Idea for raising hx boiler temperature

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mpap89
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#1: Post by mpap89 »

I have a brugnetti mc-1 that i've been trying to get up to temperature. I've slowly been unscrewing the pstat and checking the brew water temp with a thermocouple in a drilled single basket. The highest i've gotten thus far is 91c which i'm not entirely impressed with. This is after leaving the machine one for over an hour to make sure everything has warmed up. The shots are tasting underextracted. the highest i've gotten the internal pressure to build to is 1.25 bar. I've been unscrewing the pstat more and more but to no avail. I'd still like to raise the boiler temp and to raise the temperature of my brew water. My idea is to bypass the pstat with a PID. First i'll install the thermocouple on (or in, which is best?) the boiler to monitor the max temperature it gets with the pstat then bypass the pstat and let the PID take over the heating element all while closely monitoring the pressure to make sure it doesn't raise above 1.5 bar. Is this a horrible idea? are there other measures i should take before go to such drastic measure? Thanks
Michael

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allon
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#2: Post by allon »

The problem may not be the boiler temperature.
When you flush the HX do you get boiling water, a gush of steam, or just non-boiling water?

If just steam, you may be having a thermosyphon stall.
If just water, it might be scale blocking a restrictor.
If boiling water, then you aren't measuring temperature correctly, since it can't be boiling at 91c.

Could be other things, but this is a start. So, what do you get from the group?
LMWDP #331

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HB
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#3: Post by HB »

In addition to Allon's suggestions, the brew temperature may be too low because the heat exchanger is covered with scale. Scale buildup in the steam boiler on the heat exchanger acts as an insulator.
Dan Kehn

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allon
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#4: Post by allon »

Another possibility is that the vacuum breaker (anti-syphon) valve is stuck. This would cause the pressure in the boiler to be an inaccurate gauge of temperature. Easy enough to check mechanically, or if you are up to pressure, open the steaming wand and see if the pressure gauge drops dramatically. If not, and you get good steam, then this isn't the problem. If you get anemic steam and pressure drops quickly, then close the wand, wait for pressure to build and try again. If you now get good steam and group temps, then clean or replace the vacuum breaker valve.
LMWDP #331

mpap89 (original poster)
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#5: Post by mpap89 (original poster) »

I descaled the brew pipe and replaced the vacuum breaker gasket. Both didn't help. I managed to get the pstat unscrewed a little more. The pressure gauge says it's roughly 1.3 bar but the thermocouple I stuck in my boiler says 264f which equated to 1.93 bar. Kind of odd. I think I'll probably just switch the heating element control over to the pid in the next week since I know what temperature I'm looking for now.

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allon
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#6: Post by allon »

How is the water temp from the group?
Have you tried another pressure gauge, on the steam wand, to double check the built in boiler pressure gauge?
Are you sure your thermocouple is reading correctly? It seems to me that boiler temp isn't the problem (except that it is too high) and that the problem lies elsewhere. Have you descaled the boiler? Scale on the outside of the HX can be a problem as well. A PID won't help you, if the temperature reading in the boiler is as you said.

Good luck and don't blow up your boiler.
LMWDP #331

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Randy G.
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#7: Post by Randy G. »

mpap89 wrote:I descaled the brew pipe and replaced the vacuum breaker gasket. Both didn't help. I managed to get the pstat unscrewed a little more. The pressure gauge says it's roughly 1.3 bar but the thermocouple I stuck in my boiler says 264f which equated to 1.93 bar. Kind of odd..
1 - If scale is suspected then the entire machine needs to be descaled.
2 - The vacuum relief valve needs to be tested. When the machine first heats up, open the steam valve, release the pressure in the boiler, and see if the temperature increases after that
3 - AND MOST IMPORTANTLY, before you get a boiler explosion, stop relying on one pressure gauge, particularly when making such radical p'stat adjustments. If you suspect scale, and particularly if this is a used machine with unknown history, you might consider replacing the safety valve.

You are going about this in a dangerous way. Be careful.
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HB
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#8: Post by HB »

mpap89 wrote:The pressure gauge says it's roughly 1.3 bar but the thermocouple I stuck in my boiler says 264f which equated to 1.93 bar.
Huh? Unless I'm mistaken, the gauge reading is not off by that much:

Image
From is there a temperature vs boiler pressure table?

I'm with Allon; the pressurestat isn't the problem and replacing it with a PID won't accomplish anything.
Dan Kehn