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"False" pressure in boiler while heating up
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Discussions > Espresso > Machines > "False" pressure...  
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grumpybarista
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grumpybarista
Joined: 19 Feb 2007
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Location: Detroit
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Posted Mon Oct 29, 2012, 8:43am
Subject: "False" pressure in boiler while heating up
 

My machine, a La Pavoni Pub 1M, has this interesting issue when it's heating up from a cold start. It'll start to warm up and the pressure gauge will read around 1.4 bar. As soon as I open the steam wand or water tap, it'll immediately drop the pressure on the gauge to zero; there will only be a quick blast of steam or water, then nothing, and then start the warm up cycle again. I've noticed it'll do this a couple of times before it actually stays at full pressure. Typically it's not a problem because I tend to leave the machine on constantly (it's only when I turn it off and then restart it cold). But this weekend, no matter how many cycles, it never fully warmed up or got to full pressure.

My first guess would be something electrical. Something seems to tell the warming up process to stop before it's fully pressurized.

Incidentally, I was out of town a couple weeks ago so I turned it off. Did not turn of the water line pressure, however, and I came home to a huge puddle of water. Turns out the pressure relief valve located on top of the boiler was leaking. I killed the line pressure and it stopped. I then restarted the machine, with line pressure, and the leaking also did not recur. I am still puzzled why the valve would have been leaking while the machine was off (ie, no heating), despite the line pressure being on.

These might be two separate issues, but I have a feeling they are probably related.
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GVDub
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Posted Mon Oct 29, 2012, 9:12am
Subject: Re: "False" pressure in boiler while heating up
 

That's usually the function of a vacuum breaker valve - to vent to system so false pressure doesn't build up. As far as a little quick web research goes, your Pub 1 M should have a vacuum breaker. However, it's possible for them to get stuck. Get yourself a set of the hydraulic schematics for the machine, identify the vacuum breaker, and make sure it's functioning properly.
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calblacksmith
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calblacksmith
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Posted Mon Oct 29, 2012, 9:21am
Subject: Re: "False" pressure in boiler while heating up
 

I would say two different things.

The false pressure is a classic problem with machines that do not have a vacuum breaker, often these machines are warmed up either with the wand open until steam starts to flow or you need to open the wand after the boiler has heated,to release the pressure so that the Pstat can work properly, the warming air causes a pressure that turns the Pstat off before the boiler is to temp, bleed the air and the boiler can finish going to temp.

The water leak MAY have come from the vacuum valve if water had continued to flow into the boiler after it should have been shut off and if the boiler was cold, the valve should have been open and thus a place for the water to get out of the system.

The two MAY be sort of related in that you seem to have an issue with the vacuum breaker not letting pressure out of the boiler and yet you have water leaking.

You need to really watch it with the cases off to see if you can see where it is leaking and if the vacuum breaker is open and doing it's job.

 
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grumpybarista
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grumpybarista
Joined: 19 Feb 2007
Posts: 226
Location: Detroit
Expertise: I live coffee

Espresso: LP Pub1
Grinder: Mazzer Mini w/ doser, NS...
Vac Pot: Yama 5-cup
Drip: French Press, aeropress
Roaster: Behmor 1600
Posted Mon Oct 29, 2012, 10:45am
Subject: Re: "False" pressure in boiler while heating up
 

Thanks, these are good ideas. I'm at the office now and will need to take a look later when I'm back home. Another thing had got me thinking -- I went to the LP website and downloaded the electrical and hydraulic schematics -- was that lately it seemed like the steam wand blew out a LOT of water. I wonder if it's possible that the boiler is full of water, or almost full. According to the schematic there's a valve, prior to the pump inlet, that feeds the pump and the boiler. Could it be that this valve is allowing a constant filling of the boiler? Could this explain the leak through the relief valve? I don't see anything about a vacuum breaker in the schematic but it's all in Italian.
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GVDub
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Posted Mon Oct 29, 2012, 10:54am
Subject: Re: "False" pressure in boiler while heating up
 

Sometimes it's referred to as an "Anti-Syphon Valve".
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grumpybarista
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grumpybarista
Joined: 19 Feb 2007
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Location: Detroit
Expertise: I live coffee

Espresso: LP Pub1
Grinder: Mazzer Mini w/ doser, NS...
Vac Pot: Yama 5-cup
Drip: French Press, aeropress
Roaster: Behmor 1600
Posted Mon Oct 29, 2012, 12:58pm
Subject: Re: "False" pressure in boiler while heating up
 

GVDub Said:

Sometimes it's referred to as an "Anti-Syphon Valve".

Posted October 29, 2012 link

There's a "safety valve". Is that the same?
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GVDub
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Roaster: Behmor 1600+
Posted Mon Oct 29, 2012, 1:33pm
Subject: Re: "False" pressure in boiler while heating up
 

grumpybarista Said:

There's a "safety valve". Is that the same?

Posted October 29, 2012 link

I don't think so. Safety valves open when the pressure's too high. Vacuum breakers open when the pressure's too low and close when it's high enough.

Look for "Valvola Antivuoto"
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GVDub
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Roaster: Behmor 1600+
Posted Mon Oct 29, 2012, 3:31pm
Subject: Re: "False" pressure in boiler while heating up
 

From what I've been able to find, on later machines, it shares a T-connector with the pressurestat. On earlier machines, it's apparently on the top of the sight glass. It looks like a little mushroom with a stem coming out the top. Look on the Chris Coffee site for the compact vacuum breaker valve to get an idea of what you're looking for.
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grumpybarista
Senior Member
grumpybarista
Joined: 19 Feb 2007
Posts: 226
Location: Detroit
Expertise: I live coffee

Espresso: LP Pub1
Grinder: Mazzer Mini w/ doser, NS...
Vac Pot: Yama 5-cup
Drip: French Press, aeropress
Roaster: Behmor 1600
Posted Mon Oct 29, 2012, 6:36pm
Subject: Re: "False" pressure in boiler while heating up
 

GVDub Said:

From what I've been able to find, on later machines, it shares a T-connector with the pressurestat. On earlier machines, it's apparently on the top of the sight glass. It looks like a little mushroom with a stem coming out the top. Look on the Chris Coffee site for the compact vacuum breaker valve to get an idea of what you're looking for.

Posted October 29, 2012 link

I did find it on top of the sight glass. Couldn't tell if anything was wrong with it. I cranked up the machine, leaving the steam wand open for a while. It began heating up. I closed the wand and it went to pressure. I opened it and it was the same as usual: a short blast followed by no pressure. But I let it re-pressurize and then it was working fine, maintaining pressure and temperature.

I noticed that the level indicator in the sight glass was not visible and the tube itself looks full, implying that the water level in the boiler is very high. I don't see a way to remove water other than removing a tube somewhere. I also don't know how to prevent the water from refilling to that point again.
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GVDub
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Joined: 25 Jan 2008
Posts: 866
Location: Los Angeles, CA
Expertise: I live coffee

Espresso: Londinium I, Arrarex...
Grinder: Gaggia MD85, Dienes Mokka,...
Drip: Behmor Brazen, Abid Clever
Roaster: Behmor 1600+
Posted Mon Oct 29, 2012, 7:13pm
Subject: Re: "False" pressure in boiler while heating up
 

MIght be scale on the fill probe, or it might have a loose connection. I'd check the connection and pull the probe to check for scale accumulation. According to the hydraulic schematic I found there's a boiler drain. You can also drain from the hot water spigot.
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