ethorson Senior Member Joined: 4 May 2009 Posts: 50 Location: Port Townsend Expertise: Just starting
Espresso: Bunn ES-1A, Bezzera BZ35 Grinder: Mazzer Mini Roaster: Homemade
Posted Sat Dec 31, 2011, 10:35am Subject: Re: Mysterious Livia 90 overpressure
I rebuilt my Bezzera BZ35, which is essentially the same as the Livia 90. My machine had a cracked heat exchanger that let high pressure water bleed into the boiler during a shot. This would fill the boiler and cause an overpressure event. I suspect that the crack was caused by storing the machine without draining it in freezing weather.
If the crack in your heat exchanger is very small then the short time for a backflush would not be long enough to fill the boiler while a long shot would. You can test this hypothesis draining some water from the boiler from the hot water tap to a level just before the autofill turns on. Then try a long shot and see if you get an overpressure event. Then let the autofill top off the boiler and try again. If you get an overpressure then you most likely have a cracked heat exchanger.
The heat exchanger can be repaired by unscrewing it from the boiler and having the crack brazed shut.
That was a good suggestion, but wasn't the problem. I pulled the heat exchanger; it's in perfect condition -or at least isn't in any way obviously ruptured. I even pressurized it slightly to see if it would leak air. -it didn't.
The inside of the boiler is very clean too. No scale whatsoever. The only thing that's a little weird was that when I turned the machine upside down over the sink to empty the boiler, a short length (maybe 5 inches) of 1/4 or 3/16 inch hard plastic tubing fell out. I really wonder where that came from and/or what it was supposed to do.
The machine runs fine, I let it heat for maybe a 1/2 hour to check for leaks, used the blind filter and backflushed for an extended period of time to see if I could get anything to give. No dice, but I did eventually end up with a really good shot. That makes everything worthwhile.
sgreen Senior Member Joined: 4 Apr 2011 Posts: 63 Location: Minneapolis Expertise: I love coffee
Espresso: Viblemme Replica, ECM... Grinder: Mazzer Major and Mini,... Drip: Technivorm Moccamaster Roaster: Behmor 1600
Posted Sun Feb 5, 2012, 6:25pm Subject: Re: Mysterious Livia 90 overpressure
It turns out that the mysterious tubing was a length of teflon tube that acts as a siphon for the hot water tap. Apparently it had broken off and was replaced, but the old one had never been removed from the boiler. So that's one mystery solved.
I got to thinking that maybe my pressure test of the heat exchanger wasn't valid because it was cold. Given that I had isolated everything else, I bought a new one for $60 and replaced it.
ethorson was exactly correct. Thanks for the suggestion. I would have never figured it out on my own.
I was excited that swapping the heat exchanger seemed to have helped, until it started doing it again. Bummer.
After living with this for awhile, I finally emailed Pasquini support and received the following reply:
"Well if you replaced the heat exchanger then the only other way inside the boiler is the auto fill pipe. Meaning the auto fill valve.
You can try this, locate the 2-way solenoid valve aka auto fill valve. Follow the pipe to the boiler, unhook the pipe where it connects to the boiler. Leave the pipe loose and hold with your hand about a inch above the boiler aiming it into the opening of the boiler. Then hit the brew button, if water comes out of that pipe when pulling a shot then your 2-way is bad. Just remember to do this test when the machine is cold so there is no pressure in the boiler. Do all the unhooking first then start the machine and do a quick test. Once you find out your answer then turn off the machine."
I took the valve apart, cleaned and lubed it -very lightly, and then stretched the spring. It works fine now. A replacement valve is about $100 and I'll probably need one eventually, but so far so good.
What is interesting is that my extractions are distinctly different. I had been dark roasting to avoid sour shots. Now, with what I think is probably a more optimal extraction pressure, I'm getting much more palatable shots out of lighter roasts. I'm actually curious to see if the problems I posted about Sweet Maria's Liquid Amber blend actually stemmed from a problem with my machine.
Symbols: = New Posts since your last visit = No New Posts since last visit = Newest post
Forum Rules: No profanity, illegal acts or personal attacks will be tolerated in these discussion boards. No commercial posting of any nature will be tolerated; only private sales by private individuals, in the "Buy and Sell" forum. No cross posting allowed - do not post your topic to more than one forum, nor repost a topic to the same forum. Who Can Read The Forum? Anyone can read posts in these discussion boards. Who Can Post New Topics? Any registered CoffeeGeek member can post new topics. Who Can Post Replies? Any registered CoffeeGeek member can post replies. Can Photos be posted? Anyone can post photos in their new topics or replies. Who can change or delete posts? Any CoffeeGeek member can edit their own posts. Only moderators can delete posts. Probationary Period: If you are a new signup for CoffeeGeek, you cannot promote, endorse, criticise or otherwise post an unsolicited endorsement for any company, product or service in your first five postings.