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How does a solenoid group HX machine work

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  • How does a solenoid group HX machine work

    I am in the process of restoring / reworking an old two group machine. During the course of this work and the previous restoration I have gained some knowledge of the workings of an HX machine, but it wasnt until I did the wiring diagram for the current machine that i realised, i know what various parts do in isolation but not how the whole process from pump to cup works together - or at least im a little fuzzy on the details.
    Can someone detail me exactly what happens when i flick the brew switch to on?
    some questions are - is there any pressure in the HX or if it is solely determined by the pump?
    is there a valve that opens to allow water out of the group that is normally closed?
    Id like to get an idea of the chain of events that directs the water through the machine so maybe i will start and people can correct me of fill in the blanks.

    So you turn on the brew switch, the pump comes on and pumps water to the HX - is there normally a solenoid inline between the HX and the pump? I know there is a solenoid associated with the autofil but is this also involved in brewing? what prevents the water from draining backwards when the pump is off?
    The water exits the HX at temp and under the 9 bar of pressure from the pump and enters the group. - can someone explain the switching function of the solenoid on the group. I have some idea but want to hear someones explaination. When the pump is engaged it directs water through the group to the coffee and when the pump is off it switches to dump the pressure to the exhaust pipe to the drip tray.

    Once I have all this straight in my head i want to talk about preinfusion. but lets get the basics worked out first

  • #2
    Re: How does a solenoid group HX machine work

    stumbled on this just after posting which answered some questions, but it is for an E61 group which is a little different to a straight up solenoid group.