Re: Definition and function of a vacuum breaker

The imploded RR car in the photo had been steam cleaned and then sealed. I
think you need the condensation of steam to create the vacuum - just normal
expansion and contraction of air wouldn't create enough for an implosion.
You can easily reproduce the effect at home by filling an empty milk or soda
bottle with steam from the steam wand and then sealing the lid. Fun to
watch.

My Simonelli Oscar has no vac breaker and even an anti-suction valve on the
steam wand (to prevent milk from being sucked in), so the only way to
"break" the vacuum is to heat the machine and open the wand. Nevertheless,
it does not collapse - I would guess that the thickness of the boiler
relative to its small volume is even greater than 1/2" steel relative to
the volume of a tankcar (which BTW is not meant to be pressurized). We know
that an espresso boiler can easily withstand 1 bar of (steam) pressure from
the inside pushing out without exploding, so it should withstand the same
pressure from the outside pushing in without imploding. In the case of a
complete vacuum inside the boiler, that's the most you get - 1 bar of air
pressure pushing in on the zero pressure interior. My guess is that the vac
breaker is there mostly so that you don't have to "burp" the machine every
time it warms up. As the others have pointed out, in a machine that is
operational 24/7 (which I think is the better course for a variety of
reasons) the vac breaker does not really do anything.

"Rob van Loenhout" <wontwork@xxxxxxxxxxxxxx> wrote in message
news:43c09bb4@xxxxxxxxxxxxxxx
> The "number one" function of the vacuum breaker valve is to break the
> vacuum
> and stop a possible implosion as you described. I doubt the manufacturers
> would bother putting a valve in when the steam wand does a fine job of
> expelling the air in the "false pressure" scenario.
> If the valve was designed primarily to let the air out then it doesn't do
> a
> very good job of that.
>
> Even a 20 ton capacity railway tank, made from 1/2" steel will implode if
> the covers are bolted down on a hot day and it cools overnite. IIRC
> someone
> posted a link to a pic of an imploded railway tank a few years ago.
>
> Far be it for me to correct you on anything technical relating to espresso
> machines.
>
> Rob "Pedant" vL
>
>
>
> "sprsso" <acritzer@xxxxxxxxxx> wrote in message
> news:oel0s11da0gejh0ap7eatr77ti71k4mn0q@xxxxxxxxxx
>> For those newer to this group, there seems to be some confusion about
>> the function of the vacuum breaker, so I will try to define it so that
>> the intended function of this device is simplified.
>> Vacuum breakers are almost always a threaded-in fitting with a piston
>> with an o-ring at the bottom of the piston. Sometimes they are a
>> teflon coated piston designed to fit against a concave teflon gasket
>> in a fitting that contains both. It is always mounted on top of the
>> boiler, and is purely mechanical.
>> The function of the vacuum breaker is, number one, to allow for the
>> expulsion of air heated by the expansion of water in the boiler to
>> allow for steam development. Steam and air cannot effectively exist in
>> the same pressurized environment as to be effective in an espresso
>> machine. As the air is heated and expands, it is exhausted through
>> this valve until steam pressure accumulates to the point that it
>> closes this valve, and allows steam pressure to develop until the
>> pressurestat or other regulating device determines that the
>> appropriate steam or temperature level has been achieved.
>> Two failure levels exist with this device. One is that the valve is
>> stuck in the closed position, where the pressurestat mistakenly
>> interprets expanded air pressuire as steam development and interrupts
>> electrical flow to the element. This is what is widely described here
>> as false pressue. Sigh. The pressure is not false, it is just air
>> pressure as opposed to steam pressure. It is not the desired pressure.
>> Reaeasing the air pressure, as described in another post will allow
>> steam pressure to develop. It, however, is not necessary to release
>> the air pressure over and over again. With experience, one will know
>> when stream pressure has developed.
>> An equal but much less discussed function of this valve is to allow
>> the safe decompression of the boiler as it cools when the machine is
>> turned off.
>> As the boiler cools, along with all accompanying tubing, a vacuum is
>> created that exists throughout the machine. The vacuum breaker at a
>> certain pressure level is designed to open to allow air back into the
>> system to equalize the pressures that naturally occur during
>> contraction during cooling. The contraction is severe enough with some
>> of the more poorly constructed machines as to cause boiler implosion
>> and line failure when the vacuum valve fails.
>> False pressure is a failure symptom of a vacuum valve, not a
>> definition of the valve.
>> To label a vacuum breaker as a false pressure valve is a misnomer. It
>> probably shouldn't bother me as much as it does, but it does....al
>
>


.

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