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Thread: What's behind these grouphead bolts??

  1. #1
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    What's behind these grouphead bolts??

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi

    I have just acquired an old (15-16yrs I have been reliably told) La Pavoni p/tre 2 group machine. This is my first real foray into trying to 'fix one up'.

    The right hand group had no flow when I first got it but I removed the top bolt - is this the 'mushroom' ? - and gave the jet and filter a soak in some citric acid. The group now has flow but when I flick the switch off - its a manual switch - there is no purge from the three way solenoid valve. I swapped the coil and the body over with the other group but still the right hand group has the same problem, the left hand group runs fine with either solenoid so I hope I am correctly assuming the problem is not with the solenoid valves but a blockage in the grouphead. It was roughly transported and I am pretty sure there has been some dislodging of scale or the likes.


    Looks like I may have to take the group heads off to give them a good clean but before I do that I would like to know what lies behind the 2 bolts on the left side of the grouphead? Please see attached picture. Do I need to undo these to clean it out or are they better left alone? I can't find any parts diagram that show what these do or hide.

    With the solenoid valves removed, the water flows out of the rear of two holes on the grouphead. I can't quite get my head around what happens when the valve is attached or what the actual flow path is, where it starts and where it goes before hitting the shower screens. I assume it goes from the rearward hole into the 3way valve then into the front hole of the group head. Which hole does the purge happen through?

    Also will the group heads be fine in mild citric acid?

    Appreciating your help in advance!!

    Thanks

    G
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  2. #2
    Not a Shoe Jimmytheboot's Avatar
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  3. #3
    Not a Shoe Jimmytheboot's Avatar
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    Quote Originally Posted by ScruffyG View Post
    Hi

    With the solenoid valves removed, the water flows out of the rear of two holes on the grouphead. I can't quite get my head around what happens when the valve is attached or what the actual flow path is, where it starts and where it goes before hitting the shower screens. I assume it goes from the rearward hole into the 3way valve then into the front hole of the group head. Which hole does the purge happen through?
    When the 3 way is activated there is flow between the two holes where its mounted, when not activated there is flow between the forward most hole and the hole at the end of the shaft where the coil mounts

  4. #4
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    Thanks Jimmy

    The exploded parts diagram is great. More detailed than I had been able to find.

    I am pretty sure that the forward hole is blocked then, but I can't tell from the diagram if I can get to it from those plugs. English translation of the parts diagram says group delivery, I am just hesitant to take it off if it is unnecessary.

    Thanks again
    G

  5. #5
    Not a Shoe Jimmytheboot's Avatar
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    The forward hole for the 3way? if it was blocked you wouldn't have flow from the group, are you testing the purge with a blind filter?

  6. #6
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    Thanks again Jimmy

    I didn't use a blind filter as the LH group was purging without one. I put one in for the RH group and that did the trick, makes sense really!!

    There is a lot of sediment coming out. I can't tell if it is stuff that has shaken loose from the boiler or if the groupheads need a really good clean and good long backflush with a cleaner, or indeed both!

    I would still like to know if it is worth taking the bolts off and if that would help in cleaning them.

    Cheers
    G

  7. #7
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    I have a question regarding the autofill.

    It is not working on this machine. When I remove the probe wire it takes 2-3 seconds for the pump to kick in, is this normal or should it be instant?

    It is instant when this switch is flicked for the grouphead. Could this be a start capacitor issue do they normally just fail completely?

    I have taken the probe out and it looks as clean as a whistle.

    Also the manual fill push button on the front of the machine seems to want to work but doesn't. It has been making an air blocked sounds after switching the grouphead switch off and a similar sound when pushing the manual fill button. Sometimes 'something' happens when I push it and it sounds like water is circulating but the pump doesn't kick in other times nothing happens at all.

    I cant see any wires for the manual fill button so is it pressure related and how exactly does it work? Could it be blocked with sediment or is that unlikely because of the diameter of the pipes?

    Thanks

    G

  8. #8
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    Perfectly normal behaviour for autofill on a commercial machine. The water/steam inside the boiler has alot of energy and moves around a bit from the action of the element. The purpose of the delay is to slightly overfill and make sure the probe is immersed by at least a few m/m so that small breaks in the probe's signal caused by the agitation of the liquid doesn't trigger the autofill constantly - which would be extremely aggravating to the user.

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    Hi Just another question regarding the autofill.

    I have dismantled the machine to transport it and it has now been reassembled. It has been tripping out the Earth Leakage Circuit Breaker intermittently, before and after assembly. We have tested the element with a Megga and it is fine so that doesn't seem to be the problem. It is a semi automatic, so just a couple of switches for the 2 groups and the fill box controller so nothing too complicated in there. It is about 15 years old.

    Is it possible that the very nature of the autofill's working would cause the earth leakage trip? The amount just enough to cause the problem on sensitive circuits? or are we barking up the wrong tree, it got us thinking we may be trying to fix a problem that wouldn't have been an issue before ELCB's.

    Of course there is the possibility the leakage is happening somewhere else but we are trying to start with the obvious and cheapest solutions first!!

    It's a la Pavoni 2 group P/Tre

    Thanks

    G

  10. #10
    Site Sponsor coffee_machinist's Avatar
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    i think it's the element. You may have tested it with a megger, but did you test it under the conditions where it's actually causing the fault current - ie. pressurised and immersed in water at 120 degrees for a period of time.

    Never seen an auto-fill circuit draw enough current to trip an RCD.

  11. #11
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    Thanks CM.

    It is definitely the earth leakage and not the rcd's. Not sure if that makes a difference.

    would a faulty starting capacitor cause an earth leakage problem. The pump works fine but I have just been told that when the pump is disconnected from the machine the problem seems to disappear.

    We have also had the fault when the main switch is set to 1 ie no element on. Is there a small amount of current running through the element even though the switch is 'off'?

    Thanks again.

    G

  12. #12
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    What's behind these grouphead bolts??

    ELCB and RCD are the same device. Current is leaking to earth essentially. Please have a qualified professional fix your machine. It's a peace of mind that it is fixed correctly and will be safe for anyone in the future to use that machine.

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    I appreciate the concern, rest assured it is in safe hands in an electronic manufacturing business with a qualified electrician handy. Although this the first foray into espresso machines, hence all the questions.

    The Earth leakage is tripping when we turn the grouphead switch off, either switch seems to do it but not all the time. Intermittent faults are great!!!

    One question is since this machine is 15 years old could it be that the 30ma threshold for the earth leakage circuit breaker is too much and as such there isn't an actual fault.

    The pump has been megga tested and it's all good. The element the same, although not under load as suggested above but with the element off the ELCB still trips.

    I guess we are imagining a scenario where we replace auto fill box, element, pump, contactor/terminal box and it still trips, there isn't that much in these machines which make us wonder if we are trying to fix and unfixable fault.

    As I am writing this I have just heard that the LH group solenoid coil is leaking to earth so hopefully that's the fault. It's wired to the RH group so would explain why either switch will do it. Fingers crossed!!

  14. #14
    Site Sponsor coffee_machinist's Avatar
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    yeah the crucial piece of information here is that the fault occurs when the groups are activated, you can be pretty sure it's a solenoid coil then if the pump has been ruled out.

  15. #15
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    Thanks CM. Its been running fine with the solenoid coil disconnected, so far so good, a new one should be with the machine tomorrow so we will see how we go.

    It was tripping only when the switch was turned off. We aren't ruling out a second fault just yet as it has tripped when left alone. The boiler had a small leak so maybe it was because the auto fill kicked in when the level dropped. I'm not sure if the fill solenoid is on the same circuit and would recreate the fault.

    I'm also not sure if once tripped by the GH switch and then when the machine is switched off and back on it would trip straight away without the solenoid being activated. At least this feels like a cheap step in the right direction!!

    Cheers

    G

  16. #16
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    What's behind these grouphead bolts??

    If this machine is quite old then I am thinking that the problem could be back EMF. It's common practice in DC circuits to use some diodes on the solenoid coil to counter this problem.

    It makes some sense ( to me only perhaps) when the group is switched off the solenoid coil creates back EMF while the magnetic field collapses, which may be enough to trip the RCD. If you think it's plausible then an oscilloscope could tell you.

  17. #17
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    Behmor Brazen - $249 - Free Freight
    Thanks for the info.

    The machine has been running fine for three days with a replaced solenoid coil so it looks like that's the culprit. In saying that there was a small amount of earth leakage from the element but apparently well with in the threshold for a trip. We have isolated that part of the element to be sure, so now its 2kw instead of 3kw and as it won't be a high volume cafe machine we think we will be OK.

    It has had a few people scratching their heads as it seemed to be intermittent and mostly when the switch was flicked off, but then it wouldn't always allow us to turn the machine on straight away, when the switch tripped the breaker, without tripping again, it was like the fault was still there, so maybe it has been a combination of faults that are hopefully now taken care off.

    Next challenge is getting used to the power of the steam.

    Thanks for all the input

    G



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