Re: Gaggia Evolution pid&adjustable double pump

I think he was confirming that 150C translates to almost 5 bar of pressure.
Now the steam tables are written in terms of absolute pressure, so that
really this is less than 4 bar of gauge pressure, which is what we normally
think about when working with espresso machines.

The Gaggias have steam thermostats that are set somewhere just short of
150C, but I don't think this translates to an actual steam temperature of
150C because of the thermostat placement where it picks up heat from the
heating element. The brew thermostat is set at something like 110C but they
are shooting for brew temeperatures maybe 15C lower, so the same is probably
true about the steam - the 145C steam thermostat probably gives you an
actual 130C steam temperature, which would give you gauge pressure of around
1.7 bar. Of course with the tiny boiler, the minute you open the valve the
pressure drops off rather quickly from there.

It would not surprise me if the brew valves were set to open at 5 bar or so.
It is a characteristic of spring loaded valves that they begin to leak at
pressures far lower than the full pressure that springs them fully open, so
you would want a margin, and 5 bar is comfortably in between the 2 bar or so
of steam pressure and the 9+ bar of brew pressure. However, mocha's theory
that the effort of opening the spring "consumes" that much pump pressure is
not at all correct. The calculation of pressure drop or head loss is
complex, but to put it simply, a spring loaded valve (that is working
properly) will result in some pressure drop when it is open but nowhere near
the full pressure required to open it.






("J. Clarke" <jclarke.usenet@xxxxxxxxxxxxxxxx> wrote in message
news:dn1itr11069@xxxxxxxxxxxxxxxxxxxx
> mocha wrote:
>
>> Thank you to all for that discussion.
>>
>> I would encourage Gaggia for a better (more clever) valve design with
>> respect to their entry level machines. To control flowing water, there
>> are 3 basic solutions:
>>
>> manual operated mechanical valve (example: Krups)
>> spring loaded mechanical valve (Evolution etc.)
>> servo valve (for example solenoid if electric)
>>
>> Spring loaded valve is the cheapest and most problematic solution if
>> it's not a piece of precision. Gaggia should be able to design a
>> manual valve, may be not that sophisticated like Krups (ceramic) but
>> still allowing to let hot water flow.
>>
>> Mocha
>>
>> BTW. I can read 150 C on pid display and 5 bar of pressure on manometer
>> at the high end of steam mode. It's confirmed here:
>> http://www.connel.com/freeware/steam.shtml
>
> I don't see anything there that "confirms" anything that you have said.
> All
> I see is a steam table calculator.
>
> "Confirmed" means that someone other than you put instruments on a machine
> of the same brand and model as yours, made measurements that turned out to
> be in agreement with yours, and published those measurement results in
> some
> accessible venue.
>
> I really wish you would get someone who knows what they are about to
> repair
> your machine.
>
>> Andy Schecter yazdi:
>>> Jack Denver wrote:
>>> > I always thought a check valve was a one way or non-return valve - the
>>> > more pressure you push against it, the tighter it closes. The brew
>>> > valve is more like an expansion or pressure regulator valve - as long
>>> > as the pressure (e.g. normal steam pressure of 1 to 2 bar) is less
>>> > than
>>> > the strength of the spring, it remains completely closed. When the
>>> > pump
>>> > comes on, the pressure goes way up and the valve opens.
>>>
>>> OK, thanks, Jack, now I think I understand the function that these
>>> valves
>>> perform. I've never had a machine without a solenoid, hence my
>>> ignorance
>>> of their basic operating principles.
>>>
>>> BTW, there are "spring check" valves that use a spring and a ball. Takes
>>> a certain amount of pressure to crack them open. For flow the other way,
>>> they close tighter with higher pressure -- as you say.
>>>
>>> --
>>>
>>>
>>> -Andy S.
>>> picture page: http://tinyurl.com/eh0x
>
> --
> --John
> to email, dial "usenet" and validate
> (was jclarke at eye bee em dot net)


.

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