pipedreams86 I have noticed that the pump engages for a millisecond every hour or so on my machine, it’s very occasional so I haven’t been able to time it exactly, and it’s happening when it’s sat idle. I
The pressurestat has a deadband (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.
