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Thread: Help me diagnose pressure drop after shots - Brugnetti Simona Top HX

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    Help me diagnose pressure drop after shots - Brugnetti Simona Top HX

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

    My Brugnetti Simona Top HX machine has served me very well for probably five years now (second hand off the bay), only requiring a couple of group seal replacements and, recently, self-refurbishment of the anti-vac valve on the boiler.

    During this time its steam performance has been outstanding, allowing me to pull two doubles and then steam milk right away (or concurrently if I was coordinated enough).

    However, over the last week there have been 3 occasions where, having pulled my shots, there is no steam available. The pressure guage drops from its usual 1.3-1.4 bar (or whatever the unit of measure is, I'm not at home to confirm) to 0.4 bar. I have to wait a minute or two for the pressure to return to normal.

    I had thought the pump may be going a few weeks ago when I got the choking 'beep beep' during shot pulling when it obviously wasn't choking, but that doesn't seem to have continued. Would the current problem to be a symptom of a failing pump? The pump engages when I pull my shots.

    The machine seems to heat up as quickly as it always has, implying to me that there's no problem with the element.

    Any help would be appreciated.

    Thanks,
    Tristan

  2. #2
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    I don't think it will be the pump, as the pump is not required for steaming. Could perhaps be a pressurestat issue?

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    Thanks MrJack.

    I've now studied a couple of diagrams of the typical HX setup and can see that the pump has no influence on pressure. Also, drawing shots also has little or no influence on pressure (only in that drawing cold water through the HX pipe presumably lowers the water temp in the boiler as heat is transferred from the boiler water to the HX pipe fluid). I wouldn't expect that to influence boiler temp/pressure to the extent experienced.

    So where is all the boiler temp/pressure going during or immediately post pulling the shot?

    There is no evidence of water leakage so I can only assume that you may be right MrJack. The pressure stat/autofill solenoid is injecting cool water into the boiler during or after the shot pull?

    The previously faulty (corroded) anti vac valve meant that there was a fair bit of steam exiting into the body of the machine. Maybe that has damaged the pressure stat, solenoid or control board (worst nightmare for a machine long discontinued in Aus).

    What I don't get though is if cool water is injected into the boiler, how is there room for it? There doesn't appear to be excess water in the drip tray.

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    Do you have a HX leak?

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    Quote Originally Posted by Hildy View Post
    Do you have a HX leak?
    So that would be where water flowing through the HX tube leaks into the main boiler as you're pulling the shot? That sounds like a logical possibility. Sounds like that would require a visit to a service centre.

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    TC
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    ....or the boiler fill solenoid is on its way out. You'd see cold added to the boiler- potentially leading to overfill as well and compromised shot performance.

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    What sort of pump is it? Would a boiler fill solenoid failure on a vibe pump not lead to inadequate brew pressure (because all the water from the pump is going through the low pressure path of into the boiler)?

    Come to think of it, a HX leak would lead to the same thing, unless it's a tiny leak.

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    Can you see the pressure drop when you are pulling water through the group, i.e. its not a sudden drop when you open the steam wand itself?

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    Quote Originally Posted by burr View Post
    Can you see the pressure drop when you are pulling water through the group, i.e. its not a sudden drop when you open the steam wand itself?
    I'll have to check in the morning, I wasn't paying enough attention last time.

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    Quote Originally Posted by Hildy View Post
    What sort of pump is it? Would a boiler fill solenoid failure on a vibe pump not lead to inadequate brew pressure (because all the water from the pump is going through the low pressure path of into the boiler)?

    Come to think of it, a HX leak would lead to the same thing, unless it's a tiny leak.
    It's an Ulka EX5 vibe pump.

    As mentioned in the OP, I did possibly experience indications of low brew pressure a couple of weeks ago - the choke warning when no choke was occurring. Flow was slower than usual though. The problem is that symptoms aren't consistently occurring.

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    So I've just now done my usual routine of two doubles then milk. Pressure remained stable during shots. Between the second shot and starting steaming it actually rose from 1.3 to 1.5 bar. As soon as I open the steam knob the pressure drops to 0.4 and there is barely a dribble of steam. Shut it down and over the space of a minute or so pressure rises back to 1.3 and then I steam as normal.

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    Super Moderator Javaphile's Avatar
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    I'm assuming that this problem occurs when pulling the first shots/steaming the first just of milk after the machine has been turned on. If that is the case it sounds like a sticking anti-vac valve where it is not releasing when the boiler cools down from the previous power on. As a result of the sticking closed anti-vac valve you get a false steam pressure indicated. When you open the steam valve to froth and the pressure drops and you close it and the pressure builds back up is it then fine? If so clean your anti-vac valve so that it operates properly.

    As a stop gap measure when your machine is heating up open the steam valve until a steady flow of steam is coming out of it and then close it.


    Java "All steamed up" phile
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    Thanks Javaphile. I'm not entirely sure I follow the logic there, but I'll give it a try.

    I recently cleaned up the anti vac valve after I noticed it was effectively partially open full time because of some corrosion/gunk where the o-ring seats into the valve. I soaked the whole valve (less the o-ring) in some descaler and cleaned up the inside with some wet and dry taped to the end of a dowel attached to my cordless drill. Cleaned up very nicely. However, since the repair of the valve coincides with the steam problem, it's a logical place to investigate.

    I didn't use any lubricant on the valve. Would some food grade silicone lube be ok to use here? I figured it would quickly melt away (into the boiler) given the heat of the metal work.

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    I can usually hear my anti-vac valve close (a hissing sound followed by a light thud and then silence).

    Do these gauges really indicate "normal" pressure when under vacuum Java?

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    When the boiler is powered up from cold if it is sealed the air does not become super-saturated and you end up with a false (Technically it's not false as the pressure really is as indicated but the air is dry rather than super-saturated with steam.) pressure reading. The anti-vac valve not only prevents the boiler from possibly imploding under the vacuum created when it cools down but also to vent the boiler while the water comes up to a boil and produces steam at which point the anti-vac valve seals and the system comes up to full operating temperature and pressure.

    In an HX machine if at turn on the machine appears to come up to proper temp and pressure yet when you open the steam valve the pressure immediately drops to near zero and with closing the steam valve the system comes back up to pressure and then operates normally the anti-vac valve is sticking and not doing its job.

    Pulling shots before the steam valve is opened in this situation will usually result in an off shot as the brew water is not hot enough as the air in the boiler is not super-saturated with steam and hence the brew water being passed through the HX is not being brought up to proper temp before hitting the grounds.

    It is for this reason that on boiler machines with-out an anti-vac valve upon warm-up you have to leave the steam valve open until it emits steam. It is doing the job of the anti-vac valve.


    Java "Got steam?" phile
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    An excellent explanation. Thank you Java. I'll test the theory by leaving the steam valve open while warming up tonight and then check the operation of the anti vac valve. If this turns out to be the explanation then it's an easy and free fix - WIN!

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    Edit - duplicate post.

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    Heheh yeah this is what I was getting at, I just though surely it couldn't be that simple a problem if people are looking into HX leaks and the such!

    I have the same issue at the moment, I'll replace the valve but in the meantime I crack the steam wand open the *smallest* amount after turning the machine off. Then after warming up to brew pressure close it off - easy as.

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    Various sized anti vac valves can be found on the talkcoffee and coffeeparts websites (I hope it's not bad form to mention a competing sponsor after coffee_talk has contributed here). For about $15 to $25, it's a cheap and easy part to replace once you're satisfied as to the cause of the problem Burr.

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    Problem solved. Thank you very much Javaphile.

    I tested the theory last night by leaving the steam valve open while it warmed up. Closed it once steam started and then checked steam when full pressure was reached. Nice and strong.

    This morning I took the top off before starting the machine and the anti vac valve was up. Popped it down and started the machine and everything now works as normal.

    I don't know why it was sticking, as the valve is nice and clean. I guess I'll just have to keep an eye on it and maybe replace the o-ring first, then the whole valve if it persists.

    Thanks for all your help guys.
    Last edited by tristanp; 8th May 2014 at 12:39 PM.

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    The problem is likely to continue unless you replace it. Some claim that cracking the steam wand open before+after brewing extends the life of the anti-vac valve, but then there isn't much point of having it at all if you are doing it manually!

    What I wonder is with the new Giotto, being PID controlled rather than pressurestat... when the anti-vac valve sticks will the machine continually try to heat up, eventually hitting a pressure which triggers the boiler safety relief valve?



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