar, because boiler is above boiling point even for making coffee (thermostat is set to 105°C) so under some pressure. If possible, measure the level in the reservoar immediately after purging, then check again after a few minutes to see if that's the reason in your case

Boler leakage should be very obvious, maybe not immediately, but surely after some time ...

bean74 (original poster)

#6: Post by bean74 (original poster) » replying to vit »

I'll check for this. My boiler indeed builds pressure when heating, even without boiling. Just firing it up in the morning, it probably builds 4 bar. Water is relatively incompressible, and has positive CTE, it doesn't take much. But I also don't see any drop in boiler pressure, which I'd expect with even a very small leak, (again...) as water is not very compressible.

I suspect in my case, it's likely just the siphon tube dropping water, when left for long periods. I do tend to leave my machine on and heated 3 - 4 hours every morning, and it can be more than 2 hours between shots. It seems very likely to me, based on everything else I'm seeing, that this is the primary lag, along with a little evaporation in the short path between 3-way valve and group head.