Hugonl37 I found a couple of references in my doc archive.
ONE
These were from @DavecUK’s earlier notes either elsewhere or here. I won’t touch the dead band unless ACS or Dave suggests otherwise, given the risk.
Sealed Brew circuit Leak, PressureStat, Deadband, milli-second pump run
The pressure-stat has a dead-band (small screw, leave it alone)….adjustable from 0.2 bar to 0.8 bar. One would presume the manufacturer of the stat sets it to 0.5 bar. This deadband or hysteresis as they call it is the “slack” so the pressurestat doesn’t constantly click on and off for very tiny reductions in pressure.
In something like an HX machine, the thing would be clicking on and off every few seconds or so with no deadband as the boiler constantly cools and heats.. The deadband allows the temp and hence pressure to drop a little before firing up the stat. a typical deadband of 0.5 bar, allows the stat to fire the heating element every 2 minutes or so.
In the Evo the pressurestat is used to run the pump when you pull the lever towards you, the little pin at the back of the group is depressed, the valve opens and the pressure in the sealed brew circuit drops. This causes the pump to run.
If there is the slightest leak in that sealed brew circuit from, the one way valve after pump, group valve or vacuum breaker, then after a tiny drop in pressure the pump will cut in for a fraction of a second, the pressure bumps up and the pump stops….the amount of leakage for this to happen will be in the region of 5 -7 ml. So very small and if it’s slow, heat evaporation will make it unnoticeable. trying to fix it is pointless if it’s only firing the pump for a fraction of a second every 30m - hour.
I mentioned earlier not to touch the deadband, because some people will say, if I increase the dead band to 0.8 bar, then it might only happen ever 2 or 3 hours…but the CEME stats can be broken by incorrect/heavy handed adjustment.
TWO
Brew Circuit and frequent pump activation
Brew Circuit and frequent pump activation
Quick question: the first few months my machine was working perfectly, but now it has started pumping every few seconds (~ 30 second interval). This was with steam boiler on or off. I already lowered the pre-infusion pressure down to 1.5 bar then the intervals where again very long (~ 20 minutes). But now it’s back to 30 seconds although I changed nothing. Was there ever a solution found, other than lowering pre-infusion? Anywhere I should look?
Dave :
The one way valve, is another place where leakage back can occur and drop pressure…but that would tend to happen more when the machine is cold rather than hot.
There is potentially 1 other place where a pressure drop could happen, this is across the autofill solenoid to the service boiler….a little test you can try. Once the pump is activating once per minute, switch on the service boiler and set it to it’s maximum temperature…..does the frequency of activations slow down once the service boiler reaches max temp?
It would be quite normal for the pump to activate at regular intervals to maintain pressure in the brew circuit, as nothing it completely leak free, especially as things age.. try cleaning the autofill solenoid.
The dead-band on the pressure stat should ideally be set to max, which reduces the frequency. If it’s doing it verboften like the other guy, or you have to keep service boiler on, better to find source of gradual pressure drop and fix it. Also, absolutely report it to ACS.
Fix I’m not sure, the brew circuit can never be completely leak free and with time will gradually depressurise. Perhaps once every 5-15 minutes would still be quite acceptable…it’s not going to damage anything and is simply repressurising the system. I think it if was doing it more often, I’d want to start looking. You have to remember this pressure is hydraulic pressure not steam type pressure, so the slightest leak drops the pressure a lot.
If the machine is old, might need replacement parts, if it’s new cleaning, as the evo is new, it’s likely to need a seat or seal cleaning. If you disassemble the water valve on the group (note how it comes apart), and clean it it might solve the problem, especially if the portafilter is getting wet, or there is the occasional drop of water coming from the group when idle.
If it’s the one way valve, you generally won’t see a lot, although the water input tube in the tank may show a rising meniscus over time, if held up.
The water inlet valve is accessed from underneath, as there is just a pin at the top.
karl_kaefer
I finally found the time to test a little bit and followed your instructions. During the first 10 minutes of heating up the service boiler, no pump activations were audible. After the service boiler reached 130°C the pump activations started :
3mins - 1 min - 1 min - 1:45 mins - 1:13 mins - 1 min - 2min - 1 min - 2:51 mins - 2:51 mins - 1 min
And so on it went back into the around 1 pump activation per minute cycle.
BUT Paolo messaged me right before he went on vacation to turn the pressostat that controls the preinfusion pressure ¼ turn clockwise (lower pressure). This magically solved the frequent pump activations for me (at the cost of lower preinfusion pressure).
I now have one pump activation per 30 minutes - after the machine is running for 4 hours. He also has the theory that there is a small leak - unfortunately, I don’t know where and he’s on vacation now :)
Additionally, I opened the group water inlet valve as you suggested earlier, but I couldn’t find any (visible) crud there.
