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Hole in a heat exchanger?
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florentvade
Senior Member


Joined: 24 Apr 2008
Posts: 16
Location: nz
Expertise: I live coffee

Posted Wed Dec 4, 2013, 6:41pm
Subject: Hole in a heat exchanger?
 

Hi,

I have a wega evd 2 group.
It is not plumbed in so it sucks water from a bucket.
Since a while, when the machine warms up, the needle for the pressure of the pump goes up before the needle for the steam pressure.

I do have a couple of other same machine not plumbed in either, and they don t do that.
Does that mean that there could be a hole in 1 of the heat exchanger?

Thanks
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SStones
Senior Member
SStones
Joined: 24 Nov 2012
Posts: 456
Location: Canada
Expertise: Professional

Espresso: Giga 5, ECM Giotto, Rocket...
Grinder: Anfim Milano-Best
Vac Pot: No  :(
Drip: Some $30 thing from Walmart
Roaster: I buy pre-roasted.
Posted Wed Dec 4, 2013, 7:56pm
Subject: Re: Hole in a heat exchanger?
 

It isn't abnormal for it to go up if the pump comes on to fill the boiler. How high does it go?
It seems very unlikely that the heat exchanger would leak inwardly. The boiler pressure outside the HE doesn't exceed 1.5 Bars, even when extreme, so it couldn't raise the pressure inside the HE above 1.5 Bar, which is nothing on the pump-pressure gauge that goes to 12 or 15+ Bar.
The closed off HE is getting hot inside the boiler, so it will build some pressure.  The real test to determine if the HE is leaking is if the boiler pressure is going up over 1.5 Bar and blowing the safety when you're dead-heading a group with a blind filter to backflush.

Are there any other symptoms?
And if it's only going up a tiny bit, then it's no problem at all. Just a more sensitive gauge than your others.
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florentvade
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Joined: 24 Apr 2008
Posts: 16
Location: nz
Expertise: I live coffee

Posted Wed Dec 4, 2013, 8:10pm
Subject: Re: Hole in a heat exchanger?
 

Hi ,

Thanks for your reply.
It goes up slowly,  (about as slow as the steam pressure needle when it goes up) and the pump doesn't kick in.   It goes to the 9 bar (same place as where the pump stops when it goes).        

I'll try to back flush and see what happened.

Thanks
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SStones
Senior Member
SStones
Joined: 24 Nov 2012
Posts: 456
Location: Canada
Expertise: Professional

Espresso: Giga 5, ECM Giotto, Rocket...
Grinder: Anfim Milano-Best
Vac Pot: No  :(
Drip: Some $30 thing from Walmart
Roaster: I buy pre-roasted.
Posted Thu Dec 5, 2013, 5:08am
Subject: Re: Hole in a heat exchanger?
 

Then it's certainly not leaking to the outer boiler. It would only get up to the 1.2 bar of the steam boiler if it were.

So the water inside the HE is being brought to a boil by the boiler around it. It escapes out the relief valve once it hits 9 Bar..  I've got to suspect that your machine that is showing this is either different than your other two, or there is a check-valve (Non-return valve) leaking backward toward the Relief (And the T where the gauge reads pressure).

If you trace your plumbing from the pump you should get to the first T where the boiler-fill water diverges from the HE water. Then another T where the Brew Gauge (Pump Gauge) monitors the pressure, then another T after which each path has a Check valve to prevent that HE's water from coming back through when heated inside the HE.  Check, clean and descale those check valves.

I may be way off base, but this is what I imagine from your description.
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calblacksmith
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calblacksmith
Joined: 25 Nov 2007
Posts: 7,499
Location: Riverside, Ca, U.S.A.
Expertise: I live coffee

Espresso: ECM Vene. A1, La Cimbali M32
Grinder: Azkoyen Capriccio, Major
Vac Pot: 40s era Silex
Drip: Msl. Com. brewers
Roaster: gave it a try, decided no
Posted Thu Dec 5, 2013, 6:51am
Subject: Re: Hole in a heat exchanger?
 

Stephen, I think you are on track. I doubt there is a leak from the HX system.

The fact it is taking water from a bottle is moot.

The pump pressure gauge reads 10 times as much pressure as the boiler pressure gauge,  yet the pump pressure gauge is showing up to 9 bar as the machine warms up? There is not that kind of pressure in the boiler system so I need to wonder why the pump gauge is showing 9 bar when there isn't that much pressure there.

The pump pressure gauge can and will read static line pressure if the machine is plumed into the water system but as this machine is on a bottle and no external water pump was said to be used, the pump pressure should remain at 0 until the brew pump is activated, then and only then should it show the line pressure of 9 bar from the pump.

I do not think my machines show 9 bar when filling the boiler as no back pressure is in the system, the valve to the boiler is open so the pressure can not build, at least I don't remember seeing this, I never really paid attention to it though so I guess I may be off here but logic is not on the side of high pressure in my humble view anyway. I need to watch this and confirm.

Most likely, the check valve is in the solinoid valve, many are though it is possible that it is a stand alone check valve.

There is something that is not adding up, the pressure in the system does not exceed what the Pstat is set for, likely 1.3 to 1.4 bar, until the pump is turned on, only then is there more pressure in the system, there is no way to generate 9 bar without the pump, even with a leaking check valve.

 
In real life, my name is
Wayne P.
Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!

Feed the newbs, starve the trolls and above all enjoy what you drink!
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skydragondave
Senior Member


Joined: 18 Feb 2013
Posts: 130
Location: Ontario, Canada
Expertise: Professional

Espresso: Commercial Only
Grinder: Commercial Only
Roaster: Has Garanti HG5
Posted Thu Dec 5, 2013, 6:13pm
Subject: Re: Hole in a heat exchanger?
 

Hello,
What you are observing is normal operation of the machine's expansion valve. When cold water enters the heat exchanger and is heated to steam boiler temperature, this water expands. Since there is no compressible air in the heat exchanger and the SCNR valves or check valves if you like, prevent water from going back from where it came, the water is trapped and will rupture the heat exchanger unless an expansion valve is installed. I like to set these valves to release at just under 12BAR. Any higher than that and when the brew cycle begins, the pressure ramping to the puck will be much shorter, increasing the likelihood of channelling.
Although your expansion valve setting is low for me, you are probably doing ok at 9, but what concerns me more is the other machines you have that aren't doing that. If they are HX machines, then your expansion valve is set way too low or the SCNR/check valve is leaking back and should be replaced. Although if these machines are on reservoir, its possible they are not HX units. SBDU or DB units operate on different principles and the above info does not apply to them. Good Luck
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calblacksmith
Moderator
calblacksmith
Joined: 25 Nov 2007
Posts: 7,499
Location: Riverside, Ca, U.S.A.
Expertise: I live coffee

Espresso: ECM Vene. A1, La Cimbali M32
Grinder: Azkoyen Capriccio, Major
Vac Pot: 40s era Silex
Drip: Msl. Com. brewers
Roaster: gave it a try, decided no
Posted Fri Dec 6, 2013, 8:07am
Subject: Re: Hole in a heat exchanger?
 

Interesting.
I have been using HX for years, commercial and have not seen the indication mentioned but then two things prevent me from doing so, mostly because I run the machines on a timer and dont see them warm up and even when I am up while they are warming, I don't watch the gauges, why should I? I can hear the vacuum breaker letting pressure out and I can hear it seal, all is well with the world LOL!


There is some good logic in what you say though, somehow in the many years with commercial HX machines, I have never seen it. It could also depend on where in the system the gauge is taped into. If it is after the pump but before the expansion valve, you will not see the pressure. The pump pressure will still be accurate though when the pump is running. Perhaps that is why I have not seen it on my machines. YMMV!

 
In real life, my name is
Wayne P.
Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!

Feed the newbs, starve the trolls and above all enjoy what you drink!
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