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Pressure in Group head
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dabaron2
Senior Member


Joined: 21 Dec 2013
Posts: 2
Location: California
Expertise: I like coffee

Posted Sat Dec 21, 2013, 4:00pm
Subject: Pressure in Group head
 

Hi,

I've had a La Pavoni for several months now, cleaned, rebuilt, all new gaskets, heating element.

1st try, the pressure gauge registered near zero after 30 - 45 minutes, never moved. Removed cleaned the relief valve and from then on there was a slight hiss. Pressure was slightly higher, but after instructions on this site, adjusted the pressure gauge under the base, and now it's set at .9 - 1. Works great. Makes the best caps I've ever tasted!

It worked great until I received a new tamper, at which time when finished with the pull, remove the porta filter, there was pressure in the group head, which had not been present in the past. Caused grounds to spray up into the group head.

I .. wrongly thought.. it had to do with the tamper, possibly being too small. The tamper I received is 49.4mm, and fits the basket fine. Tried several other tampers, with the same result, till I realized the safety valve was no longer releasing pressure - it wasn't hissing.

Removed the safety valve, ball dropped on the floor, and took some time to find. Note to self, do it over a box on table! Reassembled safety valve, now hear steam being release slightly, and when a shot is pulled, the group head no longer pressurized. Taking the portafilter off doesn't spray grounds up the side anymore.

I could use some clarification please: I assume the La Pavoni safety valve always releases some pressure, yes or no. The videos I've seen seem to confirm this.

For a month - month and a half, the machine worked flawlessly. The ball in the safety valve became stuck in a fairly short time. Is there something that will prevent this, or does the valve need to be cleaned every month or so? I'm using filtered water; the safety valve looks to be the stock ss ball bearing.

TIA,

Danny
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SeekingGodShots
Senior Member


Joined: 22 Jan 2006
Posts: 21
Location: California
Expertise: I live coffee

Posted Sat Dec 21, 2013, 7:50pm
Subject: Re: Pressure in Group head
 

Need some clarification:

Is the steam venting valve ball attached to the spring?  If you have hard water in your area, dunk the spring, ball and vent head into a solution of GoJo or other suitable cleaner to remove any build-up.  The La Pavoni safety valve only releases pressure when heating gets out of control.  It may sputter, but that's because of the rubber gasket.  As for sticky valve prevention, I put a fine coat of food grade silicone grease (the same stuff for the piston valve gaskets) on the ball and inside the valve head.  It's harmless and may inhibit any accumulation of minerals from your water source.  Check your water source, it might be a good investment of buying a gallon jug and buying RO/filtered water at the grocery store.

When you tamp down on the ground espresso, how much room do you leave from the top of the basket?  There is a 'sweet spot' of about 1/4" or so.  Too much and the top of the tamped coffee compresses to the bottom of the group head screen.  In my experience, that's where you experience the sneeze or worse.

Adjust that under the base to .9 - 1 per spec.  During the 30-45 minutes at near zero, did the boiler heat up with water boiling or just simmer?  

I doubt if the tamper size has anything to do with the operation of the machine.

Safety valve should not be hissing as it ramps up to ~1 bar pressure.  The valve should be closed to allow pressure build up to it's rated level.  It only releases steam when it exceeds the safety level.

HTH

 
La Pavoni Europicola
Rocky Doserless
Barber Tampers
Technivorm Moccamaster
Hario Kettle & V60
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crazy4espresso
Senior Member
crazy4espresso
Joined: 19 Jan 2008
Posts: 147
Location: Toronto
Expertise: I love coffee

Espresso: Silvia, La Pavoni...
Grinder: Pharos
Posted Sat Dec 21, 2013, 8:57pm
Subject: Re: Pressure in Group head
 

The steel ball in the pressure safety valve doesn't do too well of a job sealing, so it's normal to see steam escaping below 1 BAR. This is the reason why people choose to upgrade to the plastic mushroom in place of the ball.  Also, the portafilter sneeze you've experienced is completely normal, as these machines do not have a valve to release group pressure. You simply have to wait about 1 minute or so for the pressure to dissipate before removing the portafilter.
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dabaron2
Senior Member


Joined: 21 Dec 2013
Posts: 2
Location: California
Expertise: I like coffee

Posted Sun Dec 22, 2013, 2:12am
Subject: Re: Pressure in Group head
 

Valve ball is not attached to the spring, though residue/build up would have caused hang up. In the tear down, I did soak in GoJo, and buffed the ball best I could. I'll give it a try with the food grade silicon. If it continues I'll change the ball out to the plastic mushrooms.

In tamping down there is room between the top of the basket and the group head screen, about 1/4".

Sneeze, read about that starting out didn't know what it was till now, makes sense. The only reason I considered the tamper was because I'd not noticed the sneeze until I received the correct tamper, and even then it was more like a small explosion of grounds rather than just a sneeze. Cleaned coffee out of the basket and the group head! Since the tamper was the only thing I'd changed, I assumed that was the source. Once I cleaned the ball, excessive pressure in the group head was gone after a shot was pulled, and the sneeze was minimal.

The machine's set at .9, I've been considering upping it to 1, which I'll do. It doesn't hiss until it's at it's max, and then only slightly.

During the 30-45 minutes at near zero, it seemed to do nothing, neither simmer or boil. If I remember correctly, at near zero the tank barely warmed up to the touch. It's as though the pressurestat was turned down so low, the heating coil wouldn't turn on. Once I understood it's operation and adjusted properly, I could hear the water boil, and the operation of the unit worked well.

Thanks for the information, it's a big help, and much appreciated.
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sarahalyssa537
Senior Member


Joined: 28 Dec 2013
Posts: 1
Location: new york
Expertise: Just starting

Posted Sat Dec 28, 2013, 4:31am
Subject: Re: Pressure in Group head
 

both inside and outside if it is up if it is to be is up to you and only you feel joy today and this is how we tell you can get older and younger at the very same time please.
http://www.ketoneadvancedfacts.co.uk/
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