Re: Gaggia Evolution pid&adjustable double pump

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. I'm guessing that it begins cracking open
at around the 3 bar figure that mocha mentions and by the time to get to 9
bar it should be wide open and not providing much restriction or pressure
drop if it is working properly. If something was wrong with the valve and it
was stuck in a mostly closed position, as on mochas machine, it might create
a large pressure drop such that the only way you could get 9 bar at the PF
would be to supply 15 bar of pressure and the volume provided by 2 pumps on
the other side of the valve. Of course it would be easier to just fix the
valve, but you have to give mocha credit for finding a solution of his own.


"Andy Schecter" <schecter@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:ckrkf.54466$DL6.24387@xxxxxxxxxxxxxxxxxxxxxxx
> D. Ross wrote:
>> Most (all?) non-solenoid machines have a spring-pea valve in the
>> showerhead
>> in place of the solenoid.
>
> Oh. A check valve.
>
>> Mocha believes (based on his speculation+his own
>> machine) that the energy required to hold this valve open while brewing
>> saps
>> so much of the pump's power that only 5-6 bars are left for brewing.
>
> A properly designed check valve will produce a negligible pressure drop.
> As you say, easy enough to prove or disprove his theory will a
> pressure-measuring portafilter.
>
>
> --
>
>
> -Andy S.
> picture page: http://tinyurl.com/eh0x


.

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