A3 static pressure rises to 7.5 bar

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DrDregs
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Postby DrDregs » Mar 06, 2012, 3:01 am

Well, I tried to adjust the brew pressure on the down on the A3 from 10 bar - without success. Now the static pressure rises slowly from around 3 bar at the end of a shot. Pressurestat is at 1.1 bar.

I need a bit of help :oops: !

When I turned the adjustment on the pump could I have dislodged some gunk and it's stuck somewhere? I've tried putting successive shots through, drawn water from the boiler and it still goes back to 3 or 4 then rises slowly to 7 plus bars.

Arrrrgh!

Edit; I just checked and it's crept to 9 bar static :shock: . I drew water and it went back to 2 when the pump finished filling then very slowly back to 7.
"24 hours in a day, 24 beers in a case. Coincidence? I don't think so."

DrDregs
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Postby DrDregs » Mar 06, 2012, 4:07 am

This is the pressure reducing valve installed before the filter.

http://cdn2.clean-machine.com.au/cm/i/PSL511.jpg
"24 hours in a day, 24 beers in a case. Coincidence? I don't think so."

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HB
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Postby HB » Mar 06, 2012, 8:07 am

What do you mean by "static" pressure? For the purpose of preparing espresso, we're interested in the brew pressure reading during an extraction, not when the machine is idle. In the configuration you have, the pressure reading when the machine is idle will naturally rise after the pump turns off since the pressure regulator is (correctly) acting as a backflow preventor.

To elaborate on this point, pulling a shot introduces cooler water into a closed system, but then you suddenly close off the main exit at the end of the extraction. As the water in the heat exchanger warms up, it expands and the pressure rises. The expansion valve is typically set to open around 12 bar for rotary pump espresso machines since they have their own bypass valve to regulate brew pressure. This valve vents water to avoid subjecting the hydraulic system to excessive pressure.
Dan Kehn

DrDregs
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Postby DrDregs » Mar 06, 2012, 8:19 am

Static as in pressure reading at idle. Ideally, according to various posts including yours it should be around 2.5 bar. Mine varies between 3 and just over 5 bar. It is now steady at 5 but when I first posted it would slowly rise to around 8 bar after extraction with the pump off and the machine idling :?: .

Your pic. My gauge will (sometimes) creep up to 8 plus.
Image
"24 hours in a day, 24 beers in a case. Coincidence? I don't think so."

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HB
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Postby HB » Mar 06, 2012, 9:17 am

You're confusing the standing pressure of the water mains with your espresso machine's internal hydraulic pressure. Because of thermal expansion, the espresso machine's internal pressure will always rise when the system is sealed and the boiler water is heated. As long as the expansion valve is doing its job of keeping the internal pressure below a safe maximum and the pressure reading is correct when brewing, all is well.

To clarify my earlier posts on this subject, the pressure reading at the water inlet should be around 2.5 bar. The reading on the espresso machine's internal gauge when idle will vary depending on where its tee is located and what check valves/bleeder valves/solenoids are on the same pathway.

For what it's worth, my La Marocco Strada brew boiler pressure gauge sits at 12 bar when the machine is on and 2.5 bar when it's off. The former is the setpoint of the expansion valve and the latter is the water mains standing pressure.
Dan Kehn

Ben Z.
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Postby Ben Z. » Mar 06, 2012, 10:24 am

I know what you mean. My A3 started doing the same thing when turned back on this fall. I haven't worried about it. It never used to read above mains pressure even after sitting on for days. Now it creeps up to 8 bar in an hour or so. Maybe air where there shouldn't be air or water where there shouldn't be water? An anti-reversing valve gone wrong somewhere? I haven't given it much thought. Othere machines seem to do the same thing from what I've read.

DrDregs
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Postby DrDregs » Mar 06, 2012, 7:36 pm

HB wrote:You're confusing the standing pressure of the water mains with your espresso machine's internal hydraulic pressure. Because of thermal expansion, the espresso machine's internal pressure will always rise when the system is sealed and the boiler water is heated. As long as the expansion valve is doing its job of keeping the internal pressure below a safe maximum and the pressure reading is correct when brewing, all is well.

To clarify my earlier posts on this subject, the pressure reading at the water inlet should be around 2.5 bar. The reading on the espresso machine's internal gauge when idle will vary depending on where its tee is located and what check valves/bleeder valves/solenoids are on the same pathway.

For what it's worth, my La Marocco Strada brew boiler pressure gauge sits at 12 bar when the machine is on and 2.5 bar when it's off. The former is the setpoint of the expansion valve and the latter is the water mains standing pressure.


I understand (I think). There is a 350kpa pressure limiting valve outside the kitchen on a dedicated water supply to machines only. I understand that line pressure and internal static (idle) pressure are different. That's why I thought indicated idle pressure should be around 2.5 bar continuously at idle and not creep up to 8.

As mentioned in my other post the 3 way exhausts continuously whilst brewing.

Just as an aside, when I tap the retension valve at idle the gauge needle will drop a fraction.

When you refer to the Strada being on or off do you mean power on or off or the difference between idle and brewing?
"24 hours in a day, 24 beers in a case. Coincidence? I don't think so."

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erics
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Postby erics » Mar 06, 2012, 8:39 pm

As mentioned in my other post the 3 way exhausts continuously whilst brewing.

That should be fixed FIRST - http://www.coffeeparts.com.au/elektra/700158 - oftentimes you can purchase simply the internal piston if $ are short but I would opt for the valve assembly less solenoid.

In lieu of this pressure limiting valve, you need a pressure regulating valve. This is a good choice - https://www.watts.com/pages/_products_details.asp?pid=3428 in the 1/4" size.

Disconnect the pump electrically, hit the brew switch, and adjust the regulator such that the machine's brew pressure gage reads 2.25 to 2.75 bar. 2.50 bar is nice but it doesn't need to be exact.

Reconnect pump. Install a blind filter and "brew away". Adjust the pump's pressure regulating such that your brew pressure gage reads 12 bar. Now adjust the expansion valve (maybe that's what you're calling the retension valve) such that it is slightly dripping into the box while the pump is running.

Let the pump cool off for a couple of minutes - even rotary pumps have an overtemp breaker. Restart pump with the blind filter in place and adjust the pump's pressure regulator such that the brew gage reads 9.0 bar or wherever you would like. Remove the blind filter and simply flush water through the group - the gage should read 9.0 bar - adjust as necessary.

The reading on the brew pressure gage is, for all practical purposes, MEANINGLESS unless you are actually brewing coffee - as Dan explained
Skål,

Eric S.
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E-mail: erics at erols dot com

DrDregs
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Postby DrDregs » Mar 07, 2012, 1:32 am

Thanks for all the help. I found a spare solenoid body off another machine which seems to working okay. Next is a regulator.

Thanks again
"24 hours in a day, 24 beers in a case. Coincidence? I don't think so."

 
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